The organic materials in effluent derived from a biological treatment process usually have high values on THMFP (Trihalomethane formation potential) /DOC, in comparison with those in raw wastes. A study was made to obtain the quantity of organic chloride precursor expressed as THM, Total Potential THM and TOX precursors produced with activated sludge. The quantity of dissolved organic chloride precursor derived from selfdecomposition of activated sludge and the quantity of organic chloride resulting from activated sludge by chlorination were estimated through the batch experiment, using the return suldge of a wastewater treatment. Also, the quantity of dissolved trihalomethane precursor during the reduction process of substrate was evaluated. The results obtained are as follows :
1) THMFP/DOC, Total Potential THMFP/DOC and TOXFP/DOC of the dissolved matter liquated from selfdecomposition of activated sludge in the case of the initial MLSS concentration was 3000 mg·l^-1 were 24.4μg·mgC^-1, 48.3μg·mgC^-1 and 122μg as Cl·mgC^-1, respectively. As the initial MLSS concentration got larger, the ratio of each formation potential/DOC that was liquated out got smaller.
2) The ranges of THMFP/SS and TOXFP/SS derived from activated sludge were 0.5-1.4μg·mgSS^-1 and 27μg as Cl·mgSS^-1, respectively.
3) The range of THMFP of the dissolved matter on the substrate reduction process with activated sludge was from 96 to 114μg·l^-1 regardless of either the amount of activated sludge, or the removal Df DOC.

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In this paper, the behavior of flood induced particulate nutrients (nitrogen and phosphorus) in lake Kasumigaura based on field survey was discussed.
The results obtained was as follows.
(1) 70% of total particulate loading settled before the flood finished. After 5days, the quantity of suspended nutrients in lake was approximatly 3-4% of total loading induced by flood.
(2) Settling velocity of flood induced particulate soild was about 1 (m/day) except for flood peried.

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The organic materials in the effluent from activated sludge treatment have a high THM FP ·DOC^-1 (as much as 25.5μg·mgC^-1). The particular substrate as well as the soluble substrate are metabolized by microorganisms during the activated sludge treatment. On the other hand, during the contact oxidation-biological filtration, the soluble substrate is metabolized by microorganisms, but the particular substrate is mainly removed by filtration. Therefore, it is assumed that the effluent from the contact oxidation-biological filtration contains a smaller amount of organic chloride precursor than that from the activated sludge treatment. This study was made to obtain the quantity of organic chloride precursor produced from the contact oxidation-biological filtration process. The results were as follows :
1) This process reduced the THM precursor, the total potential THM precursor and the TOX precursor to 52-65%, 45-50% and 37-46% of the original quantities, respectively. 2) THM FP·DOC^-1 of the effluent from biological filtration was larger than that from the contact oxidation and the raw waste. There was a relationship between (COD_Cr-BOD_u) ·COD_Cr^-1, THM FP·DOC^-1, TOX FP·DOC^-1 and consumed chlorine·DOC^-1. 3) The range of THM FP·DOC^-1 of the recalcitrant resulting from the contact oxidation-biological filtration was found to be from 13 to 19μg·mgC^-1.

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