The origin and bacterial utilization of organic matters in tidal-flat sediment were investigated using stable isotope and fatty acid analysis. Sedimentary organic matter (SOM) and potential food sources such as land plant, marine particulate organic matter (POM), benthic microalgae, riverine POM were taken from Gamo lagoon and Nanakita River Mouth. Land plant (δ¹³C = －26.6 and δ¹⁵N = 3.6) and riverine POM (δ¹³C = －25.5 and δ¹⁵N = 8.9) were isotopically distinct from benthic microalgae (δ¹³C = －16.3 and δ¹⁵N = 6.2) and marine POM (δ¹³C = －20.3 and δ¹⁵N = 10.3). In the degradation experiment of SOM for 50 days, the δ¹³C value of SOM decreased from －19.1 ‰ to －20.7 ‰. This was due to the preferential utilization of higher δ¹³C organic matter such as benthic microalgae and marine POM by bacteria. Land plant and riverine POM had begun to degrade after the degradation of benthic microalgae and marine POM progressed.

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The pure and mixed culture experiments of blue-green alga Microcystis aeruginosa and diatom Cyclotella sp. were carried out under N:P ratios of 1, 10, 50 and 100 and temperatures of 15, 20 and 25℃ to determine their growth characteristics and competition abilities. In the pure culture experiment, the N:P ratio did not affect the growth rate of both species at the same temperature. In the mixed culture experiment, the higher temperature of 25℃ would favor the dominance of M. aeruginosa, whereas Cyclotella sp. would become a dominant species at lower temperature of 15℃ without any influences of N:P ratio in the competitive circumstance. The dominance of these species at the intermediate temperature around 20℃ was strongly affected by N:P ratio. Although generally accepted N:P ratio rule suggested that M. aeruginosa favored low N:P ratio, our results clearly indicated that M. aeruginosa could grow and outcompete Cyclotella sp. at higher N:P ratios ranged from 10 to 100 rather than lower N:P ratio of 1. Moreover, M. aeruginosa could not become dominant species under the N:P ratio of 1 at 20℃, suggesting that the dominance of M. aeruginosa could be inhibited by N-limited condition rather than N:P ratio.

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FBBR （Fluidized Bed Biofilm Reactor） method is one of the most popular method to remove organic pollutants and ammonia in the wastewater. FBBR involves introducing small free floating media into the aeration tanks where they provide a large surface area to which biological growths attach. The deposition of the media in the aeration tanks cause some serious failure in the wastewater plant. We measured the critical tractive velocity of sponge media in full-scale FBBR aeration tanks operating in various conditions and researched the actual situation for deposition in the full-scale FBBR aeration tank. Sponge media used in FBBR were found to be large in dimensionless critical tractive shear stress and needed much bottom shear stress to be re-suspended compared with gravel particles. The empirical equation was obtained to derive the critical tractive velocity from the easily measurable terminal settling velocity. In the full-scale FBBR aeration tank, the deposition of sponge media was actually observed where the CFD simulated velocity was smaller than the critical tractive velocity.

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Microbial fuel cell (MFC) is a quite interesting technology in the field of wastewater treatment because that direct recovery of electrical energy is possible along with treatment. The one of issues on MFC reactor is the characteristics and performance of ion-exchange membrane between anode and cathode. In this study, MFC performance and bacterial community were investigated using three types of ion-exchange membranes by sequential batch experiments. Maximum voltages were obtained at the same level in all the MFC reactors using two proton-exchange membranes (PEMs) and a conventional cation-exchange membrane (CEM). Coulombic efficiency was also comparable between them although it was slightly higher in the reactor with CEM than PEMs. A little difference was observed in bacterial community of the biomass on anodic electrode between each MFC reactor and contribution of Lactococcus species to MFC performance was suggested in this study.

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A new biological process for selenium removal from metal refinery wastewater was developed using selenate- and selenite-reducing bacteria. Bacterial reduction of selenium oxyanions into elemental selenium plays a role in soluble selenium detoxification. First, two pilot-scale anaerobic bioreactors (256 l each) were constructed. One was inoculated with granular sludge of an upflow anaerobic sludge blanket reactor (Reactor A). The other was equipped with the acrylic biomass carrier and was inoculated with suspended sludge of a sewage sludge digestion reactor (Reactor B). However, those bioreactors inoculated with anaerobic sludge failed to remove selenium. As a bioaugmentation strategy, an aerobic selenium-reducing bacterium, Pseudomonas stutzeri NT－I, was inoculated to the bioreactors with slight aeration. Regarding selenite-containing wastewater, Reactor A, where granular sludge and P. stutzeri NT－I coexisted, removed 95 % of 65 mg-Se l^－1 quickly within only 2 days. Reactor B equipped with the biomass carrier and inoculated with P. stutzeri NT－I needed 5 days for 98% selenite removal. For selenate-containing wastewater, Reactor A removed only 54% of 30 mg-Se l^－1 in 7 days. In stark contrast, Reactor B showed selenium removal from selenate–containing wastewater of over 90% within only 3 days. The effluent of each reactor turned deep red, indicating formation of elemental selenium, which can be removed easily from the aqueous phase because of its insoluble characteristics.

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Six kinds of lactic-acid forming bacteria were isolated from an environmental preservation material (Ehime AI) and fermented and matured sediment mud from Osaka Bay. Among these isolated bacteria, strain Ob from Osaka Bay showed the highest COD removal of sediment mud (30.4% reduction) after 4 weeks. Strain Aa from Ehime AI showed 13.8% COD removal as the highest active strain of lactic acid formation. High lactic-acid forming ability of bacteria was not correlated to high COD reduction. Strain Ob was identified as Paenibacillus motobuensis using genetic analysis.

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