A new equipment for treating gray water from individual household was tested at 9 houses during apploximately 18 monthes. The equipment is composed of 200 liter tank (first tank) for pre-treatment and 200 liter submerged biofilter tank (second tank) packed with artificial gravels. The volume and the concentration of gray water discharged from each house were different and varied greatly with time. However, the qualities of the treated water were good enough as follows ; the 50% probability values of BOD, COD, SS, TOC and MBAS were 13, 15, 17, 13 and 1.1mg/l, and their standard deviations were 20, 11, 24, 8 and 3.8mg/l respectively. The correlations between BOD and COD or TOC were obtained distinctly, but BOD and SS did not show any clear relationship.

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The effects of reaction time, pH and humic substances on the aqueous chlorination were studied with respect to the quantitative formation of dichloroacetic acid (DCA), trichloroacetic acid (TCA), chloral hydrate (CH), chloroform, and total organic chlorine (TOCl).
Humic acid was chlorinated at following conditions : total organic carbon 5mg·l^-1, chlorine dose 20mg·l^-1, reaction time (5min, 1, 6, and 24h), pH (4, 6, 7, 8, and 10), and at room temperature.
At the neutral pH, the concentration of DCA, TCA, and CH increased with the increase of reaction time similar to the case of chloroform or of TOCl. The amount of TCA formed was greater than chloroform.
The concentration of chloroform increased with increase of pH from 4 to 10. However, TCA and CH formation decreased at pH range of 810. The pH dependence of DCA and CH formation was smaller than the cases of chloroform and of TCA.
The DCA, TCA, and CH formation from fumic acid was similar to that from humic acid.

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The effect of nitrate nitrogen in culture solution on the growth of waterhyacinth, the absorption of nitrate nitrogen and the nitrogen contents of tissues of waterhyacinth were studied.
(1) The contents of waterhyacinth and total nitrogen of waterhyacinth and specific absorption rate of nitrate nitrogen increased with increasing concentration of nitrate nitrogen in culture.
(2) It is clear that nitrate nitrogen is limiting below a concentration of 0.6mg·l^-1 and concentrations higher than this exert less influence on the nitrogen content of the plant.
(3) When nitrate nitrogen are present in excess (above 0.5mg·l^-1), the value of the specific growth rate of waterhyacinth remain constant.

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[in Japanese]

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