Comparative evaluation of nitrogen removal in moving bed biofilm reactors (MBBRs) treating anaerobic digestion effluent: effect of external carbon source and biocarrier autopsy.

This study investigated nitrogen removal performance in an anoxic/oxic moving bed biofilm reactor (A/O MBBR) using two external carbon sources: food waste condensate (FWC) and methanol (MeOH). FWC supported effective denitrification (95.4 ± 4.2 %) due to the enrichment of diverse heterotrophic denitrifiers, including Thauera, Paracoccus, and Azospira, despite its chemical complexity. However, nitrification efficiency in the FWC-fed system was lower than in the MeOH-fed system (5.5 % lower), likely due to inhibitory organic constituents and fewer nitrifying bacteria (Nitrosomonas and Nitrolancea). In contrast, the MeOH-fed system achieved higher nitrification efficiency (97.7 ± 2.9 %) and stable biofilm formation. Despite the limitations of MeOH's substrate diversity, FWC proved to be a viable, sustainable carbon source for nitrogen removal in A/O MBBR systems. Future research should focus on enhancing nitrification through microbial enrichment and process optimization to achieve balanced nitrogen removal under complex substrate conditions.