Elimination of contaminants of emerging concern and their environmental risk in world-real municipal wastewaters by electrochemical advanced oxidation processes

In this study, sixteen contaminants of emerging concern (CECs), present in the effluent of the wastewater treatment plant (WWTP) “Salitre” (Bogotá – Colombia), were subjected to several electrochemical advanced oxidation processes (EAOPs). Thus, the elimination of the pharmaceuticals diclofenac, carbamazepine, venlafaxine, Irbesartan, losartan, metronidazole, sulfamethoxazole, trimethoprim, clindamycin, norfloxacin, ciprofloxacin, clarithromycin, erythromycin, and azithromycin, the illicit drug cocaine, and its major metabolite benzoylecgonine was assessed by electro-Fenton (EF), photo-electro-Fenton (PEF), and photo-electro-Fenton in the presence of added oxalic acid (PEFox). A boron-doped diamond and a gas diffusion electrode were used as anode and cathode. After 1 h of treatment, the total concentration of CECs decreased by 36% when PEFox was applied. In the case of EF and PEF, the degradation percentages were lower (29% and 19%, respectively). The highest degradation by using PEFox was due to the enhanced availability of soluble iron ions by forming Fe(III)-oxalate complexes at near-neutral pH values. This allows the Fenton reaction to yield additional HO• radicals. Finally, the effect of EAOPs to reduce the environmental risk associated with the CECs in the WWTP was evaluated. The best system, PEFox, lowered by more than ten times the environmental hazard of the tested CECs in the effluent. This work shows the high potential of PEFox, as tertiary treatment, to eliminate emerging pollutants and reduce their risk in effluents from WWTP. In this system, the added oxalic acid, which has a biodegradable character, could be eliminated in a subsequent biological step.