Electrochemical Generation Of H₂O₂and Disinfection Based On MWCNTs-GDE Cathode

Electrochemical disinfection has been widely discussed as an alternative toconventional techniques of water disinfection due to its high efficiency and otheradvantages, such as:High environmental compatibility; Low cost and easy to operate;Removal of dissolved heavy metal, organic matter and other harmful substances inwater simultaneously; Have a residual disinfection effect.One form of electrochemical disinfection is the application of gas diffusionelectrode （GDE） as cathode in the electrochemical system. The main sterilizationfactor is the electro-generated hydrogen peroxide and other oxidative free radicals like OH.The catalyst material exerts important influence on the performance of the electrode.Carbon nanotube has several advantageous electrochemical properties for its uniquestructure. In this study, the GDE with multi-wall CNTs （MWCNTs） serving aselectrochemically active material was fabricated and applied to the electrolysis systemas to producing hydrogen peroxide and raising the sterilization efficiency.Electrochemical analysis results showed that MWCNTs have higher catalytic activitythan normal carbon black toward the two-electron oxygen reduction reaction process.The MWCNTs-loaded GDE have a stable production of H2O2during the intermittentoperation of360h. The H2O2generation was recorded with respect to variousoperational conditions including phosphate buffer solution electrolyte concentration,current density applied as well as initial pH value, and the optimized operationcondition is J=15mA/cm2，C=50mmol/L，pH=7.The MWCNTs-loaded GDE was then applied for disinfection purpose at optimizedconditions for H2O2generation, and after10min disinfection, the overall inactivationefficiency could achieve above99.9%, and the total amount of E.coli experiencednearly3.08log losses. The AFM images showed the morphological changes of E.coliduring the disinfection process. The E.coli experienced internal collapse, followed bycompletely dissolution. And the FCM results showed that after15min of electrolysis,necrotic cells accounted for more than70%, and the survival cells accounted for onlyabout8%.The result indicated that the E.coli cell experienced irreversible damage viaelectrolysis, and does not likely to revive in the appropriate environment.The electrochemical system have residual disinfection effects owing to a certainconcentration of hydrogen peroxide after electrolysis. The experiment results showedthat the total amount of E.coli reduced nearly1log within10h after10min ofelectrolysis. Several significant factors which influence disinfection efficacy including current density, pH value, COD and Cl-concentration of influent were investigated, andthe result showed that: the sterilization efficiency increased with the increase of currentdensity; the sterilization efficiency operated in the acidic and neutral condition is betterthan that in alkaline condition; when the COD concentration was below60mg/L, italmost had no impact; when the concentration was higher than80mg/L, the oxidizingsubstances may partial participated in the oxidation of dissolved COD, led to thereduction of sterilization efficiency; when the current density was low, affection ofchloride ion concentration on the efficiency of sterilization was more significant, thesterilization efficiency increased with the increase of concentration; when the currentdensity was high, oxygen evolution took place in the anode at the same time, the effectof chloride ion concentration was smaller. The practical application of theMWCNTs-GDE electrochemical system was investigated by using the secondaryclarifier effluent as influent, the result showed that after30min of operation, the totalbacteria and coliform counts were decreased more than99%.