Tratamiento de Electrodesinfección aplicado a Efluentes de Humedales Bioelectrogénicos (MET-Lands)

UAH – IMDEA Agua

Antonio Berná Galiano

MET Microbial Electrochemical Technologies

Ø Microorganismos capaces de transferir electrones directamente a una superficie sólida externa (electrodo) Science 2002; 295: 483-5

Ø  Los microorganismos respiran el electrodo Ø Pueden formar biofilm sobre el electrodo Ø Mejora de la eficiencia en los procesos biológicos de

tratamiento de aguas Ø Bajos rendimientos en biomasa (baja producción de

fangos) Ø Eliminación de la limitación por concentración del

aceptor de electrones Ø No es necesario airear (el electrodo es el aceptor final) Ø Ausencia de olores (CH4) ✕

Wetlands –Humedales Artificiales

Ø  Tecnología extensiva Ø Humedal horizontal de flujo subsuperficial Ø Exitosa implantación MET (www.aquaelectra.es) Ø Patente (PCT/ES2012/070153) Q= 2m3/día Ø Biofiltros conductores Ø Aquaelectra, SmartWetland, EM4M, iMetland

Wetlands –Humedales Artificiales

ENTRADA

SALIDA

Antes  7cm Lecho  12cm

Después  17cm Lecho Conductor (Ánodo)

CÁTODO

MET-Land Rendimientos de eliminación (%)

DQO 85 STS 90

Nitrógeno 40-70 Fósforo 90

Agua Residual Humedal Convencional

Carga Entrada 4x MET-Land

Carga Entrada 4x

MET-Land

Rendimientos de eliminación (%)

DQO 85 STS 90

Nitrógeno 40-70 Fósforo 90

Ø Reutilización Ø Etapa de desinfección Ø Sostenible Ø Aplicable en instalaciones remotas Ø Bajo mantenimiento

Soluciones tecnológicas electroquímicas

Ø Electrodepósito Ø Electrocoagulación Ø Electroflotación Ø Electrooxidación Ø Electroreducción Ø Electrodesinfección Dependerá:

Ø Naturaleza de los electrodos Ø Composición del medio Ø Reacciones electroquímicas que tienen lugar Ø Configuración del reactor

¿Por qué electrodesinfección?

Ø Ozonización, cloración, filtración y radiación UV

Ø Bajo riesgo por almacenamiento de sustancias peligrosas

Ø Desinfección residual (filtración y radiación UV)

Ø Costes de instalación moderados

Ø Ocupa poco espacio Ø Costes de mantenimiento moderado

Condiciones de Operación

Ø Valores de DQO bajos Ø Un valor umbral de contenido en Cl-

Ø Agente desinfectante: Cloro Activo (ánodo) Ø Cloro libre, Cloro Combinado, Cloro Total

Ø Reacción catódica: H2

Ø Agente desinfectante: H2O2 (cátodo)

Reacciones de Formación

Mecanismos de Acción Germicida:

Ø  Inhibición de actividad enzimática necesaria para el crecimiento y a un posible daño de la capacidad de transporte de la membrana celular

CLEANlNG AND DlSlNFECTlON USlNG SODlUM HYPOCLORlTE 149

FIG. 1. Distribution of HOCl in aqueous solution as afunction of pH. Curve for HOCI--OCl equilibrium wasderived from the calculation by using pKa of 7.5. CurvesA and B are the hypothetical curves in the absence and

presence of additional 100 mM NaCl, respectively.

generate are approximately 2.8 and 4.5 in the ab-sence and presence of additional 100 mM NaCl, re-spectively (lwasawa et al., 2004), as depicted bycurves A and B in Fig. 1.

hypochiorite solution depends on the concentrationof HOCI but not on the total AC concentration (Braziset al., 1958, Charlton and Levine, 1935; Dantec, et al.,2002; Sagripanti and Bonifacino, 1996). This is attrib-uted to the penetration of HOCl into the microbial cellacross the cell wall and membrane. It is believed thatthe mechanism of the germicidal activity of HOCl or-OCl is due to the inhibition of enzyme activity essen-tial for the growth, damage to the membrane andDNA, and perhaps an injury to membrane transportcapacity although it has not been fully elucidated.HOCl stress is also suggested to generate commondeleterious oxidative species which can damage cel-lular components (Dunkan and Touati, 1996; Dukanet al., 1999). On the other hand, the germicidal activ-ity of a concentrated sodium hypochiorite solution isbased on its high pH (-OH action) and -OCl oxida-tion (Estrela et al., 2002).

Membrane permeability and germicidal activityA model for the germicidal actions of HOCl and-OCl based on their ability to penetrate into the mi-

(4)

(5)

Thus, in aqueous solution chlorine exists in threedifferent forms, i.e., C12, HOCI, and -0C1, which arecalled free available chlorine or free residual chlorine.The solubility of Cl2 (aq) in water is very low andtherefore Cl2 (aq) readily escapes from the solution.Also, in the neutral pH region (6.5 to 7.5),undissociated HOCl tends to be decomposed at arelatively high rate (Adam et al., 1992) and its con-centration decreases gradually during the storage pe-riod. On the other hand, dissociated -OCl is morestable in alkaline water, especially at pHs above 10,and AC concentration is almost constant even after a6-month storage (Siqueira, 2000).

