To investigate the effect of oxygen, pH shock, and H₂S inhibition on the competition between methane-producing archaea (MPA) and sulfate-reducing bacteria (SRB), a UASB reactor treating sulfate-rich wastewater was operated for 360 days. With micro-aeration in the upper part of the upflow anaerobic sludge blanket (UASB) reactor, sulfate removal increased from 45.0% to 68.6%. However, methane production was still the main reaction in the reactor. In addition, following the influence of pH shock and the organic loading rate, the free sulfide concentration increased to more than 200 mg·L^-1 owing to the enhanced sulfate reduction. As a result, the methane production was completely inhibited, which indicated that the free sulfide concentration seriously affected the MPA. The UASB performance and 16S rRNA cloning and sequencing results proved that in the complete sulfate-reducing stage, ethanol was mainly utilized by incomplete-oxidizing SRB for sulfate reduction.

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The Edo Castle is located in central Tokyo and its Outer Moat provides a precious water environment in the urban area. The water sources are limited to precipitation and combined sewer overflow (CSO); therefore, the hydraulic retention time (HRT) becomes very long (tens of days), resulting in the poor water quality. Particularly in summer, serious algal bloom is observed, and it causes the problems of bad landscape and undesirable odor. To develop effective countermeasures for water quality improvement, the estimation of CSO inflow and water-quality prediction by means of runoff and algal growth models were conducted. Furthermore, the actual water level and water quality were regularly measured through field surveys for checking the adequacy of models. The analysis with the models proved that the combination of CSO prevention and introduction of reclaimed water (4,653 m³·day^-1) could prevent the algal blooms. The cost of the countermeasure was estimated to be 390 million yen·year^-1. The benefit was evaluated by the contingent valuation method (CVM) and estimated to be 750 million yen·year^-1. Finally, the cost and benefit were compared and the feasibility of the countermeasures was shown.

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In this study, we investigated the seasonal changes in the concentration of microcystins by HPLC, the composition of cyanobacteria based on the16S rRNA gene, and the presence of toxic Microcystis sp. by quantitative PCR in the surface water of Lake Hachiro, Akita prefecture, Japan. Moreover, the unialgal cultures of 8 strains of Microcystis sp., Anabaena sp., and Pseudoanabaena sp. were isolated from algal bloom. The concentration of chlorophyll a increased and algal bloom occurred when the water temperature exceeded 25°C in Lake Hachiro. The concentrations of microcystins increased from August 2008, probably because of the growth of toxic Microcysis sp., which was determined by quantitative PCR of the mcyB gene. Furthermore, the mcyA gene was also detected from a unialgal culture of Microcystis sp., and it was confirmed that some Microcysts sp. strains in Lake Hachiro was toxic. The results of this study were suggested that the change in concentration of microcystins was related to the ratio of toxic Microcystis sp. equivalents to total Microcystis sp. equivalents in Lake Hachiro.

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To assess the water environment of irrigation reservoirs in Nara City and to improve the understanding of the basic characteristics of the reservoir and other factors affecting water quality, including land use of the catchment area, water quality analysis and the collection of basic characteristic data were conducted. Analysis revealed that the water quality in the irrigation period is worse than that in the nonirrigation period. In addition, the principal component analysis carried out using 8 water quality parameters (pH, EC, transparency, DTN, DTP, COD, Chl.a, and SS) showed that the water quality characteristics of the irrigation reservoir can be explained using two major components (the levels of organic and inorganic contamination). Furthermore, the Water Quality Index (WQI) formulated using 5 water quality parameters (DTN, DTP, COD, Chl.a, SS) showed that 29% of irrigation reservoirs indicated water quality deterioration, and the water qualities of reservoirs in the western region were worse than those in the eastern region of the study site. The results of the analysis of the relationship between WQI and the basic characteristics of reservoirs, suggested that the water quality of reservoirs is affected by 5 main parameters; proportion of forested area per catchment area, proportion of residential area, proportion of farming area, dam height, and use of reservoir for culturing fish.

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