Experimental assessment of a process for nitrogen removal from AD digestate using microbial fuel cell technology

The main objective of the research was to verify the effectiveness of a MFC (Microbial Fuel Cell) based reactor for the removal of nitrogen from digested sludge (from anaerobic treatment of livestock manure and agricultural wastes). Preliminary tests were performed to study the development of biofilm at the electrodes, by running small Htype MFC under different conditions. Results of the preliminary lab scale tests showed an increase of more than 60 % of the potential (of both, EOCV and ECCV), in the case of biofilm enrichment. Moreover, scale-up tests were run in continuous, using a 17 L reactor designed and assembled to the scope, constituted by an anaerobic anodic chamber, followed by an aerobic cathodic stage and an anoxic stage. Results of five months operation showed that anodic potential quickly achieved a stable negative potential, in the typical range of the MFC, also leading to a volatile solids removal of about 60 %, thus confirming the good efficiency of the double anaerobic/aerobic system in carbon degradation. However, current generation and power produced was rather low, in comparison to previous results obtained in small batches. In the aerobic chamber, a good nitrogen removal was observed (up to 60 %), as a consequence of both, carbon degrading biomass uptake and nitrification. Mass balances performed, considering the nitrogen content in the waste sludge (about 3 % with respect to TS content), allowed to exclude a significant ammonia nitrogen volatilization.