In order to develop a new treatment plant which is easily maintained at low cost, does not cause secondary pollution, and is suitable for an operator of small business like dry-cleaning, photodegradation of tetrachloroethylene (PCE) in the wastewater from dry-cleaning with three types treatment apparatus (45ml Spiral, 270ml Hollow Circular Cylinder, and 3,000ml Circular Cylinder) and test plant (1,200ml) were examined.
The degradation rate, the degradation efficiency and the concentration of trichloroethylene (TCE), and the intermediate compounds produced by photodegradation of PCE were investigated under the UV irradiation alone at 185nm and 254nm in the presence (oxygenic condition: Oxyg) and absence (oxygen free condition: OxyF) of dissolved oxygen (DO).
Though the difference of the degradation rates of PCE under Oxyg and OxyF was not observed for all of three types, an intermediate TCE product was prevented under OxyF.

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Experimental studies on the removal of natural and artificial 2-MIB in the surface water of Lake Biwa were conducted using a biological filter pilot plant with porous granular ceramic media. Microbiological and biochemical studies on the mechanism of bio-degradation of 2-MIB were also conducted.
From the results of a series of the pilot plant study, the removal efficiencies of 2-MIB under the filtration rate of 180 and 120m·d^-1 were 70% and 80%, respectively. Performances of water treatment by the biological filter pilot plant were almost the same as those by the commercial slow sand filter, when the filtration rate of the biological filter was decreased to 12m·d^-1. 2-MIB removal efficiency by the biological filter pilot plant after 48 hours' pause of filtration recovered in about 12 hours.
In addition, two different types of bacteria belonging to the genera Pseudomonas and Enterobacter were isolated from the backwashed water of the pilot plant. Also, four degradation products of 2-MIB such as 2-methylcamphene, 2-methylenebornane, camphor and 4,7,7-trimethyl-2-oxabicyclo [2.2.1] heptan-3-one were detected.

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In this paper, Vollenweider model was studied by using water quality data during irrigation periods in irrigation ponds. At first, it was clarified that Vollenweider model could predict the average T-N concentration during an irrigation period within 1.0 mg·l^-1 of error to the observed, where inflow N loads from the basin were estimated by using the product of applied N fertilizer by the effluent rate revised with water inflow rate for upland field and orchard, the regression equation of effluent N load to the input load for forest, the product of the annual average N concentration by the amount of precipitation for the other non-point sources, and basic units for point sources. Secondary, a guideline for water quality improvement was conducted in accordance with Vollenweider model equation in respect of the reduction of inflow N loads and of the dilution with cleanly water. The effects of such measures depend on the α factor which is defined as α=νV/zQ, where ν is the apparent settling velocity of nitrogen (5.0 m per irrigation period); V is the irrigation pond capacity (m³); z is the mean depth of the irrigation pond(m); Q is the water inflow rate before the measure (m³ per irrigation period).

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Ultraviolet (UV) light inactivation of Escherichia coli was investigated with the endonuclease sensitive site (ESS) assay which can detect the UV-induced pyrimidine dimers in the genomic DNA. High correlation was observed between the UV dose irradiated for E.coli and the number of ESS induced in the DNA of E.coli (r²=0.996). The survival ratio of E.coli also showed high correlation with the number of ESS induced in the DNA (r²=0.999). Photoreactivation of E.coli after 99.9% inactivation by UV irradiation was also investigated with ESS assay. During the exposure to fluorescent light, ESS in the DNA of E.coli were continuously repaired while the survival ratio of them gradually recovered. The number of ESS was correlated with the survival ratio of E.coli during fluorescent light irradiation (r²=0.937), indicating that the repair of pyrimidine dimers in the genomic DNA would contribute to the survival recovery of E.coli during photoreactivation. It was indicated, in this study, that ESS assay was useful to investigate UV inactivation and photoreactivation of E.coli quantitatively.

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The kinetics of water treatment using thin-filmed photocatalyst of titanium dioxide were investigated using phenol and methylene blue as a test substrate, respectively. Effects of initial concentration of substrates, specific surface area of titanium dioxide to sample volume, UV intensity and rotating rate of stirrer tip were correlated with reaction rate to elucidate the kinetics of photocatalytic reaction. The kinetics of immobilized photocatalytic reaction followed the Langmuir-Hinshelwood (L-H) equation. The reaction rate increased in proportion to surface area coated with titanium dioxide. The rate coefficient of L-H equation was affected by UV intensity and was independent from rotating speed, while the adsorption coefficent of L-H equation was affected by rotating rate of stirrer tip and independent from UV intensity. Using a pilot scale plant in Tamagawa water purification, degradation rates of phenol and methylene blue were comparable to those based on the kinetics above. River water was also used as source water and treated with photocatalytic reactor, where TOC and 260nm absorbance were decreased 13 and 25% after 500-minute UV irradiation, respectively.

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A demonstration UV photooxidation system for the treatment of trichloroethylene (TCE) gas extracted from contaminated soil or ground water has been fabricated to design the operation method. The apparatus involves a complete mixing flow type UV reactor connected in series with a multiple stage one and a gas absorption tower filled with crashed marble. The data that is necessary to design the reactor for promoting the photooxidation reaction effectively under relatively high to low TCE concentration could be obtained. Based on the test result, the concrete method to design the reactor is discussed.
Phosgene is one of the acidic products produced by TCE photooxidation. This substance could be eliminated more than 99% by the absorption tower.

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The application of the sulfur oxidizing bacteria to wastewater including high concentration of nitrate was basically examined by the experiment using artificial wastewater. As a result, the following were clarified.
Sulfur oxidizing bacteria having the denitrification function was acclimated by using artificial wastewater containing only nitrate as a nitrogen source from the activated sludge of the sewage plant in about three weeks This bacteria was able to remove nitrogen from artificial wastewater which included nitrate of 900-1300mg-N·l^-1 under the condition of 1.5-3 hours of HRT (The water temperature: 20°C). This sulfur source was thiosulfate and 3.5-4 was suitable in the S/N ratio. As for the acclimated sulfur oxidizing bacteria, the denitrification rate was presumed to be large since it was easy to make self-immobilized and was maintained to be hightly concentrated in the reactor. On the other hand, it was thought that there was a problem in the maintenance management by accumulating sulfur when an excessive high load operation was continued.

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