Net-Zero-Emissions and Chemical-Free Photoelectrochemical System for Saline Sewage Treatment with H2 Evolution

Abstract

Sewage treatment processes are carbon- and energy-intensive, inefficient at degrading emerging pollutants (EPs), and require added chemicals. A chemical-free photoelectrochemical (PEC) system, an alternative to biological treatment and disinfection, is developed for saline sewage treatment to remove multiple contaminants and produce H2, aiming for net-zero emissions. The bismuth- and oxygen-vacancies containing BiVO4 (BvOv-BVO) photoanode with enhanced photoelectrocatalytic activity is developed for the PEC system. Under simulated solar light, the PEC process using BvOv-BVO can treat saline sewage to satisfy the discharge standards of chemical oxygen demand (removing 100% EP), ammonia-N, and bacteria in 40 minutes coupled with producing 725.6 μmol H2 (7.26 mol/m3, equals 0.29 kWh/m3 of electricity). Additionally, it achieves 100% and 92.3% reduction of GH4 and N2O emissions respectively compared with conventional wastewater treatment plants. The PEC system's performance closely correlates with chloride concentration in sewage and applied voltages, which notably influence chloride activation to produce ClO• as the predominant species for contaminant removal. Additionally, the PEC system exhibits promising practicability under natural sunlight, treating saline sewage that meets discharge standards and achieves net-zero emissions by reducing greenhouse gas generation and producing substantial H2. This study demonstrates a novel PEC process for net-zero-emissions saline sewage treatment.

Keywords: chemical-free treatment, green H2 evolution, multifunctional PEC system, multiple contaminant removal, net-zero emissions, saline sewage treatment