The effects of salt concentration and dilution rates on self-purification of nitrogen were experimentally investigated by continuous stirred tank reactor. Setup conditions were the salt concentration of 0%, 25%, 50%, 75%, 100%, and HRT 4, 8, 16, 24, 48hr, it cleared a degree of participation under the coexistence of microorganisms such as algae and nitrification bacteria. Under the salinity concentration; 1) Poor conditions when the dilution rate is low, assimilation of nitrogen by the algae was predominant. When the dilution rate is high, the nitrification by nitrifying bacteria is predominant. 2) Rich conditions when the dilution rate is low, assimilation of nitrogen by the algae was predominant. When the dilution rate is high, the nitrification by nitrifying bacteria is predominant. The response of nitrite oxidizing bacteria the was high to the salt concentration, and nitrite nitrogen accumulated it.

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We investigated the database of fish species in the National Census on the Environment by statistical analysis. A summary of this study is given as follows. (1) The number of fish species found in Class A rivers was 183 and the major five species accounted for 50% of the total. (2) The proportion of fish species can be represented by four principal components with 0.754 of contribution rate in principal component analysis. (3) Variation of the proportion and diversity index of fish species can be quantitatively estimated by adopting classification of river morphology and segment of river longitudinal profile as explanatory indexes. (4) The diversity index of fish species has a significant correlation with the slope of river bed and the ratio of vegetated area in the river area.

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The allelopathic effects of the extracts of a brown alga Sargassum horneri on red tide microalgae were examined using Skeletonema costatum, Chattonella antiqua and Heterosigma akashiwo. The growth of S. costatum and C. antiqua were inhibited remarkably by the extracts of S. horneri while H. akashiwo needed higher amount of the extracts than S. costatum and C. antiqua to attain same level of growth inhibition, confirming the difference in the allelopathic effects with microalga species. The microscopic observation indicated that the growth inhibition effects of the potential allelochemicals produced by S. horneri were associated with the change of the body form of the red tide microalgae tested.

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In this research, the fate of cyanobacterial toxin, microcystin in Lake Biwa were investigated. And we also examined the toxin analysis using ELISA method. Microcystin was detected in the Lake Biwa water and its filtrate. The concentration was varied depending upon the sampling stations, and increased to 2, 200pg/mL in the maximum with the coincidence of the water bloom. Microcystin was not detected in the tap water from Lake Biwa, which suggested that the microcystin would be removed in the water treatment process. The ratio of filtrate micocystin to total microcystin was varied. Although the ratio of microcystin in filtrate decreased with increase of total micocystin concentration, relationship between the ratio and the pH value of lake water was not observed.

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In order to remove phosphorus from domestic wastewater it is useful to add coagulants to activated sludge process. The amount of coagulant addition is usually determined by the molar ratio of coagulant to phosphorus. The precise mechanism of the coagulation process of phosphorus removal in activated sludge has not been clarified yet. So coagulant reduction and accumulation experiments using activated sludge were conducted in order to reduce the amount of coagulant addition. From the results, the coagulation process was discussed using a new phosphorus removal model, in which the coagulant in activated sludge was divided into two fractions. The coagulant contents in the accumulation process as well as the effluent phosphorus concentration were effectively computed using the model. The model is suggested for application in the determination of the amount of coagulant addition.

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To estimate evapotaranspiration rate and drainage water quality from vagetation on rooftop, meteorological and hydrological observation on rooftop planting has been carried out at Kinki University since 2001. The evapotranspiration from the grass surface was measured by the column buried in the grass-coverd area. It was found that the average evapotranspiration rate form grass-cover area on rooftop is 4.4mm to 6.2mm. Chemical analysis of dranage water from rooftop planting showed that the concentration of NO₂-N and NO₃-N is 7 to 10 times of the most strict water quality standard of lakes in Japan, and the concentration of PO₄-P is 800 to 1400 times of that.

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The population dynamics model describes the annual change of total biomass of benthic animals in river. We developed a recovery model assessing the influence of an artificial pulse type (temporal) impact with two evaluation indexes, i. e. Recovery Rate and Ecological Loss Time. Recovery simulations from a virtual impact were performed in 70 river sites in Tokyo with an assumption that the biomass decreases to 0.08 times just after the impact in each site. This recovery model confirmed the tendency of high resilience of macroinvertebrate as well as the effectiveness of the two indexes for impact assessments in river ecosystem.

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For the purpose of recycling of timbers from wooden house we devised the handworked demolition system that was possible to get main components such as pillars, beams etc. in perfect, and to reuse for building woods after processing. We compared this system to classified demolition one that was now in use, on environmental and economical point of view, through demolition, waste disposal and recycling processes.
This system was proved to be better than classified one, because it consumed less energy and expenses, and provided useful building woods, and was used exist wood manufacturing.

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To change the present flush type toilets into the composting toilets is the one of solution methods of prevention of water resource and recycling of nutrition. However it is necessary to mind about secondary infection of a pathogen through this type toilet because the excrement is left in it.
In this research, the microbial risk assessments were applied to the composting toilet for investigating the hygienic safety of it. For the exposure assessment, direct and indirect routes were assumed and required removal ratio of pathogen was discussed. Consequently, viral risks were assumed to be higher than bacterial risks, and it was also assumed that risks through indirect routes were as high as the case through direct routes.

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In order to understand the tolerance to high-level contamination and the long-term cultivation and nitrate fertilization effects for turnip, we conducted cultivation experiments. The main results of the experiments are the following: (1) Two steps of marginal values exist. (2) By nitrate fertilization, positive effects for copper accumulation and negative effects for cadmium accumulation were observed. (3) In the long-term experiment, metal accumulation advanced at the shoot and root of turnip, if the contaminant level was appropriate.

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