Carbon-coated TiO₂ photocatalysts were prepared by a simple heat treatment of powder mixtures of anatase-type TiO₂ (ST-01) with poly (vinyl alcohol) at 700 and 900°C in a N₂ gas flow. The diffuse optical reflectance spectra of carbon-coated TiO₂ showed on absorption edge for the anatase-type structure with a clear overlap with the absorption edge caused by carbon coated over the whole range of wavelengths used. These carbon-coated anatase photocatalysts had a relatively large apparent BET (Brunauer-Emmett-Teller) surface area, from 50 to 170m²·g^-1, which suggests the formation of porous carbon layers, and showed a relatively high adsorptivity for various pollutants, e.g., methylene blue, reactive black-5, phenol and iminoctadine triacetate in water. The photocatalytic activity of the carbon-coated anatase thus prepared was evaluated by determinating rate constant for the decomposition of different pollutants in water. Rate constant was strongly dependent on the type of pollutant, but its dependence on the crystallinity of anatase phase, which was characterized by behavior the full width at half maximum intensity of its 101 X-ray diffraction line, was different, however, its tendency was similar. The relationsips between adsorptivity and rate constant for the four pollutants looked similar, and the pollutants adsorbed in the large amount was decomposed at a higher rate.

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The aim of this study was to estimate the nitrate removal rate in paddy fields, which were irrigated from a reservoir. The reservoir stores the water that inflows from four small rivers to which spring water from tea fields drains. The study area was Makinohara, in Shizuoka, Japan, which is a tea field zone. The water quality and discharge were measured from June 2001 to May 2003. The results are as follows: The annual average concentrations of NO₃-N were 25.5 mg·l^-1 for inflow water, 21.3 mg·l^-1 for irrigated water from reservoirs, and 4.7 mg·l^-1 for outflow water from the paddy fields. The annual runoff load of NO₃-N from the tea field zone was estimated to be 260 kg·ha^-1·y^-1. The average NO₃-N removal rate during the irrigation period was 0.39 g·m^-2·d^-1 in the paddy fields. The NO₃-N removal load in the paddy fields was about 3 times the runoff load from the tea field zones. It was estimated that the removed nitrate load, which ran off from the tea field, could be greatly decreased by the irrigation of the paddy fields all season.

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To estimate the effect of the dominant mussel, Musculista senhousia, on water and sediment qualities in the closed-off section of Hakata Bay, we developed an ecosystem model of M. senhousia through its life cycle and obtained the following conclusions.
1) The calculated distributions of M. senhousia are spatially inhomogeneous and patchy owing to spatial differences in water and sediment qualities around it.
2) The amount of dead mussels in summer is 5.8- to 9.4- fold that in winter due to oxygen deficiency.
3) M. senhousia introduces a time delay for organic matter to settle as sediment, and a rapid settling of organic matter in oxygen-deficient water encourages the continuance of the oxygen-deficient water state.
4) The dominant macrobenthos work as intermediates in the cycling of substances settling as sediment and constitute an essential component of the ecosystem model. More precise information on their life cycle and effect on water quality is important.

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In some water treatment plants, floating foam scum, which concentrates micropollutants such as di-2-ethylhexyl phthalate (DEHP), is a serious problem. We assumed the mechanism of foam scum generation to be as follows: DEHP in water adsorbs onto the gas-liquid interface of bubbles and accumulates on the water surface by floating bubbles, and then is concentrated in foam generated by surface-active matter in raw river water. To apply this mechanism, in this study, the removal of DEPH from river water by generating foam using dispersed bubbles was investigated. When river water passed through a foam generator installed in a strong aerator, foam was continuously generated on the water surface and separated as collapsed-foam water. This collapsed-foam water was yellow-brown, and contained high amounts of suspended solids and colloids. However, the amount of collapsed-foam water generated was very small, less than 1% of the total flow volume. In comparison with suspended solids and dissolved organic matters, DEHP was highly concentrated in the collapsed-foam water. The removal efficiencies of DEHP ranged from 7% to 63% using the foam generator. The use of a simple process involving only intensive aeration and foam collection resulted in a high removal efficiency for hydrophobic micropollutants, such as DEHP, which accumulated in the gas-liquid interface from raw tap water.

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In this study, we conducted a weathered crude oil (w. oil)-degrading experiment with five different soil samples in order to investigate the biodegradation of alkanes. Two soil samples, soil one (I) and five (V), showed the excellent ability to biodegradade both normal alkanes (C₁₀-C₃₆ alkanes) and branched alkanes (pristane, phytane). We isolated several alkane-degrading bacteria from these soil samples. Isolated bacteria were classified into 3 groups based on their 16S rDNA sequences. The changes in population of these alkane-degrading bacteria were analyzed quantitatively by polymerase chain reaction (PCR) using specific primer sets. As a result, the concentration of group 1 bacteria (Rhodococcus spp.) that were able to degrade both normal and branched alkanes markedly increased due to enrichment with w.oil in soil one (I) and five (V). These results indicated that the group 1 bacteria that belong to the Rhodococcus genus played an important role in degrading alkanes in petroleum-contaminated soil under biostimulated conditions.

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Experiments on disinfection by chlorination, ozonation and ultraviolet-irradiation methods were performed with secondary effluents from domestic wastewater treatment plants, independently. Each treated water sample was evaluated for mutagenicity by the sensitive Ames test. Chlorinated water samples had a high mutagenic activity (the maximum average was 7,120 net rev·l^-1 when 50mg·l^-1 chlorine was used), depending on chlorine dose. Ozonated water samples and ultraviolet-irradiated water samples showed no or low mutagenicity. Even under good treatment conditions for each method, chlorinated effluents had a strong mutagenicity, but ozonated effluents and ultraviolet-irradiated effluents had a mutagenicity of almost zero.

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