[in Japanese]

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The management of excess sludge in wastewater treatment accounts for a major portion of the cost for wastewater treatment and entails significant technical challenges. Swim-bed technology containing an innovation attached-growth material named biofringe (BF) allows the retention of large amounts of biomass, which could contribute to the reduction of excess sludge production. The treatment performances of a lab-scale reactor packed with BF material under various operational conditions and volumetric loading rates were investigated. The process demonstrated effective treatment of high-strength wastewater. COD removal efficiencies greater than 80% were consistently achieved even with volumetric loading rates as high as 7 kg-COD/m³/d. Observed sludge yields (Y_obs) from 0.13 kg-MLSS/kg-COD_removed to 0.29 kg-MLSS/kg-COD_removed were obtained in swim-bed wastewater treatment. The occurrence of an abundance of protozoa and mentozoa in the activated sludge floc could account for this significantly low production of excess sludge. The long sludge retention time (SRT) was also regarded to be another reason for the low excess sludge production. The attachment of large amounts of biomass on the BF material might be due to the extremely high ratios of extracellular polymers (EPS) to biomass, which varied from 64% to 84%.

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The volumes and mechanisms of CH₄ and N₂O emission, wastewater treatment characteristics and constituent microanimals and microalgae in lagoon system were studied. The lagoon system plays an important role in wastewater treatment in developing countries. Various microanimals such as protozoa and metazoa were observed in lagoon system. It revealed that the microfauna in the lagoon consist of various microanimals that are suitable for anaerobic and aerobic conditions. The conversion ratio from influent nitrogen to N₂O in a bench-scale lagoon system was estimated as 0.21% for N₂O emitted into the atmosphere and 0.22% for N₂O dissolved in treated water, and the result showed a large proportion of N₂O released into the water environment in dissolved form. The conversion ratio from influent BOD to CH₄ in the bench-scale system was estimated as 17%.

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Water purification characteristics and attraction effect of aquatic animals in floating type edible aquatic plant purification system (FEAPPS) were investigated. FEAPPS is one of the ecological engineering techniques, where aquatic plants were set to raft floating on water and their roots were suspended below the surface of water. The concentration of SS and turbidity in FEAPPS in each state of eutrophic level was lower than that in control system because the existence of aquatic plant benefits the SS and turbidity removal in FEAPPS due to filter effects of the root. The average of crustacean biomass and transparency in FEAPPS was higher than that in control system and mutual relationship between these values was very high. It reveals that the application of FEAPPS contributes to keeping the amount of large crustacean as filter feeder, and high transparency can be attained in the system.

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Microcystins are a group of cyclic heptapeptide hepatotoxins produced by the cyanobacteria. Two microcystin-degrading strains of bacteria (MG－15 and MG－22) were isolated from a monoxenic culture of Monas guttula preying on Microcystis viridis. Both strains were related to Sphingopyxis and Novosphingobium groups based on phylogenetic analysis of 16S rDNA. Degradation of microcystin by these strains was tested under the following conditions: temperature from 20 to 30℃, pH from 6.8 to 10.0, three different microcystin analogs and initial microcystin concentrations from 17 to 917 μg･l^–1. The rate of microcystin RR degradation by strain MG－15 significantly increased at 30℃, whereas the effect of temperature on the degradation rate by strain MG－22 was small. Both strains could degrade microcystin under alkaline pH. Both strains could degrade microcystin RR, YR and LR. The degradation rate of microcystin RR by the two strains was faster than the degradation rates of microcystin YR and LR. Both strains could degrade microcystin LR at all initial concentrations.

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Planktonic flora and fauna were investigated at the former Hachirogata Lake shore in 2006. A total of 131 species of planktonic microorganisms were recorded including 13 species of Cyanophyceae, 79 species of Protoctista (30 species of Chlorophyceae, 1 species of Ulvophyceae,17 species of Bacillariophyceae, 2 species of Sarcodina, 11 species of Mastigophora, 10 species of Cliophora), 27 species of Trochelminthes (20 species of Rotatoria, 1 species of Gastrotricha, 6 species of Nematoda), 8 species of Arthropoda (5 species of Branchiopoda, 3 species of Copepoda), 2 species of Tardigrada, 2 species of Oligochaeta. Dominant species appearing around aquatic plants were Sida crystalline, Alona quadrangularis, and Chydorus sphaericus. These Crustaceans especially related with communities of submergent aquatic plants such as Potamogeton maackianus and Cabomba caroliniana.

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