Decentralized pilot-scale biofilm-based system integrated with microbial electrolysis cell for household wastewater treatment: Enhanced pollutant removal and hydrogen production

Abstract

Abstract The septic tank is the most commonly used decentralized wastewater treatment systems (DEWATS) for household wastewater treatment in on-site applications. However, the removal rate of various pollutans is lower. The integration of a microbial electrolysis cells (MEC) into biofilm-based system can be a green and sustainable DEWATS technology for enhanced household wastewater treatment. In this study, a 50-L septic tank was converted into a 50-L biofilm-based system coupled with MEC for household wastewater treatment and hydrogen production. The maximum pollutant removal rate was achieved with an HRT of 1.5 d and an applied voltage of 1.0 V. Global COD removal ranged from 79 to 84%, and for TN, removal rates ranged from 45 to 71%. Concentrations of COD, BOD, NH4+, TN, TP, and TSS in the final effluent were all below 66, 30, 3, 19, 8.5, and 72 mg/L, respectively. The current density generated in the MEC (0.21–0.41 A/m2) contributed to hydrogen production and pollutan removals. The maximum volumetric hydrogen production rate in the MEC was 0.007 L/L.d. The integration of the MEC into biofilm-based system generate anodic and cathodic reactions, allowing different bioelectrochemical nitrogen and phosphorus transformations within the system, generating a simultaneous denitrification-nitrification process with phosphorus removal, allowing to increase the removal of the pollutans. The novel filter module and biocarriers developed in this work were successful permitting high biofilm-based reactors performance during household wastewater treatment.