In the Hinuma River, changes of periphyton biomass were observed weekly from September 1987 to March 1990 and compared with a model simulation to evaluate the dynamics of periphyton biomass.
A model was developed for simulating the periphyton biomass in a river system. The model consists of two sub-models : growth and scouring models. Parameters of the growth model were estimated based on the daily observation for a two-week period in each season. The change of the periphyton biomass was compared with that calculated through the model. Reasonably close agreement was found between the observed and calculated biomass ; however, a significant deviation was observed for the winter seasons when the biomass loss did not occur through scouring due to storm events. This deviation may be caused by significant detachment of the periphyton biomass and intensive grazing by benthic animals during the winter seasons.
The annual growth of periphyton biomass and the annual periphyton biomass scoured were found to be 110 g·m^-2 and 80 g·m^-2 as carbon, respectively. The periphyton communities may absorb dissolved nitrogen and phosphorus from river water for their growth. If this is case, in the Hinuma River, at 10-km downstream, 0.6% and 6.7% of the dissolved nitrogen and phosphorus in terms of the annual runoff loading may be utilized by the periphyton, respectively.

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To apply biological phosphorus removal for domestic wastewater treatment plant, characteristics of balancing tank effluents and it's influence for biological phosphorus release were studied.
In 20 different balancing tank effluents, the percentage of dissoluble organic substance (D-BOD₅/BOD₅) varied 20-70% and the variation depend on different operational conditions of balancing tank. Dissoluble TOC (D-TOC) of balancing tank effluent agitated under aerated condition was lower than that agitated in anaerobic condition. And low molecular weight substances of the effluent agitated in aerobic condition were decreased. When flesh wastewater was agitated in anaerobic condition for 24 hours, D-TOC was decreased, and BOD₅ and D-BOD₅ were not changed. Other hand, when flesh wastewater was seeded by effluent of balancing tank, D-TOC, BOD₅ and D-BOD₅ were decreased. Especially polysaccharide decreased, and concentration of protein didn't change. The effluent agitated in anaerobic condition have more effects for phosphorous release compared with the effluent agitated in aerobic condition. At the same concentration level of D-TOC, the effluent agitated in anaerobic condition had 12 time effects for the amount of phosphorus release.
It was concluded by these results that operational condition of balancing tank was very important for biological phosphorus removal.

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The performance of ultra membrane filtration to reject viruses in activated sludge suspension was examined by laboratory experiments. Coliphage T1 and coliphage Qβ were applied as models of infectious viruses, and 4 type's ultra membrane filters were used in the experiments.
The rejection rate of coliphage is affected by the cut off molecular weight of ultra membrane filters, size of coliphages and resistance values (Rcg) of cake- and gel-layers. In the loosest ultra membrane filter used, coliphage T1 was not permeated at the filtration condition that develops the cake- and get-layers with Rcg of 5×10¹²m^-1 and more. In the case of coliphage Qβ, the Rcg was 1×10¹³ m^-1 and more.
When the concentration of viruses is 5.2×10³ PFU·l^-1 in the treated wastewater by the activated sludge process and the inactivated rate of viruses of 99.9% is reached by chloriration process, the introduction of ultra membrane filtration process for liquid-solid separation can produce the fecal effluent with 5.2×10^-5 PFU·l^-1 of viruses. In this condition, the health risks caused by viruses is calculated to be 5.2×10^-5.

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The mutagenicity of tetrachloroethylene (PCE) was used to study the advantage of a modified Ames test devised to detect volatile liquid mutagens with bacteria. The test compound, dissolved in DMSO, was spread with filter paper on the lid of a glass plate. These plates were then sealed up with adhesive tape to allow the compound to vapor. A PCE sample containing epoxides was directly mutagenic for Salmonella Typhimurium His^- strains, TA100, TA102, TA104 and TA1535. However a purified sample did not increased the number of his⁺ revertants over the control value when tested with or without CD1 male mice S9 mix. The quantity of the test compound in the soft ager after exposure was achieved by gas chromatography. The quantity of PCE ; 30, 20, 10, 5, 2.5 and 1.25 mg/filter paper in the plate was 4.41, 1.04, 0.49, 0.13, 0.11 and 0.09 mg/soft ager in test plate, respectively. This concentration of PCE may have a great effect on bacteria, and this method may be useful for evaluating the mutagenicity of a volatile liquid. Thus, it is implied that PCE is one of the non-mutagenic carcinogen in Ames test.

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