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INHIBICIÓN DE MICROORGANISMOS PATÓGENOS PRESENTES EN AGUA POR
MÉTODOS COMBINADOS
KATHERIN CASTRO RÍOS
UNIVERSIDAD DE CALDAS
FACULTAD DE CIENCIAS AGROPECUARIAS
DOCTORADO EN CIENCIAS AGRARIAS
MANIZALES
2014
2
INHIBICIÓN DE MICROORGANISMOS PATÓGENOS PRESENTES EN AGUA POR
MÉTODOS COMBINADOS
KATHERIN CASTRO RÍOS
COMITÉ TUTORIAL
Gonzalo Taborda Ocampo, Ph.D. Universidad de Caldas.
Amanda Lucía Mora Martínez, Ph.D. Universidad Nacional (Sede Medellín)
Ricardo Torres Palma, Ph.D. Universidad de Antioquia.
UNIVERSIDAD DE CALDAS
FACULTAD DE CIENCIAS AGROPECUARIAS
DOCTORADO EN CIENCIAS AGRARIAS
MANIZALES
2014
3
4
TABLA DE CONTENIDO
RESUMEN .......................................................................................................................................... 5
CAPÍTULO I ....................................................................................................................................... 6
INTRODUCCIÓN .......................................................................................................................... 6
OBJETIVOS DEL PRESENTE ESTUDIO .................................................................................... 7
CAPÍTULO II ..................................................................................................................................... 8
REVISIÓN DE LA LITERATURA ............................................................................................... 8
CAPÍTULO III .................................................................................................................................. 18
Experimental design to measure Escherichia coli removal in water through electrocoagulation . 18
CAPÍTULO IV .................................................................................................................................. 25
Removal of chemical oxygen demand in coffee mucilage by electrocoagulation ........................ 25
CAPÍTULO V ................................................................................................................................... 31
Reducción de la demanda química de oxígeno, coliformes, mohos y levaduras en mucílago de
café mediante electrocoagulación ................................................................................................. 31
CAPÍTULO VI .................................................................................................................................. 39
Eficiencia de inactivación de coliformes totales y Escherichia coli en agua natural dopada
mediante Fenton heterogéneo........................................................................................................ 39
CAPÍTULO VII ................................................................................................................................ 47
Effect of supporting electrolyte on inactivation efficiency of Escherichia coli and degradation
pathways by electrooxidation with Ti/IrO2 anode ......................................................................... 47
CAPÍTULO VIII ............................................................................................................................... 57
Electrochemical oxidation with RuO2 anode coupled with ultrasound in the disinfection of urban
wastewater ..................................................................................................................................... 57
CAPÍTULO IX .................................................................................................................................. 69
Inactivation of Escherichia coli by combination of ultrasound, ultraviolet irradiation and iron .. 69
CAPÍTULO X ................................................................................................................................... 76
CONCLUSIONES GENERALES ................................................................................................ 76
RECOMENDACIONES ............................................................................................................... 77
BIBLIOGRAFÍA ............................................................................................................................... 78
5
RESUMEN
Este trabajo evaluó experimentalmente la inhibición de microorganismos patógenos,
mediante la combinación de procesos avanzados de oxidación y procesos electroquímicos.
Para ello fue necesario establecer una línea base sobre la eficiencia de inhibición,
empleando diferentes tratamientos alternativos de inactivación como: electrocoagulación,
electrooxidación, Fenton heterogéneo y ultrasonido, en diferentes tipos de agua.
Los resultados indican que es posible la inhibición de los microorganismos mediante la
aplicación de las técnicas estudiadas, siendo los tratamientos de electrooxidación y
ultrasonido los más prometedores, con inactivaciones superiores a 2.7-log (99.8%) en bajos
tiempos de tratamiento; esto se debe a los efectos químicos y físicos sobre los
microorganismos, que mejoraron la mortalidad de estos respecto a los otros tratamientos.
Se combinaron técnicas como electrooxidación, ultrasonido, radiación ultravioleta y hierro.
Estos procesos combinados fueron efectivos en la inhibición de microorganismos,
existiendo un marcado efecto del tiempo de tratamiento en la eficiencia de inhibición. Se
observaron inactivaciones superiores a 3.0-log (99.9%), en diferentes tipos agua.
Los modelos que mejor se ajustaron a las curvas de inactivación de los tratamientos
combinados (R2
> 0.9), fueron Doble Weibull y Bifásico para la combinación de
ultrasonido, irradiación ultravioleta y hierro; mientras que los modelos Weibull y Doble
Weibull fueron los más ajustados para la inactivación mediante la combinación de
ultrasonido y electrooxidación.
6
CAPÍTULO I
INTRODUCCIÓN
Entre las estrategias para el control de la calidad microbiológica de las aguas residuales, se
encuentra la desinfección, que busca la destrucción de microorganismos por la aplicación
de técnicas químicas y físicas. El principal método de desinfección utilizado en la
actualidad es la cloración, esto se debe a su costo bajo y poder oxidante alto; sin embargo
existe una creciente preocupación por la formación de subproductos relacionados con la
desinfección, como los Trihalometanos, algunos de ellos identificados por la Agencia
Internacional para la Investigación en Cáncer como posibles carcinógenos en humanos
(Matamoros, Mujeriego, & Bayona, 2007; The International Agency for Research on
Cancer, 2010; G. S. Wang, Deng, & Lin, 2007; Watson, Shaw, Leusch, & Knight, 2012).
Diferentes técnicas han mostrado ser alternativas para la remoción e inactivación de
microorganismos, entre estas se encuentran los tratamientos electroquímicos como la
electrocoagulación y la electrooxidación que remueven contaminantes por el paso de una
corriente eléctrica a través de electrodos de diferentes materiales. En la electrocoagulación
se generan coagulantes que permiten la remoción de materia orgánica e inorgánica y en la
electrooxidación se forman oxidantes in-situ que degradan los contaminantes (Akbal &
Camci, 2011; Anglada, Urtiaga, & Ortíz, 2009; Durango-Usuga et al., 2010; Katal &
Pahlavanzadeh, 2011; Saravanan, Sambhamurthy, & Sivarajan, 2010; Tchamango, Nanseu-
Njiki, Ngameni, Hadjiev, & Darchen, 2010; Tezcan Ün, Koparal, & Bakır Ögütveren,
2009). En ambos casos se han realizado estudios que evidencian su potencial en la
remoción e inactivación de microorganismos. Mediante la electrocoagulación se han
removido exitosamente algas, bacterias y virus (Azarian, Mesdaghinia, Vaezi, Nabizadeh,
& Nematollahi, 2007; Barashkov et al., 2010; Zhu, Clifford, & Chellama, 2005), evaluando
parámetros como el pH y la intensidad de corriente. Mediante la electrooxidación, se han
inactivado principalmente bacterias indicadoras como los coliformes, además de otras
bacterias patógenas de interés(Cano, Cañizares, Barrera, Sáez, & Rodrigo, 2011; Delaedt et
al., 2008; Frontistis, Brebou, Venieri, Mantzavinos, & Katsaounis, 2011; Griessler et al.,
2010; Polcaro et al., 2007; Schmalz, Dittmar, Haaken, & Worch, 2009).
Existen además los procesos avanzados de oxidación (PAO) que presentan las ventajas
como: la transformación química de los contaminantes, generación baja o nula de lodos,
posibilidad de tratar contaminantes a baja concentración, no formación de subproductos de
reacción y aumento de la biodegradabilidad (Forero, Ortiz, & Ríos, 2005). Estas
tecnologías involucran la generación de especies altamente oxidantes como el radical
hidroxilo. Entre los PAO se encuentran tecnologías no-fotoquímicas y fotoquímicas, como
los procesos tipo Fenton y el ultrasonido, ambos procesos también tienen la habilidad de
eliminar microorganismos, principalmente bacterias en diferentes tipos de aguas (Al Bsoul
et al., 2010; Boateng, Price, Huddersman, & Walsh, 2011; Shinobu Koda, Masaki
Miyamoto, Maricela Toma, Tatsuro Matsuoka, & Masahiro Maebayashi, 2009; Mahamuni
& Adewuyi, 2010; Moncayo-Lasso, Torres-Palma, Kiwi, Benitez, & Pulgarin, 2008; Nieto-
Juarez & Kohn, 2013).
7
La combinación de los tratamientos antes citados, permitirá la ampliación del conocimiento
en cuanto a técnicas alternativas de desinfección, ya que pese a los avances que se han
realizado, aún es necesario investigar con mayor detalle el efecto de los tratamientos
combinados y los factores de operación en la eficiencia de inhibición de microorganismos,
por esta razón el objetivo de este trabajo fue estudiar los procesos avanzados de oxidación
y los procesos electroquímicos en la eficiencia de inactivación de microorganismos
patógenos en agua.
OBJETIVOS DEL PRESENTE ESTUDIO
Objetivo General
Generar un sistema teórico y experimental basado en la combinación de procesos
avanzados de oxidación y procesos electroquímicos, para la inhibición de
microorganismos patógenos.
Objetivos Específicos
Establecer una línea base conceptual sobre la eficiencia de la inhibición de
microorganismos patógenos en agua, empleando procesos avanzados de oxidación y
procesos electroquímicos.
Construir un modelo experimental para la inhibición de microorganismos patógenos
basado en la combinación de procesos avanzados de oxidación y/o procesos
electroquímicos.
Estudio de la cinética de inhibición de microorganismos patógenos de agua,
empleando procesos avanzados de oxidación y/o procesos electroquímicos
combinados.
8
CAPÍTULO II
REVISIÓN DE LA LITERATURA
La desinfección de aguas residuales tiene por objetivo la destrucción de microorganismos
potencialmente patógenos (Gerardi & Zimmerman, 2005), esto se puede lograr aplicando
diversas técnicas. La cloración es el método tradicional para la desinfección de aguas,
debido a su efectividad y economía, sin embargo está relacionada con la formación de
subproductos como los Trihalometanos, los cuales son reconocidos como potenciales
cancerígenos(Hrudey, 2009; G. S. Wang et al., 2007). Esto requiere la evaluación de
técnicas alternativas que sirvan como pre-tratamiento o reemplazo de la cloración.
En vista de esta problemática se han propuesto alternativas como los métodos
electroquímicos, ultrasonido, procesos tipo-Fenton y la combinación de estas y otras
técnicas.
Electrocoagulación
La electrocoagulación es el proceso empleado para remover contaminantes en un medio
acuoso, por el paso de una corriente eléctrica a través de electrodos principalmente de
hierro o aluminio, generando de forma electroquímica iones coagulantes en el ánodo que
permiten desestabilizar los contaminantes, para luego formar flocs que sedimentan o flotan.
Las reacciones involucradas se pueden resumir de la siguiente forma (Mollah et al., 2004):
En el ánodo
M(s) → M(ac)n+
+ ne-
2H2O(l) →4H+ + O2 +4e
-
Enel cátodo
M(ac)n+
+ ne- →M(s)
n+
2H2O(l) + 2e-→ H2
- + 2OH
-
Los procesos de electrocoagulación, son de fácil operación, efectivos en un amplio rango
de contaminantes, no requieren la adición de productos químicos y los lodos generados son
menores que en la coagulación química. Sin embargo requieren un reemplazo periódico de
los ánodos de sacrificio y los costos operacionales pueden ser altos, dependiendo del costo
de la energía.
Como se observa en la Tabla 1, la electrocoagulación ha sido exitosa en la remoción de
bacterias, algas y virus, presentes en aguas residuales y soluciones con el microorganismo.
Los valores de remoción reportados se encuentran por encima del 79%, hasta alcanzar la
remoción completa. En la electrocoagulación los microorganismos son adsorbidos en los
flocs formados que posteriormente flotan hacia la superficie o sedimentan en el fondo del
9
reactor, sin embargo también es posible la desinfección de aguas en presencia de cloruros,
promoviendo la electrogeneración de especies cloradas con potencial desinfectante (Castro-
Ríos, Taborda-Ocampo, & Torres-Palma, 2014; Ricordel, Miramon, Hadjiev, & Darchen,
2013; Zaleschi, Sáez, Cañizares, Cretescu, & Rodrigo, 2013). Hasta la fecha solamente ha
sido combinada la electrocoagulación con electrodos de hierro y aluminio, junto con la
electrooxidación con ánodos de diamante dopado con boro (BDD). Los resultados son
prometedores por el papel que juegan los electrodos tipo BDD en la formación de
sustancias oxidantes y por lo tanto en la desinfección, mientras que la electrocoagulación
favoreció principalmente la disminución de turbidez (Cotillas, Llanos, Canizares, Mateo, &
Rodrigo, 2013; Llanos, Cotillas, Cañizares, & Rodrigo, 2014).
Tabla 1. Microorganismos removidos mediante electrocoagulación
Microorganismo Tipo de
Agua
Electrodos Parámetro
eléctrico
Remoción Referencia
E.coli Solución
CaCl2,
K2HPO4,
Na2SO4,
MgSO4
Acero inox. 30-110 mA 100% (Pareilleux &
Sicard, 1970)
Virus Solución
NaHCO3 y
CaCl2
Hierro,
Acero
Inox.
0.25 mA/cm2 99.99% (Zhu et al.,
2005)
Bacteriófago Solución
NaHCO3 y
CaCl2
Hierro y
Acero inox.
0.25 mA/cm2 99.99% (Zhu et al.,
2005)
Microcystis
aeruginosa
Agua
residual
Aluminio 6 -550
W/dm3
99.5 - 100% (Azarian et
al., 2007)
E.coli Agua
destilada
Aluminio,
Acero,
Acero inox.
0.1 - 1 A 80 - 100% (Ghernaout,
Badis, Kellil,
& Ghernaout,
2008)
Microcystis
aeruginosa
Agua
ajustada a
pH 7
Aluminio
Hierro
0.5- 5
mA/cm2
79- 100% (Gao, Yang,
et al., 2010)
Salmonella
typhimurium
Agua
producción
avícola y
Solución
(NH4)2SO4
Acero
Inox.
0.21 A 99.9% (Barashkov et
al., 2010)
E.coli Lixiviado Aluminio 30 V 97% (Ricordel et
10
de
vertedero
al., 2013)
Coliformes
fecales
Agua
residual
municipal
Aluminio
Hierro
10 A/m2 100% (Zaleschi et
al., 2013)
E.coli Solución
Na2SO4
Aluminio 2.27 mA/cm2 99% (Castro-Ríos
et al., 2014)
Electrooxidación
La electrooxidación es un proceso electroquímico que se perfila como una alternativa
atractiva a la cloración, ya que empleando electrodos como grafito, Pt, IrO2, RuO2, SnO2,
PbO2 y BDD sobre un medio acuoso, permite por medio de la oxidación directa o indirecta
la reducción de diversos contaminantes (Figura 1), entre ellos microorganismos patógenos
(Anglada et al., 2009). En la oxidación directa ocurre una difusión y oxidación de los
contaminantes en la superficie del ánodo. En la oxidación indirecta la descontaminación se
logra por la electro-generación de oxidantes como el Cl2, ClO, H2O2, O3 y OH•, que sirven
como mediadores en la reacción (Cong, Wu, & Li, 2008b; Martinez-Huitle & Brillas,
2008).
Figura 1. Esquemas de electrooxidación directa e indirecta.
Fuente: Adaptado (Anglada et al., 2009)
La principal ventaja de la electrooxidación es su potencial como tecnología limpia, ya que
el reactivo empleado es el electrón, además la técnica demanda muy poco o ningún
producto químico, ya que estos son generados in-situ. Entre las desventajas se encuentran
los altos costos operativos por el consumo de energía, y la formación de productos
intermediarios tóxicos (M. E. H. Bergmann, Rollin, & Iourtchouk, 2009; Sánchez-
Carretero, Sáez, Cañizares, & Rodrigo, 2011).
11
Tabla 2. Inactivación de microorganismos mediante electrooxidación
Microorganismo Tipo de
Agua
Electrodos Parámetro
eléctrico
Inhibición Referencia
Coliformes y
Streptococos
Agua
potable
TiO2 125-250 mA 100% (Patermarakis
&
Fountoukidis,
1990)
Aeromonas
hydrophila
Agua
potable
TiN 1.2 V 68% (Matsunaga et
al., 1992)
Bacillus subtilis 96%
E. coli 100%
Klebsiella
pneumoniae
98.2%
Pseudomonas
cepacia
82.2%
P. fluorescens 61.2%
Saccharomyces
cerevisiae
93.4%
E.coli,
P. aeruginosa
Bacteriófago
Solución
150nM KCl
Platino y
Cobre
25 - 350
mA/cm2
Reporte
gráfico
(Drees,
Abbaszadegan,
& Maier,
2003)
E.coli Solución
NaCl,
NaNO3,
Na2SO4
Acero Inox.
Y TiO2
1-5 mA/cm2 99.5 -100% (X. Y. Li et
al., 2004)
E.coli Solución
NaCl
TiO2, RuO2,
ZrO2
16-25 mA
/cm2
99.98-100% (Diao, Li, Gu,
Shi, & Xie,
2004)
Legionella spp. Solución
NaCl
Ti/RuO2 1-1.5 kV 99.5-100% (Feng et al.,
2004)
E.coli y
Bacteriófago
Solución
NaCl,
NaH2PO4,
Na2SO4
Platino y
Acero
24 mA/cm2 99 –
99.99%
(M.I. Kerwick,
S.M. Reddy,
A.H.L.
Chamberlain,
& D.M. Holt,
2005)
Bacterias halófilas Solución Platino 0.5 A 100% (Y. Birbir &
12
20% NaCl Birbir, 2006)
E.coli Buffer
fosfato 0.2
M (pH 7)
Platino y
Grafito
0.1 -100
mA/cm2
80% (Joonseon
Jeong, Kim,
Cho, Choi, &
Yoon, 2007)
Microcystis
aeruginosa (alga)
Solución
con el alga
Ti-RuO2 y
Grafito
3-12 mA/cm2 92% (Xu, Yang,
Ou, Wang, &
Jia, 2007) Ti-RuO2 y
Acero inox.
Grafito y
Acero inox.
E. coli Solución
1mM
Na2SO4
BBD y
Acero inox.
1.5 a 13.3
mA/cm2
100% (Polcaro et al.,
2007) Enterococcus
faecalis
Solución con
coliformes
Bacterias mesófilas Agua
residual de
curtiembre
Platino 2 – 6 A 100% (Y. Birbir,
Ugur, &
Birbir, 2008)
Bacterias halófilas Agua
residual de
curtiembre,
Solución
NaCl
Platino 0.1-0.5 A 100% (Y. Birbir,
Degirmenci, &
Birbir, 2008)
E.coli Agua
potable
Titanio 0.25-0.75 A 100% (Delaedt et al.,
2008) Legionella
pneumophila
99.9%
Deinococcus
geothermalis
Agua
residual de
industria
papelera
MMO
(Mixed
Metal
Oxide)
5 - 65
mA/cm2
100% (Särkkä,
Vepsäläinen ,
Pulliainen, &
Sillanpää,
2008)
Pseudoxanthomonas
taiwanensis
Meiothermus
silvanus
Coliformes Agua
residual
PbO2 y
Aleación de
Ni-Cr-Ti
0-7 mA/cm2 99.9% (Cong et al.,
2008b)
E. coli Sln. NaCl,
NaH2PO4,
Na2SO4
Ti/IrO2,
Ti/RuO2,
Ti/Pt-IrO2,
17-167
mA/cm2
< 99% (J. Jeong, Kim,
& Yoon, 2009)
13
NaHCO3 Pt, BDD y
Acero Inox.
E.coli Agua rio y
mar
Platino 0.5 A 100% (M. Birbir,
Hüsniye,
Birbir, &
Gülşen, 2009)
1 A
1.5 A
2 A
Coliformes Aguas
residuales
BDD 2.5 - 120
mA/cm2
99.99% (Schmalz et
al., 2009)
Staphylococos
aureus
Solución
0.08M
Na2SO4
Ti/RuO2 y
Acero Inox.
25 y 75
mA/cm2
100% (Gusmão,
Moraes, &
Bidoia, 2009)
E.coli Agua de
balasto
Ti/Ti 1.25 mA/cm2 23-100% (Nanayakkara,
Alam, Zheng,
& Chen, 2012)
E.coli Efluente
pre-
clorinado
contaminado
con
disruptor
endocrino
BDD 2.1 mA/cm2 100% (Frontistis et
al., 2011)
E.coli Agua
residual
municipal
BDD 40 – 120
mA/cm2
100% (Perez,
Gomez,
Ibanez, Ortiz,
& Urtiaga,
2010)
Pseudomonas
aeruginosa
Agua
potable
BDD 80-118
mA/cm2
99.9 –
99.99%
(Griessler et
al., 2011)
E.coli
Coliformes totales
Agua
residual
municipal
BDD 15-105
mA/cm2
99.99% (Daniela
Haaken,
Dittmar,
Schmalz, &
Worch, 2012)
Coliformes fecales Agua
residual
municipal
BDD/Acero
inoxidable
1.3-130 A/m2 100% (Cano et al.,
2011)
E.coli Agua
potable
Grafito/Pt 0.1-0.4 V 99.97 a
100%
(Shang, Qiao,
Sun, Fan, &
Ai, 2013)
14
Como se puede apreciar en la Tabla 2, existen varios estudios que evidencian el potencial
de desinfección de la electrooxidación. La mayoría de las bacterias estudiadas por
electrooxidación son indicadores de contaminación fecal usadas ampliamente, entre ellas se
encuentran Coliformes, Coliformes fecales, E.coli, Estreptococos fecales y Enterococos
fecales. También se han investigado otras bacterias como Pseudomonas aeruginosa,
considerada un indicador alternativo enfocado a evaluar el proceso de desinfección química
y Legionella pneumophila, importante por su capacidad para formar biofilms y como
agente etiológico en la “enfermedad de los legionarios”. Los principales materiales de
electrodos estudiados han sido los ánodos dimensionalmente estables (DSA) y BDD, estos
junto con la composición del medio, tienen un papel importante en el tipo de oxidante
formado. En general el mecanismo de la electrooxidación en la inactivación de los
microorganismos parece estar relacionado con un incremento en la permeabilidad de la
membrana celular inducida intercambio de electrones en la oxidación directa (Park et al.,
2003; Tolentino-Bisneto & Bidoia, 2003), y una posterior difusión de las sustancias
oxidantes al interior de la célula, generadas mediante la oxidación indirecta. (H. Bergmann,
Koparal, Koparal, & Ehrig, 2008).
