Nitrogen and phosphorus removal using fluidized-carriers in a full-scale A2O biofilm system

A full-scale biofilm system using fluidized-carriers integrated with anaerobic-anoxic–aerobic process (treatment capacity of 3.75 × 10⁵ m³ d⁻¹) was used for municipal wastewater treatment. The results indicated relatively higher removal efficiencies of 86% total nitrogen (TN), 97% ammonium (NH₄-N) and 97% total phosphorus (TP) were achieved, with 0.32 mg L⁻¹ TP, 0.81 mg L⁻¹ NH₄-N and 8.07 mg L⁻¹ TN in the effluent, which meet the Class A of Discharge standard of pollutants for municipal wastewater treatment plant (GB18918-2002) of China. The results of microbial analysis indicated that the dominant microorganisms in the suspended sludge were Proteobacteria and Bacteroidetes at phylum level and β-Proteobacter at class level. The dominant microorganism in the biofilm was Proteobacteria at phylum level, with γ-Proteobacter (17.5%), β-Proteobacter (14%) and δ-Proteobacter (13.08%) distributed at class levels. The presence of Proteobacteria and Bacteroidetes in this system may be related with the phosphorus removal. A reddish color biofilm was formed on the surface of fluidized-carriers in the anaerobic tank and showed specific anammox ability, this may be related with the dominance of 0.0278% Planctomycetaceae at family level and 0.0278% Planctomycetales at order level. Besides the denitrification effects, the possible anammox bacteria present in the anaerobic tank might have also contributed to high nitrogen removal efficiency.