Wastewater from electroplating plants contains several metallic ions such as iron, nickel and zinc. In general, neutralization followed by sedimentation has been used for the treatment of electroplating wastewater. However, this process results in the production of large amounts of heavy metal sludge. The objective of this research is to achieve selective metal separation, metal recovery and reduction in sludge volume. We have examined the feasibility of a biological process using iron-oxidizing bacteria in the treatment of electroplating wastewater from steel works. It was proved that iron-oxidizing bacteria acclimated from activated sludge have the ability to oxidize ferrous ion (Fe²⁺) to ferric ion (Fe³⁺) in electroplating wastewater. A bioslurry reactor, which promotes both Fe²⁺ oxidation and Fe(OH)₃ generation in the pH range from 3.0 to 4.0, showed an almost complete Fe²⁺ oxidization after 2 hours of hydraulic retention time. The produced Fe(OH)₃ was recovered by sedimentation in the same pH range with almost no trace of nickel or zinc. Nickel and zinc hydroxides were easily recovered by sedimentation at pH 9.0.

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The toxicities of copper, zinc and chlorine to free-swimming cercariae of five trematode taxa were assayed. The hazard ratios of the test solutions of copper, zinc and chlorine to the control were calculated using the Cox proportional hazard model. Copper significantly reduced the survival rates of Centrocestus armatus, Cercaria nipponensis and Metagonimus spp at 1.0×10^-1 mg · l^-1 and the encystment rate of Notocotylus magniovatus at 1.0 mg · l^-1. Zinc reduced the survival rate of Cer. nipponensis at 5.0 mg · l^-1 and the encystment rate of N. magniovatus at 1.0 mg · l^-1 but it did not affect those of the other three species even at the highest concentration tested (1.0×10 mg · l^-1). Chlorine reduced the survival rates of Cen. armatus, Cer. nipponensis and Genarchopsis goppo at 4.2×10² mg · l^-1, and those of Metagonimus spp. at 2.1×10³ mg · l^-1. At the chlorine concentration of 4.2×10² mg · l^-1, N. magniovatus cercariae did not die during the experiment, but they ultimately did not metamorphose into metacercariae. Chlorine at lower concentrations increased the survival rates of Cer. nipponensis, Metagonimus spp. and G. goppo. These results indicate that copper influences the survival of some trematode species even at a concentration lower than the quality standard for drinking water, and therefore these trematode species are useful bioindicators.

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Ultraviolet irradiation could be one of the alternatives to conventional treatments against algal bloom. In this study, the efficacy of UV treatment was investigated against the growth of indigenous Microcystis collected from the Terauchi reservoir, which was suffering from algal bloom on the day of sampling. Surface water from the reservoir was subjected to lab-scale UV exposure using a low-pressure UV (LP UV) lamp or a medium-pressure UV (MP UV) lamp. UV-irradiated samples were compared with non irradiated control samples to determine the growth inhibitory effect of UV irradiation. Several exposure conditions were adopted by varying UV fluence and UV fluence rate to investigate their effects on algal growth. The growth inhibition observed after MP UV irradiation was about 3-fold higher than that after LP UV irradiation, up to 50 [mJ · cm^-2]. In the case of MP UV irradiation, growth inhibition was almost constant regardless of UV fluence rate at constant UV fluence. A 1.35 [mW · cm^-2] UV fluence rate resulted in a growth inhibitory effect 4.6-fold higher than that of a 0.37 [mW · cm^-2] UV fluence rate at constant UV fluence in the case of LP UV irradiation. The results of this study indicate that UV irradiation is effective in inhibiting the growth of indigenous Microcystis.

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In this study, we investigated the spatial and seasonal distributions of dissolved organic matter (DOM) and iron in Matsushima Bay, Japan from November 2003 to October 2004. The chemical characteristics of DOM, such as concentrations of dissolved organic carbon (DOC) and XAD resin absorbed organic carbon (XOC), UV absorbance, molecular weight and carbon stable isotope ratio, were also studied in the bay and the Takagi River. In the bay, DOC concentration increased particularly in summer. The XOC concentration and molecular weight of DOM decreased along the river to the bay. The carbon isotope ratio of DOM indicated that a significant amount of humic substance was produced in the bay. Dissolved iron concentration rapidly decreased with the increase in salinity from the river to the bay and was extremely low in seawater of high salinity. It was considered that this decrease in dissolved iron concentration was attributable to the precipitation of dissociated iron from organic compounds caused by the increase in the concentration of metal cations as river water meets seawater.

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This study was carried out to clarify the influence of sewage effluent on the temperature of urban river water. This investigation focused on the river basin of the Yodo River. The annual mean water temperature of the river depended on the annual mean atmospheric temperatures at all monitoring points except the Katsura River (Miyamaebashi) located on the lower reaches of a large-scale sewage treatment plant. The annual mean water temperature of Katsura River (Miyamaebashi) was significantly higher than the annual mean atmospheric temperature and increased by approximately 1.2°C within the period from 1972 to 2001. The increase in the water temperature of the Katsura River (Miyamaebashi) was attributable almost entirely to effluent from the sewage treatment plant. Because the temperature of the effluent from the sewage treatment plant was higher than the river water temperature before the inflow of the effluent, Katsura River water warmed significantly following the inflow of the sewage effluent. Katsura River water temperature after the inflow of sewage effluent increased considerably within the period from 1970 to 2003. The influence of sewage effluent was remarkable in winter in comparison with summer. These results suggest that effluent from sewage treatment plants is one of the factors causing the increase in river water temperature.

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