Pese al interés en la electro-desinfección, aún son pocos los tratamientos que han sido
combinados con esta técnica, probablemente por las eficiencias que se han reportado, sin
embargo se ha realizado la combinación con electrocoagulación como se exponía
anteriormente (Cotillas et al., 2013; Llanos et al., 2014), y con ultrasonido para la
desinfección de Klebsiella pneumoniae y E.coli en soluciones con el microorganismo, la
eficiencia en estos procesos combinados mejoró por el efecto físico del ultrasonido, que
hizo más susceptible al microorganismo frente a las sustancias oxidantes generadas por
electrooxidación (Joyce, Mason, Phull, & Lorimer, 2003; Ninomiya, Arakawa, Ogino, &
Shimizu, 2013).
Ultrasonido
Se denomina ultrasonido a la onda acústica que se encuentra por encima de los 20 kHz, se
encuentra dividido en ultrasonido de alta, media y baja frecuencia (Goncharuk,
Malyarenko, & Yaremenko, 2008). Esta técnica posee un potencial para el tratamiento de
aguas y aguas residuales, además ha demostrado la habilidad para inactivar diferentes
bacterias coliformes principalmente en soluciones con los microorganismos (Tabla 3); sin
embargo requiere mucha energía para efectuar la inactivación (Al Bsoul et al., 2010; S.
Koda, M. Miyamoto, M. Toma, T. Matsuoka, & M. Maebayashi, 2009; Mahamuni &
Adewuyi, 2010). Por esta razón se ha combinado con otras técnicas como radiación
Ultravioleta (Bazyar Lakeh, Kloas, Jung, Ariav, & Knopf, 2013; Chrysikopoulos,
Manariotis, & Syngouna, 2013), Foto-Fenton (Giannakis et al., 2014), electro-catálisis
(Ninomiya, Arakawa, et al., 2013) y electrólisis (Joyce et al., 2003). La combinación con
otras técnicas ha permitido disminuir los tiempos de desinfección, repercutiendo en los
costos energéticos y una mejor inactivación de los microorganismos, por el aumento en la
concentración de sustancias altamente oxidantes o por la sinergia entre el efecto físico del
ultrasonido y el efecto químico de las otras técnicas.
15
Tabla 3. Inactivación de microorganismos mediante ultrasonido
Microorganismo Tipo de Agua Frecuencia Potencia Inhibición Referencia
Bacillus subtilis Solución con el
microorganismo
20 - 850 kHz 0.064 – 0.24
W/cm3
< 80% (Joyce et al.,
2003)
Mycobacterium
spp
Solución con el
microorganismo
20 - 612 kHz 58 – 411 W/L 35.5– 93% (Al Bsoul et
al., 2010)
Legionella
pneumophila
Solución con el
microorganismo
36 kHz 0.064 – 0.191
kW/L
90– 99.9% (Declerck et
al., 2010)
E.coli
Pseudomonas
aueruginosa
Flavobacterium
breve
Aeromonas
hydrophila
Solución con los
microorganismos
20-25 kHz 700 -1000 W 99 –100 % (Hulsmans et
al., 2010)
E.coli
Streptococcus
mutans
Solución con el
microorganismo
20 – 500 kHz 1.7- 12.8 W 90 – 99% (S. Koda et
al., 2009)
E.coli Solución con el
microorganismo
20 – 1071
kHz
80 -140 W 99.9% (Hua &
Thompson,
2000)
E.coli Solución con el
microorganismo
27.5 kHz 42 W/mL 99% (Furuta et al.,
2004)
Enterobacter
aerogenes
Bacillus subtilis
Staphylococcus
epidermis
Solución con el
microorganismo
20 kHz 1-12.7 W 99.9% -
100%
(Gao, Lewis,
Ashokkumar,
& Hemar,
2014a,
2014b)
E.coli K-12 Solución con el
microorganismo
20 kHz 12.57 – 18.86
W/m3
99.9% (Hunter,
Lucas,
Watson, &
Parton,
2008)
E.coli Agua residual 24 -80 kHz 90 – 450 W 100% (Antoniadis,
16
Fenton Heterogéneo (Fe2+
/H2O2)
La tecnología Fenton, ha sido ampliamente estudiada en la degradación de contaminantes
orgánicos en agua. A través del reactivo Fenton (Fe2+
/H2O2) se generan radicales hidroxilo,
que pueden oxidar la materia orgánica rápidamente. Sin embargo esta técnica tiene la
desventaja que requiere la acidificación del medio para el tratamiento y una posterior
recuperación del hierro de los lodos. Para evitar lo último, se viene utilizando el Fenton
heterogéneo, en donde se emplean catalizadores para soportar el hierro. Las reacciones
involucradas en este proceso son:
Fe2+
+ H2O2→ Fe3+
+ OH- + OH
• (1)
Fe3+
+ H2O → Fe2+
+ H+
+ OH• (2)
H2O2→ 2OH• (3)
Aunque la desinfección mediante Fenton y foto Fenton ha sido estudiada, aún son pocos los
trabajos que involucran la inactivación de microorganismos mediante Fenton heterogéneo.
Los trabajos desarrollados mediante esta técnica han evaluado la eliminación de bacterias
como E.coli, Pseudomonas aeruginosa, Staphylococcus aureus y Virus (Boateng et al.,
2011; Moncayo-Lasso, Torres-Palma, Kiwi, Benitez, et al., 2008; Nieto-Juarez & Kohn,
2013). Los resultados son variables, ya que dependen del tipo de catalizador y la
concentración de H2O2, sin embargo es posible lograr la inactivación de los
microorganismos, una ventaja es que permite trabajar con soluciones con pH cercano a la
neutralidad. La desinfección de los microorganismos se atribuye a la adsorción de estos en
el catalizador, que luego son atacados por los radicales hidroxilos y demás oxidantes
formados.
municipal Poulios,
Nikolakaki,
&
Mantzavinos,
2007)
Enterobacter
aerogenes
Bacillus subtilis
Staphylococcus
epidermis
Aureobasidium
pullulans
Solución con el
microorganismo
850 kHz 50-62 W 99-100% (Gao,
Hemar,
Ashokkumar,
Paturel, &
Lewis, 2014)
17
18
CAPÍTULO III
Experimental design to measure Escherichia coli removal in water through
electrocoagulation
Abstract
The experimental design herein was used to evaluate the influence of electrocoagulation
parameters, such as initial pH and electrolyte support (Na2SO4) concentration, on
Escherichia coli (E.coli) removal. The initial pH and Na2SO4 concentration influenced the
response variable. E.coli removal is more efficient with a decrease in pH and an increase in
Na2SO4 concentration. The predicted values from the empirical model were consistent with
the experimental values. In a final experiment under optimal conditions (2.5 mg L-1
of
Na2SO4 and initial pH 4.0), the electrocoagulation with aluminum electrodes was able to
remove 1-log after 40 min and 1.9-log in a contact time of 90 min of E.coli. The study
shows electrocoagulation as a promising alternative to remove microorganisms in water.
Keywords: Factorial design, electrochemistry, microorganism, pH, electrolyte support
Introduction
Chlorination is the primary method for disinfecting water because it is effective and
inexpensive, but this method is related to trihalomethanes (THMs) byproduct formations,
which are recognized as a potentially carcinogenic substances (Hrudey, 2009; G. S. Wang
et al., 2007). This requires evaluating alternative techniques that may serve as a
pretreatment or chlorination replacement.
Electrocoagulation is an alternative for water treatment and reduces or removes
contaminants in an aqueous medium by passing an electric current through iron or
aluminum electrodes and generating coagulants at the anode that form flocs, which settle or
float with the contaminants (Mollah et al., 2004). This technique has successfully removed
19
inorganic and organic contaminants (Akbal & Camci, 2011; Durango-Usuga et al., 2010;
Katal & Pahlavanzadeh, 2011; Saravanan et al., 2010; Tchamango et al., 2010; Tezcan Ün,
Koparal, & Bakır Ögütveren, 2009), including microorganisms such as algae, bacteria and
viruses (Azarian et al., 2007; Barashkov et al., 2010; Zhu et al., 2005). In previous studies
using electrocoagulation, Azarian, et al. (2007) removed between 99.8% and 100% of the
Microcystis aeruginosa in the final effluent from a water treatment plant, and Gao, Du, et
al. (2010) entirely removed the algae in a NaCl solution using aluminum electrodes.
Ghernaout, et al. (2008) removed between 80-100% of the bacteria Escherichia coli using
aluminum and stainless steel electrodes; evaluated certain parameters, such as pH and
current; and observed a positive impact on microorganism removal by using a neutral pH
and increasing the current.
For this study, the influence of electrocoagulation parameters, such as initial pH and
Na2SO4 concentration, on E.coli removal was studied using the experimental design
described herein. This statistical methodology facilitates an assessment of two or more
factors relevant to a response variable and generates an appropriate number of experiments;
the results are expressed as a regression model (Montgomery, 2001).
Experimental
Reagents
Sodium sulfate and nitric acid were purchased from Sigma-Aldrich; the microbiological
reagents, peptone water, and Endo agar were purchased from Oxoid. Sulfuric acid and
sodium hydroxide were acquired from Merck and were used to adjust the pH. Distilled
water was used to prepare the aqueous solutions and for the experiments.
Electrochemical experiments
Figure 1.Schematic diagram of electrocoagulation experiment
20
Electrochemical tests were performed in a batch reactor, which comprised a 500 mL glass
beaker equipped with 4 aluminum electrodes, a 44 cm2
effective area, and a 1.0 cm
interelectrodic space (Figure 1). The electrodes were connected to a direct current power
supply (MCP Lab electronics) at 2.27 mA cm-2
. Before each experiment, the aluminum
electrodes were washed, sanded, dipped in a nitric acid solution (0.1 mol L-1
), and rinsed
with distilled water.
Na2SO4 was selected as the support electrolyte to avoid forming organic chlorine by-
products (Yildiz, Koparal, & Keskinler, 2008). Before the electrocoagulation process, the
initial pH of the water was adjusted using NaOH or H2SO4 (0.1 mol L-1
). Samples were
collected at different time intervals for microbiological analysis.
E.coli preparation and quantitation
A suspension comprising native E.coli in peptone water was prepared and incubated at 37
°C until the sample was at 105-10
6 CFU mL
-1. The samples were analyzed using the
filtration membrane technique in accordance with standard methods (APHA, 1999). Sterile
cellulose membranes (Advantec MFS) comprising a 0.45 µm pore size were placed in a
Petri dish with Endo agar (Oxoid). The E.coli colonies were counted after incubation at 35
°C for 24 h.
Experimental design
A two-level factorial design (2k) with three replicate center points was used; the factors
considered for this study were initial pH and support electrolyte (Na2SO4) concentration.
The levels for the factors studied are shown in Table 1. The response variable was E.coli
removal, which was defined as Log (Nt/No), where No is the initial E.coli concentration,
and Nt is the remaining E.coli population at time t. The experiments were performed in a
random order in duplicate, and the data were analyzed using the software
Statgraphics®plus.
Table 1. Factors and levels used in the experiment
Variables Low Level, -1 Center points, 0 High Level, +1
Initial pH 4.0 5.5 7.0
Na2SO4 (mg L-1
) 0.25 1.38 2.5
21
Results and discussion
Experimental design applied to E.coli removal through electrocoagulation
Table 2 shows the design matrix generated using the software Statgraphics®plus. It includes
the experimental conditions and results for each experiment and response variable, which is
defined as E.coli removal after electrocoagulation for 50 min. The study was conducted
using a 95% confidence level.
Table 2. Design matrix and experimental results
Assays Initial pH Na2SO4 (mg L-1
) Log (Nt/No)
1 5.5 1.38 –0.83
2 5.5 1.38 –0.79
3 4.0 0.25 –0.18
4 7.0 0.25 –0.47
5 4.0 2.5 –1.36
6 5.5 1.38 –0.72
7 7.0 2.5 –0.22
8 5.5 1.38 –0.66
9 5.5 1.38 –0.79
10 4.0 0.25 –0.24
11 7.0 0.25 –0.46
12 4.0 2.5 –1.29
13 5.5 1.38 –0.51
14 7.0 2.5 –0.15
The primary-effects plot (Figure 2) shows the effect of each factor on the response variable.
An increase in the Na2SO4 concentration had a positive effect on the response variable and
may be explained by an increase in conductivity, which would improve microorganism
removal (Otenio, Panchoni, Cruz, Ravanhani, & Bidóia, 2008; Tezcan Ün, Koparal, &
Ögütveren, 2009). A decrease in initial pH also had an effect on E.coli removal, which is
consistent with previous research that shows higher efficiency at acidic and neutral pH
values using aluminum electrodes; in addition, an acidic pH can limit E.coli growth and
22
survival (G. Chen, 2004a; Mates, Sayed, & Foster, 2007; McQuestin, Shadbolt, & Ross,
2009).
Figure 2.Primary-effects plot for E.coli removal through electrocoagulation
The Pareto chart (Figure 3) was used to draw conclusions on the most significant variables
and variable interactions. This chart shows both the magnitude and importance of the
effects (variables and interactions). The chart comprises a reference line (discontinuous
vertical plot), and any effect that extends past this line is potentially important. An
interaction between the initial pH and Na2SO4 (AB) as well as initial pH (A) and Na2SO4
(B) concentration is considered important in E.coli removal.
Figure 3.Pareto chart for E.coli removal through electrocoagulation
The experimental design used herein included a reduced model that directly relates the
response variable with the factors to facilitate subsequent evaluation of the data.
23
Figure 4.Comparison of the experimental and predicted values for E.coli removal through
electrocoagulation using the empirical reduced model
The reduced empirical model for E.coli removal through electrocoagulation is shown in
Equation 1. The R2
value for Equation 1 is 0.9153, which indicates that 91.53% of the total
variation in E.coli removal is attributed to the factors studied.
Log (Nt/No) = 0.388 – 0.137[pH] – 1.322 [Na2SO4] + 0.207[pH][Na2SO4] (1)
Figure 4 shows a comparison between the experimental values generated from each
experiment (Table 2) and the predicted values for E.coli removal, which were calculated
using Equation 1. The predicted values are consistent with the experimental data.
E.coli removal through electrocoagulation under optimal conditions
24
Figure 5.Variation of E.coli removal through electrocoagulation
In a final experiment, the removal of E.coli through electrocoagulation was conducted
under optimal conditions (2.5 mg L-1
of Na2SO4 and initial pH 4.0) in distilled water. As
seen in Figure 5, the electrocoagulation with aluminum electrodes is able to remove 1-log
after 40 min and 1.9-log in a contact time of 90 min, similar results had been reported
previously (Ghernaout et al., 2008; Otenio et al., 2008). The water without electrolysis
(control) did not show significant effect on the growth of E.coli, indicating that removal of
the microorganism is due electrocoagulation, this is attributed to the adsorption of E.coli in
the flocs formed, which float to the surface or settle to the bottom of the reactor (G. Chen,
2004a; Ghernaout et al., 2008; Zhu et al., 2005), as seen in the Figure 6. The
microorganism can survive in the flocs, therefore is important to complement this technique
for a complete elimination.
Figure 6.Schematic representation for E.coli removal through electrocoagulation
Conclusions
The experimental design, it allowed to observe the influence of the factors initial pH and
electrolyte concentration support on the removal of the bacteria E.coli using
electrocoagulation. The results indicated that the factors initial pH and electrolyte support
(Na2SO4) concentration as well as the interaction between these factors affected
microorganism removal, which improved with a decrease in initial pH and an increase in
Na2SO4 concentration. An empirical model was established that describes E.coli removal
using electrocoagulation. The removal of E.coli is attributed to the physical effect promoted
by electrocoagulation.
© 2013 by ESG (www.electrochemsci.org)
25
CAPÍTULO IV
Removal of chemical oxygen demand in coffee mucilage by electrocoagulation
Abstract
The mucilage and the coffee pulp, are semi-liquid by-products involved in the generation of
wastewater with high values of solids and chemical oxygen demand (COD), negatively
impacting the efficiency and costs of the traditional treatments. A factorial design was
applied to evaluate the removal of COD in coffee mucilage by electrocoagulation,
analyzing the effects and interactions of three parameters (current intensity, pH and time) in
the response variable (percentage of COD removal). The electrocoagulation process using
Fe-Al electrode pair, showed a maximum removal of the COD of 46%, in a treatment time
of 50 min, 3.0 A and initial pH of 6.3. The statistical analysis showed a significant effect
from initial pH and treatment time in the removal of COD. The electrocoagulation is a
suitable alternative for pre-treatment of liquid waste of the coffee
Introduction
The coffee cherry is composed of skin, pulp, mucilage, parchment, silver skin and seed. To
remove these layers and obtain the product of commercial importance, it is necessary to
submit the coffee cherry to various stages. The mucilage and coffee pulp, are by-products
mainly composed of polysaccharides, proteins and polyphenols (Avallone, Guiraud, Guyot,
Olguin, & Brillouet, 2000; Mussatto, Machado, Martins, & Teixeira, 2011), and constitute
wastewater with COD levels between 1500 to 101200 mg L-1
(Chanakya & Alwis, 2004;
Olvera & Gutiérrez, 2010b; Rodríguez, Silva, & Boizán, 2000a; Selvamurugan, Doraisamy,
Maheswari, & Nandakumar, 2010; Zambrano-Franco & Cárdenas-Cárdenas, 2000).
Anaerobic treatment is traditionally used for the removal of organic matter in wastewater
from coffee processing, however this technique requires a long treatment time, impacting
on cost and efficiency. This was observed in some studies, which evaluated the anaerobic
biodegradability of wastewater from wet processing of coffee, using as inoculum the cow
manure and sludge stabilization pond, achieving a COD removal less than 40% (Rodríguez,
Silva, & Boizán, 2000b). In a similar study using bovine rumen fluid as inoculum, for the
26
purification of water from pulping, the COD removal was 91.2%, at pH 4.6 and 28°C in 16
days (Olvera & Gutiérrez, 2010a). Other treatments such as anaerobic treatment module
system (SMTA), developed by Cenicafe reported removals of COD and BOD5 below 80%,
but the whole process takes about 5 months(Zambrano-Franco, Isaza-Hinestroza,
Rodríguez-Valencia, & Posada, 1999).
The wastewater treatment by electrocoagulation is an alternative, which reduces or removes
contaminants in an aqueous medium, by passing an electric current through electrodes of
iron or aluminum, generating coagulants at the anode involved in the formation of flocs that
settle or float with the contaminants (Mollah et al., 2004). This technique has shown
potential in removing contaminants in wastewater from agricultural and the food industry
(Drogui, Asselin, Brar, Benmoussa, & Blais, 2008; Papastefanakis, Mantzavinos, &
Katsaounis, 2010; Sundarapandiyan, Chandrasekar, Ramanaiah, Krishnan, & Saravanan,
2010; Tchamango et al., 2010).
The complexity of coffee mucilage demand the evaluation of new techniques, that
effectively reduce COD in a shorter time, and serve as an alternative for the pre-treatment
of wastewater from coffee processing. The aim of this study was to evaluate the
electrocoagulation and some process parameters, on the removal of COD from the coffee
mucilage.
Experimental
Effluent characteristics
The effluent sample was mainly composed by coffee mucilage, it was collected from two
farms in Manizales (Colombia), and the sample was stored between 24-48h at 4°C. The
coffee mucilage contained a high amount of COD (66000 mg L-1
), the conductivity was 4.2
mS cm-1
and the initial pH 3.8, these conditions were determined before the
electrocoagulation process.
Electrocoagulation Experiments
The electrochemical experiments were performed in a batch reactor, which consisted in a
glass beaker of 500 mL, equipped with Fe electrode and a cathode of Al, with effective area
of 44_cm2 and interelectrodic space of 1.0 cm (Figure 1). The electrodes were connected to
a DC power supply of 30 V and 20 A (MCP Lab electronics). Before each experiment the
electrodes were washed, sanded and dipped in a nitric acid solution. Previous to the
electrocoagulation process the initial pH of the water was adjusted with NaOH or H2SO4
(0.1 M) acquired from Merck. Influent and effluent pH values were measured by a pH
meter (Metrohm 744), and COD were conducted by the procedures described in the
Standard Methods (APHA, 1999).
27
Figure 1.Schematic diagram of the electrochemical reactor
Experimental Design
A factorial design was selected, the variables studied were: initial pH, current intensity and
treatment time. The levels of the variables studied are show in Table I. The response
variable was the percentage of COD removal. The data analysis was done with the software
Statgraphics®plus.
Table 1.Levels of selected variables for the experimental design.
Variables Level 1 Level 2 Level 3
Initial pH 3.5 6.3 9.0
Current Intensity (A) 1.5 2.3 3.0
Treatment Time (min) 15 30 50
Results and Discussion
COD removal by electrocoagulation treatment
The experimental results of electrocoagulation with Fe-Al electrode pair in coffee mucilage
(Figures 2-4), show a COD maximum removal of 46% in a time of 50 min, these values are
close to studies reported by other authors (30-55%), in wastewaters with high COD value
(Abraham, Radhakrishnan Nair, & Madhu, 2009; Agustin, Sengpracha, & Phutdhawong,
2008; Chavalparit & Ongwandee, 2009; Inan, Dimoglo, ÅžimÅŸek, & Karpuzcu, 2004;
Tezcan Ün, Ugur, Koparal, & Bakır Ögütveren, 2006). The lowest efficiency of the process
is presented in the shortest treatment time, with COD removal between 10-18%; therefore
the increase in treatment time, improves the removal of COD. Also was observed a better
efficiency in COD removal with the increasing of current intensity, showing the best results
between 2.3 A and 3.5 A, this behavior is attributed to a greater dissolution of the anode
according to Faraday's law, improving the amount of coagulant and consequently the
28
removal of pollutants (Abdelwahab, Amin, & El-Ashtoukhy, 2009; Tezcan Ün, Koparal, &
Ögütveren, 2009).
Initial pH was evaluated in the electrocoagulation process, due their impact on the
contaminant removal efficiency (G. Chen, 2004b; C. T. Wang, Chou, & Kuo, 2009). The
COD removal is better at initial pH 6.3, using currents intensity of 2.3 A and 3.5 A, this
coincides with other research that showed improved efficiencies in the removal of
contaminants at pH close to 7.0, using electrocoagulation with iron anodes, due to the
formation of iron complexes which allow a more efficient coagulation (Escobar, Soto-
Salazar, & Toral, 2006; Kobya, Ciftci, Bayramoglu, & Sensoy, 2008; Kobya & Delipinar,
2008).
Figure 2. Electrochemical removal of COD in coffee mucilage, as function of time,
applying a current intensity of 1.5 A.
Figure 3. Electrochemical removal of COD in coffee mucilage, as function of time,
applying a current intensity of 2.3 A.
