A proof of concept study for wastewater reuse using bioelectrochemical processes combined with complementary post-treatment technologies

Abstract

This article describes a proof-of-concept study designed for the reuse of wastewater using microbial electrochemical cells (MECs) combined with complementary post-treatment technologies. This study mainly focused on how the integrated approach works effectively for wastewater reuse. In this study, microalgae and ultraviolet C (UVC) light were used for advanced wastewater treatment to achieve site-specific treatment goals such as agricultural reuse and aquifer recharge. The bio-electrosynthesis of H₂O₂ in MECs was carried out based on a novel concept to integrate with UVC, especially for robust removal of trace organic compounds (TOrCs) resistant to biodegradation, and the algal treatment was configured for nutrient removal from MEC effluent. UVC irradiation has also proven to be an effective disinfectant for bacteria, protozoa, and viruses in water. The average energy consumption rate for MECs fed acetate-based synthetic wastewater was 0.28 ± 0.01 kWh per kg of H₂O₂, which was significantly more efficient than are conventional electrochemical processes. MECs achieved 89 ± 2% removal of carbonaceous organic matter (measured as chemical oxygen demand) in the wastewater (anolyte) and concurrent production of H₂O₂ up to 222 ± 11 mg L⁻¹ in the tapwater (catholyte). The nutrients (N and P) remaining after MECs were successfully removed by subsequent phycoremediation with microalgae when aerated (5% CO₂, v/v) in the light. This complied with discharge permits that limit N to 20 mg L⁻¹ and P to 0.5 mg L⁻¹ in the effluent. H₂O₂ produced on site was used to mediate photolytic oxidation with UVC light for degradation of recalcitrant TOrCs in the algal-treated wastewater. Carbamazepine was used as a model compound and was almost completely removed with an added 10 mg L⁻¹ H₂O₂ at a UVC dose of 1000 mJ cm⁻². These results should not be generalized, but critically discussed, because of the limitations of using synthetic wastewater.