Application of light scattering intensities has been investigated to water quality determination by using Xe lamp and He-Ne laser as light sources. The samples obtained in a lake, pond, river, dam reservoir and secondary effluent were submitted to the investigation. The analyzed water qualities are Suspended Solids (SS), Nitrogen oxide (NOx), Chlorophyll a (Chl.a), Protein and Total Organic Carbon (TOC).
The coefficient of determination between Chl.a concentration and the fluorescence intensity at 685nm was obtained as 0.993. Single correlation coefficients on other water qualities showed comparatively low values (r²=0.386-0.894). Whereas it is clear that the calculated values by multiple regression correlated to the observed values by adopting some light scattering intensities as predictor valuables (r²=0.982 in SS, 0.984 in NOx, 0.967 in Protein and 0.965 in TOC). This method is unnecessary of pre-treated samples such as filtration and addition of reagent and can determine rapidly and simply to monitor the water quality in natural watershed.

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Effects of nutrients released from suspended solids (SS) discharged by urban runoff on eutrophication in enclosed water body is not well known. In order to estimate the effects, amounts of nitrogen (N) and phosphorus (P) released from SS with decomposition were measured. Bottom sediment and periphyton in an urban river and sediment on road were collected from urban area as postulated SS discharged by urban runoff. The amounts of N and P released from SS measured by the repeated batch experiment were larger than those measured by batch experiment. This result showed adsorption and desorption equilibrium of nutrients between SS and ambient water was important for estimating the amounts of N and P released from SS. The amounts of released N and P were related to the initial amount of organic matter in SS. The percentage of released amounts to initial amounts of N and P in SS were rather small : 5-30% for N and 0-40% for P in 30 days. This result showed nutrients loads expressed by T-N and T-P parameters would be overestimated from the viewpoint of nutrients availability. Characterization of extractable P in SS before and after decomposition experiment showed that the fraction of organic P was released easier than the fractions of inorganic P, e.g., Fe-P and Al-P.

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Some fishes grow eating directly fresh water grass or phytoplankton. Transplanted grass carp, silver carp and tilapia are living in Japan. We can see natural propagation of the first two fishes in Tone river system and artificial production of their seedlings has been successful. Hera-crucian is also phytoplanktivoraus fish.
In the fishery field, aquaculture has been operated utiliging natural productivity of such water area and its basic technology has been developed.
Therefore, it is urgently required to establish a systematic organization of nutrient removal under the conditions as follows:
1) To release such fishes into eutrophicated water area under strict management for the purpose of predating water hyacinth or algal bloom.
2) To catch the all released fishes every year without fail and to use the harvest as the material of fish meal.
Feeding culture is the source of nutrients load for water area. Large amount of production and harvest of phytoplanktivorous fish which is equal to the double amount cultured fish is required for removal of excessive load by phytoplanktivorous fish.
However, when aquacultural production utilizes herbivorous fish living water area, much attention has to be payed to this point.

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Primary sludge and thickened surplus sludge were separately digested in a mesophilic and a thermophilic anaerobic digestion. As a result, the primary sludge was digested easier in the mesophilic digestion than the thickened surplus sludge. However, in the thermophilic digestion vice versa occured. On the basis of these results, a two-series digestion process with a thermophilic liquefaction of only thickened surplus sludge was proposed (hereafter called modified two-series digestion process).
In the thermophilic liquefaction of the thickened surplus sludge, the maximum volumetric loading rate of VSS of 14g·l^-1·d^-1 (HRT, 1.8d) could be achieved with respect to liquefaction of the sludge. On the other hand, in the mesophilic digestion of the mixture of thickened surplus sludge liquefied and primary sludge, the maximum volumetric loading rate of VSS of 8g·l^-1·d^-1 (HRT, 2.3d) could be achieved. In order to evaluate the performance of the modified two-series digestion process, a conventional mono-phase digestion was also investigated. As a result, the maximum volumetric loading rate of VSS in the modified two-series digestion process was about twice as much as that in the conventional process. The VSS digestion efficiency also increased up to about 10% compared to that in the conventinal process at the same volumetric loading rate of VSS.

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To evaluate bacterial biodegradation of organic contaminants in a tidal rier, the effects of salinity on the activity of heterotrophic bacteria were examined. It was revealed from experiment that salinity content affect bacterial respiration and population. It was observed that, the greater the change in salinity the greater the effect on the bacteria. With a stable level of salinity, the surviving bacteria managed to acclimate and return to normal respiration and population levels after a period of several hours. Experiments in the actual tidal river with chambers verified the laboratory results and demonstrated that the damage caused to the bacteria by salinity variation.

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Wastewaters from oil refinery factories often contain high concentrations of sulphide and the pH is over 12. Sulphide in wastewater causes the problems of the odor, toxicity and oxygen demand. We have studied an efficient biological process to oxidize sulphide to sulphate at neutral pH. A method to acclimate sulphur bacteria from activated sludge of sewage treatment plant at neutral pH by synthetic wastewater containing thiosulphate and the thiosulphate removal rate by the sulphur bacteria were examined.
Sulphur bacteria could be acclimated from activated sludge of sewage treatment plant for about 10 days. The thiosulphate removal rate by the sulphur bacteria was from 350 to 600 mg S₂O₃^2-·g VSS^-1·h^-1 under the neutral pH when the water temperature was from 20°C to 35°C. And the thiosulphate removal rate was 150 mg S₂O₃^2-·g VSS^-1·h^-1 at 5°C. The sulphur bacteria are thought to be bacillus and maintained good settleability even at 5°C. The biological process using the sulphur bacteria acclimated from activated sludge could remove both sulphide of 200 mg·l^-1 and thiosulphate of 600 mg·l^-1under the HRT of 3 hours and the water temperature of 5°C.

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A hydride generation-atomic absorption method for the precise and sensitive determination of arsenic, selenium and antimony in sediments is described. The environmental certified reference materials sample was digested with HF/HNO₃/HCIO₄/KMnO₄, and the residue was disolved in dilute hydrochloric acid with heating 1 hour on a boiling water bath. For As and Sb, potasium iodide-ascorbic acid were added to prereduction and acidfied sample solutions with hydrochloric acid were lead to automated hydride generator and determined As, Se and Sb by atomic absorption spectrometer individually.
Analytical results of As, Se and Sb obtained by proposed method are in good agreement with the certified or reference values for the CRMs included BCSS-1, Pond Sediment, NIST 1646 and SL-1, the relative standard deviations are less than 5%. Determination of analytes could be performed with only one digestion procedure and small modification of pretreatment for these hydrides generation.
On the other hand, several acid digestion procedures were examined for routine analysis of environmental samples, the best results which gave high recoveries were obtained by using the procedure with HNO₃/HClO₄/KMnO₄ for As, Se and with hydrochloric acid for Sb. Application of the procedure with HNO₃/HClO₄/KMnO₄ for the determination of Sb resulted in unsatisfactory recoveries, it was suggested that antimony formed insoluble compounds in dilute hydrochloric acid, and sorbed on the residue of sediment.
Ratios of analytical results of analytes for 4 CRMs obtained by recommended acid digestion to obtained by HF/HNO₃/HClO₄/KMnO₄ procedure were about 0.70-0.90 for arsenic, larger than 0.90 for selenium and almost 0.87 for antimony respectively.
The limits of determination of anlytes are 0.0375 μg·g^-1 for 2g of sediment.

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