Hydrogen sulfide is highly toxic and fatal to benthic organisms. It also depletes dissolved oxygen and generates blue tide when oxidized. Therefore, it should be controlled to maintain healthy ecosystems. The purpose of this study is to evaluate the removal of hydrogen sulfide from seawater using granulated coal ash produced from coal thermal electric power stations. The batch experiments revealed that the removal kinetics of hydrogen sulfide were expressed as a first-order rate equation and that the adsorption maximum of hydrogen sulfide was 108 mg-S · g^-1. The K-edge X-ray adsorption fine structure spectra of sulfur adsorbed by granulated coal ash indicated that hydrogen sulfide was adsorbed as sulfur and formed FeS₂ when the hydrogen sulfide concentration was high. Results imply that applying granulated coal ash to organically enriched sediment can effectively reduce the concentration of hydrogen sulfide in interstitial water.

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Bamboo charcoal was examined to assess its nitrate ion adsorption capacity and mechanism in aqueous solutions. Three types of bamboo charcoal were prepared from Moso bamboo at different carbonization temperatures, namely, 400, 600 and 800°C (i.e., BC400, BC600, BC800). Although BC600 had the largest BET surface area and micropore volume (245.4m² · g^-1 and 0.162cm³ · g^-1, respectively), the batch adsorption experiment showed that BC800 had the highest nitrate ion adsorption capacity (3mg-N · g^-1 at about 80mg-N · l^-1). In addition, at the initial pH of the aqueous solutions of 2, the adsorption capacity was larger than that at about pH 6. Furthermore, the effects of acid and alkali treatments were examined. BC800_NaOH-HCl treated with acid following alkali treatment had a higher adsorption capacity than BC800_HCl-NaoH treated with alkali following acid treatment. This suggested that some hydroxide ions adsorbed onto BC800_NaOH-HCl were replaced with chlorine ions with the last acid treatment, although all of the anion exchange groups on BC800_HCl-NaOH adsorbed only hydroxide ions with the last alkali treatment. In other words, bamboo charcoal with partial substitution of chlorine ions for hydroxide ions can adsorb ions better. Therefore, it was concluded that the mechanism of nitrate ion adsorption onto bamboo charcoal is through ion exchange chemical adsorption.

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Urban river ecosystems are under the influence of treated wastewater effluent, but the relationship between the effluent and aquatic food web has not been well understood. In the Tama River, we investigated the effects of treated wastewater on a benthic macroinvertebrate community and main food sources for aquatic organisms including periphyton and fine particulate organic matter (FPOM). After the discharge point, the nutrient concentration significantly increased, and the δ¹⁵N of periphyton increased from 4.2‰ to 14.5‰. Furthermore, FPOM collected after the discharge point and suspended solids contained in wastewater effluent showed higher δ¹⁵N values than FPOM collected from the upstream section having no treated wastewater effect. In a macroinvertebrate community, an increase in δ¹⁵N was also observed for gatherers and filterers mainly feeding on FPOM after the discharge point. These results imply that the effects of treated wastewater discharge extend to consumers in the food web structure through primary production and FPOM.

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Kumamoto City is a worldwide exceptional urban area where 100% of its water supply comes from groundwater; however, reductions in groundwater amount and nitrate pollution level are current concerns. In this study, the water quality characteristics of well water samples collected in Kumamoto City were investigated. Most of these samples showed water quality characteristics of the “alkali metal-bicarbonate type”, which are typical of Japanese groundwater. They also contained equivalent amounts of Ca²⁺, Mg²⁺ and Na⁺. The well water samples were divided into 11 large groups on the basis of their water quality characteristics related to groundwater flow. No significant change in the water quality of wells in Kumamoto City has been observed over the past 20 years except for a few wells. From the results of a water tasting test, the taste of Kumamoto City tap water was considered to be the same or better than that of commercial bottled waters, and a truly tasty water index (TTWI) was established on the basis of the relationship between the water characteristics and the results of the water tasting test.

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