Synergistic membrane-biofilm-sludge system coupling partial nitritation and anammox: achieving efficient nitrogen removal in high-ammonia/low-carbon condensate wastewater

Abstract

Condensed wastewater treatment faces challenges from elevated ammonia-nitrogen levels (1972-2365 mg/L), a low carbon-to-nitrogen ratio (0.02-0.03), and inhibitory sulfides. To overcome these, a novel hybrid system integrating an effluent membrane-enhanced fixed-biofilm activated sludge (IFAS) reactor with partial nitritation/anammox (PN/A) was developed. The system demonstrated exceptional nitrogen removal performance at a maximum nitrogen removal rate of 1.5 kg N/(m³·d) with a nitrogen removal efficiency of 82.3 %. Denitrification enhanced advanced nitrogen removal with a low nitrate production ratio (4.5 %), minimizing secondary pollution risks. Microbial analysis revealed substantial enrichment of anaerobic ammonium-oxidizing bacteria, with Candidatus Brocadia dominating the biofilm community (24.3 %). Membrane-mediated biomass retention selectively enriched Nitrosomonas (10.1 %) in suspended sludge, while biofilm detachment promoted granular anammox biomass development and further elevated Candidatus Brocadia abundance by 4.8 %. This synergistic configuration enhances process stability for treating high-ammonia/low-carbon wastewater and promotes the practical implementation of IFAS-PN/A systems.

Keywords: IFAS; Industrial wastewater; Low COD/N ratio; Membrane separation; PN/A.