Some reports (Hashimoto, Ozaki, and Matsunari, 1984) have indicated an approximately 80% T-N removal rate for contact aeration processes using small scale laboratory tests. However, actual small prototype sewage treatment plants have large variations of discharge and pollutant loads. Hence it will sometimes happen that the removal rates obtained at actual plants differ greatly from experimental plants (Nakasone and Ozaki, 1984), because they have the same shape but different surface areas of contact media which will have serious effects on denitrification. Hence the authors constructed three test plants which only differ in the surface area of the contact media and performed numerous experiments. As a result of three experiments, we understand that if we want to obtain a T-N concentration of less that 20mg/l in areal effluent during winter, a nitrification rate of more than 20% and NH+4-N areal loading of less than 3.0g/m2/day are necessary at the same time. It also became clear that the surface area of contact media will require at least 50m 2/m3. The phosphorus removal rate is about 60% without any dephosphorization process. Treatment results for other water quality parameters such as BOD, COD, SS, and pH were no problem at all.

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