Application of Air Cathode Microbial Fuel Cells for Energy Efficient Treatment of Dairy Wastewater

Microbial Fuel Cells (MFCs) offer a promising new solution for wastewater treatment due to their advantageous characteristics: lower energy demand and less excess sludge compared to the conventional activated sludge wastewater treatment technology. In this study, two systems of single chamber air cathode MFCs with a working volume of 14 L were investigated for the energy efficient treatment of dairy wastewater. Biomass-originated carbon cathode and noble-metal free cathode catalyst were applied to meet the demand for a lower investment cost. Influent chemical oxygen demand (COD) was in the range of 900 to 3830 mg L–1, while hydraulic retention time was ~ 2.4 days. Systems provided 156 mW m–3 and 170 mW m–3 maximum power densities and coulombic efficiencies of 11.5 % and 12.8 % in average. Organic removal efficiency of 71.1 ± 8.0 % was observed when influent COD was between 900 and 1500 mg L–1, however effluent quality and removal efficiency (67.9 ± 12.6 %) deteriorated as influent COD was increased (1500 – 3830 mg L–1). At high influent CODs (over 3000 mg L–1), an organic elimination rate of 0.82 ± 0.11 kg COD m–3 d–1 was calculated, that can be considered as the upper limit of organic removal in the systems. Based on the results, MFCs may offer a potential solution for small-scale dairy factories for the pretreatment of their effluent to meet the criteria for wastewater discharge to sewer systems. The modular MFC design also facilitates to tailor the system to actual capacity requirements.