There is a growing public awareness of environmental issues these days; sewage treatment is no exception to this trend. Advanced sewage treatment is thus becoming indispensable, the purpose of which is to conserve the water environment into which effluent is discharged, prevent eutrophication of closed waters, maintain the quality of raw water, and recycle treated sewage as water resources. There are a variety of technologies for treating sewage to a high degree, such as sand filtration, biological filtration, and activated carbon filtration. In particular, biological filtration is becoming a focus of attention because of its unique combination of physical filtration (through sand filters) and microbial filtration. We have developed a biological filtration system for treating sewage to a high degree. This is a unique system that can be characterized by granule ceramic filter materials and a lower collection tub. Biological filtration is quite effective in treating sewage because it can remove both highly toxic ammonia nitrogen and nitrite nitrogen.