The nitrogen removal characteristics of sludge floc and biofilm along the anaerobic anoxic oxic process

• Published in: Journal of water process engineering 2024-03, Vol.59, p.105069, Article 105069
• Main Authors: Peng, Zhaoxu, Zhang, Wangcheng, Lou, Tianyu, Huang, Zehan, Jiang, Kun, Yu, Luji, Ji, Jiantao
• Format: Article
• Language: English
• Subjects: AAO; Biofilm; Carriers; Nitrogen removal; Sludge floc
• ISSN: 2214-7144; 2214-7144
• DOI: 10.1016/j.jwpe.2024.105069

This study focused on the horizontal distribution of nitrogen removal characteristics of biofilm and sludge floc in anaerobic/anoxic/oxic (AAO) process. Fixed carriers were placed in a full-scale AAO system, and the nitrogen removal kinetics associated with microbial community between biofilm and sludge floc along the process were investigated. The results showed sludge floc exhibits superior nitrification capability, particularly around the middle of aerobic tank with specific NH4+-N (NO2−-N) oxidation rates of 1.67 mg·g−1·h−1-3.46 mg·g−1·h−1 (1.32 mg·g−1·h−1-1.56 mg·g−1·h−1). The biofilm exhibits superior denitrification ability, particularly in anoxic and middle of aerobic tank with specific NO3−-N (NO2−-N) reduction rates of 4.34 mg·g−1·h−1-10.16 mg·g−1·h−1 (2.95 mg·g−1·h−1-4.93 mg·g−1·h−1). In aerobic tank, extracellular polymeric substance (EPS) of sludge floc was positively correlated with specific oxidation rates of NH4+-N (R = 0.93) and NO2−-N (R = 0.89), but EPS of biofilm was negatively correlated with specific NH4+-N oxidation rate (R = -0.68). Nitrospira was the dominant nitrifying bacteria in sludge floc which distributed evenly in the AAO process with the relative abundance of 4.28 %–5.95 %, while in biofilm it mainly enriched in anoxic (2.33 %–3.27 %) and aerobic tank (1.04 %–1.89 %). Dechloromonas and Thauera were main denitrifying bacteria in sludge floc (2.77 % ± 0.61 % and 1.80 % ± 0.25 %), while Saccharibacteria was dominant denitrifying bacteria in biofilm (4.44 % ± 1.51 %). Candidatus Kuenenia was Anammox bacteria in both sludge floc (0.01 % ± 0.01 %) and biofilm (0.02 % ± 0.01 %). The nitrogen removal potential in each tank was evaluated through comparing the differences between actual concentrations of NH4+-N, NO2−-N, NO3−-N and the associated half-saturation constants, and the strategy of specifically installing fixed carriers to improve nitrogen removal was proposed. •Sludge floc exhibited better nitrification ability than biofilm.•The effect of EPS in sludge floc and biofilm on nitrification is different.•Saccharibacteria was the dominant denitrifying bacteria in biofilm.•Dechloromonas was the dominant denitrifying bacteria in sludge floc.•The strategy of specifically installing fixed carriers to improve nitrogen removal was proposed.