Tests were carried out on a heater-type, oxidation-decomposition system to study whether this system could achieve complete decomposition of volatile chlorinated organic compounds (TCE, PCE), major contaminants of groundwater and soil. Test results revealed a decomposition characteristic that there is less residual TCE/PCE (higher decomposition percentage) with greater inflow load, longer retention time, and higher temperature of the reactor used. This system was capable of about 100% decomposition of TCE into CO₂ and HCI, when the temperature of the reactor was 950°C, the retention time was over 8.0 seconds, and the TCE concentration was over 3%. Under these conditions, it was possible to carry out stable continuous treatment. CCl₄, PCE, CHCl₃ were detected below the limited value as by-products and there was no forming of Dioxins under these conditions. Tests which involved the treatment of a gas which contained both TCE and PCE revealed a TCE decomposition of approximately 100%, and a PCE decomposition of below the limited value, when the reactor temperature was 950°C, the retention time was over 8.0 seconds, and the TCE and PCE concentrations were over 3% and 0.3%, respectively. This system has the efficiency of more than two times that of a UV system.

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The objectives of this study were to determine (i) the concurrent action of four polyphenols ; pyrogallic acid, gallic acid, (+)-catechin and ellagic acid secreted by Myriophyllum spicatum on their inhibitory effects on growth of blue-green algae (Microcyctis aeruginosa) and (ii) their contribution to allelopathy between M. spicatum and M. aeruginosa.
Comparing the inhibitory effects of a mixture of the four polyphenols with those expected by Colby's equation suggested that the mixture of the four polyphenols caused synergistic growth inhibition of M. aeruginosa. There was much difference between the EC₅₀ (the concentration inhibited normal growth of M. aeruginosa by 50 %) of each polyphenol and an apparent concentration detected in the culture solution of M. spicatum, because the four polyphenols were easily autoxidized in the culture solution of M. spicatum. Total amounts of the four polyphenols secreted from M. spicatum were estimated from their apparent concentrations and their autoxidation rates. The artificial solution was prepared based on the total amounts of the four secreted polyphenols. A comparison of the inhibitory effects of the culture solution of M. spicatum with those of the artificial culture solution prepared by using the four polyphenols was made on the basis of the equivalent M. spicatum concentrations of both culture solutions. The results showed that the four polyphenols could contribute to the allelopathic effects of M. spicatum at 10-100%.

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Effects of suspended and accumulated kaolinite particles on the adhesion and the development of Undaria pinnatifida zoospores on the substratum were investigated under the following three types of condition; Case-1: suspended particles together with zoospores, Case-2: zoospores released after accumulation of particles on the substratum, and Case-3 : accumulated particles on zoospores adhered on the substratum.
Case-2 was the most effective inhibition for the adhesion of zoospores, and 50% of effective concentration of particles (EC₅₀) was 29 μg·cm^-2. It was difficult for gametophytes to develop to sporophytes in Case-3. Furthermore, in comparing Undaria zoospores with Porphyra conchospores, the zoospores showed higher tolerance to suspended particles.

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Production and degradation of nitrous oxide(N₂O) were investigated in agricultural water system consisting of paddy fields, a small river, and the groundwater. In this area, anthropogenie nitrogen, as fertilizer, animal wastes etc., causes the occurrence of high nitrate-nitrogen (20-30mgN·l^-1). Denitrification actively occurred and N₂O was produced both in the paddy field and the small river receiving organic wastewater. Dissolved N₂O concentration in this area ranged from 10 to 400 μgN·l^-1, which was much higher than the concentration in the equilibrium with the ambient atmosphere. N₂O gas flux from the small river was about 500μgN·m^-2·h^-1. The conversion from NO_3-N to N₂O varied from 0.06 to 20.5% depending on season and other circumstances. This suggests that the agricultural water system is potential source of N₂O emission.

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The data for the purification of actual groundwater polluted with tetrachloroethylene by a photocatalytic treatment plant are reported.
The pilot plant was very effective in removing tetrachloroethylene (PCE) from water ; the highest PCE removal efficiency was ca. 99%.
The results obtained by the experiment were summarized as follows :
1) The PCE removal ratio was dependent on the initial PCE concentration in air.
2) Removal ratio of PCE in the photocatalytic reactor reached a maximum at the air flow rate of about 7 l/min.
3) No organic chlorinated product of the degradation reaction was detected.
4) It was confirmed that the photocatalytic activity did not change during the experimental period of 8 months.

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The saturated magnetization (σ) of the ferrite sludge formed by two-step treatment of wastewater containing heavy metal (cadmium sulfate) and potassium dihydrogen phosphate was measured over a wide concentration range of potassium dihydrogen phosphate. Simultaneously, the concentration of cadmium and iron ions in treated water was measured. From the results of measurement, the effect of the two-step treatment on the above parameters was quantitatively discussed by comparing the three different process treatment : conventional, excess-iron and two-step treatments.
The σ value of ferrite sludge formed by the two-step treatment was larger than that by conventional treatment in phosphate ion concentration above 330 mg·l^-1. The ferrite sludge formed by conventional treatment was reformed to the sludge from which cadmium ion was not easily eluted by the ferrite coating effect of two-step treatment. The pre-treatment by sodium hydroxide was effective in removing phosphate ion and increasing the σ of ferrite sludge. The concentration of cadmium ions in treated water produced by ferrite process was lower than that in treated water produced by neutralization method. The two-step treatment is favorable for steady operation of the ferrite process, industrial utilization of the sludge and good quality of the treated water.

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