Synergistic role of active chlorine species and hydroxyl radicals during disinfection and mineralization of carwash wastewater

The effect of UVC light (lambda = 254 nm) on chlorine generation through a sequential combination of three wastewater treatments was evaluated to disinfect and mineralize carwash wastewater. Electrocoagulation, electrooxidation, and catalysis processes were sequentially performed in the presence and absence of UVC radiation. Toxicity changes during the photoEC process were detected using Artemia salina as a model organism, which improves the LD50 of the raw carwash effluent from 13.4 to 52.1. Disinfection trials showed a colony-forming unit decrease by approximately 90%; however, the mineralization degree was only 7%. The subsequent electrooxidation treatment showed that the IrO2-RuO2 anode generated the highest concentration of active chlorine species (400 mg L-1 at pH = 3). However, during UVC irradiation, a better efficiency in producing (OH)-O-center dot radicals was observed. Thus, the total organic carbon abatement using photoelectrocoagulation followed by photoelectrooxidation of carwash wastewater was 57%. As a final step, photocatalysis using crystalline TiO2 increased the mineralization degree, reaching 80% at the end of the tandem protocol. Thus, it was proposed that the sequential UVC-based treatments degrade organic matter and reduce pathogens in a raw carwash effluent in the presence of chloride ions.

Automated summary

The effect of UVC light on chlorine generation in three wastewater treatment processes was studied for carwash wastewater disinfection and mineralization. Electrocoagulation, electrooxidation, and catalysis were sequentially performed with and without UVC radiation. Toxicity changes were detected using Artemia salina, with the LD50 improving from 13.4 to 52.1 in the photoEC process. Disinfection trials showed a 90% decrease in colony-forming units, but only a 7% mineralization degree. Electrooxidation with the IrO2-RuO2 anode produced the highest concentration of active chlorine species, while UVC irradiation was more efficient in producing (OH)-O-center dot radicals. The combined photoelectrocoagulation and photoelectrooxidation achieved a 57% total organic carbon abatement, and photocatalysis with TiO2 reached 80% mineralization at the end of the protocol. The sequential UVC-based treatments were proposed to degrade organic matter and reduce pathogens in carwash wastewater with chloride ions.