29
Figure 4. Electrochemical removal of COD in coffee mucilage, as function of time,
applying a current intensity of 3.0 A.
Experimental Design
According to the ANOVA (Table II) the factors with statistical significance in the response
variable was the initial pH and treatment time (p<0.05), while the current intensity and the
interactions between variables did not show a statistically significant effect on the response
variable.
Table2. ANOVA table for electrocoagulation of coffee mucilage with Fe-Al electrode
pair.
Source Sum of
Squares
Mean Square P-Value
A: Time 1152.67 576.333 0.0001
B: Current Intensity 132.667 66.3333 0.0695
C: pH 182.0 91.0 0.0357
AB 7.33333 1.83333 0.9776
AC 69.3333 17.3333 0.4651
BC 130.667 32.6667 0.2098
Figures 5-6 shows the differences between the initial pH and treatment time, calculated by
Fisher's Least Significant Difference (LSD) test, showing the existence of statistical
differences in the averages calculated. It can be seen differences between the times 15-30
min, 15-50 min and 30-50 min, verifying the effect of increased time on COD removal
30
efficiency. About the initial pH, there were differences between 3.9-9.0 and 6.3-9.0, while
values between 3.5-6.3 did not show significant differences, suggesting a better removal of
COD, for the coffee mucilage at acidic-neutral initial pH.
Figure 5. COD removal means for each treatment time and 95% LSD Intervals
Figure 6.COD removal means for each initial pH and 95% LSD Intervals
Conclusions
The results demonstrate that electrocoagulation is effective for partial COD removal from
coffee mucilage, and can be considered as a suitable alternative for pre-treatment of liquid
waste of the coffee, when is used a treatment time of 50 min, 3.0 A and initial pH value of
6.3.
31
CAPÍTULO V
Reducción de la demanda química de oxígeno, coliformes, mohos y levaduras en mucílago
de café mediante electrocoagulación
Resumen
El mucílago y la pulpa de café, son subproductos semilíquidos involucrados en la
generación de aguas residuales con alta concentración de materia orgánica y diversas
especies de microorganismos, afectando negativamente la eficiencia de los tratamientos
tradicionales, que requieren hasta cinco meses para la descontaminación total de este tipo
de aguas. Esto demanda la evaluación de diferentes técnicas de tratamiento, que mejoren la
eficiencia de los procesos tradicionales.
Se evaluó la electrocoagulación con electrodos Fe/Al, 2.3 A y pH natural, en la reducción
de la demanda química de oxígeno y algunos microorganismos, presentes en mucílago de
café. El proceso electroquímico propició una remoción máxima de 93% para bacterias
coliformes, mohos y levaduras, en un tiempo de tratamiento de 50 min. La reducción de la
demanda química de oxígeno fue 32% para la muestra sin diluir, 45% para la muestra
diluida al 50% (v/v) y 51%, para las muestra diluida al 25% (v/v); indicando una mejor
eficiencia con la disminución de la materia orgánica. El consumo energético fue inferior a
los 0.083 kWh/m3, para las muestras analizadas. Esta técnica es una alternativa adecuada
para el pre-tratamiento o reutilización de aguas contaminadas con mucílago de café.
Palabras claves: Bacterias, electroquímica, hongos, materia orgánica, subproductos de
café.
32
Abstract
The mucilage and coffee pulp are by-products involved in the generation of wastewater
with high concentration of organic matter and different species of microorganisms,
adversely affecting the efficiency of traditional treatments, which require up to five months
to complete decontamination of this type of water. This demands the evaluation of different
treatment techniques that improve the efficiency of traditional processes.
The electrocoagulation was assessed with Fe/Al electrodes, 2.3 A and natural pH, in the
reduction of chemical oxygen demand and some microorganisms present in coffee
mucilage. The electrochemical process led to a maximum of 93% removal for coliform
bacteria, molds and yeasts, in a treatment time of 50 min. The reduction of chemical
oxygen demand was 32% for the undiluted sample, 45% for the sample diluted at 50% (v /
v) and 51% for the sample diluted at 25% (v / v), indicating better efficiency with reduced
organic material.
The energy consumption was less than 0.083 kWh/m3 for the samples analyzed. This
technique is a suitable alternative for pre-treatment or reuse of contaminated water with
coffee mucilage.
Key Words: Bacteria, coffee by-products, electrochemistry, fungus, organic matter.
Introducción
El fruto de café se encuentra compuesto de cáscara, pulpa, mucílago, pergamino, película
plateada y semilla. Para retirar estas capas y obtener el producto de importancia comercial,
es necesario someter a este a diversas etapas conocidas como beneficio, generando diversos
productos secundarios. El mucílago de café, es un subproducto semilíquido compuesto
principalmente por polisacáridos, proteínas y polifenoles (Avallone et al., 2000; Mussatto et
al., 2011); además alberga microorganismos de los géneros Enterobacter, Staphylococos,
Serratia, Candida, Torulopsis, Rhodotorula, Escherichia y Citrobacter (Blandón-Castaño,
Dávila-Arias, & Rodríguez-Valencia, 1999). Sus características físico-químicas y
biológicas lo convierten en un subproducto complejo y altamente contaminante; implicado
en la generación de aguas residuales con altos porcentajes de sólidos y demanda química de
oxígeno (DQO), con reportes entre 1500 a 101200 mgO2/L, dependiendo de la etapa del
proceso y la tecnología empleada (Chanakya & Alwis, 2004; Olvera & Gutiérrez, 2010b;
Rodríguez et al., 2000a; Selvamurugan et al., 2010; Zambrano-Franco & Cárdenas-
Cárdenas, 2000).
El tratamiento anaerobio es empleado tradicionalmente para la remoción de materia
orgánica en las aguas residuales del beneficio del café, sin embargo esta técnica demanda
un largo tiempo de tratamiento, lo que incrementa los costos y eficiencia del proceso. Esto
se observa en trabajos como el de Rodríguez et al. (2000b) que determinaron la
biodegradabilidad anaerobia de las aguas residuales procedentes del beneficio húmedo del
café, empleando como inóculo el estiércol de vacuno y lodos de laguna de estabilización,
33
alcanzando una reducción de la DQO menor al 40%. En un estudio similar empleando
fluido ruminal vacuno como inóculo para la depuración de agua del despulpado, alcanzaron
una remoción de 91.2% con pH de 4.6 y 28 °C en 16 días (Olvera & Gutiérrez, 2010a).
Otros sistemas más robustos como el Sistema Modular de Tratamiento Anaerobio
(SMTA), desarrollado por Cenicafé para el tratamiento de las aguas residuales del
lavado, han reportado remociones de DQO y DBO5 (Demanda bioquímica de oxígeno)
inferiores al 80%, pero todo el proceso requiere un tiempo aproximado de 5 meses
(Zambrano-Franco et al., 1999).
El tratamiento de aguas residuales mediante electrocoagulación es una alternativa que
reduce o remueve contaminantes en un medio acuoso, mediante el paso de una corriente
eléctrica a través de electrodos de hierro o aluminio, generando de forma electroquímica
iones coagulantes en el ánodo que desestabilizan los contaminantes, para luego formar flocs
que sedimentan o flotan (Mollah et al., 2004). Esta técnica ha evidenciado un potencial en
la remoción de contaminantes de aguas residuales de la agroindustria y la industria de
alimentos (Drogui et al., 2008; Kobya & Delipinar, 2008; Papastefanakis et al., 2010;
Tchamango et al., 2010), y recientemente un efecto en la reducción del contenido de
microorganismos (Gao, Yang, et al., 2010; Ghernaout et al., 2008; Martinez-Huitle &
Brillas, 2008).
Las características del mucílago del café, implican la evaluación de nuevas técnicas que
reduzcan eficientemente los contaminantes físico-químicos y biológicos, proporcionando
alternativas de reutilización o pre-tratamiento de los residuos líquidos del beneficio de café.
El objetivo del presente trabajo es la evaluación de la electrocoagulación y algunos
parámetros intrínsecos del proceso, en la reducción de DQO y microorganismos (bacterias
coliformes, mohos y levaduras) en mucílago de café.
Materiales y métodos
Localización
Se recolectaron muestras provenientes de dos fincas del municipio de Manizales
(Colombia), con condiciones similares de procesamiento del café cereza, la temperatura
promedio de la zona es de 23°C y pluviosidad máxima de 280mm/mes. Las muestras
fueron almacenadas entre 24-48h a 4°C, hasta el momento de ser electrocoaguladas. Las
características físico-químicas del mucílago de café recolectado se muestran en la Tabla 1.
Tabla 1. Características físico-químicas del mucílago de café antes de la
electrocoagulación.
Parámetro Valor
Humedad (%) 96.20
Materia seca (%) 3.80
34
Nitrógeno total (%) 2.08
Proteína bruta (%) 13.00
Fósforo (%) 0.17
Potasio (%) 0.44
Hierro (mg/L) 264.30
Cobre (mg/L) 19.20
Manganeso (mg/L) 44.10
Zinc (mg/L) 18.20
DQO (mg/L) 67500
Sólidos Totales (mg/L) 46680
Conductividad (mS/cm) 4.2 (22.7°C)
pH 3.56
Procedimiento experimental
Los experimentos electroquímicos fueron realizados en un reactor tipo batch, que consistió
en un beaker de vidrio de 500 mL, equipado con dos electrodos de hierro (ánodos) y dos
electrodos de aluminio (cátodos), con área efectiva de 44 cm2 y una distancia inter-
electródica de 1.0 cm (Figura 1). Los electrodos se conectaron a una fuente de corriente
directa (MCP Labelectronics) de 30 V y 20 A. La intensidad de corriente aplicada fue 2.3
A, pH natural, sin adición de electrolito soporte a la muestra, debido a la conductividad
presentada (Tabla 1), estos parámetros fueron seleccionados con base a resultados previos
(Castro-Ríos, Orozco, & Taborda, 2012; Castro-Ríos, Orozco, & Taborda Ocampo, 2012).
Adicionalmente, se realizó un estudio modelo utilizando los mismos parámetros, con el fin
de determinar la eficiencia del proceso electroquímico según la concentración de materia
orgánica presente, empleando diluciones al 50% (v/v) y 25% (v/v) de la matriz inicial. Los
datos fueron analizados mediante estadística descriptiva y análisis de varianza, realizado
con el software Statgraphics® plus.
35
Figura 1.Esquema reactor electroquímico
Análisis de las muestras tratadas
La DQO, fue medida empleando el método de reflujo cerrado por técnica colorimétrica,
según procedimiento APHA 5220 D (APHA, 1999), luego fue determinada la
concentración de DQO en un fotómetro Spectroquat® Nova 60 (Merck, Alemania). Las
medidas de pH, se realizaron empleando un potenciómetro Metrohm Mod. E-744
(Metrohm, Suiza). Las muestras para el análisis microbiológico fueron asépticamente
pipeteadas, y posteriormente diluidas hasta 10-3
, en agua peptonada (Oxoid). Luego se
inocularon mediante la técnica de siembra en superficie en agar EMB (Oxoid) y agar YGC
(Scharlau). Las muestras se incubaron a 37°C durante 24-48h para coliformes, y 25°C
durante 5 días para mohos y levaduras. Finalmente se efectuó el conteo de las colonias.
Consumo energético
El consumo de energía eléctrica es un parámetro económico muy importante en el proceso
electroquímico y fue calculado usando la ecuación (1) (Akbal & Camci, 2011):
𝐄 =𝐔. 𝐈. 𝐭
𝐕 (1)
Donde E es el consumo de energía (kWh/m3), U es el voltaje aplicado (V), I es la
intensidad de corriente (A), t es el tiempo de EC (h), y V es el volumen del agua residual
tratada (L).
Resultados
Reducción de DQO presente en mucílago de café
La reducción de las sustancias orgánicas disueltas en mucílago de café fue confirmada por
la disminución en la DQO, y la diferencia estadística evaluada mediante análisis de
varianza (p<0.05) y contraste de Fisher (LSD, Least significant difference test) de los
resultados previos y posteriores al proceso electroquímico. El valor promedio de DQO
antes de la electrocoagulación fue 67500 mg/L, el cual fue reducido a 45825 mg/L (50
min), correspondiente a 32.11% de reducción (Figura 2). En lo relacionado con el pH de la
solución se aprecia un aumento de 3.56 a 5.32 (Figura 3).
Los resultados de las diluciones del mucílago de café, se observan en la Figura 4, allí se
evidencia el incremento del porcentaje de reducción de DQO, a mayor dilución. La máxima
reducción, fue 51.16% para la dilución al 50% (v/v) y un 45.34% para la dilución al 25%
(v/v), en 50 min. Los valores de DQO inicial para las muestras diluidas al 50 y 25% (v/v)
fueron 32250mg/L y 14750 mg/L respectivamente.
36
Figura 2. Reducción de DQO
Figura 3.Variación del pH durante el tratamiento electroquímico
37
Figura 4.Reducción de DQO en muestras diluidas
Reducción de mohos, levaduras y coliformes presentes en mucílago de café
La Figura 5, muestra la reducción de microorganismos por electrocoagulación, en esta se
observa que el 70% de la reducción de mohos y levaduras, y el 90% de bacterias coliformes
ocurre durante los primeros 30 min del proceso de electrocoagulación. La reducción
máxima para ambos microorganismos, fue 93% en 50 min.
Figura 5. Reducción de microorganismos
Consumo energético
Se analizó el consumo de energía eléctrica empleando la ecuación (1), para lo cual se
utilizó el potencial (v) registrado durante el tiempo de electrocoagulación y los valores de
los parámetros de corriente, tiempo, pH y volumen citados anteriormente. El consumo
38
energético obtenido fue 0.0368 kWh/m3, 0.0524 kWh/m
3 y 0.0827 kWh/m
3 para la muestra
sin diluir, diluida al 50% (v/v) y diluida al 25
Discusión y conclusiones
Los resultados muestran, que la electrocoagulación puede reducir hasta un 32% la cantidad
de materia orgánica presente en el mucílago de café con los parámetros evaluados, aunque
los porcentajes de reducción de DQO son menores en comparación con estudios similares
(Agustin et al., 2008; Khoufi, Feki, & Sayadi, 2007; Tezcan Ün et al., 2006); debido al alto
contenido de materia orgánica en el mucílago de café. Esto se puede comprobar con los
resultados de las muestras diluidas (Figura 4), ya que al disminuir la concentración de
materia orgánica, es posible obtener porcentajes de reducción de DQO mayores. En lo
relacionado con el pH de la solución, se aprecia un aumento de 3.56 a 5.32 (Figura 3). Esto
podría ser explicado por la formación de iones hidroxilo y de Fe+3
(ac) conforme las
reacciones (2-4):
Reacción ánodo:
Fe → Fe3+ + 3e− (2)
Reacción cátodo:
2H2O + 2e− → 2OH− + H2 (3)
Reacción total:
2Fe + 6H2O → 2Fe(OH)3 + 3H2 (4)
El hierro también puede reaccionar directamente con compuestos orgánicos que contienen
átomos con carga negativa, o formar complejos de hidróxidos poliméricos tales como:
Fe(H2O)63+
, Fe(H2O)5(OH)2+
, Fe(H2O)4(OH)2+, que dependen del pH del medio acuoso.
Estos hidróxidos, polihidróxidos o compuestos polihidroximetálicos tienen fuerte afinidad
por las partículas dispersas, así como contra-iones, lo cual provoca la coagulación (Mollah
et al., 2004).
La reducción de microorganismos muestra un proceso en dos etapas (Figura 5). La etapa
inicial promueve una rápida reducción y se presenta entre los 25 y 30 min, y la segunda
etapa se caracteriza por una reducción más lenta. El porcentaje máximo de reducción fue
93% para los dos grupos de microorganismos, un valor similar al obtenido por Ghernaout,
et al. (2008) empleando electrodos de aluminio y acero en un agua residual contaminada
con la bacteria E.coli. La mínima eficiencia del proceso se presentó en el menor tiempo
de tratamiento, con valores de 90% para la reducción de coliformes y 72% para la
reducción de mohos y levaduras; por lo tanto el aumento en el tiempo de tratamiento,
mejora la reducción de microorganismos, esto coincide con los resultados presentados por
otros autores (Azarian et al., 2007; Gao, Yang, et al., 2010).El proceso de
electrocoagulación bajo las condiciones estudiadas, generó resultados satisfactorios en la
reducción de DQO, coliformes, mohos y levaduras, perfilándose como una alternativa de
pre-tratamiento o reutilización de aguas contaminadas con mucílago de café.
39
CAPÍTULO VI
Eficiencia de inactivación de coliformes totales y Escherichia coli en agua natural dopada
mediante Fenton heterogéneo
Resumen
Se evaluó la inactivación de coliformes totales y Escherichia coli (E.coli) mediante el
proceso avanzado de oxidación conocido como Fenton heterogéneo, catalizado con arcilla
pilarizada preparada por ultrasonido y por microondas, en un reactor semibatch empleando
como factores, la concentración del agente oxidante, la carga del catalizador, el pH y el
tiempo de reacción.
El análisis estadístico demostró que los factores evaluados, tienen un efecto significativo
(p<0.05) en el porcentaje de inactivación de coliformes totales y E.coli, con un 95% de
confianza, independiente del tratamiento empleado en la elaboración del catalizador
(ultrasonido y microondas). La eficiencia de inactivación para coliformes y E.coli fue
superior al 70%. Las mejores condiciones para la inactivación de los microorganismos se
presentaron cuando se utilizó pH de 3.7, carga de catalizador de 0.5 g/L, tiempo de 240 min
y concentración de H2O2 entre 0.12 y 0.18 mg/L.
Palabras clave: Procesos avanzados de oxidación, oxidación catalítica en fase húmeda,
inactivación bacteriana, desinfección de agua, catalizador.
Abstract
Was evaluated the inactivation of total coliforms and Escherichia coli (E.coli) by using the
advanced oxidation process known as Heterogeneous Fenton, catalyzed with pillared clay,
prepared by ultrasound and microwave in a semibatch reactor using as variables of reaction,
the concentration of the oxidizing agent, catalyst load, pH, and the reaction time.
Statistical analysis showed that the factors evaluated, have a statistically significant effect
(p<0.05) in the percentage of inactivation of total coliforms and E. coli, with 95%
confidence, regardless of the treatment used in the preparation of the catalyst (ultrasound
and microwave). Inactivation efficiency for coliforms and E.coli was greater than 70%. The
best conditions for the inactivation of microorganisms were pH of 3.7, catalyst load of 0.5
g/L, time of 240 min and H2O2 concentration between 0.12 and 0.18 mg/L.
40
Keywords: Advanced oxidation processes, wet catalytic oxidation, bacterial inactivation,
water desinfection.
Introducción
La falta de agua potable, definida por la Organización Mundial de la Salud como aquella
“…adecuada para consumo humano y para todo uso doméstico habitual, incluida la higiene
personal” (OMS, 2004), continua siendo un problema mundial ligado a la deficiencia del
suministro seguro de este líquido (Boateng et al., 2011), generando 3 millones de muertes
al año en el mundo, de las cuales 2 millones son ocasionadas por enfermedades diarreicas,
con un alto impacto en la mortalidad infantil (UNICEF., 2008). También hay influencia en
el desarrollo del individuo, puesto que se ha demostrado, que la seguridad y sanitización del
agua, impactan en la salud física e intelectual y el desarrollo social y económico humano
(Spuhler, Rengifo-Herrera, & Pulgarin, 2010). Esta realidad, sumada a las implicaciones
del desarrollo tecnológico, la contaminación de los recursos hídricos y el cambio climático
a nivel mundial, hace prever deficiencias en el suministro inocuo del agua.
El principal desinfectante empleado en los procesos de potabilización es el cloro, debido a
su disponibilidad, economía, carácter oxidante y potencial de eliminación de
microorganismos patógenos (Diao et al., 2004), sin embargo, también se considera una
sustancia corrosiva y potencialmente peligrosa para la salud humana, ya que puede generar
subproductos de desinfección como los Trihalometanos (THMs), que se forman al
reaccionar con la materia orgánica presente en el agua (Moncayo-Lasso, Torres-Palma,
Kiwi, Benítez, & Pulgarín, 2008; A. G. Rincón & Pulgarín, 2007; Romero, 2009), algunos
THMs han sido identificados por la Agencia Internacional para la Investigación en Cáncer
como posibles carcinógenos en humanos (2010), generando una creciente conciencia en los
riesgos que presenta para la salud (Moncayo-Lasso, Sanabria, Pulgarín, & Benítez, 2009;
The International Agency for Research on Cancer, 2010) y para la conservación ambiental
(Diao et al., 2004).
Lo planteado anteriormente ha llevado a valorar métodos alternativos, como los procesos
avanzados de oxidación (PAO), estos involucran la generación de especies oxidantes
altamente reactivas, capaces de atacar y degradar sustancias orgánicas y
microorganismos (Gómez, González, Santa, Chiroles, & García, 2007; Mamane, Shemer,
& Linden, 2007; Pham, Brar, Tyagi, & Surampalli, 2010), estas técnicas tienen ventajas
como, la transformación química de los contaminantes, generación baja o nula de lodos,
posibilidad de tratar contaminantes a baja concentración, no formación de subproductos de
reacción y aumento de la biodegradabilidad(Forero et al., 2005). Entre los PAO se
encuentran tecnologías no-fotoquímicas y fotoquímicas, como los procesos Fenton y foto-
Fenton. Estos tratamientos buscan la formación de radicales hidroxilo, por la aplicación del
proceso Fenton (Fe2+
/H2O2) o la combinación de este e irradiación con luz UV (λ >
300nm)(Osorio, Torres, & Sánchez, 2010). La efectividad de estos procesos, se han
evaluado en la remoción de contaminantes de aguas de origen textil (Blanco, Torrades,
41
Varga, & García-Montaño, 2012), farmacéutico (Sirtori et al., 2009), hospitalario (Berto et
al., 2009), y en la eliminación de microorganismos patógenos (Chong, Jin, Zhu, & Saint,
2010; De Oliveira, Rosso, Cabonelli, & Giordano, 2011; A.-G. Rincón & Pulgarin, 2006b;
Watts, Washington, Howsawkeng, Loge, & Teel, 2003).
El objetivo del trabajo fue la evaluación eficiencia de inactivación de coliformes totales y
E.coli, en agua natural dopada destinada para consumo humano, empleando Fenton
heterogéneo con catalizadores preparados mediante ultrasonido y microondas.
