Bioelectrochemical system as an oxidising filter for soluble and particulate organic matter removal from municipal wastewater

A bioelectrochemical system (BES) configuration was designed and tested as a polishing process to remove soluble chemical oxygen demand (SCOD) and suspended solids (SS) from municipal wastewater. The configuration was designed such that the anodic carbon felt could behave as a filter enabling removal and bioelectrochemical oxidation of particulate and soluble organic matter from wastewater. Three reactors (each with approximately 10 L liquid volume) were set up to evaluate three different operational settings: (i) close-circuit operation enabling current production; (ii) open-circuit operation without current production; and (iii) control reactor without electrode to account for the effect of electrode as a filter. The reactors were operated for over 200 days during which key process parameters (SCOD removal, SS removal, turbidity, electricity production, electrolyte pH) were quantified. The results indicated that current production (maximal current of approximately 120 mA) could increase the SCOD removal efficacy from 11% to 77% at a SCOD removal rate of approximately 0.1 kg SCOD/m3 d. No measurable difference between SS removal efficiencies in open and close circuit (83%), and clogging of the electrode filter were observed. A high coulombic efficiency (more than 80%, based on the SCOD removed) and low internal resistance (2.7 Ω) were achieved, indicating that the configuration is suitable for handling real wastewater containing particulate matter. However, active maintenance of a neutral pH at the anode and an acidic cathodic environment (pH < 7) were essential to sustain the optimum performance of the system. Overall, this study affirms the potential of using a BES to serve as both a physical filter and an oxidising medium for effluent polishing.