Simultaneous organic wastewater treatment and bioelectricity production in a dual chamber microbial fuel cell with Scenedesmus obliquus biocathode

Algal biocathode MFCs (ABMs) are recently being heavily studied due to their advantage over abiotic cathode MFCs (ACMs) as dissolved oxygen (DO) generated by algal growth in the cathodic chamber is directly utilized in cathodic oxidant reduction. In this work growth of pure algae species Scenedesmus obliquus used in the cathode chamber has been studied under a photoperiod of 24 h illumination to supplement oxygen for continual MFC operation without any external supply of air or carbon dioxide and treatment of synthetic wastewater having chemical oxygen demand (COD) equivalent to medium strength domestic wastewater (5.35 g/L COD). Results of ABM showed the highest continuous current density generation of 23.93 mA/m2 and the highest continuous volumetric power density generation of 13.24 mW/m3 were around 120 h with COD removal efficiency of 92.52 % and coulombic efficiency (CE) of 41.88 %. Initial ohmic (Roh) and charge transfer (Rct) resistance values of ABM were found to be 8.3 ohm and Rct of 22.5 ohm which after 216 h of algal growth got reduced to 1 ohm and 15.1 ohm respectively. 16S microbiome profiling of the mixed microbial sludge inoculum used in the anodic chamber showed dominance of Xanthomonadaceae stenotrophomonas (9.7 %), Chitinophaga flexibacter (8.65 %), Sphingomonadaceae sphingomonas (6.82 %), Sphingobacterium multivorum (6.55 %), Dyadobacter fermentans (6.05 %), and Alcaligenaceae achromobacter (5.51 %). Elemental investigation of the bioanode's and biocathode's surface carried out using EDS analysis also shows that oxygen was generated in the cathodic chamber by pure Scenedesmus obliquus species.