Materiales y métodos
Catalizadores
La solución pilarizante fue preparada previamente mediante un trabajo desarrollado en el
grupo de investigación (Cárdenas, 2012), allí se sintetizó la solución a partir de
AlCl3•6H2O, FeCl3•6H2O y NaOH. La relación de hidrólisis OH/metal fue de 1.6. Una vez
la hidrólisis se completó, la temperatura se mantuvo a 80oC durante 1h, para un total de 7 h
de tratamiento térmico, transcurrido este tiempo la solución se dejó en reposo durante una
noche. La arcilla montmorillonita fue dispersada en tres medios: agua, etanol y acetona, a
tres concentraciones 2, 25 y 50 % (p/p).Para el proceso de intercalación se preparó la
disolución que contenía los policationes a intercalar y la suspensión con la arcilla, estos
fueron posteriormente sometidos a tratamiento por microondas o ultrasonido, para después
conseguir los óxidos correspondientes, de esta forma se obtuvo el catalizador preparado por
ultrasonido (CAT-US) y el catalizador preparado por microondas (CAT-MO).
Procedimiento Experimental
Los experimentos se desarrollaron en un reactor de vidrio (pyrex) semibatch, con capacidad
1000_mL y agitación constante (300 rpm). Se utilizaron 450 mL de agua natural,
proveniente del río Pasto (DQO 26 mgO2/L). La muestra fue dopada con los
microorganismos estudiados. El pH fue ajustado con NaOH y H2SO4 (0.1 mg/L) y el
registro de las variaciones fue medido con un potenciómetro (Metrhom, Suiza). Los
ensayos se realizaron a una temperatura promedio de 17±1°C.
Análisis Microbiológico
Se preparó una suspensión con coliformes totales y E.coli nativos, hasta alcanzar una
concentración de ~106 UFC/mL. Las muestras fueron analizadas mediante el método de
filtración por membrana de acuerdo con los métodos estándar (APHA, 1999). Las
membranas de celulosa de 0.45_µm, se situaron en una caja de petri con el medio de
cultivo Chromocult (Merck, Alemania) y se incubaron a 35±2°C, durante 24-48 h.
42
Diseño experimental
Se aplicó un diseño experimental factorial donde se evaluaron las variables tiempo de
tratamiento (30 a 240 min), pH (3.7 y 7.3), concentración del oxidante (0.06 a 0.18 mg/L) y
carga del catalizador (0.5 a 5 g/L). Estos parámetros fueron seleccionados basados en
investigaciones previas (Cárdenas, 2012; S.-P. Sun & Lemley, 2011). La variable de
respuesta fue la eficiencia de inactivación de coliformes totales y E.coli. Los datos fueron
analizados mediante el software estadístico Statgraphics® plus.
Resultados y discusión
Inactivación de coliformes totales y E.coli
Los factores concentración de H2O2, carga del catalizador, pH y tiempo de tratamiento,
tienen importancia estadística significativa (p<0.05) en la eficiencia de inactivación de
coliformes totales y E.coli, con un 95% de confianza, independiente del proceso
microondas o ultrasonidoempleado en la elaboración del catalizador.
Efecto del tiempo en la eficiencia de inactivación de coliformes totales y E.coli
En la Figura 1, es posible observar un aumento en la inactivación de coliformes totales y
E.coli, al incrementar el tiempo de tratamiento, esto coincide con los resultados presentados
por otros autores, en trabajos desarrollados con los procesos Fenton y Foto-Fenton (M.
Cengiz, M. O. Uslu, & I. Balcioglu, 2010; Moncayo-Lasso, Torres-Palma, Kiwi, Benitez, et
al., 2008; A.-G. Rincón & Pulgarin, 2006a). La mayor eficiencia de inactivación de los
microorganismos se alcanzó a los 240 min, la cual fue superior a 50 y 70% empleando
CAT-MO y CAT-US respectivamente. Existieron diferencias estadísticas entre los
diferentes tiempos evaluados, excepto entre 180 y 240 min para el CAT-US, señalando la
fase final de la inactivación.
43
Figura 1. Eficiencia de inactivación de coliformes totales y E.coli respecto al tiempo,
empleando CAT-US y CAT-MO
Efecto del pH en la eficiencia de inactivación de coliformes totales y E.coli
Se presentó una diferencia estadística significativa en los porcentajes de inactivación de
coliformes totales y E.coli según el pH. La eficiencia de inactivación de los
microorganismos fue mejor al emplear un pH de 3.7 (Figuras 2 y 3), con una inactivación
superior al 50%. Cuando se utilizó pH 7.3, los valores de inactivación fueron inferiores al
40% para CAT-US y 12% para el CAT-MO. Esto se debe a que la reacción Fenton se ve
favorecida al emplear pH<3, mejorando la solubilidad del Fe y la interacción con el H2O2,
por lo tanto hay un incremento en la eficiencia del tratamiento (Moncayo-Lasso, Torres-
Palma, Kiwi, Benitez, et al., 2008; Nogueira, Trovó, Silva, Villa, & Oliveira, 2007; Small,
Blankenhorn, Welty, Zinser, & Slonczewski, 1994); esto se ajusta a las interacciones
encontradas mediante el análisis estadístico, entre la dosis de H2O2 y el pH (p<0.05).
Figura 2. Eficiencia de inactivación de coliformes totales y E.coli respecto al pH,
empleando CAT-US.
44
Figura 3. Eficiencia de inactivación de coliformes totales y E.coli respecto al tiempo,
empleando CAT-MO.
Efecto de la carga del catalizador en la eficiencia de inactivación de coliformes totales y
E.coli.
En las figuras 4 y 5 se observa un incremento en la inactivación de los microorganismos, al
disminuir la carga del CAT-US, con valores de 56% y 60% para coliformes y E.coli
respectivamente. El análisis estadístico comprobó diferencias al emplear CAT-US, entre
0.5-2.17g/L y 0.5- 5.0g/L. Para CAT-MO, existió un incremento en la eficiencia de
inactivación de coliformes totales y E.coli, al emplear la carga mínima y máxima; con
reducciones superiores al 40%. El análisis estadístico comprobó diferencias en la
inactivación, al utilizar concentraciones del catalizador entre 0.5-2.17 g/L y 2.17g– 5.0 g/L.
Los resultados sugieren que mayores dosis de catalizador pueden propiciar reacciones
competitivas con la materia orgánica presente el agua natural evaluada, afectando la
generación de radicales hidroxilo, que inciden en la inactivación de los microorganismos
(Lin & Lo, 1997; Spuhler et al., 2010).
Figura 4. Eficiencia de inactivación de coliformes totales y E.coli respecto a la carga del
catalizador, empleando CAT-US.
45
Figura 5. Eficiencia de inactivación de coliformes totales y E.coli respecto a la carga del
catalizador, empleando CAT-MO.
Efecto de la dosis de H2O2 en la eficiencia de inactivación de coliformes totales y E.coli.
Cuando se emplearon concentraciones superiores a 0.12 mg/L de H2O2 con CAT-US y
CAT-MO (Figura 6 y 7), se observó un incremento en la inactivación de coliformes totales
y E.coli, excepto en los coliformes totales con CAT-US, en donde la mayor eficiencia es
con 0.18 mg/L de H2O2. El análisis estadístico mostró diferencias en los porcentajes de
inactivación de los microorganismos, entre 0.06 – 0.12 mg/L y 0.06– 0.18 mg/L. Algunos
autores indican que el exceso de H2O2, puede disminuir la eficiencia del proceso, al
producir la recombinación de los radicales hidroxilo en HO2, (Gil Pavas, Quintero Olaya,
Rincón Uribe, & Rivera Agudelo, 2007; Nogueira et al., 2007); sin embargo los resultados
evidencian un incremento en la eficiencia de inactivación de los microorganismos, al
emplear las mayores dosis de H2O2, esto indica que las concentraciones empleadas no son
suficientes para comprometer la efectividad del tratamiento sobre la inactivación de los
microorganismos.
46
Figura 6. Eficiencia de inactivación de coliformes totales y E.coli respecto al H2O2,
empleando CAT-US.
Figura 7. Eficiencia de inactivación de coliformes totales y E.coli respecto a al H2O2,
empleando CAT-MO.
Acción del tratamiento Fenton heterogéneo en los microorganismos.
Existen diversos estudios que sugieren que la formación de radicales hidroxilo durante el
proceso Fenton, inciden en la destrucción de las células microbianas (Berto et al., 2009;
Blanco et al., 2012; Boateng et al., 2011; Murat Cengiz, Merih Otker Uslu, & Isil
Balcioglu, 2010; Moncayo-Lasso et al., 2009; Moncayo-Lasso, Torres-Palma, Kiwi,
Benítez, et al., 2008; Pham et al., 2010; A.-G. Rincón & Pulgarin, 2006b; A. G. Rincón &
Pulgarín, 2007; Sirtori et al., 2009). Mamane, et al. plantea la coexistencia de dos
mecanismos de destrucción bacteriana por radicales hidroxilo, la oxidación y destrucción
de la membrana y pared celular, y al interior de la célula, la inactivación de enzimas,
deterioro de estructuras e interrupción de la síntesis proteica (Mamane et al., 2007). En el
caso específico de E. coli, se ha demostrado su mineralización a CO2 y H2O a través de una
cadena de reacciones, resaltándose como clave principal, la adhesión de los radicales
hidroxilo, para la destrucción de las uniones C-O en el exterior de la membrana celular (D.
D. Sun, Tay, & Tan, 2003).
Conclusiones
La aplicación del proceso avanzado de oxidación Fenton heterogéneo, permitió una
eficiencia de inactivación de coliformes totales y E.coli superior al 70% al emplear el
catalizador preparado mediante ultrasonido, los factores pH, carga de catalizador y pH,
fueron significativos en la eficiencia de inactivación.
El proceso Fenton heterogéneo evidenció un potencial para la disminución de los
contaminantes biológicos del agua natural destinada al consumo.
47
CAPÍTULO VII
Effect of supporting electrolyte on inactivation efficiency of Escherichia coli and
degradation pathways by electrooxidation with Ti/IrO2 anode
Abstract
It was found that inactivation of E.coli is better in the presence of NaCl and NaHCO3,
reaching 2.9-log and 2.8-log respectively in 5 min of treatment, in Na2SO4 solution, the
inactivation was 0.2-log. In natural water, the inactivation was 2.7-log in 7 min of contact
time, with a maximum oxidant concentration of 4.4 µmol L-1
. The high inactivation
efficiency with Ti/IrO2 anode when NaCl and NaHCO3 were used as supporting
electrolytes, is due mainly to the electro-generation of oxidants (indirect oxidation) with
bactericide effect, while in the presence of Na2SO4, the inactivation of the microorganisms
is due mainly for the direct electron transfer between the electrode and the microorganism
(direct oxidation), however for a better inactivation is necessary that both degradation
pathways occur simultaneously.
Keywords: Electrodisinfection, direct oxidation, indirect oxidation, electrooxidation
pathways.
Introduction
The waterborne diseases such as gastroenteritis, diarrhea, cholera, typhoid fever and
bacillary dysentery, are among the leading causes of death in developing countries,
affecting more than two million deaths annually, mainly in children (Cabral, 2010;
Woodall, 2009). This can be prevented with water disinfection, which allows the
inactivation of pathogenic microorganisms (bacteria, viruses and protozoa), that cause these
diseases. Chlorination is the primary method of water disinfection because it is effective
and economical, however is related to the formation of byproducts such as trihalomethanes
(THMs), which are recognized as potential carcinogens (Hrudey, 2009; G. S. Wang et al.,
2007).
The electrooxidation is an attractive alternative to chlorination, which allows the
degradation of different pollutants through direct or indirect oxidation, using electrodes as
graphite, Pt, Ti, DSA® and BDD on an aqueous medium (Palma-Goyes, Guzmán-Duque,
Peñuela, & González, 2010; Torres, Torres, Peringer, & Pulgarin, 2003). Through this
technique also have been successfully eliminated indicators microorganisms as coliforms,
fecal coliforms, E.coli, Streptococcus faecalis and Enterococcus faecalis(Cano et al., 2011;
48
Cotillas et al., 2013; Cui, Quicksall, Blake, & Talley, 2013; Frontistis et al., 2011; Schmalz
et al., 2009). Electrooxidation effectiveness was also studied in others bacteria such as
Pseudomonas aeruginosa(Griessler et al., 2010), which is considered an alternative
indicator aimed to evaluate the chemical disinfection process and L. pneumophila(Delaedt
et al., 2008), important for their ability to form biofilms and as an etiologic agent in the
"Legionnaires' disease". There are several studies that show the potential for disinfection of
the electrooxidation, but still there is little research related to parameters such as the
concentration and type of supporting electrolyte and its effect on the electrodisinfection
process. Some of these studies (Cong, Wu, & Li, 2008a; M. I. Kerwick, S. M. Reddy, A. H.
L. Chamberlain, & D. M. Holt, 2005; X. Li et al., 2004) have evaluated the effect of
supporting electrolytes NaCl, Na2SO4 and NaNO3 and its effect on the inactivation of
coliform bacteria, obtaining greater efficiency disinfection with NaCl, depending on the
concentration of the electrolyte, the current density and the treatment time. It can be
observed in these works, that the type of electrolyte and the electrode material has an
important role in electrodisinfection. So far, there are no reports of the effect of supporting
electrolytes using Ti/IrO2 anodes.
Therefore, the main objective of this study was to evaluate the influence of different
supporting electrolyte (NaCl, NaHCO3 and Na2SO4) in degradation pathways and
inactivation efficiency of E.coli using as anode Ti/IrO2.
Experimental
Reagents
Sodium sulfate (Sigma-Aldrich), sodium bicarbonate (Merck), sodium chloride
(Honeywell) were used as supporting electrolytes. Potassium iodide (JT Baker) and
ammonium heptamolybdate (Merck) were used in the measurement of oxidants. The
microbiological reagents, peptone water, and Endo agar were purchased from Oxoid. All
solutions were prepared with distilled water.
Aqueous solutions
Distilled water and natural water, contaminated with native E.coli were used in the
experiments. Inorganic species contained in natural water are shown in Table 1.
Table 1.Characteristics of natural water
pH Conductivity
(µS cm-1
)
Cl-
(mg L-1
)
Ca2+
(mg L-1
)
SO42-
(mg L-1
)
HCO3-
(mg L-1
)
Na+
(mg L-1
)
7.7 1149 54.8 179 445 239 33.6
Electrochemical experiments
49
Electrochemical tests were performed in a 200 mL batch reactor equipped with Ti/IrO2
anode, with an effective area of 6.25 cm2, and a 1 cm interelectrodic space. The electrodes
were connected to a direct current power supply (MCP Lab electronics), at a current density
of 16 mA cm-2
. The system was continuously stirred at 200 rpm. Assays were performed in
triplicate.
E.coli preparation and quantitation
A suspension with native E.coli in peptone water was prepared and incubated at 37 °C until
the sample was at 105-10
6 CFU 100 mL
-1. The bacterial suspension was adjusted according
to McFarland standard. The detection and quantitation of E.coli in the electrochemically
treated solution was performed by the membrane filtration technique according to standard
methods (APHA, 1999). The treated samples were filtered through cellulose membranes
(Advantec MFS) and then placed in Petri dishes with Endo agar, subsequently incubated at
37 °C for 24 h and counted.
Analysis
The oxidants evolution in the electrochemistry system, was determined by the Iodometric
method (Kormann, Bahnemann, & Hoffmann, 1988), in which the aliquots taken from the
electrochemical cell were placed in a quartz cell, containing a solution of potassium iodide
(0.1 mol L-1
) and ammonium heptamolybdate (0.01mol L-1
), the absorbance of this solution
was measured at 350 nm in a UV/Vis spectrophotometer (XLS Perkin Elmer, USA).
The energy consumption was calculated using the following equation (Akbal & Camci,
2011):
𝐸𝑐 =𝑈. 𝐼. 𝑡
𝑉 (2)
Where EC is the energy consumption (kWh m-3
), U is the applied voltage (V), I is the
current (A), t is the time of the electrooxidation (h), and V is the volume of treated water
(L).
50
Results and discussion
Effect of supporting electrolyte in the inactivation efficiency of E.coli
Figure 1.Effect of supporting electrolyte: a) Inactivation of E.coli, b) Evolution of oxidants.
[E.coli]o=106 CFU 100 mL
-1 ; [NaCl, NaHCO3, Na2SO4]o = 0.4 mol L
-1. Error bars indicate
standard deviation.
The Figure 1 shows the effect of the supporting electrolyte NaCl, NaHCO3, Na2SO4,
employing a concentration of 0.4 mol L-1
in the inactivation of E.coli and the oxidant
formation. In presence of NaCl the inactivation of the microorganism was efficient,
increasing with the time of treatment to 2.9-log in 5 min, with an energy consumption of
0.16 kWh m-3
. Similar results were obtained for other authors, using short contact time and
Ti/RuO2 anodes in E.coli inactivation(Diao et al., 2004; X.Y. Li et al., 2004). The
generation of oxidants with NaCl (Figure 1b), was superior to 221 µmol L-1
, this is due to
the catalytic activity of IrO2 anode in presence of chloride (Panizza & Cerisola, 2009),
generating active chlorinated species with bactericide effect, according to the equations:
51
2Cl- → Cl2 + 2e
- (2)
Cl2 + H2O → HOCl + H+ + Cl
- (3)
HOCl → H+ + OCl
- (4)
The formation of these active chlorinated species are depending on the pH solution, the
solutions with NaCl used in this study submitted an average pH of 6.7, therefore the
disinfection could be attributed mainly to the formation of HOCl, because is the main
chlorinated species in the pH range between 3 to 7 (McPherson, 1993; Torres, Sarria,
Torres, Peringer, & Pulgarin, 2003).
The disinfection of E.coli in presence of NaHCO3 was very effective (2.7-log) in the first 3
min of treatment, reaching 2.8-log at 5 min, with an energy consumption of 0.17 kWh m-3
.
The rapid decrease of E.coli (Figure 1a) and the formation of oxidants (Figure 1b), suggest
that the inactivation of the microorganism is because the formation of oxidants species with
disinfectant potential (J. Jeong et al., 2009). Some authors propose the formation of
percarbonate as a result of the indirect reduction of carbonate ions (Amstutz, Katsaounis,
Kapalka, Comninellis, & Udert, 2012; Osetrova, Bagotzky, Guizhevsky, & Serov, 1998),
this substance has an oxidant potential of 1.8V, superior to HOCl (1.49V) and OCl-
(0.89V), this could justify the fast inactivation in the first minutes at low concentration of
the oxidant (1.3 - 1.9 µmol L-1
).
When Na2SO4 is present in the aqueous medium not significant inactivation of E.coli was
observed. The results of the Figure 1a, shows a reduction of 0.2-log in 5 min of treatment,
with an energy consumption of 0.17 kWh m-3
. In Figure 1b is observed that the formation
of oxidants is low (0.2 µmol L-1
), this suggest that the inactivation is due to the direct
oxidation of the microorganism in the anode surface, because was not observed
instantaneous inactivation, as usual in the presence of oxidants (Joonseon Jeong et al.,
2007). Also is possible an inhibitory effect when is employed Na2SO4, due to increased
oxygen evolution with IrO2 anodes (Carlesi Jara, Fino, Specchia, Saracco, & Spinelli, 2007;
Siedlecka et al., 2013; Turro et al., 2011).
Effect of supporting electrolyte on degradation pathway in the inactivation of E.coli
A organic pollutant degradation by electrooxidation can occur in two ways: by direct
oxidation where the contaminants are destroyed at the anode surface or by indirect
oxidation where electrochemical generated substances may also destroy or convert the
oxidizable contaminants (Anglada et al., 2009). As can be seen from the results of this
study, biological contaminants such as E.coli can be degraded by electrooxidation,
therefore in order to understand the main degradation pathway of this microorganism were
performed electrooxidation tests under the conditions studied previously. Oxidizing
species were accumulated for 5 min, then was disconnected the power source and was
added the microorganism to the reactor, which remained in contact for 5 minutes with the
oxidants electro-generated, the results are shown below.
52
Oxidation in the presence of NaCl
Figure 2.E.coli inactivation and oxidants generated in NaCl solution. The electrochemical
treatment was stopped after 5 min (dotted line). [E.coli]o=105 CFU 100 mL
-1 ; [NaCl]o =
0.4 mol L-1
. Error bars indicate standard deviation.
Figure 2 shows an increase of oxidants concentration over time until the moment that the
electrochemical treatment is stopped, while the microorganism shows a rapid decrease
when it was in contact with the electro-generated oxidants; in less than a minute there is a
reduction of 3.1-log, this is a typical behavior in the presence of oxidants (Joonseon Jeong
et al., 2007), this result confirms that the main mechanism for the inactivation of
microorganism is due indirect oxidation. Figure 2 also shows that some microorganism
survives and grows even after being in contact with oxidants, which does not occur in the
presence of electrochemical treatment, as shown in Figure 1a. This result indicates that
although the indirect oxidation is the main mechanism of degradation in the inactivation of
E.coli, the direct oxidation also is an important mechanism on the inactivation and has an
important role on the total inactivation efficiency.
Oxidation in the presence of NaHCO3
Figure 3.E.coli inactivation and oxidants generated in NaHCO3 solution. The
electrochemical treatment was stopped after 5 min (dotted line). [E.coli]o=106 CFU 100
mL-1
; [NaHCO3]o = 0.4 mol L-1
. Error bars indicate standard deviation.
53
In Figure 3, there is an increase of oxidants with time until the electrochemical treatment is
stopped, after switching off the device the oxidants are quickly consumed in the first
minute, impacting in the inactivation of E.coli which decreases rapidly after 9 min to a 2.1-
log. This inactivation behavior is similar to Figure 1a in the presence of NaHCO3, verifying
that the main mechanism for the inactivation of E.coli in presence of this electrolyte is the
indirect oxidation, which can lead to the formation of oxidants such as percarbonate
(Amstutz et al., 2012; Osetrova et al., 1998). However unlike the behavior exhibited by the
inactivation in Figure 1a, the inactivation of E.coli in the absence of electrochemical
treatment is slower, this could be explained for the effect of the direct oxidation in the
microorganism, which improves the efficiency of inactivation.
Oxidation in the presence of Na2SO4
Figure 4. E.coli inactivation and oxidants generated in Na2SO4 solution. The
electrochemical treatment was stopped after 5 min (dotted line). [E.coli]o=106 CFU 100
mL-1
; [Na2SO4]o = 0.4 mol L-1
. Error bars indicate standard deviation.
Figure 4 shows a lower generation of oxidants, which are fully consumed one minute after
the electrochemical treatment stop. The low concentration of oxidants generated in the
presence of Na2SO4, has no significant impact on the inactivation of E.coli (0.02-log). By
comparing these results with the results of Figure 1a, allows verifying that the main route of
inactivation of microorganisms in the presence of Na2SO4, is by direct oxidation, justifying
the low efficiency of inactivation. These results validate a hypothesis previously exposed
by Gusmão, et al (Gusmão, Moraes, & Bidoia, 2010), indicating that one of the possible
mechanisms of disinfection of E.coli using DSA® electrode in a solution of Na2SO4, was
the direct electron transfer between the electrodes and the organism.
