Contaminants removal characteristics between floc sludge and aerobic granular sludge in domestic sewage treatment at low temperature

Low temperature may result in low metabolic capability of microorganisms in the treatment units, and then cause the lower removal efficiency for contaminants removal. Therefore, the treatment of domestic sewage at 6°C was studied between floc sludge and aerobic granular sludge. Due to the compact interior structure of aerobic granular sludge, it can provide a proper temperature and dissolved oxygen (DO) for denitrifying bacteria and phosphorus accumulating organisms (PAOs), consequently, the NH₄⁺-N and TN removal efficiency were higher than those of floc sludge, which were 81.06% and 68.31%. Except chemical phosphorus removal by extracellular polymeric substances (EPS), biological phosphorus removal ability of aerobic granular sludge also increased, however, TP removal efficiency was only 32.50%. The temperature dependency of nitrification, denitrification and phosphorus removal were lower for aerobic granular sludge than usually found for floc sludge. However, the activity of phosphorus accumulating organisms (PAOs) was low at 6°C, which indicates PAOs may not be fit for in such circumstance. Aerobic granular sludge technique exhibits outstanding advantages in treating domestic sewage at low temperature, exploring psychrotrophs and rapid cultivating aerobic granular sludge may make the trend for pollution control to face the challenges between the resource crisis and eutrophication.