Field survey and laboratory experiments were conducted to clarify the effect of secondary effluent from wastewater treatment plant on nitrogenous BOD (N-BOD) behavior in the river.
The results showed that the average contribution ratio of N-BOD to total BOD in upstream side where secondary effluent was not discharged, was 9.3%. Whereas the ratio raised to 42.3% in downstream side. It was observed that water temperature and NH₄-N concentration were associated with N-BOD. The experiments through the acclimation of biofilm on the river-bed showed that the time lag of nitrification in BOD test during 10-25°C was 1-3 days if C/N ratio was 1. On the other hand, if C/N ratio was more than 5, N-BOD was not recognized at 25°C. The correlation between the observed N-BOD and the calculated N-BOD were obtained (γ=0.89). The values of calculated N-BOD were about 1.3 times larger than those of observed N-BOD. The water temperature and C/N ratio for nitrifying bacteria on the river-bed were found to be important factors to affect N-BOD in the river.

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Enzyme-linked immunosorbent assay (ELISA) by use of monoclonal antibodies (MAbs) is very useful and helpful for the detection and quantification of the specific bacteria in a mixed bacterial habitat. In this study, seven monoclonal antibodies were raised using mice(BALB/c) that are specific for the surface antigen of the two kinds of nitrifying bacteria. Three were directed against Nitrosomonas europaea (IFO 14298) and four were directed against Nitrobacter winogradskyi (IFO 14297). Cross-reactivities of MAbs against other strains of nitrifying bacteria as well as some kinds of representative heterotrophic bacteria in activated sludge and biofilm were checked to determine the usefulness of MAbs. It was found that there were some strain specificities between the same genera of IFO and ATCC strain. By means of a competitive ELISA, correlation curves for quantifying nitrifying bacteria was developed in a pure culture. It was made clear that this monoclonal antibody method could be used as a quick and powerful tool for estimating the population of nitrifying bacteria.

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The analytical method using frit/fast atom bombardment (FAB)-liquid chromatography/mass spectrometry (LC/MS) was developed for the quantitative determination of nonvolatile and thermolabile pesticides in water. A sample water was passed through a polystyrene solid phase extraction (SPE) cartridge to extract pesticides. The reextraction of the pesticides was performed by back-flushing the cartridge with acetonitlile. The eluate with an addition of 2-phenoxybutyric acid as internal standard was analyzed by frit/FAB-LC/MS-selected ion monitoring (SIM) method without any derivatization procedure as a pretreatment.
The recovery ratio of 11 pesticides (2,4-D, bensultap, MCPA, MCPB, MCPP, mefenacet, methomyl, NAC, thiuram, tricyclazole and pyrazolate) spiked into ground water, river water and tap water were shown a figure such as 70% or more except bensultap for the routine analysis of them. In addition, their coefficient of variation (relative standard deviation) except bensultap ranged from 2.6 to 23.3% at detection limit level. Therefore, we have concluded this analytical method has an advantage to reduce the pretreatment of sample such as derivatization of nonvolatile and thermolabile pesticides.
However, some pesticides such as bensultap, methomyl and thiuram showed less quantitative accuracy, and so it needs further studies such as developing more efficient extraction procedure.

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The roles of the microflagellate, Monas guttula, that is a grazer on algae, is important in aquatic food chain. In order to understand the interaction of vertical migration on the relationship between the grazer and Microcystis viridis as a food source, grazing characteristics of M. viridis by a microflagellate M. guttula was studied using a large scale microcosm with a depth of 4m. Although the growth of M. guttula was inhibited during light period, the flagellate could favorably graze on the viable cells of M. viridis under the dark condition and was found to move to the dense layer of M. viridis. Finally, M. guttula perfectly grazed and degraded the M. viridis for 3 days.

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Removing dissolved nutrients from river water flowing into lakes and marshes is an effective method of preventing eutrophication of them. We have proposed the continuous cultivation of filamentous algae outdoors in artificial waterways to remove phosphorus and nitrogen from the water.
The ability of filamentous algae to absorb dissolved nutrients depends on the radiation (illuminance on the water surface in the daytime, diurnal periodicity), the concentration of nutrient in raw water, the temperature, and the stream regime (flow velocity, shape of the substratum which the filamentous algae are attached to, water depth). This study investigated the effects of the diurnal periodicity on the ability of filamentous algae to absorb phosphorus and nitrogen.
The results of field experiments in the artificial waterway have clearly confirmed that the ability of filamentous algae to absorb phosphorus and nitrogen is influenced by the diurnal periodicity of the radiation. The results indicated that in the case of river, lake, or marsh water in which the major constituents of inorganic nitrogen in the water are NO₃-N, more dissolved orthophosphate is absorbed at night than during the day, and more inorganic nitrogen is absorbed during the day than at night.

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In this study we investigated the effect of the way inputting rice straw on nitrogen removal efficiency. We prepared 52 mm inner diameter and 400 mm height soil columns, and input rice straw by three different ways as follows: 1) mono-layered, 2) cutting rice straw into 20-30 mm pieces and then mix it with soil, 3) milling rice straw into under 1 mm pieces and the mix it with soil. We supplied potassium nitrate solution of 50 mg-N·l^-1 to these columns at the rate of 200 ml·d^-1. The column with rice straw input mono-layered showed steady nitrogen removal, the nitrate nitrogen concentration of its outflow did never exceed 20 mg·l^-1 during 44 days of operation. On the other hand, other columns reveals poor nitrogen removal. The nitrate nitrogen concentration of their effluents came as high as 40 mg·l^-1 in ten days. We concluded that if we use rice straw as a carbon source for denitrification to remove nitrogen from soil percolate, it will be better that rice straw be put into soil as mono-layer, not mixed with soil.

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