The concentration of 21 odor compounds of water and air, odor index and DOC of the water were measured at nine sewerage process stations. The odor indexes of water decreased as the sewage treatment progressed. According to the dilution ratio given by dividing the concentration of an odor compound in the head space of a triangle flask with its threshold, it was suggested that sulfur-containing compounds are the main cause of odor at the upstream treatment process including the biological reaction process. Since the odor index obtained by the triangle flask method had a positive correlation with the concentration of aldehydes in water, it was suggested that the decrease in odor index depends on the concentration of aldehydes. The dilution ratios in air supported the suggestion that sulfur-containing compounds are the main cause of odor at the upstream treatment process, and acetaldehyde is the main cause of odor at the outflow of final sedimentation and final effluent. The concentration of acetaldehydes of air at the final effluent was 15 times as high as that of a natural environment. Deodor methods by both photocatalysis and ozonation treatment were considered feasible for decreasing the odor of the final effluent.

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Applicability of a new simple method for estimating heterotrophic plate count (HPC) in environmental samples was investigated. In this method, 0.1-1.0 ml of sample is incubated in a cell equipped with a dissolved oxygen (DO) electrode. The HPC in the sample is estimated from the time required until the DO is depleted (detection time). This method was applied to a pure culture sample and environmental samples to evaluate the validity and reliability of this method.
The results indicated that (1) the HPC estimated by this method was in agreement with that determined by the plate count method in environmental samples (r = 0.85), (2) 95 % confidence interval of detection time of this method was shorter than the generation time of bacteria in the samples with HPCs higher than 10²-10³ CFU·ml^-1, (3) In the case in which the same amounts of heterotrophic bacteria existed in the sample cell, the detection time (mean value and 95 % confidence interval) for bacteria captured on a polycarbonate membrane filter (0.2 μ m) was comparable with that for bacteria suspended in the sample cell.
Thus, it could be concluded that this simple method could more rapidly estimate the HPC in environmental samples than the conventional plate count method with comparable accuracy and could be sufficiently applied to low-HPC samples.

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In the basin of Lake Biwa and Lake Kasumigaura, relationships between fractionation data of dissolved organic matter (DOM) and in inflowing river water and watershed characteristics were investigated by regression analysis and specific unit modeling. Most hydrophobic neutrals were found to originate from domestic sewage. Domestic wastewater treatment plant effluent was found to significantly contribute to the load of hydrophilic acids in river water. Specific unit modeling based on the load of DOM fraction and the ratio of land use contribution in watershed enabled source identification for each DOM fraction including refractory dissolved organic matter. In the north basin of Lake Biwa, forest outflow significantly contributed to the load of aquatic humic substances and refractory fractions. The loads of other DOM fractions were found to be dominated mainly by urban drainage.

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A high nitrate nitrogen concentration in leaching water from a tea field is observed in Japan. A small river called the Tanno River is located in a watershed where a tea field is caltivated. There are paddy fields along the Tanno River and denitrification occurs there during irrigation period. The authors and the Ministry of Agriculture and Fishery measured the discharge and water qualities at four poins on the Tanno River and measured denitrification rate at three paddy fields. The authors simulated the discharge and N concentration for the four points using the water quality tank mode (WQSTM), which takes into account the denitrification of paddy fields and N accumulation in soils. The authors also simulated the water qualities for the four points and evaluated the quantity of N removed from the on the basis of the obtained results. An aerial ratio of the paddy field to the tea field is 19.6% in the watershed, and the rate of nitrogen removal reached 41% during the irrigation period. The annual average rate of N removal was 14%. Moreover, the authors demonstrated that a future change in N concentration can be predicted by this WQSTM.

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