A low-carbon-emission photoelectrochemical system using Ov-Fe2O3@BiVO4 photoanode for integrated multiple pollutant removal and energy harvesting from real saline sewage

Abstract

Conventional wastewater treatment plants (WWTPs) face challenges due to high carbon emissions and energy consumption. Herein, a low-carbon-emission photoelectrochemical (PEC) system using an oxygen-vacancy-rich Fe2O3@BiVO4 (Ov-Fe2O3@BiVO4) photoanode that is aimed at replacing biological treatment and disinfection, is developed to simultaneously remove organic compounds, ammonia (NH4+-N), and bacteria from real saline sewage (after primary treatment) while generating green H2. The PEC system demonstrates remarkable performance in the treatment of real saline sewage, as evidenced by the fact that the treated sewage is able to meet local discharge standards of chemical oxygen demand (COD), ammonia-N, and Escherichia coli (E. coli) after two hours of operation under simulated solar light at 2.0 V (vs. Ag/AgCl). Most importantly, it generates 11.51 mol/m3 of green H2 (equal to 0.458 kWh/m3 of electricity) and results in notable reductions of 76.7 % in scope 1 emissions (direct GHG emissions) and 62.5 % in total carbon emissions compared to conventional WWTPs. The scavenging tests and estimated steady-state concentrations of reactive species indicate that Cl•, ClO•, and Cl2•− are the primary contributors to the degradation of organic pollutants, while ClO• is dominant in converting ammonia to N2. Additionally, the excellent reusability, stability and easy regeneration of the Ov-Fe2O3@BiVO4 photoanode and its good performance in treating different batches of real sewage guarantee the high practicability of the PEC system. This study has successfully validated the PEC system as a low-carbon-emission technology approach for saline sewage treatment coupled with green H2 generation, demonstrating its enormous practical potential.