Enhanced nitrogen removal from low C/N municipal wastewater through nitrification, partial denitrification and anammox via a step-feed strategy: Synergistic contribution by bacteria in biofilm and floc sludge

Energy-efficient nitrogen removal from carbon-limited municipal wastewater poses challenges. This study developed a novel partial denitrification and anammox (PD/A) process using a step-feed strategy in a single-stage integrated fixed-biofilm activated sludge (IFAS) system operated under sequencing batch mode. Despite relatively low temperatures (15.9-21.6 degrees C), biological nitrogen removal efficiency reached 80.5 % without the addition of external carbon sources. With the total inorganic nitrogen (TIN) of 48.9 f 1.2 mg N/L, and C/N of 4.0 in influent, the TIN in effluent achieved 9.6 f 1.5 mg N/L. Anammox bacteria (AnAOB) activity in the biofilm was 27.96 mg N/(g VSS & sdot;d), which was threefold greater than in floc sludge. Candidatus Brocadia (AnAOB) presented a high relative abundance in biofilm (0.53 %), whereas denitrifying bacteria including Thauera and Candidatus Competibacter were mainly retained in floc sludge. Overall, the coupling of step-feed strategy and IFAS offers novel insights into the efficient nitrogen removal from low C/N domestic sewage for retrofitting of municipal wastewater treatment plants, not only saving the energy consumption for aeration, but also fully utilizing carbon sources and ammonium in the influent for the PD/A process.