The characteristics of the degradation of excess activated sludge in the acidogenic phase were investigated by the laboratory-scale batch and continuous experiments at 35±1°C. The effects of organic loading and digestion period on the production of volatile fatty acids and digester gas were studied by the batch experiments. On the other hand, the continuous experiments were performed using four kinds of excess activated sludges collected at different periods at SRTs of 0.5, 1.5, 3.0 and 5.0 days in order to clarify the behavior of the degradation of excess activated sludge. About 60% of total COD of excess activated sludge was degraded in 130 days by batch experiment. The hydrolysis reaction is the rate-limiting step in overall anaerobic digestion. The hydrolytic rate of degradable materials in excess activated sludge is expressed as a linear equation, and hydrolytic rate constants were : 0.44 0.89 days^-1 on the basis of volatile suspended solids (VSS) and 0.32 0.65 days^-1 on the basis of COD. The distribution ratios of degradable materials in the excess activated sludge are shown in the following order : lipid> protein> carbohydrate.

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Laboratory scale sequencing batch reactor (SBR) activated sludege processes were operated by introducing anaerobic reactions into the operational schedule of SBR to study the performance for simultaneous removal of nitrogen, phosphorus and BOD from high strength of wastewater assuming treatment of wastewater from small scale factories and to clarify the behavior of microorganisms responsible for phosphorus removal during operations of the SBR.
The best performance for phosphorus removal was noted in operations where anoxic/anaerobic reactions were introduced into the fill period. Denitrification and remarkable release of phosphate from the solid into water phase (supernatant of mixed liquor) during the fill was followed by the luxury uptake of phosphate under aeration. On the contrary, little phosphorus was removed in conventional operations in which aeration continued throughout a cycle. Change from the operation with anoxic/anaerobic reaction during the fill to that with aerobic reaction throughout a cycle immediately deteriorate the activity of phosphorus removal. Operation with anaerobic reaction, however, was not sufficient condition to remove phosphorus and, in addition, ecological selection and/ or enrichment of the phosphorus accumulating bacteria were also necessary to remove phosphorus under operation with anaerobic condition.

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The behavior of total organic halogen formation potential (TOXFP) in Yodo River Basin has been investigated and Yodo River water evaluated for the drinking water.
The water quality of Yodo R. is mainly regulated by diffusion and mixing process of three rivers which compose Yodo R.; Uji R., Kizu R. and Katsura R.. TOXFP of Yodo R. ranges from 200 to 600μg·l^-1.
The pollution load of TOXFP of Katsura R., remaining a stable figure (1800kg · d^-1), is independent of water flow rate. It proves that this river is contaminated by various kind of human activities. A 45% of the load is attributed to municipal sewage treatment plants.
The water pollution at the left bank of Yodo R. is also effected by tributaries which flow through Hirakata city and gives an adverse effect on the drinking water quality.
Considering cancer risk of chloroform and mutagenic activity of drinking water, it is desirable that TOX level of tap water is below 150μg·l^-1 and TOXFP level of raw water is below 240μg·l^-1. These levels are satisfied only at Kuzuha water work.
The most effective way to attain better water quality is to improve municipal sewage treatment plants, which leads TOXFP concentration in Yodo R. below 500μg·l^-1.

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