Two types of laboratory-scale experiments were conducted to investigate nitrate removal by sulfur oxidizing denitrifiers fed with thiosulfate as electron donor. One was a batch-type activity test of denitrification with glass vials using enrichment culture. The other was a downflow column experiment at 20°C and at a filtration velocity of 4m·day^-1, in which artificially contaminated water was supplied to packed-bed filled with granular anthracites. The stoichiometries of denitrification from nitrate and nitrite by oxidation of thiosulfate were discussed with removal and production data in several batch tests. The conversion rate from nitrate to nitrite was much higher than from nitrite to nitrogen gas in the batch test. The nitrogen concentration profile along the column showed that rapid removal of nitrate was observed at the upper part of the filter after development of biofilm in bed, although remarkable accumulation of nitrite took place there. The accumulation was reduced downward to some extent by distribution of attached biomass to the lower part. However, nitrite in the effluent was not removed completely after ammonium was added as an easily assimilable nitrogen source in order to promote the activity and growth of sulfur-denitrifiers. There was a possibility that their activity and growth was not controlled by nitrogen source for synthesis but suppressed by lower pH condition within the biofilm than bulk water in the column.

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For the control of COD load in Lake Kojima, this study was performed to estimate dissolved COD inflows from domestic effluent and paddy field which were considered as main COD source.
Degradation and remaining of fractions of the dissolved COD substances were discussed by the gel chromatography.
By calculation with the increase of lake water level, water inflows were 7.6×10⁵m³·d^-1 in the clear non-irrigation period and 12.1×10⁵m³·d^-1 in the clear irrigation period, and annual average run-off ratio of precipitation was 0.46 from Apr. '91 to Mar. '92.
Dissolved COD remaining through the process of sewage treatment and natural purification from domestic effluent showed about 21% of COD load factor (20g·person^-1·d^-1) in estimation with UV absorbance and dissolved COD pattern of domestic effluent and downstream river water by Sephadex G-15 gel chromatography.
On the basis of synthesis of UV absorbance pattern and dissolved COD concentration of waters sampled at lake, paddy field, forest and urban area, dissolved COD inflow from paddy field was estimated at 7,200kg·km^-2·y^-1.

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In order to grasp the nationwide river pollution by synthetic detergents and surfactants, monitoring data of MBAS (Methylene Blue Active Substances), an indicator of anionic type sharing a major part of surfactant production, were analyzed statistically at 957 river monitoring stations of nine prefectures in Japan.
Average MBAS concentrations during 1985-89 indicated the log-normal distribution with 35% of low level below 0.1mg·l^-1, 49% of middle level between 0.1 and 1mg·l^-1 and 15% of high level above 1mg·l^-1.
The testings for the variation of MBAS concentration during 1980's at each monitoring station showed that the variations for about half of the stations were statistically significant in each of three prefectures, Saitama, Tokyo and Hyogo, where trends of variations were relatively similar at each concentration level.
From the analysis of MBAS data in rivers of Kinki Region in 1989, the percentage of monitoring station with high concentration appearing for three months or more was estimated to be 20% and 60% in case of MBAS exceeding 1mg·l^-1 and 0.1mg·l^-1, respectively. In the estimation by average BOD, these percetages grew high as the level or average BOD increased.

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Seasonal characteristics of the spatial distributions of COD and DO in Tokyo Bay were revealed by applying statistical methods to the monitoring data obtained at 41 observation points every month from April 1985 to March 1990.
High concentrations of COD and DO in the surface layer were observed at the head and along the west coast of the bay during late spring to early autumn. They were especially prominent in June off the mouth of the R. Ara, where nutrients were abundant and phytoplankton multiplied rapidly. On the other hand, the concentration of COD in the bottom layer was higher near land than offshore, and was almost inversely proportional to depth at the head of the bay. A lower concentration of DO in the surface layer was observed off the mouth of the R. Ara than off the mouths of the R. Edo and R. Tama. The concentration of DO in the bottom layer at the head of the bay decreased at a rate of about 1 mg·l^-1 per month during spring to early summer, and reached a level lower than 1 mg·l^-1 in September. Furthermore, the strengthening of the wind from the northeast in September caused a drop of the concentration of DO in the bottom layer in the northeastern part of the bay.

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Samples of drinking water collected from New Delhi, Calcutta (as representative urban area), Punjab (rural area), Darjeeling (mountain area) in India. Samples were carefully collected so that no air vesicle came in the vacuum polyethylene bottle and all water quality examinations were performed in Japan. 22 items were analyzed. However, bacterial test were not carried out.
Levels of NO₃^-, Br^-, Cl^- in drinking water of both city area were high. TOC and THM in Calcutta and Punjab were high. The concentrations of fluoride in Punjab were very high and the maximum concentration was 9.7mg·l^-1. In general, the concentrations of fluoride in the drinking water in India was higher than that of in Japan.
Judging from the levels of SO₄^2-, Br^-, Cl^- and F^- in well water samples, much of the drinking waters can be considered as contaminated from soil and therefore, it is not suitable for drinking.

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