54
Proposed degradation pathway of E.coli in the presence de NaCl, NaHCO3 and Na2SO4 as
supporting electrolyte
Figure. 5. Microorganism degradation pathways. 1) Direct oxidation, 2) Indirect Oxidation.
The results presented in the study allow to state that the inactivation of E.coli in the
presence of NaCl, NaHCO3 and Na2SO4 as supporting electrolyte by electrooxidation with
Ti/IrO2 anode can be given in two ways as outlined in Figure 5. The first path is the direct
oxidation which involves the transfer of electrons between the anode and the
microorganism, and the second way is the indirect oxidation, where electro-generated
oxidizing substances act on the contaminant, in this case the microorganism.
The main mechanism of degradation of E.coli with the anode studied, for the case of NaCl
and NaHCO3is attributed to the indirect oxidation, unlike Na2SO4 attributed to the direct
oxidation. Also the fast inactivation of the microorganism is achieved to the electro-
generated substances with bactericide potential, generated by indirect oxidation (Figure 5,
pathway 2); however greater E.coli inactivation efficiency depends that the direct and
indirect oxidation occur simultaneously, and that the electro-generated substances have
sufficient oxidative capacity to inactivate the microorganism. So far, the microorganism
degradation employing electrooxidation with DSA® type electrodes has been attributed to
the formation of oxidants or the electric current independently (Y. Birbir & Birbir, 2006; Q.
Chen et al., 2009; Diao et al., 2004; Gusmão et al., 2009; X. Li et al., 2004; Li, Ding, Lo, &
Sin, 2002). Only Jeong, et al(Joonseon Jeong et al., 2007) had proposed a simultaneously
mechanism for the degradation of microorganism (direct and indirect oxidation), but using
Pt anodes in a phosphate buffer solution.
The efficient inactivation of the E.coli by electrooxidation, suggest that the effect on the
microorganism is due to an increased permeability of the cell membrane induced by
55
electron exchange in the direct oxidation (Park et al., 2003; Tolentino-Bisneto & Bidoia,
2003), and later the diffusion of bactericidal substances into the cell (H. Bergmann et al.,
2008), generated in the indirect oxidation pathway.
Effect of electrooxidation in natural water with Ti/IrO2 anode
Figure 6.E.coli inactivation in natural water with Ti/IrO2 anode. Error bars indicate
standard deviation.
In a further test, was evaluated the effect of electrooxidation on E.coli inactivation in
natural water which had a high concentration of the electrolytes studied (Table 1). The
generation of oxidants in the first minute was 1.3µmol L-1
, enough to quickly decrease the
microorganism 2.3-log, with an energy consumption of 0.09 kWh m-3
. The oxidant
concentration increased with time, reaching a maximum of 4.4 µmol L-1
in 7 min,
corresponding to a 2.7-log inactivation and an energy consumption of 0.53 kWh m-3
. The
fast inactivation observed in Figure 6, shows that the electro-generation of oxidants
(indirect oxidation), is the main route of degradation of the microorganism in this type of
water. The results demonstrated the technological capabilities of the electrooxidation for
the disinfection of water, because in short time and without the need of add supplementary
electrolytes, it is possible to inactivate E.coli.
Conclusions
The following conclusions were obtained from this study:
The study shows the electrooxidation with Ti/IrO2 anode as a promising alternative,
efficient and with low energy consumption, for disinfection of microorganisms in water.
E.coli inactivation by electrooxidation with Ti/IrO2 anode, is more effective when NaCl and
NaHCO3 are used as supporting electrolyte.
56
The main degradation pathway of the microorganism in the presence of NaCl and NaHCO3
as supporting electrolyte is the indirect oxidation; while the main mechanism with Na2SO4
as electrolyte is direct oxidation.
To improve the efficiency of inactivation of E.coli, it is necessary that direct and indirect
oxidation occur simultaneously, and the electro-generated substances have the sufficient
oxidative capacity to inactivate the microorganism.
On the electrooxidation of natural water contaminated with E.coli, predominated electro-
generation of oxidants, with a positive effect on the inactivation of the microorganism.
57
CAPÍTULO VIII
Electrochemical oxidation with RuO2 anode coupled with ultrasound in the disinfection of
urban wastewater
Abstract
This work focuses on coupling electrooxidation, with RuO2 anodes and ultrasound (sono-
electrolysis), for the inactivation of E.coli from actual treated urban wastewaters. Results
show that the electrooxidation is a promising technology in the inactivation of
microorganisms; however, when this technology is coupled with ultrasound is possible to
obtain better efficiency in inactivation. E.coli is inactivated not only by the
electrochemically produced chlorine disinfectant species but also by the physical effect
of the cavitation and pulses and the formation of free radicals in the ultrasound treatment.
Keywords: Electrolysis, Electrodisinfection, Sono-electrolysis, Power ultrasound, E.coli.
Introduction
The regeneration of urban wastewater is an interesting alternative for the efficient use of
water resources, because with the fulfilling of some quality requirements is possible to
apply this water on agricultural and urban irrigation, fire protection systems, industrial
cleaning or cooling systems (R.D 1620/2007). However, this type of water is characterized
by the microbiological risk associated with the presence of coliforms; therefore, the
reduction or elimination of pathogen microorganism is necessary in the treated effluent for
its safe reuse.
Traditionally, chlorination (for persistent) or ultraviolet (for non-persistent) disinfection
have been used for the inactivation of pathogenic microorganisms. These traditional
processes of water disinfection present some limitations as the possible formation of
disinfection byproducts (e. g. trihalomethanes) by using chlorination (Matamoros et al.,
2007), or the limitations related to presence of total suspended solids and the possibility of
the reactivation of bacteria for UV disinfection (Gehr, Wagner, Veerasubramanian, &
Payment, 2003; D. Haaken, Dittmar, Schmalz, & Worch, 2014; Quek & Hu, 2008).
Electrooxidation arises as a promising technique, which allows the inactivation of coliform
microorganism through direct or indirect oxidation. In this context, several investigations
have shown the potential of this technique on the elimination of coliform bacteria as
Escherichia coli (E.coli) in natural water, ballast water and wastewater, with different
anode materials (Cui et al., 2013; Lopez-Galvez et al., 2012; Ma, Liu, Tang, Yin, & Ai,
2011; Nanayakkara et al., 2012). In addition, our research group has previously
demonstrated the successful application of electrodisinfection on the elimination of
coliforms bacteria in urban wastewater using BDD anodes (Cano et al., 2011; Cano,
Cañizares, Barrera, Sáez, & Rodrigo, 2012; Cotillas et al., 2013; Llanos et al., 2014). In
these works, it was observed that the main mechanism of inactivation is the indirect
oxidation of E. coli by the oxidants formed by the oxidation of chlorides, one of the anion
most common in municipal treated wastewaters. Moreover, it was shown that both the
58
electrode material and the physicochemical characteristics of the water are key parameters
for the efficient disinfection of the target effluent.
Among the most commonly electrodes used for electrodisinfection are the dimensionally
stable anodes (DSA), these are generally made with a base of titanium and coated with
metal oxide material like PbO2, SnO2, PtO2, RuO2, IrO2 and TiO2 (Comninellis & Chen,
2010; Panizza & Cerisola, 2009). When some DSA-type anodes are used in the presence of
chloride, the principal chlorinated species generated is chlorine, which in water solution can
rapidly disproportionate to hypochlorite and chloride, as shown in the equations (1-3)
(Panizza & Cerisola, 2009). Moreover, hypochlorite can react with the ammonium ions,
produced from the reduction of nitrates present in the urban wastewater, producing
chloramines(4-6) (Lacasa, Llanos, Cañizares, & Rodrigo, 2012). These oxidant species has
a disinfectant potential, and help to minimize the formation of disinfection byproducts
(Krasner, 2009).
2Cl- → Cl2 + 2e
- (1)
Cl2 + H2O → HOCl + H+ + Cl
- (2)
HOCl → H+ + OCl
- (3)
NH3 + HClO → NH2Cl +H2O (4)
NH2Cl + HClO → NHCl2 + H2O (5)
NHCl2 + HClO → NCl3 + H2O (6)
In addition, ultrasound has demonstrated its ability to disinfect different types of water and
microorganisms, however requires a lot of energy to achieve inactivation, for this reason
there is increasing interest in coupling or combining with other techniques such as UV
(Bazyar Lakeh et al., 2013; Chrysikopoulos et al., 2013), Photo Fenton (Giannakis et al.,
2014), electrocatalysis(Ninomiya, Arakawa, et al., 2013) and electrolysis (Joyce et al.,
2003). In the sono-electrolysis published work, were evaluated electrodes of different
material (copper, carbon and stainless steel), featuring better treatment with copper
electrodes, attributed to its antibacterial properties.
Based on the potential of electrooxidation and ultrasound in water disinfection, the main
objective of this study was to evaluate the performance of an electrochemical oxidation
with RuO2 anode, as a single technique and coupled with ultrasound in the disinfection of
treated urban wastewater, putting special attention in the E.coli inactivation and the
formation of disinfection byproducts.
59
Material and Methods
Wastewater characterization
An effluent from the municipal wastewater treatment facilities (Ciudad Real, Spain) was
used. The samples were taken under similar weather conditions. Their main characteristics
are shown in Table 1.
Table 1. Main characteristics of treated wastewater
Parameter Value
Total Nitrogen (mg dm-3
) 37.86
TOC (mg dm-3
) 37.86
Conductivity (µS cm-1
) 1386
pH 7.93
E.coli (MPN 100 ml-1
) 750 - 18000
TOC – Total organic carbon
MPN – Most probable number
Experimental setup
The electrodisinfection experiments were carried out in a single-compartment
electrochemical flow cell, coupled with an ultrasound generator (Cañizares, Lobato, Paz,
Rodrigo, & Saez, 2005). RuO2 anode (Tiaano, India) was used as anodic material and
stainless steel (SS) AISI 304 (Mervilab, Spain) as cathodic material. The electrodes were
circular with a diameter of 10 cm. The ultrasound generator was a UP200S (Hielscher
Ultrasonics GmbH, Germany) equipped with a titanium glass horn of 40 mm
diameter, length 100 mm, emitting 24 kHz and maximum ultrasonic power of 200
W. The output can be continuous or pulsed and the amplitude can be varying in a duty
range from 20 to 100%.
The urban wastewater was fed to a glass tank of 2 dm3 and recirculated through the cell
with a peristaltic pump (JP Selecta Percom N-M328). Samples were collected from the
glass tank. E.coli and chlorine compounds (free and combined) were measured
immediately. In this way, it is not necessary the addition of reagents (e.g. Na2S2O3) to stop
the reaction between microorganisms and disinfectant species and therefore, the
experimental error of the measure is minimized.
Before electrooxidation experiments, the electrode was polarized during 15 min in a 1 M
Na2SO4 solution, at pH of 2. The temperature of the system was controlled with a
thermostatic bath and a heat exchanger, maintaining the temperature at 25°C.
60
Analytical procedure
Chloride inorganic anions (Cl-, ClO
-, ClO2
-, ClO3
-, ClO4
-) were measured by ion
chromatography using a Shimadzu LC-20A (Shodex IC I-524A column; mobile phase
2.5_mM phthalic acid at pH 4.0; flow rate 1.0 ml min-1
). Because the peak corresponding to
hypochlorite interferes with the chloride peak; the determination of hypochlorite was
carried out by titration with 0.001 M As2O3 in 2 M NaOH solution. The same ion
chromatography equipment (Shodex IC YK-421 column; mobile phase, 5.0 mM tartaric,
1.0 mM dipico-linic acid and 24.3 mM boric acid; flow rate, 1.0 ml min-1
) was used to
measure the nitrogen inorganic cation (NH4+). Inorganic chloramines were measured
following the DPD standard method described in the literature (APHA, 1999). The
presence of trihalomethanes was evaluated by gas chromatography (detection limit <0.2
ppb) using a SPB 10 column (30 m x 0.25 mm; macroporous particles with 0.25 µm
diameter), the injection volume was set to 1 µL.
Due to the nature of wastewater, the faecal coliforms were determined using the most
probable technique (MPN) with a confidence level of 95%, in accordance with standard
method (APHA, 1999). Microorganism counts were carried out by the multiple-tube-
fermentation technique (24 h of incubation at 44 °C) using 5 tubes at each dilution (1:10,
1:100, and 1:1000).
Inactivation kinetics
The inactivation kinetics were obtained with GInaFiT (Geeraerd and Van Impe Inactivation
Model Fitting Tool), this is a is a freeware add-in for Microsoft©
Excel, that allows testing
experimental data with different types of microbial survival models (Geeraerd,
Valdramidis, & Van Impe, 2005): log–linear regression, log–linear regression with
shoulder and tail, Weibull and biphasic models. The best fit model was selected by
evaluating different statistical tools (Root mean sum of squared error, and R2).
61
Results and discussion
General behavior of the electrodisinfection with RuO2 anode
Figure 1. Variation of E.coli with the applied electric charge at different current densities
during electrodisinfection of urban wastewater.
Figure 1 shows the changes in E.coli during the electrodisinfection of urban wastewater at
different current densities (1.49 to 25.54 A m-2
). As it can be observed, the inactivation of
E.coli increase with the applied charge, however are necessary current densities greater
than 11.65 A m-2
, to achieve the complete inactivation. The increase of E.coli inactivation
and it relation with the current, is due an improvement in the generation of chlorine species
with bactericide effect, this could explain a better inactivation efficiency. Also is possible a
better transfer of electrons between the anode and the microorganism, increasing the
permeability of the cell membrane (Diao et al., 2004; X. Li et al., 2004; Park et al., 2003).
Q (A h dm-3
)
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16
E.c
oli
/ E
.coli
0
0.0
0.2
0.4
0.6
0.8
1.0
1.49 A m-2
4.12 A m-2
6.89 A m-2
9.77 A m-2
Q (A h dm-3
)
0.0 0.1 0.2 0.3 0.4
E.c
oli
/ E
.co
li0
0.0
0.2
0.4
0.6
0.8
1.011.65 A m-
2
16.03 A m-2
20 A m-2
25.54 A m-2
(a)
(b)
62
Figure 2. Variation of chlorine species with the applied electric charge at different current
densities during electrodisinfection of urban wastewater. (a) 4.12 A m-2
, (b) 9.77 A m-2
, (c)
25.54 A m-2
.
Q (A h dm-3
)
0.000 0.005 0.010 0.015 0.020 0.025
Chlo
rine
spec
ies
(m
mo
l d
m-3
)
0.00
0.05
0.10
0.15
0.20
ClO-
ClO3
-
ClO4
-
NH2Cl
NHCl2
NCl3
Q (A h dm-3
)
0.000 0.005 0.010 0.015 0.020 0.025
Chlo
rine
spec
ies
(m
mo
l dm
-3)
0.00
0.05
0.10
0.15
0.20
ClO-
ClO3
-
ClO4
-
NH2Cl
NHCl2
NCl3
Q (A h dm-3
)
0.000 0.005 0.010 0.015 0.020 0.025
Chlo
rine
spec
ies
(m
mo
l d
m-3
)
0.0
0.1
0.2
0.3
0.4
0.5ClO
-
ClO3
-
ClO4
-
NH2Cl
NHCl2
NCl3
(a)
(b)
(c)
63
As can be observed in Figure 2, hypochlorite concentrations ranged between 0.020 and
0.505 mmol dm-3
, increasing at higher current densities, this could explain the better
efficiency inactivation of microorganism above 11.65 A m-2
. Chlorates and perchlorates,
were not detected at the current densities evaluated, this is an advantage of the DSA type
electrodes compared with other electrodes materials as the BDD (at higher currents
densities) (M. E. H. Bergmann et al., 2009; Sánchez-Carretero et al., 2011), avoiding the
formation of substances with adverse health effects (Jung, Baek, Oh, & Kang, 2010;
Kucharzyk, Crawford, Cosens, & Hess, 2009; Vellanki & Batchelor, 2013).
As previously mentioned the reaction of hypochlorite with ammonia present in the
municipal wastewater promotes the formation of chloramines, these substances are less
reactive and aggressive than hypochlorite (Llanos et al., 2014), decreasing the formation of
disinfection by-products, and with the advantage that also affect microorganisms (Berry,
Holder, Xi, & Raskin, 2010; Holder, Berry, Dai, Raskin, & Xi, 2013). It was observed and
increase of chloramines concentration with the current density, with values over 0.032
mmol dm-3
for 20 A m-2
and 25.54 A m-2
, this also could explain a better inactivation
efficiency at higher current densities.
Figure 3. Formation of trihalomethanes at different current densities. Dashed lines indicate
the limit of trihalomethanes set by the EU in drinking water.
Figure 3 shows the variation of trihalomethanes in the urban wastewater after the
electrochemical treatment. Although the EU does not require the determination of
trihalomethanes in this type of wastewater, were measured due to the capacity of
chlorination for the formation of this byproducts, which are recognized as potential hazards
for the health (Hrudey, 2009). It can be observed the presence of trihalomethanes with a
maximum value of 40.793µg L-1
, however these were lower than the limits set by the EU of
100_µg_L-1
for drinking water (Council Directive 98/83/EC). Despite the formation of free
chlorine in the presence of organic matter, the concentration of trihalomethanes formed in
the electrochemical process is not considerable to be taken into account as a risk to health.
Current density (A m-2
)
0 5 10 15 20 25
TH
Ms
(µg L
-1)
0
20
40
60
80
100
Min
Max
64
General behavior of the electrooxidation with RuO2 anode coupled with ultrasound
In a final set of experiments, bacteria inactivation by means of sono-electrolysis was
investigated. Based on the results showed previously, a current density of 9.77 A m-2
was
selected, because at a current density lower of 11.65 A m-2
the inactivation was incomplete,
thus an improvement in efficiency can be observed easily.
Figure 4. Variation of E.coli with the applied electric charge at different ultrasound power,
during sono-electrolysis of urban wastewater. (a) Continuous, (b) Pulsed (0.5 s).
As can be observed in Figure 4, the results show a substantial improvement in the
inactivation efficiency by using the coupled sono-electrolysis process, compared to the
results obtained with a 9.77 A m-2
employing only electrooxidation (Fig. 1a). The
inactivation efficiency was better when the ultrasound was pulsed at 40 W and 80 W, in
continuous mode the best inactivation was with 200 W. This might be explained by a
mechanical effect of the pulses on the microorganism, this additional effect to cavitation
and the formation of free radicals of the ultrasound, would allow to the microorganism be
more susceptible to the chlorinated species produced by the electrooxidation.
Q (A h dm-3
)
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14
E.c
oli
/ E
.co
li0
0.0
0.2
0.4
0.6
0.8
1.040 W
80 W
120 W
160 W
200 W
Q (A h dm-3
)
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14
E.c
oli
/ E
.co
li0
0.0
0.2
0.4
0.6
0.8
1.040 W
80 W
120 W
160 W
200 W
(a)
(b)
65
Figure 5. Variation of chlorine species with the applied electric charge and ultrasound at
200W, during sono-electrolysis of urban wastewater. (a) Continuous, (b) Pulsed (0.5 s).
Figure 5 shows that the highest concentration of hypochlorite was 0.1 mmol dm-3
at 200 W
with pulsed and continued mode. The highest concentration of chloramines with pulses was
0.012 mmol dm-3
at 40W, while without pulses the highest concentration of chloramines
was 0.032 mmol dm-3
at 120 W. Chlorates and perchlorates, were not detected in the sono-
electrolysis process. In continuous mode, predominate the cavitation promoting the
formation of free radicals, and helping to oxidation of the different compounds present in
the wastewater. Therefore, the formation of chlorine species tend to be higher, this also
affects the formation of trihalomethanes (Figure 6), showing a maximum concentration of
trihalomethanes of 87.495 mg L-1
for the continuous treatment at 120 W and 37.199 mg L-1
pulsed and 80 W. Despite the values, are also below the limits set by the EU of 100 µg L-1
for drinking water (Council Directive 98/83/EC).
Q (A h dm-3
)
0.000 0.005 0.010 0.015 0.020 0.025
Chlo
rine
spec
ies
(m
mo
l dm
-3)
0.00
0.05
0.10
0.15
0.20ClO
-
ClO3
-
ClO4
-
NH2Cl
NHCl2
NCl3
Q (A h dm-3
)
0.000 0.005 0.010 0.015 0.020 0.025
Chlo
rine
spec
ies
(m
mo
l dm
-3)
0.00
0.05
0.10
0.15
0.20
ClO-
ClO3
-
ClO4
-
NH2Cl
NHCl2
NCl3
(a)
(b)
66
Figure 6. Formation of trihalomethanes at different current densities. (a) Continuous, (b)
Pulsed (0.5 s). Dashed lines indicate the limit of trihalomethanes set by the EU in drinking
water.
Inactivation kinetics
Table 2. Inactivation kinetics for sono-electrolysis in continuous mode
Power
(W)
Model
log-lineal Weibull Double Weibull Biphasic
RMSE R2 RMSE R
2 RMSE R
2 RMSE R
2
40 0.2444
0.8062 0.1050
0.9693 0.0541
0.9932 0.0828
0.9841
80 0.0842
0.9770 0.0927
0.9778 0.1070
0.9778 0.1059
0.9782
Power (W)
0 50 100 150 200
TH
Ms
(µg L
-1)
0
20
40
60
80
100
Min
Max
Power (W)
0 50 100 150 200
TH
Ms
(µg L
-1)
0
20
40
60
80
100
Min
Max
(a)
(b)
67
120 0.1194
0.9769 0.1290
0.9784 0.1490
0.9784 0.1541
0.9769
160 0.1240
0.9694 0.0697
0.9919 0.0455
0.9973 0.0483
0.9969
200 0.1339
0.9659 0.1115
0.9823 0.1087
0.9888 0.1894
0.9659
Table 3. Inactivation kinetics for sono-electrolysis pulsed mode
Power
(W)
Model
log-lineal Weibull Double Weibull Biphasic
RMSE R2 RMSE R
2 RMSE R
2 RMSE R
2
40 0.1101 0.9095 0.0901
0.9545 0.0393
0.9942 0.0745
0.9793
80 0.0712
0.9342 0.0424
0.9825 0.0369
0.9912 0.0439
0.9875
120 0.0498
0.9059 0.0548
0.9089 0.0573
0.9252 0.0643
0.9059
160 0.0888
0.9597 0.0738
0.9778 0.0852
0.9778 0.1147
0.9597
200 0.2528
0.9065 0.2696
0.9114 0.3015
0.9114 0.3097
0.9065
A non-linear analysis of regression was used to investigate the inactivation of E.coli with
different cycles and the potential of ultrasound in a coupled sonoelectrolysis treatment.
