Nitrogen Removal and Electricity Generation from High-Ammonia Sludge Digestate Using Microbial Fuel Cell

Anaerobic digestate is rich in nitrogen, and its treatment poses substantial challenges to conventional processes due to its ammonium concentration, high alkalinity, and low biodegradable carbon content. In this study, microbial fuel cells (MFCs) were investigated for the treatment of digestate. An orthogonal experimental design was employed to evaluate the effects of influent ammonium concentration (100–300 mg/L), pH (8–10), and external resistance (100–1000 Ω) on nitrogen removal and electricity generation. The MFC consistently achieved high nitrate removal efficiencies (>97%), whereas ammonium removal was strongly condition-dependent. The highest ammonium removal efficiency (66.6%) and total nitrogen removal efficiency (84.8%) were obtained at 300 mg/L NH4+, pH 10, and an external resistance of 1000 Ω. Although pH was identified as the dominant factor influencing performance, microbial community analysis revealed the enrichment of Paracoccus and Thauera, suggesting that nitrogen removal was mainly governed by the coupling of heterotrophic nitrification–aerobic denitrification with bioelectrochemical processes. This work demonstrates the feasibility of using MFCs for the treatment of high-strength digestate and provides valuable insights into the optimization of nitrogen-rich wastewater management.