The objectives of this study are to clarify the fate of phosphorus in coagulation/sedimentation process, and to determine the effects of phosphorus addition in biological activated carbon treatment on the biodegradability of organic substances and on the number and growth of attached bacteria.
The following conclusions can be made from this study: 1) The phosphorus concentration in supernatant after coagulation was 0.002 - 0.004 mg.l^-1 in water containing phosphorus of 0.063 mg.l^-1 or less. The phosphorus left in supernatant after coagulation was less than 0.011 mg.l^-1 even in water containing initial phosphorus concentration of 0.213 mg.l^-1. 2) Growth of attached bacteria and biodegradation activity on biological activated carbon were greatly affected by phosphorus.

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Settling velocity distribution of suspended solids, which is one of the most important factors for the performance of the rock bed contact-purification channel, was determined for urban canal/river water by a new settling tube method. In this method (the plural settling cylinders method), some cylinders are prepared as settling tubes, and the supernatant sample is taken from each of these cylinders with time, so that relatively large volume of sample facilitates more detailed measurement of particulate indices.
Results showed about 90% of suspended particles in the canal water were smaller than 20 μm in size and less than 10 cm·hr^-1 in settling velocity, while 70% were under 2 cm·hr^-1 and 50%, were under 1 cm·hr^-1. Pilot plant experiments in AIT showed aeration promoted the settlability of suspended matter in influent. This settling test also indicated that aeration in the head pit can increase the settling velocity of influent particles due to flocculation of fine particles. These results mean that aeration in the head pit is important for enhancing SS removal and improving effluent quality through the rock bed channel.

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The characteristics of organic compounds accumulated in bioreactors were examined by using experimental benchscale plants of the activated sludge processs with dead end or cross flow ultrafiltration system.
Use of ultrafiltration system brought easily highly concentrated activated sludge suspension in the bioreactors, compared with use of sedimentation system. At the sam time, organic compounds with wide range of molecular weight were accumulated in the bioreactors by introducing ultrafiltration system.
Accumulated organic compounds were fractionalized by the gel permeation chromatography using high performance liquid clromatograph(HPLC). A large molecular weight group was composed of organic compounds with a relatively low ratio of E₂₆₀/TOC, and accumulated predominantly according to treatment performance. A medium molecular weight group was composed of organic compounds with a large ratio of E₂₆₀/TOC, and molecular weight of the peak was estimated to he about 1,300 on the basis of polyethyleneglycol. A small molecular weight group was also composed of organic compounds with a large ratio of E₂₆₀/TOC, which might be derived from activated sludge destroyed by the feeding pump to the ultrafiltration membrane module. The small and medium molecular weight groups permeable the membrane in nature was accumulated possibly by dynamic membrane developed on the membrane.
Oxygen uptake rate for substrate metabolism of activated sludge decreased largely according to treatment performance in the process with ultrafiltration system. One possible reason for this phenomenon is assumed to be inhibitory effects of the accumulated organic compounds.

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The main precursor of chlorinated organic compounds formed during chlorination process of drinking water are humic substances. Fulvic acid in treated sewage and that in leaf mold extract were chlorinated, and the generated non-volatile compounds were analyzed by GC/MS following methylation with methanol and sulfuric acid.
Chloroacetic, chloropropionic, chloromaleic, and chlorofumalic acids were identified, and the generation of chlorinated compounds having ring structure such as aromatic ring was suggested for the chlorination of fulvic acid in treated sewage.
Chloroacetic, chloropropionic, chloromaleic, and chlorofumalic acids were identified in the chlorination products of fulvic acid in leaf mold, but the formation of chlorinated compounds having ring structure was not suggested.

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A model experiment was conducted in order to clarify the source-sink relationship of N and P between the sediments and overlying water in eutrophic lake Koyama in Tottori. Two and 10 mg·l^-1 NO₃-N and 0.2 and 1 mg·l^-1 PO₄-P were added to the 900 ml water on 150 g sediments. The water temperature was kept at 15, 20 and 25 C, respectively.
The sediments functioned as sink in both concentrations of N and P. It was likely that the NO₃-N was changed to different forms by bacteria and the PO₄-P was fixed by physico-chemical processes in the sediment.
The sediments functioned as source when distilled water was used as the overlying water. Ammonium N and organic N, PO₄-P and organic P were supplied by sediments to the overlying water.
It seemed that the sediments contributed to maintain the concentration of N and P in the overlying water as that in the lake water.

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Arsenic concentration exceeding Japanese water quality standard of 0. 01mg·l^-1 was observed in the Ina-gawa river probably due to the 1995 South Hyogo earthquake. The Kinki Regional Construction Bureau performed the intensive survey for a year to ascertain the extent of this abnormal pollution shortly after the earthquake. We discussed the distribution and the increasing of arsenic on the basis of the data from this survey. Much higher concentrations of arsenic were noticed in the tributaries such as Shio-kawa and Yato-gawa rivers, and followed by the points, which directly received these inputs, in Ina-gawa river. The arsenic concentration commenced to increase around at a time of the earthquake, and reached the maximum 1 or 2 months later. Then arsenic gradually decreased in concentration with time and the tendency apparently followed first order- kinetic model. Though the Ina-gawa river showed the decrease in concentration to below the standard level 4 months later the earthquake, most observed data in the tributaries were still continued to be above 0.01mg·l^-1 over the survey period. However, arsenic concentrations at each site during the latter half of the survey appeared to be the “background level” in the Ina-gawa river basin because of slower but rather constant in the decreasing rates.

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