Responses of biofilm characteristics to variations in temperature and NH4+-N loading in a moving-bed biofilm reactor treating micro-polluted raw water

A pilot-scale moving-bed biofilm reactor (MBBR) for biological treatment of micro-polluted raw water was operated over 400 days to investigate the responses of biofilm characteristics and nitrification performance to variations in temperature and NH4+-N loading. The mean removal efficiency of NH4+-N in the MBBR reached 71.4 ± 26.9%, and batch experiments were performed to study nitrification kinetics for better process understanding. Seven physical–chemical parameters, including volatile solids (VS), polysaccharides (PS) and phospholipids (PL) increased firstly, and then rapidly decreased with increasing temperature and NH4+-N loading, and properly characterized the attached biomass during biofilm development and detachment in the MBBR. The biofilm compositions were described by six ratios, e.g., PS/VS and PL/VS ratios showed different variation trends, indicating different responses of PS and PL to the changes in temperature and NH4+-N loading. Furthermore, fluorescent in situ hybridization (FISH) analysis revealed that increased NH4+-N loadings caused an enrichment of the nitrifying biofilm.