Although the process of inactivation by sonoelectrolysis not presented a marked log-linear
trend, this model has a good fitting to data (R2>0.806). However, the models with the best-
fitted experimental results were the Double Weibull and Weibull, with a R2 value ranged
between 0.911 and 0.997, it were the most suitable models for describing the decline of
E.coli. These models allows show different shapes of survival curves, related to a stressful
environment or different physiological state of the cells (Coroller, Leguerinel, Mettler,
Savy, & Mafart, 2006), linked to the conditions of the evaluated coupled treatment.
68
Conclusions
The following conclusions were obtained from this study:
Electrooxidation with RuO2 anodes is an efficient technology for the inactivation of E.coli
in municipal wastewater, the production of chlorine species has a key role in the
inactivation of the microorganism.
Inactivation of E.coli is more efficient when is coupled electrooxidation and ultrasound,
allowing to use lower current densities. The improve in the inactivation is due the physical
effect of the cavitation and pulses by ultrasound, and the chlorine species by
electrooxidation.
Application of a pulsed ultrasound shows a positive effect on the efficiency of the
inactivation of E.coli, probably related to a mechanical effect of the pulses on the
microorganism, allowing a better effect of the chlorinated species produced by the
electrooxidation.
The formation of dangerous compounds such as perchlorate and chlorate was not found.
Trihalomethanes were detected in low concentrations, but are below the limits set by the
EU for drinking water.
The Weibull models can be used to describe the inactivation of E.coli during the sono-
electrolysis of a treated municipal wastewaters.
69
CAPÍTULO IX
Inactivation of Escherichia coli by combination of ultrasound, ultraviolet irradiation and
iron
Abstract
This work focuses on the combination of Ultrasound (US), ultraviolet irradiation (UV) and
Iron (Fe), for the inactivation of E.coli in water. Results show that the combination US/Fe,
US/UV and US/UV/Fe are promising technologies for the inactivation of microorganisms.
The inactivation behavior of the combined treatment was better than when were applied
individually. The H2O2 formed during the ultrasound process is important for the
subsequent reaction with Iron and UV, this lead to the formation of hydroxyl radicals,
which have an important role in inactivation of microorganism. The non-linear biphasic and
double Weibull models, had the best-fitted experimental inactivation survival curves,
indicated by the lowest RMSE and values and the highest R2.
Keywords: Advanced oxidation process, disinfection, sono-photo Fenton, E.coli.
Introduction
Water-borne diseases are among the leading causes of deaths in developing countries,
affecting mainly children (Cabral, 2010; Woodall, 2009). The common strategy to
eliminate these pathogenic microorganisms in water is through chlorination; however they
are currently evaluating other alternatives due some limitations as the possible formation of
disinfection byproducts such as trihalomethanes (THMs) (Hrudey, 2009; G. S. Wang et al.,
2007).
Several studies show other techniques with a potential of microorganisms inactivation in
water, such as advanced oxidation processes (AOPs), these process involve the generation
of highly reactive oxidizing species, able to attack and degrade organic substances and
microorganisms (Gómez et al., 2007; Mamane et al., 2007; Pham et al., 2010). AOPs also
have other advantages as, the chemical transformation of the pollutants, low or no sludge
generation, possibility to treat contaminants at a low concentration, no reaction product
formation and increased biodegradability (Forero et al., 2005). Among the PAOs it can be
found the ultrasound.
It is called ultrasound to the sound waves with frequencies above the threshold of human
hearing, is divided into high, medium and low frequency ultrasound (Goncharuk et al.,
2008). It has shown great potential in the treatment of water and wastewater, and also the
ability to disinfect different types of water and microorganisms, however requires a lot of
energy to achieve inactivation (Al Bsoul et al., 2010; Shinobu Koda et al., 2009; Mahamuni
& Adewuyi, 2010). For this reason there is increasing interest in coupling or combining
with other techniques such as Photocatalysis (Ogino, Farshbaf Dadjour, Takaki, & Shimizu,
2006), disinfectants (Ayyildiz, Sanik, & Ileri, 2011), Ultraviolet irradiation (Bazyar Lakeh
70
et al., 2013; Chrysikopoulos et al., 2013), Photo-Fenton (Giannakis et al., 2014),
electrocatalysis (Ninomiya, Arakawa, et al., 2013) and electrolysis (Joyce et al., 2003),
mainly for the disinfection of bacteria like E.coli, total coliforms, and Legionella
pneumophila.
The disinfection by combined treatments with ultrasound, allow different effect in the
microorganism, like damage for mechanical stress, disaggregation of microorganism
cluster, membrane an cellular wall damage and formation of oxidants with bactericide
effect like H2O2 and hydroxyl radicals (Ninomiya, Arakawa, et al., 2013; Ninomiya, Ogino,
et al., 2013; Shimizu, Ninomiya, Ogino, & Rahman, 2010).
The main objective of this study was the evaluation of combined treatment of ultrasound,
ultraviolet irradiation and Iron in the E.coli inactivation and formation of oxidants.
Material and Methods
Reagents
Potassium iodide (Riedel-de Hanën) and ammonium heptamolybdate (Merck) were used in
the measurement of Hydrogen peroxide evolution. Ferrous sulfate, was obtained from
Riedel-de Hanën. The microbiological reagents, peptone water, and Endo agar were
purchased from Oxoid. All solutions were prepared with deionized water.
Experimental setup
The source of ultrasonic waves (600 kHz, 60 W) was a piezoelectric disk (diameter 4 cm)
fixed on a Pyrex plate (diameter 5 cm) in the bottom of a cylindrical water-jacketed glass
reactor of 500 mL of capacity, which was fed with 300 mL of the solution with the
microorganism. The cylindrical sonochemical reactor was thermostated by a water jacket at
20°C. A germicidal lamp (General electric, 4 W) emitting at a predominant wavelength of
254 nm provided UV irradiation.
Analytical procedure
Hydrogen peroxide evolution in the system, was determined by the Iodometric method
(Kormann et al., 1988), in which the aliquots taken from the reactor were placed in a quartz
cell, containing a solution of potassium iodide (0.1 mol L-1
) and ammonium
heptamolybdate (0.01mol L-1
), the absorbance of this solution was measured at 350 nm in a
UV/Vis spectrophotometer (SPECTRONIC® 20 GENESYS™).
E.coli preparation and quantitation
A suspension with native E.coli in peptone water was prepared and incubated at 37 °C until
the sample was at 105-10
6 CFU 100 mL
-1. The bacterial suspension was adjusted according
to McFarland standard. The detection and quantitation of E.coli in the electrochemically
treated solution was performed by the membrane filtration technique according to standard
71
methods (APHA, 1999). The treated samples were filtered through cellulose membranes
(Advantec MFS) and then placed in Petri dishes with Endo agar, subsequently incubated at
37 °C for 24 h and counted.
Inactivation kinetics
The inactivation kinetics were obtained with GInaFiT (Geeraerd and Van Impe Inactivation
Model Fitting Tool), this is a is a freeware add-in for Microsoft©
Excel, that allows testing
experimental data with different types of microbial survival models (Geeraerd et al., 2005):
log–linear regression, log–linear regression with shoulder and tail, Weibull and biphasic
models. The best-fit model was selected by evaluating different statistical tools (Root mean
sum of squared error - RMSE, and R2).
Results and discussion
General behavior of different advanced oxidation processes (AOPs)
Figure 1, shows the inactivation of E.coli as a function of time, when Ultrasound (US),
Ultraviolet irradiation (UV), Fe, US/UV, US/Fe and US/UV/Fe treatments were applied.
UV irradiation and iron alone are not considered AOPs, but are control for the
microorganism inactivation.
Figure 1. Inactivation of E.coli under different treatments as a function of time.
Time (min)
0 10 20 30 40 50 60
Lo
g (
N/N
o)
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
US
UV
Fe
US/Fe
US/UV
US/UV/Fe
72
Figure 2. Evolution of H2O2 under different treatments as a function of time.
Ultraviolet irradiation
As can be seen in Figure 1, UV irradiation has an impact in the inactivation of E.coli,
reaching 1.3-log in 15 min of treatment; the maximum inactivation was 2.4-log at 60 min.
The formation of H2O2 show in the Figure 2, was negligible. Is well known the effect of
UV in disinfection of water (Blatchley et al., 2012), generating a DNA damage in the
microorganism, causing loss of culturability (Suss, Volz, Obst, & Schwartz, 2009).
However there is some limitations related to presence of total suspended solids and the
possibility of the reactivation of bacteria after the treatment (Gehr et al., 2003; D. Haaken et
al., 2014; Quek & Hu, 2008).
Iron
Figure 1 illustrates, that iron alone do not have any effect on the inactivation of E.coli, and
in fact, the microorganism continue their growth during the 60 min of treatment. In
addition, as was expected there is no formation of H2O2 during the essays (Figure 2).
Ultrasound
Ultrasound alone allow a slow inactivation of E.coli, the best inactivation efficiency was at
60 min, obtaining 2.9-log. The inactivation by ultrasound is attributed to the mechanical
forces by the collapse of the cavitation bubbles affecting the cell wall of the
microorganism, moreover there is an attack of free radicals and H2O2 formed by
sonochemical reactions (Gao, Lewis, et al., 2014a, 2014b; Goncharuk et al., 2008).
O2 + H• → HO2
• (1)
O2→ O + O (2)
Time (min)
0 10 20 30 40 50 60
H2O
2 (
µm
ol L
-1)
0
10
20
30
40
US
UV
Fe
US/Fe
US/UV
US/UV/Fe
73
O + H2O → HO• + HO
• (3)
HO2•+ HO2
•→ H2O2 + O2 (4)
In Figure 2 it can be observed, that ultrasound reach the highest concentration of H2O2 with
38.73_µmol L-1
in 60 min. Despite this, the treatment did not present the best inactivation
for the microorganism, this is because in high frequency ultrasound, predominate the
sonochemistry effects over the mechanical effects (Al Bsoul et al., 2010), therefore
probably there is not sufficient damage in the cell wall to allow entry of free radicals to
interior of the microorganism cell.
US/ Fe
The inactivation of E.coli with the combined process US/Fe show in the Figure 1, was more
efficient than in ultrasound and Fe alone, with a inactivation of 2.5-log in 15 min to 3.3-log
in 60 min. This good behavior is due to a synergy of H2O2 generated by ultrasound (Figure
2), which together with Fe, allowed a Fenton reagent, generating hydroxyl radicals
(Selvakumar, Tuccillo, Muthukrishnan, & Ray, 2009) as shown in the following equations:
Fe2+
+ H2O2 → Fe3+
+ HO• + OH
– (5)
Fe3+
+ H2O2 → Fe2+
+ HOO• + H
+ (6)
The inactivation is attributed to bacterial destruction by hydroxyl radicals, the oxidation
and destruction of the membrane and cell wall and into the cell, the inactivation of
enzymes, and interruption of protein synthesis (Mamane et al., 2007).
US/UV
Under the US/UV treatment, a similar effect to US/Fe was observed, with a inactivation of
2.7-log in the first 15 min of treatment to 3.3-log in 60 min, this can be explained by the
photodecomposition at 254 nm of H2O2 produced by ultrasound (Figure 2), generating
hydroxyl radicals as shown in equation (7) (Legrini, Oliveros, & Braun, 1993). This causes
damage to the membrane and cellular wall, allowing better UV radiation into the cell (Cho,
Gandhi, Hwang, Lee, & Kim, 2011).
H2O2 + hν→ 2 HO•
(7)
US/UV/ Fe
Figure 1 shows a fast inactivation of E.coli in 15 min of treatment with 2.9-log, up to 3.2-
log in 60 min, when US/UV/Fe was applied. The inactivation efficiency was similar to
US/UV and US/Fe. The decrease of H2O2 (Figure 2), was higher that the observed with the
other combined treatments, this is explained by the reaction of Fe with the H2O2, explain in
the equations (5) and (6), and the photodecomposition of H2O2 showed in the equation (7),
74
producing additionally hydroxyl radicals. Therefore, is expected a combined effect from
H2O2 and hydroxyl radicals, over the lipidic bilayer membrane and DNA damage caused
for the UV irradiation (Cabiscol, Tamarit, & Ros, 2000).
Inactivation kinetics
Table 2. Inactivation kinetics for sono-electrolysis in continuous mode
Treatments Model
Biphasic Weibull Double Weibull Biphasic
RMSE R2 RMSE R
2 RMSE R
2 RMSE R
2
US/Fe 0.8150
0.6801 0.4931
0.9219 0.4101
0.9730 0.3461
0.9808
US/UV 0.8567
0.6882 0.1804
0.9908 0.2552
0.9908 0.1755
0.9956
US/Fe/UV 1.0119
0.5857 0.5045
0.9313 0.0740
0.9993 0.4607
0.9714
A non-linear analysis of regression was used to investigate the inactivation of E.coli with
the combined treatments US/Fe, US/UV and US/Fe/UV. The different process of
inactivation showed no marked log-linear trend, as can be observed in Table 1 (R2
< 0.688).
The models with best the best-fitted experimental inactivation survival curves, were
biphasic and double Weibull as indicated by the lowest RMSE and values and the highest
R2. Biphasic model was better for US/Fe and US/UV treatments, with a R
2> 0.980 and the
double Weibull model was better for the combined process of US/Fe/UV, with a R2 value
of 0.999.
These models show different shapes of survival curves, related to a stressful environment or
different physiological state of the cells (Cerf, 1977; Coroller et al., 2006), linked to the
conditions of the evaluated combined treatment.
Conclusions
Inactivation of E.coli is more efficient during the combination of Ultrasound, ultraviolet
irradiation and Iron; this is due the formation of H2O2 by ultrasound, the reaction of Iron
with the H2O2, and the photodecomposition of H2O2, producing additionally hydroxyl
radicals, which has a key role in the inactivation of the microorganism. Double Weibull
model and the biphasic model can be used to describe the inactivation of E.coli during the
combination of Ultrasound, UV irradiation and Iron.
75
76
CAPÍTULO X
CONCLUSIONES GENERALES
Las siguientes conclusiones se derivan de este trabajo:
La electrocoagulación demostró ser un excelente método para la remoción de
microorganismos y materia orgánica, con un bajo consumo energético. El incremento en el
tiempo de tratamiento, un pH inicial ácido resultaron ser de gran importancia en la
remoción de microorganismos.
El proceso Fenton heterogéneo, presentó una eficiencia superior al 70% en la inactivación
de E.coli y coliformes fecales. La eficiencia de inactivación fue dependiente de factores
como el tiempo de tratamiento, la dosis del catalizador y la concentración de H2O2. Sin
embargo es necesario un tiempo de tratamiento >180 min y la acidificación del medio a
tratar.
La electrooxidación con ánodos tipo DSA, presentó una buena eficiencia de inhibición de
microorganismos, un bajo consumo energético y baja o nula formación de subproductos de
desinfección, por lo que se perfila como una alternativa prometedora de desinfección. En
este proceso electroquímico, la formación de sustancias oxidantes y el intercambio de
electrones entre el ánodo y los microorganismos, tienen un papel importante en la
inactivación.
El tratamiento combinado entre electrooxidación y ultrasonido permitió mejorar la
eficiencia de inactivación del proceso de electrooxidación individual, esto se debe a la
formación de especies cloradas con un efecto bactericida durante la electrooxidación y el
efecto físico-químico generado por el ultrasonido.
Durante el tratamiento combinado entre electrooxidación y ultrasonido, no se generaron
cloratos o percloratos; y aunque se formaron Trihalometanos, estos fueron en
concentraciones inferiores a las expuestas por la Unión Europea en agua de consumo, por
lo que no representan un riesgo para la salud.
Los tratamientos combinados entre ultrasonido, radiación ultravioleta y hierro, fueron
eficientes en la inactivación de E.coli, debido a la reacción del hierro y la radiación
ultravioleta con el H2O2 formado durante el tratamiento de ultrasonido, produciendo
radicales hidroxilo, que tienen un papel importante en la inactivación de microorganismos.
77
Los tratamientos combinados de ultrasonido y electrooxidación, presentaron como modelos
más ajustados a las curvas de inactivación, los modelos Weibull y Doble Weibull; mientras
que para la combinación de ultrasonido, irradiación ultravioleta y hierro, los modelos que
mejor se ajustaron a las curvas de inactivación, fueron Doble Weibull y Bifásico.
RECOMENDACIONES
Con base en los resultados obtenidos en este trabajo, se sugiere las siguientes
recomendaciones para futuras investigaciones:
Se recomienda allegar más información para elucidar los mecanismos de inactivación, tanto
individuales como combinados.
Validar los modelos expuestos en este trabajo, que explican teóricamente las curvas de
inactivación de los tratamientos combinados estudiados.
Estudiar algunos aspectos operativos, el efecto de la matriz acuosa y otros microorganismos
desde el punto de vista de inocuidad, en los tratamientos combinados propuestos.
Se recomienda mejorar los procesos individuales y combinados desde el punto de vista
económico y tecnológico antes de una aplicación a mayor escala.
78
BIBLIOGRAFÍA
Abdelwahab, O., Amin, N. K., & El-Ashtoukhy, E. S. (2009). Electrochemical removal of phenol
from oil refinery wastewater. Journal of Hazardous Materials, 163(2-3), 711-716. doi:
10.1016/j.jhazmat.2008.07.016
Abraham, V. T., Radhakrishnan Nair, N., & Madhu, G. (2009). Electrochemical treatment of skim
serum effluent from natural rubber latex centrifuging units. Journal of Hazardous
Materials, 167(1-3), 494-499. doi: 10.1016/j.jhazmat.2009.01.004
Agustin, M. B., Sengpracha, W. P., & Phutdhawong, W. (2008). Electrocoagulation of palm oil mill
effluent. Int J Environ Res Public Health, 5(3), 177-180.
Akbal, F., & Camci, S. (2011). Copper, chromium and nickel removal from metal plating
wastewater by electrocoagulation. Desalination, 269(1-3), 214-222.
Al Bsoul, A., Magnin, J. P., Commenges-Bernole, N., Gondrexon, N., Willison, J., & Petrier, C.
(2010). Effectiveness of ultrasound for the destruction of Mycobacterium sp. strain (6PY1).
Ultrasonics Sonochemistry, 17(1), 106-110. doi: 10.1016/j.ultsonch.2009.04.005
Amstutz, V., Katsaounis, A., Kapalka, A., Comninellis, C., & Udert, K. M. (2012). Effects of
carbonate on the electrolytic removal of ammonia and urea from urine with thermally
prepared IrO2 electrodes. Journal of Applied Electrochemistry, 42(9), 787-795.
Anglada, Á., Urtiaga, A., & Ortíz, I. (2009). Contribution of electrochemical oxidation to waste-
water treatment: fundamentals and review of applications. J ChemTechnol Biotechnol,
84(12), 1747–1755.
Antoniadis, A., Poulios, I., Nikolakaki, E., & Mantzavinos, D. (2007). Sonochemical disinfection of
municipal wastewater. Journal of Hazardous Materials, 146(3), 492-495. doi:
10.1016/j.jhazmat.2007.04.065
APHA. (1999). Standard Methods for the Examination of Water and Wastewater (Version 19th).
Washington DC.
Avallone, S., Guiraud, J.-P., Guyot, B., Olguin, E., & Brillouet, J.-M. (2000). Polysaccharide
Constituents of Coffee-Bean Mucilage. Journal of Food Science, 65(8), 1308-1311.
Ayyildiz, O., Sanik, S., & Ileri, B. (2011). Effect of ultrasonic pretreatment on chlorine dioxide
disinfection efficiency. Ultrasonics Sonochemistry, 18(2), 683-688. doi:
10.1016/j.ultsonch.2010.08.008
Azarian, G. H., Mesdaghinia, A. R., Vaezi, F., Nabizadeh, R., & Nematollahi, D. (2007). Algae
Removal by Electro-coagulation Process, Application for Treatment of the Effluent from an
Industrial Wastewater Treatment Plant. Iranian J Publ Health., 36(4), 57-64.
Barashkov, N. N., Eiseinberg, D., Eisenberg, S., Shegebaeva, G. S., Irgibaeva, I. S., & Barashkova,
I. I. (2010). Electrochemical Chlorine Free AC Disinfection of Water Contaminated with
Salmonella typhimurium Bacteria. Russian Journal of Electrochemistry (Translation of
Elektrokhimiya), 46(3), 320–325.
Bazyar Lakeh, A. A., Kloas, W., Jung, R., Ariav, R., & Knopf, K. (2013). Low frequency
ultrasound and UV-C for elimination of pathogens in recirculating aquaculture systems.
Ultrasonics Sonochemistry, 20(5), 1211-1216. doi: 10.1016/j.ultsonch.2013.01.008
Bergmann, H., Koparal, A. T., Koparal, A. S., & Ehrig, F. (2008). The influence of products and
by-products obtained by drinking water electrolysis on microorganisms. Microchemical
Journal, 89(2), 98–107.
Bergmann, M. E. H., Rollin, J., & Iourtchouk, T. (2009). The occurrence of perchlorate during
drinking water electrolysis using BDD anodes. Electrochimica Acta, 54(7), 2102-2107. doi:
10.1016/j.electacta.2008.09.040
Berry, D., Holder, D., Xi, C., & Raskin, L. (2010). Comparative transcriptomics of the response of
Escherichia coli to the disinfectant monochloramine and to growth conditions inducing
79
monochloramine resistance. Water Research, 44(17), 4924-4931. doi:
10.1016/j.watres.2010.07.026
Berto, J., Rochenbach, G. C., Barreiros, M. A., Correa, A. X., Peluso-Silva, S., & Radetski, C. M.
(2009). Physico-chemical, microbiological and ecotoxicological evaluation of a septic
tank/Fenton reaction combination for the treatment of hospital wastewaters. Ecotoxicology
and Environmental Safety, 72(4), 1076-1081. doi: 10.1016/j.ecoenv.2008.12.002
Birbir, M., Hüsniye, H., Birbir, Y., & Gülşen, A. (2009). Inactivation of Escherichia coli by
alternative electric current in rivers discharged into sea. Journal of Electrostatics, 67(4),
640-645.
Birbir, Y., & Birbir, M. (2006). Inactivation of extremely halophilic hide-damaging bacteria via
low-level direct electric current. J Electrostat(64), 791–795.
