Fate of dissolved organic substance and filtration performance were observed in a pilot-scale membrane bioreactor from which excess sludge was wasted once a week. During the operation for 300 days, no substantial increase of sludge viscosity and dissolved organic carbon was observed in the bioreactor. Meanwhile the membrane bioreactor was operated without significant membrane fouling. The study, therefore, was concluded that excess sludge wasting was important to maintain good filtration conditions particularly for a long period of time.

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Chemical oxygen demand with potassium permanganate (COD (Mn)) and organic carbon concentration were determined for both dissolved and particulate components of water samples obtained in Lake Kasumigaura, Lake Biwa, influent rivers into Lake Kasumigaura, several specific sources in the watershed, outdoor experimental ponds, etc. In each water region and for each component, they correlated highly, but percentage of oxidation with potassium permanganate was rather low and their relationships were significantly different. In the case of gray water, biological degradability is fairly high, but chemical decomposability is nearly negligible. The utilization of measured COD (Mn) data to predict the concentration of total organic carbon in the past was also confirmed based on long-term monitoring data. Then, we discuss the appropriateness of organic matter indices in lakes from the views of clearness of content, feasibility of measurement and applicability to water environment management.

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The low pH of acid precipitation is buffered by soil to some extent, but the pH-buffering mechanism also releases variety of materials, which may cause wide effect on the aquatic environment. So in this research, we have permeated artificial acid rain through soil to examine the quality of soil leachates. As a result, we have found that some soils around Lake Biwa have reached the aluminium buffer range which has possibilities of deteriorating the aquatic ecosystem. We have also found that phosphorus included in the leachate causes great effect on algal growth potential under low pH condition as 4.0.

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Anaerobic treatability of foul condensate discharged from the evaporation-enrichment process of black liquor from a paper and pulp mill was investigated by using batch and a small scale UASB reactors. The foul condensate used in the experiment was anaerobically biodegraded and the removal rate of COD_Cr in anaerobic treatment was expressed as the first-order reaction with respect to the biodegradable COD_Cr, and the reaction rate constant was 3-5 X 10^-5l·mg^-1·h^-1. The COD_Cr removal efficiency in an UASB reactor was as high as 70% when the volumetric COD_Cr loading was lower than 10kg·m³·d^-1. Methane productivity of the condensate was 0.16-0.24 Nm³·kg^-1-COD_Cr.

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A mathematical model was developed to predict the un-steady state two dimensional distribution of pollutant discharged from non-point and point sources to a natural water channel. The model was composed of the hydrodynamic and dispersion models.
A hydrodynamic model was formulated following Leendertes procedure and modified to be able to apply on un-steady state flow resulted from rainfall run-off. And the dispersion model derived according to Peaceman and Rachford nonlinear formulation was made considering two-dimensional movement of dissolved pollutant in meandering non-uniform river.
Hydrological concentration of the study area were examined on site where the longitudinal dispersion coefficient of fluid practicles was determined by measuring the peak dye concentration, for hydrodynamic model as well as dispersion model.
The computational procedures were tested on the study site of Seom-jin river, Korea. The result of the application of this model was analyzed and presented in this paper.

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To remove dissolved nutrients from river water flowing into lakes and marshes, water purification by using water hyacinth, reed and other higher aquatic plants has been promoted.
Generally, however, there are many problems associated with higher aquatic plants such as low absorption of dissolved nutrients, no absorption of nutrients when nutrient concentration is low, and little adaptation when the water temperature is low. We therefore designed and tested a filamentous algae system instead of using higher aquatic plants. The system can continuously cultivate filamentous algae, has a high growth ability and can be adapted to a wide range of water temperatures, throughout the year.
We conducted in field experiments on the ability of filamentous algae of the system to absorb dissolved orthophosphate. The results showed that filamentous algae's absorption ability depends on the stream regime, the concentration of nutrient in raw water, and the temperature, except the radiation. We therefore formulated the ability of filamentous algae to absorb phosphorus using three factors as functions. Representative values obtained were as follows. When we treated raw water of dissolved orthophosphate concentration of 30 μg·l ^-1 at a water temperature of 20°C, we found that the dissolved orthophosphate absorbing ability was 70-90mg·m^-2·d^-1.

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