Electrochemical improvement of methane production via surface engineering of graphitic cathodes in anaerobic sequential batch reactors

Abstract

Five anaerobic sequential batch reactors (SBR), SBR 1−SBR 5 run in parallel were examined for biogas output trends under varying hydraulic retention times (HRT). SBR 1 was run without biomass for 1 month to study electrode stability and the effect of applied potential on sodium dodecyl sulfate (SDS) degradation. Polyaniline (PANI/Graphite) modification in reactors SBR 4 and iron-coated PANI (Fe-PANI/Graphite) in SBR 5 increased biogas production by almost 2.5 times compared to SBR 2 without electrodes. SBR 3 equipped with unmodified graphite rods was used as a control for cathode modifications. By decreasing HRT, cumulative methane production increased to 280 and 320 mL at 72 h and 350 and 500 mL at 48 h. Compared to SBR 2, an electric field increased daily biogas production. Methane composition in SBR 5 increased from 44% at 96-h to 71% at 48-h HRT after 30 days. SBR 4 recovered within 7 days after HRT modifications reduced methane output. The methane yield increased significantly with electric current in SBR 3 (2.6 times), SBR 4 (5.4 times), and SBR 5 (7.4 times). The effluent total organic carbon was stabilized at 15 mg/L for SBR 2 and SBR 3 and improved to below 5 mg/L for SBR 4 and SBR 5 during reactor operation. SBR 5, equipped with an Fe-PANI/Graphite cathode showing the lowest charge transfer resistance, developed distinct microbial community structures in both anodic and cathodic biofilms, compared to the other electrically assisted SBRs.