Once free chlorine species reacts with ammonia orN-organo compounds to form monochloramine,dichioramine, and trichioramine or a variety oforgano-N-chloro compounds, the term used is eithercombined chlorine, combined residual chlorine, orcombined available chlorine. The free and combinedavailable chlorine in water are collectively describedas total residual (available) chlorine.

MECHANlSM OF THE GERMlCIDAL ACTlON

Sodium hypochlorite has a broad antimicrobialspectrum. The germicidal activity of a diluted sodium

FlG. 2. A model illustrating the mechanisms of the ger-micidal actions of HOCl and -OCl based on their abilityto penetrate the membrane into the microbial cell.

lonized -OCl has a poor germicidal activity because ofits inability to diffuse through microbial l plasma mem-brane, and it exerts an oxidizing action only from outsideof the cell (circle A). HOCl can penetrate the lipid bilayerin the plasma membrane by passive diffusion due to itselectrical neutrality. HOCl can attack the microbial cellboth from the outside (circles A') and inside the cell(circles B and C), which is responsible for the potentgermicidal activity of HOCl.

Biocontrol Science,2006,Vol.11,No.4,147-157

Minireview

Mechanisms of Actions of Sodium Hypochloritein Cleaning and Disinfection Processes

SATOSHI FUKUZAKI*

Industrial Technology Center of Okayama Prefecture,5301 Haga, Okayama 701-1296, Japan

Received 23 August 2006/Accepted 13 October 2006

Sodium hypochlorite (NaOCI) is the most widely used disinfectant in the food industry de-spite the increasing availability of other disinfectants. Sodium hypochlorite fulfills many re-quirements as the ideal disinfectant and furthermore it has an excellent cleaning action. Theeffectiveness of sodium hypochlorite in the cleaning and disinfection processes depends onthe concentration of available chlorine and the pH of the solution. Hypochlorous acid (HOCI)is a weak acid and dissociates to the hypochlorite ion (-OCI) and proton (H+) depending onthe solution pH. It is generally believed that HOCI is the active species in the germicidal ac-tion, whereas the concentration of -OCI is a key factor determining the cleaning efficiency.This implies that the optimal pH region of the germicidal activity of sodium hypochlorite dif-fers from that of its cleaning activity. This paper describes the theory and practice of thecleaning and disinfecting operations based on the use of sodium hypochlorite solution.

Key words:Sodium hypochiorite/Cleaning action/Germicidal activity/Strong electrophile/Electrolyzed water.

INTRODUCTION

Nowadays, cleaning and disinfecting operationshave been reconfirmed as the fundamental proce-dures to sustain hygienic conditions in the food indus-try setting. The main objects to be cleaned anddisinfected are the processing equipment, productsor food ingredients, packaging materials, andworker's hands and fingers. The cleanliness of all theproduct-contact surfaces is one of the most importantfactors to prevent secondary contamination and toproduce safe and wholesome products. Cleaning anddisinfection are related complementarily to eachother, and are performed as a separate or combinedoperation. The process of cleaning should precedethat of disinfection because it is far easier to disinfecta surface unsoiled with organic matter than a soiledsurface. In a word, the role of cleaning as a process

preceding disinfection is to reduce the load of thedisinfection process by removing as much soil aspossible and by decreasing the number of microbesbefore they propagate.

At present, sodium hypochiorite (NaOCI) is themost widely used disinfectant in the food industry.Although alcohol, quaternary ammonium compounds,ozone, peracetic acid, hydrogen peroxide, and or-ganic acids are also utilized to reduce microbialpopulations, the effectiveness of those chemicals hasbeen always examined in comparison with that of so-dium hypochiorite. Some advantages and disadvan-tages of sodium hypochiorite are summarized inTable 1. The advantages of sodium hypochlorite arethat it fulfills many requirements of the ideal disinfec-tant (Rutala and Weber, 1997) and has an excellentcleaning action; furthermore, it is easily combinedwith some other cleaning elements and detergents.Actually in many food-manufacturing factories, the re-moval of the organic soils (cleaning) and control ofmicrobes (disinfection) are performed with sodiumhypochlorite in a single process. However, the

*Ｃorresｐondingauthor.Tel:+81-86-286-9600,Fax:+81-

86-286-9630.

HClO tiene una acción germicida mayor que ClO-

Condiciones de Operación

Ø Ánodo DSA Magneto®: mezcla de óxidos metálicos (Ti/(RuO2+IrO2))

Ø Más económico que BDD y otros ánodos Ø Menos selectividad que IrO2 , pero mayor duración y

resistencia a la inversión de potencial Ø Cátodo Grafito (C)

Ø Corriente constante: 1.5 mA/cm2

Ø  0.5 kWh/m3

Condiciones de Operación

Ø Valores de cloro libre de 1.5 ppm persisten 24 h Ø Alimentación por paneles solares

Ø Ensayos de toxicidad: algas Ø Búsqueda de parámetros que permitan una

monitorización in situ del proceso más rápida

Ø Ensayos de viabilidad celular más rápidos que el recuento de Unidades Formadoras de Colonias