We carried out research in Lake Suwa from 2004 to 2008 to study how retention time affects the biomass and species composition of blue-green algae. The retention time of the lake ranged from 2.3 (rainy season in July 2006) to 120 (dry season in June 2005) days. Microcystis was predominant in summer, but Aphanizomenon was predominant in 2005 and 2006. Owing to nitrogen deficiency, the Microcystis population increase was suppressed when retention time was kept at more than 80 days. The increase in the population of Aphanizomenon flos-aquae was suppressed probably owing to the dilution and discharge of cells by precipitation, and the change of the predominant species caused by nutrient inflow. In this paper, we suggest an appropriate retention time for respective blue-green algae on the basis of changes in the predominant species caused by changes in retention time.

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The effect of divalent cations (Me: Ca²⁺ and Mg²⁺) on the ligand-exchange kinetics of Fe (III) -fulvic acid complex and desferrioxamine B (DFOB) was examined by spectrophotometrically measuring the rate of Fe (III) -DFOB complex formation at the various concentrations of Me found in natural water (0-50 mM) . A kinetic model for ligand-exchange incorporating the effects of Me was also developed. The model includes the following two pathways: (1) a disjunctive pathway where Fe (III) -fulvic acid complex initially dissociates followed by complexation of free Fe (III) by DFOB; and (2) an adjunctive pathway where DFOB directly associates with the Fe (III) -fulvic acid complex followed by dissociation of the ternary complex (DFOB-Fe (III) -fulvic acid) to form Fe (III) -DFOB. The ligand-exchange rates of both pathways were accelerated in the presence of Me. The enhanced rates were well explained by considering the ternary complex formation of Me and Fe (III) -fulvic acid complex.

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The use of steelmaking slag as a recycled material is being progressed in coastal waters for marine environment improvement, by exploiting the characteristics of steelmaking slag. However, regarding its use in coastal waters, there are as yet no criteria for determining which bioassay should be used for assessing its effect on marine organisms. As a method of voluntary quality control of steelmaking slag, we selected a suitable battery of bioassays. The acute toxicity of steelmaking slag leachate on a copepod (Tigriopus japonicus) and a luminescent bacterium (Vibrio fischeri) was evaluated. As a result of the bioassay tests on some types of steelmaking slag, the leachate from the steelmaking slag with the pH preadjustment carbonation process showed smaller pH increases and no inhibitory effect on the marine organisms evaluated. On the other hand, the leachate from the steelmaking slag without carbonation showed an inhibitory effect on both organisms, as shown by an increase in its pH up to 12. This inhibitory effect was observed only in T. japonicus even when the pH was reduced to 8. The inhibitory factors of such leachate on T. japonicus and luminescent V. fischeri were examined. No hazardous substances were detected in the leachate. However, the calcium and magnesium concentrations of the leachate markedly changed compared with those of seawater. When the calcium concentration of the leachate was adjusted to that of seawater, the inhibitory effect on T. japonicus almost disappeared. Therefore, calcium concentration changes brought about by pH changes were considered to be the main inhibitory factors in the leachate. When bioassays with marine organisms are used to evaluate a recycled material such as steelmaking slag, the calcium and magnesium concentrations of the leachate should be carefully considered.

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Factors affecting propionate oxidation in a methanogenic microbial community derived from an anaerobic-digester sludge of cattle waste were investigated. The sludge was inoculated into a propionate-containing artificial wastewater medium, and cultures were incubated at mesophilic (30°C) and thermophilic (55°C) temperatures by a subculture technique. During subculture, however, the rate of propionate oxidation rapidly declined. To stabilize propionate oxidation, the use of some additives was examined. The addition of sulfate, pyruvate, fumarate, hemin, or yeast extract did not prevent the decrease in the rate of propionate oxidation. The addition sludge extract (supernatant fluid fraction of sludge autoclaved at 121°C) efficiently stabilized propionate oxidation. Although, the addition of dry powder of the sludge extract prepared at 110°C stabilized methane fermentation, that of sludge extract ash did not stabilize the process. Moreover, the addition of a low-molecular-weight fraction (below ca. 14,000) obtained by the dialysis of the sludge extract also stabilized the process. The present results indicate that effective components for stabilizing propionate oxidation in the sludge extract are low-molecular-weight organic compounds.

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