Upgrading CASS sewage treatment station of university with inverted AAO process

Abstract

Although cyclic activated sludge system(CASS) is widely used, there is a significant risk of exceeding nitrogen and phosphorus in effluent. Especially the university sewage with the characteristics of “emission peak in morning, mid-evening,and significant differences in water quality and quantity”, it's more difficult to meet the discharge standards. These CASS treatment stations are commonly faced with the upgrade problem. In this paper, the upgrading practice of a 2 200 m³/d CASS sewage treatment station in an independent college was taken as an example. Only through four-step in-situ reconstruction: 1)enhanced vertical mixing of regulating tank by installing submersible water impeller; 2)cutting and connecting the 1-3# CASS pre-reaction pool to create a baffled anaerobic pool;3)increased biological filler in 1-2# CASS main reaction pools to improve the aerobic biochemical load; 4)partitioning 3# CASS main reaction pool in a 3∶2 ratio to construct an anoxic pool and a secondary sedimentation tank. The CASS was successfully upgraded to an improved inverted AAO process. Meanwhile, the renovation project was equipped with a three-stage treatment unit of “coagulation+fiber filtration”, with an investment of only 1.2 million RMB. The upgrading process exhibited an excellent performance of denitrification and phosphorus removal. It could overcome the effects of water quality fluctuations of university wastewater effectively, significantly improve the process of nitrogen and phosphorus removal performance, and present a significant economic advantage and reference value.

Keywords

• university sewage
• cyclic activated sludge system
• fluctuations in water quality and quantity
• in-situ transformation
• inverted aao
• denitrification and phosphorus removal