Birbir, Y., Degirmenci, D., & Birbir, M. (2008). Direct electric current utilization in destruction of
extremely halophilic bacteria in salt that is used in brine curing of hides. Journal of
Electrostatics(66), 388–394.
Birbir, Y., Ugur, G., & Birbir, M. (2008). Inactivation of bacterial population in hide-soak liquors
via direct electric current. Journal of Electrostatics(66), 355–360.
Blanco, J., Torrades, F., Varga, M. D. l., & García-Montaño, J. (2012). Fenton and biological-
Fenton coupled processes for textile wastewater treatment and reuse. Desalination, 286,
394–399.
Blandón-Castaño, G., Dávila-Arias, M. T., & Rodríguez-Valencia, N. (1999). Caracterización
microbiológica y físico-química de la pulpa de café sola y con mucílago en proceso de
compostaje. Cenicafé, 50(1), 5-23.
Blatchley, E. R., Weng, S., Afifi, M. Z., Chiu, H.-H., Reichlin, D. B., Jousset, S., & Erhardt, R. S.
(2012). Ozone and UV254 Radiation for Municipal Wastewater Disinfection. Water
Environment Research, 84(11), 2017-2029. doi: 10.2175/106143012x13373550426634
Boateng, M. K., Price, S. L., Huddersman, K. D., & Walsh, S. E. (2011). Antimicrobial activities of
hydrogen peroxide and its activation by a novel heterogeneous Fenton's-like modified PAN
catalyst. J Appl Microbiol, 111(6), 1533-1543. doi: 10.1111/j.1365-2672.2011.05158.x
Cabiscol, E., Tamarit, J., & Ros, J. (2000). Oxidative stress in bacteria and protein damage by
reactive oxygen species. Int Microbiol, 3(1), 3-8.
Cabral, J. P. (2010). Water microbiology. Bacterial pathogens and water. Int J Environ Res Public
Health, 7(10), 3657-3703. doi: 10.3390/ijerph7103657
Cano, A., Cañizares, P., Barrera, C., Sáez, C., & Rodrigo, M. A. (2011). Use of low current
densities in electrolyses with conductive-diamond electrochemical — Oxidation to disinfect
treated wastewaters for reuse. Electrochemistry Communications, 13(11), 1268-1270.
Cano, A., Cañizares, P., Barrera, C., Sáez, C., & Rodrigo, M. A. (2012). Use of conductive-
diamond electrochemical-oxidation for the disinfection of several actual treated
wastewaters. Chemical Engineering Journal (Lausanne), 211-212(0), 463-469. doi:
10.1016/j.cej.2012.09.071
Cañizares, P., Lobato, J., Paz, R., Rodrigo, M. A., & Saez, C. (2005). Electrochemical oxidation of
phenolic wastes with boron-doped diamond anodes. Water Research, 39(12), 2687-2703.
doi: 10.1016/j.watres.2005.04.042
Cárdenas, V. (2012). Preparación de Arcillas pilarizadas con Al-Fe y su actividad catalítica en el
tratamiento de agua para consumo, optimizadas por medio de la superficie de respuesta.
(Magister en Química), Universidad de Caldas.
Carlesi Jara, C., Fino, D., Specchia, V., Saracco, G., & Spinelli, P. (2007). Electrochemical removal
of antibiotics from wastewaters. Appl Catal B-Environ, 70(1–4), 479-487.
Castro-Ríos, K., Orozco, L. F., & Taborda, G. (2012). Remoción de microorganismos presentes en
mucílago de café mediante electrocoagulación. Paper presented at the V Seminario
Colombiano de Electroquímica, Medellín, Colombia.
80
Castro-Ríos, K., Orozco, L. F., & Taborda Ocampo, G. (2012). Reducción de la demanda química
de oxígeno en mucílago de café mediante electrocoagulación. Paper presented at the
XXVII Congreso de la Sociedad Mexicana de Electroquímica, Toluca, México.
Castro-Ríos, K., Taborda-Ocampo, G., & Torres-Palma, R. A. (2014). Experimental Design to
Measure Escherichia coli Removal in Water Through Electrocoagulation. International
Journal of Electrochemical Science, 9(2), 610-617.
Cengiz, M., Uslu, M. O., & Balcioglu, I. (2010). Treatment of E. coli HB101 and the tetM gene by
Fenton's reagent and ozone in cow manure. J Environ Manage, 91(12), 2590-2593. doi:
10.1016/j.jenvman.2010.07.005
Cengiz, M., Uslu, M. O., & Balcioglu, I. (2010). Treatment of E. coli HB101 and the tetM gene by
Fenton´s reagent and ozone in cow manure. Journal of Environmental Management,
91(12), 2590-2593.
Cerf, O. (1977). A REVIEW Tailing of Survival Curves of Bacterial Spores. J Appl Bacteriol,
42(1), 1-19. doi: 10.1111/j.1365-2672.1977.tb00665.x
Comninellis, C., & Chen, G. (2010). Electrochemistry for the Environment. New York (USA):
Springer.
Cong, Y., Wu, Z., & Li, Y. (2008a). Electrochemical inactivation of coliforms by in-situ generated
hydroxyl radicals. Korean Journal of Chemical Engineering, 25(4), 727-731.
Cong, Y., Wu, Z., & Li, Y. (2008b). Electrochemical inactivation of coliforms by in-situ generated
hydroxyl radicals. Korean J. Chem. Eng., 25(4), 727-731.
Coroller, L., Leguerinel, I., Mettler, E., Savy, N., & Mafart, P. (2006). General model, based on two
mixed weibull distributions of bacterial resistance, for describing various shapes of
inactivation curves. Applied and Environmental Microbiology, 72(10), 6493-6502. doi:
10.1128/AEM.00876-06
Cotillas, S., Llanos, J., Canizares, P., Mateo, S., & Rodrigo, M. A. (2013). Optimization of an
integrated electrodisinfection/electrocoagulation process with Al bipolar electrodes for
urban wastewater reclamation. Water Research, 47(5), 1741-1750. doi:
10.1016/j.watres.2012.12.029
Council Directive 98/83/EC of 3 November 1998 on the quality of water intended for human
consumption.
Cui, X., Quicksall, A. N., Blake, A. B., & Talley, J. W. (2013). Electrochemical disinfection of
Escherichia coli in the presence and absence of primary sludge particulates. Water
Research, 47(13), 4383-4390. doi: 10.1016/j.watres.2013.04.039
Chanakya, H. N., & Alwis, A. A. P. D. (2004). Environmental issues and management in primary
coffee procesing. Process Safety and Environmental Protection(84 (B4)), 291–300.
Chavalparit, O., & Ongwandee, M. (2009). Optimizing electrocoagulation process for the treatment
of biodiesel wastewater using response surface methodology. Journal of Environmental
Sciences, 21(11), 1491-1496.
Chen, G. (2004a). Electrochemical technologies in wastewater treatment. Separation and
Purification Technology, 38(1), 11-41.
Chen, G. (2004b). Electrochemical technologies in wastewater treatment. Separation and
Purification Technology.(38), 11–41.
Chen, Q., Ai, S., Li, S., Xu, J., Yi, H., & Ma, Q. (2009). Facile preparation of PbO2 electrode for the
electrochemical inactivation of microorganism. Electrochemistry Communications(11),
2233-2236.
Cho, M., Gandhi, V., Hwang, T. M., Lee, S., & Kim, J. H. (2011). Investigating synergism during
sequential inactivation of MS-2 phage and Bacillus subtilis spores with UV/H2O2 followed
by free chlorine. Water Research, 45(3), 1063-1070. doi: 10.1016/j.watres.2010.10.014
Chong, M. N., Jin, B., Zhu, H., & Saint, C. (2010). Bacterial inactivation kinetics, regrowth and
synergistic competition in a photocatalytic disinfection system using anatase titanate
nanofiber catalyst. Journal of Photochemistry and Photobiology A: Chemistry, 214(1), 1-9.
81
Chrysikopoulos, C. V., Manariotis, I. D., & Syngouna, V. I. (2013). Virus inactivation by high
frequency ultrasound in combination with visible light. Colloids Surf B Biointerfaces, 107,
174-179. doi: 10.1016/j.colsurfb.2013.01.038
De Oliveira, L., Rosso, T., Cabonelli, J., & Giordano, G. (2011). Fenton’s reagent application in the
domestic sewers disinfection. Revista Ambiente e Água, 6(1).
Declerck, P., Vanysacker, L., Hulsmans, A., Lambert, N., Liers, S., & Ollevier, F. (2010).
Evaluation of power ultrasound for disinfection of both Legionella pneumophila and its
environmental host Acanthamoeba castellanii. Water Research, 44(3), 703-710. doi:
10.1016/j.watres.2009.09.062
Delaedt, Y., Daneels, A., Declerck, P., Behets, J., Ryckeboer, J., Peters, E., & Ollevier, F. (2008).
The impact of electrochemical disinfection on Escherichia coli and Legionella pneumophila
in tap water. Microbiol Res, 163(2), 192-199.
Diao, H. F., Li, X. Y., Gu, J. D., Shi, H. C., & Xie, Z. M. (2004). Electron microscopic
investigation of the bactericidal action of electrochemical disinfection in comparison with
chlorination, ozonation and Fenton reaction. Process Biochemistry (Barking, UK), 39(11),
1421–1426.
Drees, K. P., Abbaszadegan, M., & Maier, R. M. (2003). Comparative electrochemical inactivation
of bacteria and bacteriophage. Water Research, 37(10), 2291-2300. doi: 10.1016/S0043-
1354(03)00009-5
Drogui, P., Asselin, M., Brar, S. K., Benmoussa, H., & Blais, J.-F. (2008). Electrochemical removal
of pollutants from agro-industry wastewaters. Separation and Purification Technology(61),
301–310.
Durango-Usuga, P., Guzman-Duque, F., Mosteo, R., Vazquez, M. V., Penuela, G., & Torres-Palma,
R. A. (2010). Experimental design approach applied to the elimination of crystal violet in
water by electrocoagulation with Fe or Al electrodes. Journal of Hazardous Materials,
179(1-3), 120-126. doi: 10.1016/j.jhazmat.2010.02.067
Escobar, C., Soto-Salazar, C., & Toral, M. I. (2006). Optimization of the electrocoagulation process
for the removal of copper, lead and cadmium in natural waters and simulated wastewater. J
Environ Manage, 81(4), 384-391. doi: 10.1016/j.jenvman.2005.11.012
Feng, C., Suzuki, K., Zhao, S., Sugiura, N., Shimada, S., & Maekawa, T. (2004). Water disinfection
by electrochemical treatment. Bioresource Technology, 94(1), 21-25. doi:
10.1016/j.biortech.2003.11.021
Forero, J., Ortiz, O., & Ríos, F. (2005). Aplicación de procesos de oxidación avanzada como
tratamiento de fenol en aguas residuales industriales de refinería. Revista ciencia,
tecnología y futuro, 3(1), 97-109.
Frontistis, Z., Brebou, C., Venieri, D., Mantzavinos, D., & Katsaounis, A. (2011). BDD anodic
oxidation as tertiary wastewater treatment for the removal of emerging micro-pollutants,
pathogens and organic matter. J Chem Technol Biot, 86(10), 1233-1236.
Furuta, M., Yamaguchi, M., Tsukamoto, T., Yim, B., Stavarache, C. E., Hasiba, K., & Maeda, Y.
(2004). Inactivation of Escherichia coli by ultrasonic irradiation. Ultrasonics
Sonochemistry, 11(2), 57-60. doi: 10.1016/S1350-4177(03)00136-6
Gao, S., Du, M., Tian, J., Yang, J., Yang, J., Ma, F., & Nan, J. (2010). Effects of chloride ions on
electro-coagulation-flotation process with aluminum electrodes for algae removal. Journal
of Hazardous Materials, 182(1-3), 827–834.
Gao, S., Hemar, Y., Ashokkumar, M., Paturel, S., & Lewis, G. D. (2014). Inactivation of bacteria
and yeast using high-frequency ultrasound treatment. Water Research, 60C, 93-104. doi:
10.1016/j.watres.2014.04.038
Gao, S., Lewis, G. D., Ashokkumar, M., & Hemar, Y. (2014a). Inactivation of microorganisms by
low-frequency high-power ultrasound: 1. Effect of growth phase and capsule properties of
the bacteria. Ultrasonics Sonochemistry, 21(1), 446-453. doi:
10.1016/j.ultsonch.2013.06.006
82
Gao, S., Lewis, G. D., Ashokkumar, M., & Hemar, Y. (2014b). Inactivation of microorganisms by
low-frequency high-power ultrasound: 2. A simple model for the inactivation mechanism.
Ultrasonics Sonochemistry, 21(1), 454-460. doi: 10.1016/j.ultsonch.2013.06.007
Gao, S., Yang, J., Tian, J., Ma, F., Tu, G., & Du, M. (2010). Electro-coagulation–flotation process
for algae removal. Journal of Hazardous Materials(177), 336–343.
Geeraerd, A. H., Valdramidis, V. P., & Van Impe, J. F. (2005). GInaFiT, a freeware tool to assess
non-log-linear microbial survivor curves. Int J Food Microbiol, 102(1), 95-105. doi:
10.1016/j.ijfoodmicro.2004.11.038
Gehr, R., Wagner, M., Veerasubramanian, P., & Payment, P. (2003). Disinfection efficiency of
peracetic acid, UV and ozone after enhanced primary treatment of municipal wastewater.
Water Research, 37(19), 4573-4586. doi: 10.1016/S0043-1354(03)00394-4
Gerardi, M. H., & Zimmerman, M. (2005). Wastewater pathogens. New Jersey: John Wiley and
Sons, Inc.
Ghernaout, D., Badis, A., Kellil, A., & Ghernaout, B. (2008). Application of electrocoagulation in
Escherichia coli culture and two surface waters. Desalination, 219(1-3), 118–125.
Giannakis, S., Papoutsakis, S., Darakas, E., Escalas-Canellas, A., Petrier, C., & Pulgarin, C. (2014).
Ultrasound enhancement of near-neutral photo-Fenton for effective E. coli inactivation in
wastewater. Ultrasonics Sonochemistry. doi: 10.1016/j.ultsonch.2014.04.015
Gil Pavas, E., Quintero Olaya, L., Rincón Uribe, M., & Rivera Agudelo, D. (2007). Degradación de
colorantes de aguas residuales empleando UV/TiO2/H2O2/Fe2+
. Revista Universidad
EAFIT(abril-junio), 80-101.
Gómez, Y., González, M., Santa, L., Chiroles, S., & García, C. (2007). Calidad microbiológica de la
arcilla bentonita. Capacidad de remoción de E.coli ATCC Revista Higiene y Sanidad
Ambiental(7), 276-279.
Goncharuk, V. V., Malyarenko, V. V., & Yaremenko, V. A. (2008). Use of ultrasound in water
treatment. Journal of Water Chemistry and Technology, 30(3), 137-150. doi:
10.3103/s1063455x08030028
Griessler, M., Knetsch, S., Schimpf, E., Schmidhuber, A., Schrammel, B., Wesner, W., . . .
Kirschner, A. K. (2011). Inactivation of Pseudomonas aeruginosa in electrochemical
advanced oxidation process with diamond electrodes. Water Science and Technology,
63(9), 2010-2016. doi: 10.2166/wst.2011.444
Griessler, M., Knetsch, S., Schimpf, E., Schmidhuber, A., Schrammel, B., Wesner, W., . . .
Kirschner, A. K. T. (2010). Inactivation of Pseudomonas aeruginosa in electrochemical
advanced oxidation process with diamond electrodes. Water Science and Technology,
63(9), 2010–2016.
Gusmão, I. C., Moraes, P. B., & Bidoia, E. D. (2009). A thin layer electrochemical cell for
disinfection of water contaminated with Staphylococcus aureus. Braz J Microbiol, 40(3),
649-654. doi: 10.1590/S1517-838220090003000029
Gusmão, I. C., Moraes, P. B., & Bidoia, E. D. (2010). Studies on the electrochemical disinfection of
water containing Escherichia coli using dimensionally stable anode. Braz Arch Biol Techn,
53(5), 1235-1244.
Haaken, D., Dittmar, T., Schmalz, V., & Worch, E. (2012). Influence of operating conditions and
wastewater-specific parameters on the electrochemical bulk disinfection of biologically
treated sewage at boron-doped diamond (BDD) electrodes. Desalination and Water
Treatment, 46(1-3), 160-167.
Haaken, D., Dittmar, T., Schmalz, V., & Worch, E. (2014). Disinfection of biologically treated
wastewater and prevention of biofouling by UV/electrolysis hybrid technology: Influence
factors and limits for domestic wastewater reuse. Water Research, 52(0), 20-28. doi:
10.1016/j.watres.2013.12.029
83
Holder, D., Berry, D., Dai, D., Raskin, L., & Xi, C. (2013). A dynamic and complex
monochloramine stress response in Escherichia coli revealed by transcriptome analysis.
Water Research, 47(14), 4978-4985. doi: 10.1016/j.watres.2013.05.041
Hrudey, S. E. (2009). Chlorination disinfection by-products, public health risk tradeoffs and me.
Water Research, 43(8), 2057-2092. doi: 10.1016/j.watres.2009.02.011
Hua, I., & Thompson, J. E. (2000). Inactivation of Escherichia coli by sonication at discrete
ultrasonic frequencies. Water Research, 34(15), 3888 - 3893.
Hulsmans, A., Joris, K., Lambert, N., Rediers, H., Declerck, P., Delaedt, Y., . . . Liers, S. (2010).
Evaluation of process parameters of ultrasonic treatment of bacterial suspensions in a pilot
scale water disinfection system. Ultrasonics Sonochemistry, 17(6), 1004-1009. doi:
10.1016/j.ultsonch.2009.10.013
Hunter, G., Lucas, M., Watson, I., & Parton, R. (2008). A radial mode ultrasonic horn for the
inactivation of Escherichia coli K12. Ultrasonics Sonochemistry, 15(2), 101-109. doi:
10.1016/j.ultsonch.2006.12.017
Inan, H., Dimoglo, A., ÅžimÅŸek, H., & Karpuzcu, M. (2004). Olive oil mill wastewater treatment
by means of electro-coagulation. Separation and Purification Technology, 36(1), 23-31.
Jeong, J., Kim, C., & Yoon, J. (2009). The effect of electrode material on the generation of oxidants
and microbial inactivation in the electrochemical disinfection processes. Water Research,
43(4), 895-901. doi: 10.1016/j.watres.2008.11.033
Jeong, J., Kim, J. Y., Cho, M., Choi, W., & Yoon, J. (2007). Inactivation of Escherichia coli in the
electrochemical disinfection process using a Pt anode. Chemosphere, 67(4), 652–659.
Joyce, E., Mason, T. J., Phull, S. S., & Lorimer, J. P. (2003). The development and evaluation of
electrolysis in conjunction with power ultrasound for the disinfection of bacterial
suspensions. Ultrasonics Sonochemistry, 10(4-5), 231-234. doi: 10.1016/S1350-
4177(03)00109-3
Jung, Y. J., Baek, K. W., Oh, B. S., & Kang, J. W. (2010). An investigation of the formation of
chlorate and perchlorate during electrolysis using Pt/Ti electrodes: the effects of pH and
reactive oxygen species and the results of kinetic studies. Water Research, 44(18), 5345-
5355. doi: 10.1016/j.watres.2010.06.029
Katal, R., & Pahlavanzadeh, H. (2011). Influence of different combinations of aluminum and iron
electrode on electrocoagulation efficiency: Application to the treatment of paper mill
wastewater. Desalination, 265(1-3), 199 –205.
Kerwick, M. I., Reddy, S. M., Chamberlain, A. H. L., & Holt, D. M. (2005). Electrochemical
disinfection, an environmentally acceptable method of drinking water disinfection?
Electrochimica Acta, 50(25–26), 5270-5277.
Kerwick, M. I., Reddy, S. M., Chamberlain, A. H. L., & Holt, D. M. (2005). Electrochemical
disinfection, an environmentally acceptable method of drinking water disinfection?.
Electrochimica Acta.(50), 5270–5277.
Khoufi, S., Feki, F., & Sayadi, S. (2007). Detoxification of olive mill wastewater by
electrocoagulation and sedimentation processes. Journal of Hazardous Materials, 142(1-2),
58-67. doi: 10.1016/j.jhazmat.2006.07.053
Kobya, M., Ciftci, C., Bayramoglu, M., & Sensoy, M. T. (2008). Study on the treatment of waste
metal cutting fluids using electrocoagulation. Separation and Purification Technology,
60(3), 285-291.
Kobya, M., & Delipinar, S. (2008). Treatment of the baker's yeast wastewater by
electrocoagulation. Journal of Hazardous Materials, 154(1-3), 1133-1140. doi:
10.1016/j.jhazmat.2007.11.019
Koda, S., Miyamoto, M., Toma, M., Matsuoka, T., & Maebayashi, M. (2009). Inactivation of
Escherichia coli and Streptococcus mutans by ultrasound at 500 kHz. Ultrasonics
Sonochemistry(16), 655–659.
84
Koda, S., Miyamoto, M., Toma, M., Matsuoka, T., & Maebayashi, M. (2009). Inactivation of
Escherichia coli and Streptococcus mutans by ultrasound at 500kHz. Ultrasonics
Sonochemistry, 16(5), 655-659. doi: 10.1016/j.ultsonch.2009.02.003
Kormann, C., Bahnemann, D. W., & Hoffmann, M. R. (1988). Photocatalytic production of
hydrogen peroxides and organic peroxides in aqueous suspensions of titanium dioxide, zinc
oxide, and desert sand. Environmental Science and Technology, 22(7), 798-806. doi:
10.1021/es00172a009
Krasner, S. W. (2009). The formation and control of emerging disinfection by-products of health
concern. Philos Trans A Math Phys Eng Sci, 367(1904), 4077-4095. doi:
10.1098/rsta.2009.0108
Kucharzyk, K. H., Crawford, R. L., Cosens, B., & Hess, T. F. (2009). Development of drinking
water standards for perchlorate in the United States. J Environ Manage, 91(2), 303-310.
doi: 10.1016/j.jenvman.2009.09.023
Lacasa, E., Llanos, J., Cañizares, P., & Rodrigo, M. A. (2012). Electrochemical denitrificacion with
chlorides using DSA and BDD anodes. Chemical Engineering Journal (Lausanne), 184(0),
66-71.
Legrini, O., Oliveros, E., & Braun, A. M. (1993). Photochemical processes for water treatment.
Chem. Rev., 93(2), 671-698. doi: 10.1021/cr00018a003
Li, X., Diao, H., Fan, F., Gu, J., Ding, F., & Tong, A. (2004). Electrochemical Wastewater
Disinfection: Identification of Its Principal Germicidal Actions. J Environ Eng, 130(10),
1217-1221.
