Phosphorus (P) release from sediment caused eutrophication in Kojima Lake, Japan. The efficiency of iron-added sediment microbial fuel cells (SMFCs) in regulating P release from agricultural drainage sediment was investigated in this study. Surface sediment collected from an agricultural drainage canal flowing into Kojima Lake was mixed with iron oxide (Fe₂O₃) or amorphous iron oxyhydroxide (FeOOH) at 50 mmol kg⁻¹. A 14.6-cm high acrylic pipe was filled with 80 mL of deionized water after 130 g of sediment was placed. A 3 × 3 cm graphite felt was used for the anode in a dual chamber SMFC, while a carbon rod was used for the cathode. Three treatments: No Fe, Fe₂O₃, and FeOOH, were operated for 408 h under open or closed circuit conditions. Results showed that FeOOH addition lowered P release from sediment regardless of SMFC operational conditions, suggesting that higher P adsorption by FeOOH may mask the effect of SMFCs. Fe₂O₃ did not reduce total P concentration in the overlying water. In addition, electricity generation was not enhanced by Fe-added SMFCs. Although SMFCs increased sedimentary redox potential, P release was not suppressed by the SMFC operation, indicating that organic P would be released by SMFCs from P-rich sediment.

Azo dyes are common aqueous environmental pollutants in developing countries. Hydrogenation is a highly effective method for decomposition of azo dyes; however, this method requires the use of noble metals as catalysts. In this study, we investigated the use of multi-component alloy catalysts. Eight multi-component alloys (CoFeNiTiCr(800), CoFeNiTiAl(800), CoFeNiTiV(800), Fe₄₀Mn₁₀Cr₁₅Ni₂₅Al₅(800), Fe₃₅Mn₁₀Cr₂₀Ni₃₅(800), Fe₅₀Mn₂₇Cr₁₃Ni₁₀(800), Al_0.2Co_1.5CrFeNi_1.5Ti_0.5(600), and Al_0.2Co_1.5CrFeNi_1.5Ti_0.5(800)), where numbers in brackets represent calcine temperature (°C), were used for hydrogenation of methyl orange and Acid Orange 7 with NaBH₄. These multicomponent alloys were prepared from oxide precursors using a nonelectrochemical molten salt synthesis method. The reaction rates increased in the order of Al_0.2Co_1.5CrFeNi_1.5Ti_0.5(800) < CoFeNiTiAl(800) < Al_0.2Co_1.5CrFeNi_1.5Ti_0.5(600) for hydrogenation of methyl orange. Al_0.2Co_1.5CrFeNi_1.5Ti_0.5(600) rapidly decreased the methyl orange concentration to almost zero within 10 min. The reaction rates increased in the order of CoFeNiTiCr(800) < Al_0.2Co_1.5CrFeNi_1.5Ti_0.5(600) < CoFeNiTiV(800) for hydrogenation of Acid Orange 7. CoFeNiTiV(800) rapidly decreased the Acid Orange 7 concentration to almost zero within 10 min. This difference in catalytic activity for each azo dye was thought to arise because Acid Orange 7 was insufficiently decomposed by the reducing agent NaBH₄, and this affected its interaction with the catalyst.

When carbon dioxide (CO₂) is stored in sub-seabed geological formations, the environmental impact assessment assuming CO₂ leakage and monitoring CO₂ concentration in the sea are mandatory in Japan. The marine environment is not impacted by CO₂ storage itself but by the unlikely event of leakage. Thus, it is referred to as potential environmental impact assessment (PEIA). We conducted an ocean simulation for Hidaka Bay off Hokkaido, releasing passive tracers regarded as leaked CO₂. Biological impact data were newly compiled, and 4 thresholds for biological impacts depending on both the increase in partial pressure of CO₂ (pCO₂) and exposure time were set. The increase in pCO₂ estimated in the simulation, assuming CO₂ leak rates of 1,000 tonnes/y and 10,000 tonnes/y, exceeded no thresholds. The tracer concentration became almost equilibrium within about a week after the commencement of the release, and the increase in pCO₂ was much larger in summer than winter. These results suggest that the simulation of leaked CO₂ for PEIA be run for about a month in summer, and that monitoring CO₂ concentration be also conducted in summer. It is also implied that monitoring pCO₂ could detect leakage at O(10⁴) tonnes/y or larger than it.

Naturally occurring colloids, particles of diameter < 2 μm, are ubiquitous in geo environments and can potentially facilitate transport of numerous contaminants in soil via colloid-facilitated transport (CFT). Colloid mobilization, transport and CFT in various geo-media are highly sensitive to physico-chemical perturbations. This study investigated colloid, and colloid facilitated cadmium transport in saturated porous media with a series of column experiments. Soil colloids were extracted from soils belonging to two areas affected by chronic kidney disease of unknown etiology (CKDu) in Sri Lanka. Colloid breakthrough curves were obtained from the column studies under different flow rates (0.50, 1.60, and 4.00 ± 0.05 cm³/s) and ionic strengths (0.01, 0.05, and 0.10 M NaCl). The CFT was studied using Cd(II) as a model contaminant together with colloidal suspension under selected scenarios for high colloidal deposition. Elevated colloid concentrations were observed in highly CKDu affected area. The experimental results were numerically simulated on an advection-diffusion/dispersion modelling framework coupled with first-order attachment, detachment and straining parameters inversely estimated using Hydrus 1D software. Experimental and simulated colloid breakthrough curves showed a good agreement and recognized colloid attachment as the key retention mechanism. Both colloids and CFT of Cd(II) showed pronounced deposition under low flow rates and high ionic strengths.