Comparative analysis of sludge settleability of A2O-BAF process and A2O process treating higher C/N ratio domestic sewage

A²O process is an effective nitrogen and phosphorus removal process. A²O-Biological Aerated Filter (BAF) process is a new nitrogen and phosphorus removal process basing on the two-sludge theory. Separation of activated sludge is one of the difficult problems encountered in the activated sludge process. Sludge bulking is the most difficult problem. The experiment put great emphasis on the sludge settleability of the two processes, when they are used to treat the higher C/N ratio domestic sewage. The two systems were operated for 30 days at the C/N ratio of about 7.1. The experiment result showed: the sludge settleability of A²O-BAF process is far better than A²O process, the former is without the risk of sludge bulking, while the latter is more serious. The main reasons are: A²O-BAF process has long anoxic zone and short aerobic zone, so it can inhibit sludge bulking effectively; phosphorus content in sludge of A²O-BAF process is twice more than that of A²O process, the former´s is about 6%, the latter´s is about 3%; the sludge floating problem faced by A²O-BAF process is far less serious than A²O process, the floc is denser and more cohesive.