The hydrous oxides of metallic elements adsorb ions. In this study, ten Si-Fe-Mg mixed hydrous oxide samples were synthesized using various Si, Fe (III) and Mg molar ratios, and the adsorption properties of these samples were evaluated in terms of ion adsorption rate. The adsorption rate was high for most samples, and uptake occurred at the adsorption equilibrium for 24 hours. In particular, sample No. 10, for which the molar ratio of the metallic elements was Si : Fe : Mg = 0.1 : 0.1 : 0.8, which is the ratio with the highest of Mg, had adsorbed large amounts of arsenite and phosphate ions. The adsorption isotherms for fluorine, boron, arsenate, arsenite, phosphate, selenate and selenite ions had various various correspondences to the equation of Freundlich. Because the gradient of the equations was 0.1 - 0.5, sample No. 10 could adsorb from low and high concentrations of harmful ions easily.

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A highly efficient ozone disinfection system was developed to decreasing the influence of the overflow of untreated wastewater during rainy weather at pump stations and wastewater treatment plants in a combined sewer system. The ozone disinfection system is a feed forward system that controls the amount of ozone with the result of measuring the number of coliforms using the quick monitoring system within 10 minutes. Simulations for calculating the effect of saving disinfectant on the ozone disinfection model were executed using the already obtained dates. The result of the calculation showed that the amount of ozone is expected to be reduced by 21-41% using this new quick disinfection system compared with the former flow proportional control system. Two minutes of disinfection time was sufficient for the quick disinfection of coliforms, when the quick monitoring system detected the number of coliforms within ten minutes. These results lead the conclusion that this system is good for the environment and saves cost by decreasing the amount of money spent on disinfectants for coliforms.

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The reactivities of the P=S type organophosphorus pesticides (OPs) and their oxons with chlorine were investigated. The reactivity of diazinon, a typical OP, with chlorine was higher at low pHs and high chlorine concentrations but was not affected by initial diazinon concentration. The dominant reaction was the neutral reaction at pHs 7.2-8.5, whereas it was both the neutral and the acid-catalyzed reaction at pH 5.9. The main chlorination product, diazinon-oxon, was not affected by diazinon concentration, chlorine concentration or pH. The reactivities of ten OP species with chlorine were investigated under water treatment conditions. Eight of ten OPs transformed into their oxons at high rates (72-103%), although the reactivities of these OPs with chlorine differed. On the other hand, two amidates, namely butamifos and isofenphos, transformed into their oxons at 50%, and the remaining 50% was composed of hydrolysates (i.e., 5-methyl-2-nitrophenol for butamifos and isopropyl salicylate for isofenphos) and chlorinated derivatives of hydrolysates. Finally, ten oxons were examined to determine their reactivities with chlorine. After 24 hours, three oxons chlorinated were degraded by 20-30% compared with them nonchlorinated, but the other oxons were not degraded to that extent. From these results, drinking water quality control must account for stabilities of residual oxons of OPs in chlorination, particularly for those with strong toxicities.

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The iron-oxidizing bacterium, Thiobacillus ferrooxidans, is not halotolerant and cannot oxidize ferrous ions (Fe²⁺) to ferric ions (Fe³⁺) in electroplating wastewater containing high concentrations of chlorine ions. T. ferrooxidans cannot be used for the treatment of such electroplating wastewater. The acclimation of iron-oxidizing halotolerant bacteria has been studied to treat electroplating wastewater containing ferrous ions and a high concentration of chlorine ions. Iron-oxidizing bacteria that are halotolerant and able to oxidize Fe²⁺ to Fe³⁺ were obtained from the activated sludge of a steel works coke-oven wastewater treatment plant. A long-term experiment using artificial wastewater containing 20,000 mg · l^-1 chlorine ions showed the stable performance of the Fe²⁺ oxidation ability by iron-oxidizing bacteria acclimated to seawater. It seems that the acclimated iron-oxidizing bacteria can be used for the treatment of electroplating wastewater. An analysis of genomic DNA extracted from the acclimated sludge of the reactor showed the existence of an analog of the iron-oxidizing bacterium, Thiobacillus prosperus.

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