Electrochemical oxidation of landfill leachate in a flow reactor: optimization using response surface methodology.

Response surface methodology based on Box-Behnken (BBD) design was successfully applied to the optimization in the operating conditions of the electrochemical oxidation of sanitary landfill leachate aimed for making this method feasible for scale up. Landfill leachate was treated in continuous batch-recirculation system, where a dimensional stable anode (DSA(©)) coated with Ti/TiO2 and RuO2 film oxide were used. The effects of three variables, current density (milliampere per square centimeter), time of treatment (minutes), and supporting electrolyte dosage (moles per liter) upon the total organic carbon removal were evaluated. Optimized conditions were obtained for the highest desirability at 244.11 mA/cm(2), 41.78 min, and 0.07 mol/L of NaCl and 242.84 mA/cm(2), 37.07 min, and 0.07 mol/L of Na2SO4. Under the optimal conditions, 54.99% of chemical oxygen demand (COD) and 71.07 ammonia nitrogen (NH3-N) removal was achieved with NaCl and 45.50 of COD and 62.13 NH3-N with Na2SO4. A new kinetic model predicted obtained from the relation between BBD and the kinetic model was suggested.

A thin layer electrochemical cell for disinfection of water contaminated with Staphylococcus aureus / Uma célula eletroquímica de camada delgada para desinfecção de água contaminada com Staphylococcus aureus

A thin layer electrochemical cell was tested and developed for disinfection treatment of water artificially contaminated with Staphylococcus aureus. Electrolysis was performed with a low-voltage DC power source applying current densities of 75 mA cm-2(3 A) or 25 mA cm-2 (1 A). A dimensionally stable anode (DSA) of titanium coated with an oxide layer of 70 percentTiO2 plus 30 percentRuO2 (w/w) and a 3 mm from a stainless-steel 304 cathode was used in the thin layer cell. The experiments were carried out using a bacteria suspension containing 0.08 M sodium sulphate with chloridefree to determine the bacterial inactivation efficacy of the thin layer cell without the generation of chlorine. The chlorine can promote the formation of trihalomethanes (THM) that are carcinogenic. S. aureus inactivation increased with electrolysis time and lower flow rate. The flow rates used were 200 or 500 L h-1. At 500 L h-1 and 75 mA cm -2 the inactivation after 60 min was about three logs of decreasing for colony forming units by mL. However, 100 percent inactivation for S. aureus was observed at 5.6 V and 75 mA cm-2 after 30 min. Thus, significant disinfection levels can be achieved without adding oxidant substances or generation of chlorine in the water.

Uma célula eletroquímica de camada delgada foi utilizada e desenvolvida para a desinfecção de água contaminada artificialmente com Staphylococcus aureus. A eletrólise foi executada com uma fonte de corrente direta utilizando 75 mA cm-2 (3 A) ou 25 mA cm-2 (1 A). Um anodo dimensionalmente estável (DSA) de titânio revestido com uma camada do óxido de 70 por centoTiO2 e 30 por centoRuO2 (w/w) e distanciado por 3 milímetros de um catodo de aço inoxidável 304 foi utilizado para gerar uma camada delgada de suspensão bacteriana passando pela célula de camada delgada. As suspensões utilizadas eram feitas apenas com Na2SO4 0,08 M e livre de íons cloretos de forma a inativar as células bacterianas no tratamento eletroquímico sem a geração de cloro, este pode promover a formação dos trialometanos (THM). As taxas de fluxo em recirculação foram 200 ou 500 L h-1. A inativação do S. aureus aumentou com o tempo de eletrólise e a uma taxa de fluxo menor. Assim, a inativação de 100 por cento para o S. aureus foi observada após 30 min a 5,6 V e 75 mA cm-2. Em 500 L h-1 e 75 mA cm-2 a inativação decresceu em três logs de unidades formadoras de colônias por mL após 60 min. O tratamento eletroquímico utilizando uma camada delgada promove a desinfecção completa de S. aureus sem a necessidade de adicionar substâncias oxidantes ou a geração de cloro.

A thin layer electrochemical cell for disinfection of water contaminated with Staphylococcus aureus.

A thin layer electrochemical cell was tested and developed for disinfection treatment of water artificially contaminated with Staphylococcus aureus. Electrolysis was performed with a low-voltage DC power source applying current densities of 75 mA cm(-2) (3 A) or 25 mA cm(-2) (1 A). A dimensionally stable anode (DSA) of titanium coated with an oxide layer of 70%TiO2 plus 30%RuO2 (w/w) and a 3 mm from a stainless-steel 304 cathode was used in the thin layer cell. The experiments were carried out using a bacteria suspension containing 0.08 M sodium sulphate with chloride-free to determine the bacterial inactivation efficacy of the thin layer cell without the generation of chlorine. The chlorine can promote the formation of trihalomethanes (THM) that are carcinogenic. S. aureus inactivation increased with electrolysis time and lower flow rate. The flow rates used were 200 or 500 L h(-1). At 500 L h(-1) and 75 mA cm(-2) the inactivation after 60 min was about three logs of decreasing for colony forming units by mL. However, 100% inactivation for S. aureus was observed at 5.6 V and 75 mA cm(-2) after 30 min. Thus, significant disinfection levels can be achieved without adding oxidant substances or generation of chlorine in the water.

Degradation of acid blue 40 dye solution and dye house wastewater from textile industry by photo-assisted electrochemical process.

In this paper, electrochemical and photo-assisted electrochemical processes are used for color, total organic carbon (TOC) and chemical oxygen demand (COD) degradation of one of the most abundant and strongly colored industrial wastewaters, which results from the dyeing of fibers and fabrics in the textile industry. The experiments were carried out in an 18 L pilot-scale tubular flow reactor with 70%TiO(2)/30%RuO(2) DSA. A synthetic acid blue 40 solution and real dye house wastewater, containing the same dye, were used for the experiments. By using current density of 80 mA cm(-2) electrochemical process has the capability to remove 80% of color, 46% of TOC and 69% of COD. When used the photochemical process with 4.6 mW cm(-2) of 254 nm UV-C radiation to assist the electrolysis, has been obtained 90% of color, 64% of TOC and 60% of COD removal in 90 minutes of processing; furthermore, 70% of initial color was degraded within the first 15 minutes. Experimental runs using dye house wastewater resulted in 78% of color, 26% of TOC and 49% of COD in electrolysis at 80 mA cm(-2) and 90 min; additionally, when photo-assisted, electrolysis resulted in removals of 85% of color, 42% of TOC and 58% of COD. For the operational conditions used in this study, color, TOC and COD showed pseudo-first-order decaying profiles. Apparent rate constants for degradation of TOC and COD were improved by one order of magnitude when the photo-electrochemical process was used.