Regulating the in situ generation of active chlorine species in a photoelectrochemical system for the efficient simultaneous removal of ammonia nitrogen and refractory pharmaceuticals
Yu Zhang, Jun Cui, Yuansheng Pei
Abstract
The removal of chemical oxygen demand (COD) and ammonia nitrogen (NH 4 + -N) is always a critical problem in combined polluted sewage treatment. To simultaneously treat NH 4 + -N and refractory organics, a WO 3 /BiVO 4 -cobalt borate (WO 3 /BiVO 4 -CoB i ) photoanode was applied in a photoelectrochemical (PEC) system. It used Cl - in highly-saline wastewater to generate strongly-oxidizing active chlorine species in situ, which were responsible for the system’s NH 4 + -N directional oxidation and simultaneous degradation ability. Thus, the PEC system with Cl - (PEC-Cl) simultaneously removed 99% of carbamazepine (CBZ) within 40 min and 75.4% of NH 4 + -N within 120 min. It also selectively converted NH 4 + -N into N 2 (10% NO 3 – -N production rate). The {0 1 0} facet-oriented array of decahedral BiVO 4 and WO 3 /BiVO 4 heterostructure contributed to the effective separation of photo-generated electron-hole pairs. Coupled with the reduced charge-transfer resistance of the photoanode/solution interface and the greater conversion of photo-generated holes into redox equivalents by the CoB i co-catalyst, the system demonstrated efficient carrier transfer. Active chlorine species (Cl 2 , HClO, Cl•, and •ClO) were produced with the participation of photo-generated holes and •OH and could be regulated by controlling the system potential, Cl - concentration, and solution pH. This study provides a feasible method for the simultaneous removal of NH 4 + -N and refractory organics with a high efficiency and stability.