Aerobic treatment plant of non-diluted night soil was designed and built in 1969. This plant consisted of aeration tank (which had four aerobic digestion tanks), sedimentation tank, 2nd aeration tank, and clarifier. Effect of treatment was investigated, and the following results were obtained. Temperature in the 1st digestion tank was more than 24° even in Nakatsugawa city, Gifu Prefecture, where the outside temperature was below zero degree in winter. This phenomenon was advantage for biological treatment of night soil. Percentage removal of BOD, COD, and Kjeldahl-N in the 1st digestion tank were 82, 46, and 72%, and those in the effluent were 41, 61, and 51 ppm, respectively. In general, removal of NH3-N is difficult by other aerobic treatment system, but its removal percentage was good at this plant, and NH3-N stripping was observed because this aerobic treatment tank was in alkaline state. Zoogloea and Protozoa could not be found in the 1st digestion tank. The Biota of this tank was different from standard activated sludge organisms. Bad odor was not detected around the plant. It is considered that this plant of non-diluted night soil treatment gives better clearance than other treat ment plant.