Li, X. Y., Diao, H. F., F.X.J.Fan, J.D.Gu, Ding, F., & Tong, A. S. F. (2004). Electrochemical
Wastewater Disinfection: Identification of Its Principal Germicidal Actions. Journal of
Environmental Engineering., 130(10), 1217–1221.
Li, X. Y., Diao, H. F., F.X.J.Fan, J.D.Gu, Ding, F., & Tong, A. S. F. (2004). Electrochemical
Wastewater Disinfection: Identification of Its Principal Germicidal Actions. Journal of
Environmental Engineering, 130(10), 1217–1221.
Li, X. Y., Ding, F., Lo, P. S. Y., & Sin, S. H. P. (2002). Electrochemical disinfection of saline
wastewater effluent. J Environ Eng, 128(8), 697-704.
Lin, S. H., & Lo, C. C. (1997). Fenton process for treatment of desizing wastewater. Water
Research, 31(8), 2050-2056.
Lopez-Galvez, F., Posada-Izquierdo, G. D., Selma, M. V., Perez-Rodriguez, F., Gobet, J., Gil, M. I.,
& Allende, A. (2012). Electrochemical disinfection: an efficient treatment to inactivate
Escherichia coli O157:H7 in process wash water containing organic matter. Food
Microbiol, 30(1), 146-156. doi: 10.1016/j.fm.2011.09.010
Llanos, J., Cotillas, S., Cañizares, P., & Rodrigo, M. A. (2014). Effect of bipolar electrode material
on the reclamation of urban wastewater by an integrated
electrodisinfection/electrocoagulation process. Water Research, 53C(0), 329-338. doi:
10.1016/j.watres.2014.01.041
Ma, Q., Liu, T., Tang, T., Yin, H., & Ai, S. (2011). Drinking water disinfection by hemin-modified
graphite felt and electrogenerated reactive oxygen species. Electrochimica Acta, 56(24),
8278-8284.
Mahamuni, N. N., & Adewuyi, Y. G. (2010). Advanced oxidation processes (AOPs) involving
ultrasound for waste water treatment: a review with emphasis on cost estimation.
Ultrasonics Sonochemistry, 17(6), 990-1003. doi: 10.1016/j.ultsonch.2009.09.005
Mamane, H., Shemer, H., & Linden, K. G. (2007). Inactivation of E. coli, B. subtilis spores, and
MS2, T4, and T7 phage using UV/H2O2 advanced oxidation. Journal of Hazardous
Materials, 146(3), 479-486.
Martinez-Huitle, C. A., & Brillas, E. (2008). Electrochemical alternatives for drinking water
disinfection. Angew Chem Int Ed Engl, 47(11), 1998-2005. doi: 10.1002/anie.200703621
85
Matamoros, V., Mujeriego, R., & Bayona, J. M. (2007). Trihalomethane occurrence in chlorinated
reclaimed water at full-scale wastewater treatment plants in NE Spain. Water Research,
41(15), 3337-3344. doi: 10.1016/j.watres.2007.04.021
Mates, A. K., Sayed, A. K., & Foster, J. W. (2007). Products of the Escherichia coli Acid Fitness
Island Attenuate Metabolite Stress at Extremely Low pH and Mediate a Cell Density-
Dependent Acid Resistance. Journal of Bacteriology, 189(7), 2759–2768.
Matsunaga, T., Nakasono, S., Takamuku, T., Burgess, J. G., Nakamura, N., & Sode, K. (1992).
Disinfection of Drinking Water by Using a Novel Electrochemical Reactor Employing
Carbon-Cloth Electrodes. Applied and Environmental Microbiology, 58(2), 686-689.
McPherson, L. L. (1993). Understanding ORP’s role in the disinfection process. Water Eng
Manage, 140(11), 29-31.
McQuestin, O. J., Shadbolt, C. T., & Ross, T. (2009). Quantification of the relative effects of
temperature, pH, and water activity on inactivation of Escherichia coli in fermented meat
by meta-analysis. Applied and Environmental Microbiology, 75(22), 6963-6972. doi:
10.1128/AEM.00291-09
Mollah, M. Y., Morkovsky, P., Gomes, J. A., Kesmez, M., Parga, J., & Cocke, D. L. (2004).
Fundamentals, present and future perspectives of electrocoagulation. Journal of Hazardous
Materials, 114(1-3), 199-210. doi: 10.1016/j.jhazmat.2004.08.009
Moncayo-Lasso, A., Sanabria, J., Pulgarín, C., & Benítez, N. (2009). Simultaneous E. coli
inactivation and NOM degradation in river water via photo-Fenton process at natural pH in
solar CPC reactor. A new way for enhancing solar disinfection of natural water.
Chemosphere(77), 296–300.
Moncayo-Lasso, A., Torres-Palma, R. A., Kiwi, J., Benitez, N., & Pulgarin, C. (2008). Bacterial
inactivation and organic oxidation via immobilized photo-Fenton reagent on structured
silica surfaces. Applied Catalysis B: Environmental, 84(3-4), 577-583.
Moncayo-Lasso, A., Torres-Palma, R. A., Kiwi, J., Benítez, N., & Pulgarín, C. (2008). Bacterial
inactivation and organic oxidation via immobilized photo-Fenton reagent on structured
silica surfaces. Applied Catalysis B: Environmental.(84), 577–583.
Montgomery, D. C. (2001). Design and analysis of experiments (5th ed.). New York: Willey.
Mussatto, S. I., Machado, E. M. S., Martins, S., & Teixeira, J. A. (2011). Production, Composition,
and Application of Coffee and Its Industrial Residues. Food Bioprocess Technology(4),
661– 672.
Nanayakkara, K. G., Alam, A. K., Zheng, Y. M., & Chen, J. P. (2012). A low-energy intensive
electrochemical system for the eradication of Escherichia coli from ballast water: process
development, disinfection chemistry, and kinetics modeling. Marine Pollution Bulletin,
64(6), 1238-1245. doi: 10.1016/j.marpolbul.2012.01.018
Nieto-Juarez, J. I., & Kohn, T. (2013). Virus removal and inactivation by iron (hydr)oxide-mediated
Fenton-like processes under sunlight and in the dark. Photochemical & Photobiological
Sciences, 12(9), 1596-1605. doi: 10.1039/c3pp25314g
Ninomiya, K., Arakawa, M., Ogino, C., & Shimizu, N. (2013). Inactivation of Escherichia coli by
sonoelectrocatalytic disinfection using TiO2 as electrode. Ultrasonics Sonochemistry, 20(2),
762-767. doi: 10.1016/j.ultsonch.2012.10.007
Ninomiya, K., Ogino, C., Kawabata, S., Kitamura, K., Maki, T., Hasegawa, H., & Shimizu, N.
(2013). Ultrasonic inactivation of Microcystis aeruginosa in the presence of TiO2 particles.
Journal of Bioscience and Bioengineering, 116(2), 214-218. doi:
10.1016/j.jbiosc.2013.02.006
Nogueira, R. F. P., Trovó, A. G., Silva, M. R. A. d., Villa, R. D., & Oliveira, M. C. d. (2007).
Fundamentos e aplicações ambientais dos processos fenton e foto-fenton. Quimica Nova,
30, 400-408.
86
Ogino, C., Farshbaf Dadjour, M., Takaki, K., & Shimizu, N. (2006). Enhancement of sonocatalytic
cell lysis of Escherichia coli in the presence of TiO2. Biochemical Engineering Journal,
32(2), 100-105. doi: 10.1016/j.bej.2006.09.008
Olvera, J. d. R., & Gutiérrez, J. I. (2010a). Biodegradación anaerobia de las aguas generadas en el
despulpado del café Revista Colombiana de Biotecnología., 12(2), 230-239.
Olvera, J. d. R., & Gutiérrez, J. I. (2010b). Biodegradación anaerobia de las aguas generadas en el
despulpado del café Revista Colombiana de Biotecnología, 12(2), 230-239.
OMS. (2004). Guías para la calidad del agua potable 2012, from
http://www.who.int/water_sanitation_health/dwq/gdwq3sp.pdf
Osetrova, N. V., Bagotzky, V. S., Guizhevsky, S. F., & Serov, Y. M. (1998). Electrochemical
reduction of carbonate solutions at low temperatures. Journal of Electroanalytical
Chemistry, 453(1–2), 239-241.
Osorio, F., Torres, J. C., & Sánchez, M. (2010). Tratamiento de aguas para la eliminación de
microorganismos y agentes contaminantes. España: Ediciones Díaz de Santos.
Otenio, M. H., Panchoni, L. C., Cruz, G. C. A. d., Ravanhani, C., & Bidóia, E. D. (2008). Avaliação
em escala laboratorial da utilização do processo eletrolítico no tratamento de águas.
Quimica Nova, 31(3), 508-513.
Palma-Goyes, R. E., Guzmán-Duque, F. L., Peñuela, G., & González, I. (2010). Electrochemical
degradation of crystal violet with BDD electrodes: Effect of electrochemical parameters
and identification of organic by-products. Chemosphere, 81(1), 26–32.
Panizza, M., & Cerisola, G. (2009). Direct and mediated anodic oxidation of organic pollutants.
Chem Rev, 109(12), 6541-6569. doi: 10.1021/cr9001319
Papastefanakis, N., Mantzavinos, D., & Katsaounis, A. (2010). DSA electrochemical treatment of
olive mill wastewater on Ti/RuO2 anode. Journal of Applied Electrochemistry(40), 729–
737.
Pareilleux, A., & Sicard, N. (1970). Lethal effects of electric current on Escherichia coli. Appl
Microbiol, 19(3), 421-424.
Park, J. C., Lee, M. S., Lee, D. H., Park, B. J., Han, D. W., Uzawa, M., & Takatori, K. (2003).
Inactivation of bacteria in seawater by low-amperage electric current. Applied and
Environmental Microbiology, 69(4), 2405-2408.
Patermarakis, G., & Fountoukidis, E. (1990). Disinfection of water by electrochemical treatment.
Pergamon, 24(12), 1491-1496.
Perez, G., Gomez, P., Ibanez, R., Ortiz, I., & Urtiaga, A. M. (2010). Electrochemical disinfection of
secondary wastewater treatment plant (WWTP) effluent. Water Science and Technology,
62(4), 892-897. doi: 10.2166/wst.2010.328
Pham, T. T., Brar, S. K., Tyagi, R. D., & Surampalli, R. Y. (2010). Optimization of Fenton
oxidation pre-treatment for B. thuringiensis - based production of value added products
from wastewater sludge. J Environ Manage, 91(8), 1657-1664. doi:
10.1016/j.jenvman.2010.03.007
Polcaro, A. M., Vacca, A., Mascia, M., Palmas, S., Pompei, R., & Laconi, S. (2007).
Characterization of a stirred tank electrochemical cell for water disinfection processes.
Electrochimica Acta, 52(7), 2595–2602.
Quek, P. H., & Hu, J. (2008). Indicators for photoreactivation and dark repair studies following
ultraviolet disinfection. Journal of Industrial Microbiology & Biotechnology, 35(6), 533-
541. doi: 10.1007/s10295-008-0314-0
R.D 1620/2007, de Diciembre de 2007, por el que se establece el régimen jurídico de la
reutilización de las aguas depuradas.
Ricordel, C., Miramon, C., Hadjiev, D., & Darchen, A. (2013). Investigations of the mechanism and
efficiency of bacteria abatement during electrocoagulation using aluminum electrode.
Desalination and Water Treatment, 1-10. doi: 10.1080/19443994.2013.807474
87
Rincón, A.-G., & Pulgarin, C. (2006a). Comparative evaluation of Fe3+
and TiO2 photoassisted
processes in solar photocatalytic disinfection of water. Applied Catalysis B: Environmental,
63(3-4), 222-231.
Rincón, A.-G., & Pulgarin, C. (2006b). Comparative evaluation of Fe3+
and TiO2 photoassisted
processes in solar photocatalytic disinfection of water. Applied Catalysis B:
Environmental., 63(3-4), 222-231.
Rincón, A. G., & Pulgarín, C. (2007). Fe3+
and TiO2 solar-light-assisted inactivation of E. coli at
field scale Implications in solar disinfection at low temperature of large quantities of water.
Catalysis Today(122), 128–136.
Rodríguez, S. P., Silva, R. M. P., & Boizán, M. F. (2000a). Estudio de la biodegradabilidad
anaerobia de las aguas residuales del beneficio húmedo del café. Interciencia, 25(8), 386-
390.
Rodríguez, S. P., Silva, R. M. P., & Boizán, M. F. (2000b). Estudio de la biodegradabilidad
anaerobia de las aguas residuales del beneficio húmedo del café. Interciencia., 25(8), 386-
390.
Romero, J. A. (2009). Calidad del Agua. Bogotá: Escuela Colombiana de Ingeniería.
Sánchez-Carretero, A., Sáez, C., Cañizares, P., & Rodrigo, M. A. (2011). Electrochemical
production of perchlorates using conductive diamond electrolyses. Chemical Engineering
Journal (Lausanne), 166(2), 710-714. doi: 10.1016/j.cej.2010.11.037
Saravanan, M., Sambhamurthy, N. P., & Sivarajan, M. (2010). Treatment of Acid Blue 113 Dye
Solution Using Iron Electrocoagulation. CLEAN – Soil, Air, Water, 39(5–6), 565-571.
Särkkä, H., Vepsäläinen , M., Pulliainen, M., & Sillanpää, M. (2008). Electrochemical inactivation
of paper mill bacteria with mixed metal oxide electrode. Journal of Hazardous Materials,
156(1-3), 208-213. doi: 10.1016/j.jhazmat.2007.12.011
Schmalz, V., Dittmar, T., Haaken, D., & Worch, E. (2009). Electrochemical disinfection of
biologically treated wastewater from small treatment systems by using boron-doped
diamond (BDD) electrodes – Contribution for direct reuse of domestic wastewater. Water
Research, 43(20), 5260–5266.
Selvakumar, A., Tuccillo, M. E., Muthukrishnan, S., & Ray, A. B. (2009). Use of Fenton's Reagent
as a Disinfectant. Remediation Journal, 19(2), 135-142. doi: 10.1002/rem.20208
Selvamurugan, M., Doraisamy, P., Maheswari, M., & Nandakumar, N. B. (2010). High rate
anaerobic treatment of coffee procesing wastewater using upflow anaerobic hybrid reactor.
Iran. J. Environ. Health. Sci. Eng, 7(2), 129-136.
Shang, K., Qiao, Z., Sun, B., Fan, X., & Ai, S. (2013). An efficient electrochemical disinfection of
E. coli and S. aureus in drinking water using ferrocene–PAMAM–multiwalled carbon
nanotubes–chitosan nanocomposite modified pyrolytic graphite electrode. Journal of Solid
State Electrochemistry, 17(6), 1685-1691. doi: 10.1007/s10008-013-2031-5
Shimizu, N., Ninomiya, K., Ogino, C., & Rahman, M. M. (2010). Potential uses of titanium dioxide
in conjunction with ultrasound for improved disinfection. Biochemical Engineering
Journal.(48), 416-423.
Siedlecka, E. M., Fabiańska, A., Stolte, S., Nienstedt, A., Ossowski, T., Stepnowski, P., &
Thöming, J. (2013). Electrocatalytic Oxidation of 1-Butyl-3-Methylimidazolium Chloride:
Effect of the Electrode Material. International Journal of Electrochemical Science, 8(1),
5560 - 5574.
Sirtori, C., Zapata, A., Oller, I., Gernjak, W., Aguera, A., & Malato, S. (2009). Decontamination
industrial pharmaceutical wastewater by combining solar photo-Fenton and biological
treatment. Water Research, 43(3), 661-668. doi: 10.1016/j.watres.2008.11.013
Small, P., Blankenhorn, D., Welty, D., Zinser, E., & Slonczewski, J. L. (1994). Acid and base
resistance in Escherichia coli and Shigella flexneri: role of rpoS and growth pH. Journal of
Bacteriology, 176(6), 1729-1737.
88
Spuhler, D., Rengifo-Herrera, J. A., & Pulgarin, C. (2010). The effect of Fe2+
, Fe3+
, H2O2 and the
photo-Fenton reagent at near neutral pH on the solar disinfection (SODIS) at low
temperatures of water containing Escherichia coli K12. Applied Catalysis B:
Environmental, 96(1-2), 126-141.
Sun, D. D., Tay, J. H., & Tan, K. M. (2003). Photocatalytic degradation of E.coli form in water.
Water Research, 37(14), 3452-3462.
Sun, S.-P., & Lemley, A. T. (2011). p-Nitrophenol degradation by a heterogeneous Fenton-like
reaction on nano-magnetite: Process optimization, kinetics, and degradation pathways.
Journal of Molecular Catalysis A: Chemical, 349(1-2), 71-79. doi:
10.1016/j.molcata.2011.08.022
Sundarapandiyan, S., Chandrasekar, R., Ramanaiah, B., Krishnan, S., & Saravanan, P. (2010).
Electrochemical oxidation and reuse of tannery saline wastewater. Journal of Hazardous
Materials, 180(1-3), 197-203. doi: 10.1016/j.jhazmat.2010.04.013
Suss, J., Volz, S., Obst, U., & Schwartz, T. (2009). Application of a molecular biology concept for
the detection of DNA damage and repair during UV disinfection. Water Research, 43(15),
3705-3716. doi: 10.1016/j.watres.2009.05.048
Tchamango, S., Nanseu-Njiki, C. P., Ngameni, E., Hadjiev, D., & Darchen, A. (2010). Treatment of
dairy effluents by electrocoagulation using aluminium electrodes. Science of the Total
Environment, 408(4), 947–952.
Tezcan Ün, U., Koparal, A. S., & Bakır Ögütveren, Ü. (2009). Electrocoagulation of vegetable oil
refinery wastewater using aluminum electrodes. Journal of Environmental Management,
90(1), 428-433.
Tezcan Ün, U., Koparal, A. S., & Ögütveren, Ü. B. (2009). Hybrid processes for the treatment of
cattle-slaughterhouse wastewater using aluminum and iron electrodes. Journal of
Hazardous Materials, 164(2-3), 580–586.
Tezcan Ün, U., Ugur, S., Koparal, A. S., & Bakır Ögütveren, Ü. (2006). Electrocoagulation of olive
mill wastewaters. Separation and Purification Technology(52), 136-141.
The International Agency for Research on Cancer. (2010). Agents Classified by the IARC
Monographs, Volumes 1–100. Retrieved 11/10/2010, 2010, from
http://monographs.iarc.fr/ENG/Classification/ClassificationsAlphaOrder.pdf
Tolentino-Bisneto, R., & Bidoia, E. D. (2003). Effects of the electrolytic treatment on Bacillus
subtilis. Braz J Microbiol, 34(1), 48-50.
Torres, R. A., Sarria, V., Torres, W., Peringer, P., & Pulgarin, C. (2003). Electrochemical treatment
of industrial wastewater containing 5-amino-6-methyl-2-benzimidazolone: toward an
electrochemical-biological coupling. Water Research, 37(13), 3118-3124. doi:
10.1016/S0043-1354(03)00179-9
Torres, R. A., Torres, W., Peringer, P., & Pulgarin, C. (2003). Electrochemical degradation of p-
substituted phenols of industrial interest on Pt electrodes. Attempt of a structure-reactivity
relationship assessment. Chemosphere, 50(1), 97-104.
Turro, E., Giannis, A., Cossu, R., Gidarakos, E., Mantzavinos, D., & Katsaounis, A. (2011).
Electrochemical oxidation of stabilized landfill leachate on DSA electrodes. Journal of
Hazardous Materials, 190(1-3), 460-465.
UNICEF. (2008). Handbook on Water Quality. New York: UNICEF.
Vellanki, B. P., & Batchelor, B. (2013). Perchlorate reduction by the sulfite/ultraviolet light
advanced reduction process. Journal of Hazardous Materials, 262, 348-356. doi:
10.1016/j.jhazmat.2013.08.061
Wang, C. T., Chou, W. L., & Kuo, Y. M. (2009). Removal of COD from laundry wastewater by
electrocoagulation/electroflotation. Journal of Hazardous Materials, 164(1), 81-86. doi:
10.1016/j.jhazmat.2008.07.122
89
Wang, G. S., Deng, Y. C., & Lin, T. F. (2007). Cancer risk assessment from trihalomethanes in
drinking water. Science of the Total Environment, 387(1-3), 86-95. doi:
10.1016/j.scitotenv.2007.07.029
Watson, K., Shaw, G., Leusch, F. D. L., & Knight, N. L. (2012). Chlorine disinfection by-products
in wastewater effluent: Bioassay-based assessment of toxicological impact. Water
Research, 46(18), 6069-6083.
Watts, R. J., Washington, D., Howsawkeng, J., Loge, F. J., & Teel, A. L. (2003). Comparative
toxicity of hydrogen peroxide, hydroxyl radicals, and superoxide anion to Escherichia coli.
Advances in Environmental Research, 7(4), 961-968.
Woodall, C. J. (2009). Waterborne diseases – What are the primary killers? Desalination, 248(1–3),
616-621.
Xu, Y., Yang, J., Ou, M., Wang, Y., & Jia, J. (2007). Study of Microcystis aeruginosa inhibition by
electrochemical method. Biochemical Engineering Journal(36), 215–220.
Yildiz, Y. Ş., Koparal, A. S., & Keskinler, B. (2008). Effect of initial pH and supporting electrolyte
on the treatment of water containing high concentration of humic substances by
electrocoagulation. Chemical Engineering Journal (Lausanne), 138(1-3), 63-72.
Zaleschi, L., Sáez, C., Cañizares, P., Cretescu, I., & Rodrigo, M. A. (2013). Electrochemical
coagulation of treated wastewaters for reuse. Desalination and Water Treatment, 51(16-18),
3381-3388. doi: 10.1080/19443994.2012.749192
Zambrano-Franco, D. A., & Cárdenas-Cárdenas, J. (2000). Manejo y tratamiento primario de
lixiviados producidos en la tecnología Becolsub. Avances Técnicos(280), 1-8.
Zambrano-Franco, D. A., Isaza-Hinestroza, J. D., Rodríguez-Valencia, N., & Posada, U. L. (1999).
Tratamiento de aguas residuales del lavado de café Boletín Técnico. (pp. 30). Chinchiná:
Cenicafé.
Zhu, B., Clifford, D. A., & Chellama, S. (2005). Comparison of electrocoagulation and chemical
coagulation pretreatment for enhanced virus removal using microfiltration membranes.
Water Research, 39(13), 3098–3108.