Electrocoagulation-UV Irradiation Process for Urban Wastewater Reuse

Abstract

This work presents a promising process to carry out the reclamation of urban treated wastewaters that consists of the application of UV irradiation to an electrocoagulation process with aluminium electrodes (photo-electrocoagulation). Results show that it is possible to perform the simultaneous removal of the microbiological content and turbidity in wastewater by applying low current densities. During the photo- electrocoagulation process, coagulant species are formed by the electrodissolution of the anode material (aluminium), causing the removal of turbidity in wastewater. The nature of these coagulant species will mainly depend on the pH and the metal concentration. In this context, the pH during the process remained constant around 8, a value that favours the formation of insoluble aluminium hydroxides and therefore, a sweep flocculation as main coagulation mechanism. On the other hand, it has been observed the presence of disinfectant species in wastewater during the process, specifically, free and combined chlorine disinfectants. Urban wastewater present significant concentration of chlorides in their composition and these species are susceptible of being oxidized on the anode surface favouring the generation of hypochlorite. In addition, the electrogenerated hypochlorite can react with the ammonium typically present in wastewater to form chloramines. Both species have noticeable disinfectant capacity and they are the main responsible of the elimination of E. coli. Finally, the application of UV radiation during the process favours the elimination of microorganisms due to the interaction of the light on the cell membrane of E. coli. Likewise, the application of UV light during the electrocoagulation promotes the formation of free radicals from the oxidizing species previously formed. These radicals not only increase the process performance in terms of E. coli removal but also favour the chemical dissolution of the sacrificial electrode and therefore, there is an increase in the turbidity removal performance.