Development of novel anaerobic/aerobic filter process for nitrogen removal using immobilized nitrifier pellets

In Japan, priority of sewage works implementation has gradually been given to smaller communities. Sewage treatment processes for small communities must meet several requirements such as low construction and O-M cost, easy O-M, stable performance, and in some locations nitrogen and/or phosphorus removal as well as BOD and SS removal. With a view to achieving these requirements, the authors have been developing a novel anaerobic/aerobic filter process for simultaneous removal of BOD, SS and nitrogen. In this process, an upflow anaerobic filter is followed by a nitrification tank using entrapped immobilized nitrifier pellets and an aerobic filter for the polishing process. In order to demonstrate this novel process in the field, a pilot plant with a capacity of 1.75 m3/d was installed in an existing sewage treatment plant near Tokyo in January, 1996. The target effluent qualities are BOD and T-N less than 10 mg/l respectively and SS less than 5 mg/l. The pilot plant study has shown that the overall treatment performance of 96–97% in SS and BOD removal and 74–75% in T-N removal has been stably obtained under the conditions of 5.5h in total retention time, recycling ratio of 3, and 25 to 250% in load variation.