This paper deals with the influences of lightness and pH on the diel vertical migration of the phytoplankton (Gonyostomum semen). By the field observation on the water quality in Kawahara Lake, it was found that the phytoplankton biomass, of which dominant species was Gsemen, grew and aggregated densely in the middle layer in summer season. The diel migration of aggregated layer of Gsemen was observed by using the mesocosm in the field. In the daytime Gsemen aggregated at the depth of about 3m and in the nighttime about 6.5m. The light density of the aggregated layer in the daytime was fairly lower then the optimum photon flux density for Gsemen. Accordingly the laboratory experiment by using the microcosm was conducted to make clear the controlling factor other than lightness. As the results of the microcosm experiment, it was found the diel vertical migration of Gsemen was influenced by higher pH than about 7.8.

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Neutralizing precipitation and adsorption using zeolite as an adsorbent are examined and compared as methods for removing heavy metals from acid mine drainage and acid industrial wastewater. Both methods produced effluent satisfying standard pollutant levels from synthetic mine drainage (pH 2, Cd²⁺ 5 mg/L, Cu²⁺ 50 mg/L, Zn²⁺ 300 mg/L, Al³⁺ 300 mg/L, Fe²⁺ 1000 mg/L). However, neutralization produced almost twice as much sediment as zeolite adsorption. In the processing of synthetic acid industry wastewater (pH 2, Cr³⁺ 50 mg/L, Cd²⁺ 50 mg/L, Cu²⁺ 50 mg/L, Ni²⁺ 100 mg/L, Zn²⁺ 100 mg/L), all heavy metals in the precipitation-treated effluent except for Cd were below the standard level at pH 9-10, whereas all metals were reduced to below the standard with the addition of 40-60g/L of zeolite. The simple process of adding zeolite as an adsorbent simultaneously neutralizes and removes heavy metals from acid drainage. Zeolite, derived relatively cheaply from fly ash, therefore appears to be a highly suitable absorbent for the removal of heavy metals from acid drainage, and is expected to become highly cost-effective tool if a method for the regeneration of spent zeolite can be developed.

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Feasibility of laboratory-scale bio-electrochemical reactor (BER) equipped with a multipleelectrode system (multiple BER) for treatment of nitrate-contaminated water was experimentally investigated with special attention to the optimum surface area of cathode. The multiple-electrode system was employed to enlarge the surface area of cathode so that improved reactor performance could be attained because of high contact efficiency among electron donor-H₂, microorganisms and solution. Hence, the overall removal rate was increased with the increasing number of cathodes. However, the current-denitrification efficiency gradually declined with increasing current density. As a consequence, the electric energy consumption per removed nitrate was increased exponentially with current density. Thus, it was not reasonable to apply high currents for the multiple BER used in this study. An investigation on the optimum specific surface area of cathode, as a function of electric energy consumption, was carried out. Increasing number of cathodes resulted in the Ohmic potential drop due to the increasing distance between anode and cathodes. Also, the surface over-potential increased with the increasing current density. The appropriate specific surface area of cathode for the bioelectrochemical denitrification was estimated.

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To achieve higher organic loading with submerged membrane separation activated sludge (SMAS) process, effects of membrane pore size ranging from 0.03μEm to 0.4μEm on membrane fouling was investigated using pilot-scale plant with synthetic wastewater. The putative membrane foulants, colloidal microbial products (CMP) were similarly rejected regardless of the membrane pore sizes, while the increase in transmembrane pressure (TMP) with the 0.4μEm was much higher as compared to the 0.1μEm. Since the fouling was irreversible through physical cleaning operation in all the case, it was thought that CMP was trapped inside the membrane structure, and that larger pore size as 0.4μEm traps larger amount of CMP, causing greater TMP. With the membrane pore size of either 0.03μEm or 0.1μEm, continuous operation of SMAS for almost two months was possible, but requires further investigation for more stable operation.

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Thus far the pollution of closed waters has been pointed out all over the world. In this study, especially, the changing volumes of chlorophyll a and phosphate-phosphorus (PO₄) ^3- were examined with the observation of both sunlight UV-rays volume and water temperature in the reservoirs. And constructed simple water quality estimation model on the basis of the observation data was tried, and the closed water environment viewed from sunlight UV-rays by using this model was estimated. As a result, it has turned out that we could obtain the related equation, viz., D^λ=D^α on the assumption that a related equation, viz., D^λ=D^αD^βD^γ (where, D: elapsed time, λE: quantity of chlorophyll a, α: UV-rays volume, β: water temperature, γ: quantity of (PO₄) ^3-) would be applicable. It is therefore considered that the specific characteristic of closed water environment such as a lake, a marsh or a reservoir etc. could be decided from the coefficient of observation value.

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