Cultivation of aerobic granular sludge and its degradation effect on low C/N ratio wastewater

The intermittent aeration operation mode of "stirring-aeration-stirring" was employed to explore the formation rule of aerobic granular sludge (AGS) in wastewater with low C/N ratio (1~6) and its degradation effect on pollutants, so as to provide technical support for efficient treatment of wastewater with low C/N ratio. When the influent C/N ratio was 1~2.25, the seed sludge showed obvious inadaptability, the sludge volume and granulation rate increased slowly, and the removal efficiencies of chemicaloxygen demand (COD), total inorganic nitrogen (TIN) and total phosphorus (TP) were low and fluctuated greatly. When the influent C/N ratio increased to 6, the physicochemical properties of sludge gradually tended to be stable, and aerobic sludge granulation was achieved within 35 days. The removal efficiencies of ammonia nitrogen and COD by mature AGS were both more than 90%, the removal efficiency of TIN and TP was about 50% and 70%, respectively. Increasing the influent C/N ratio was beneficial to the growth of heterotrophic bacteria and the secretion of extracellular polymers, thus accelerating the formation of AGS. The removal of TIN under "stirring-aeration-stirring" operation mode included exogenous denitrification and endogenous denitrification. Reactions in the aeration section were mainly the degradation of COD and oxidation of ammonia nitrogen, and there was almost no removal of TIN. Profiles of different kinds of nitrogen indicated that the contribution rates of exogenous denitrification and endogenous denitrification were 2.82%~18.45% and 18.30%~48.28%, respectively.