Recently, biomass immobilization technique has been put to practical use in advanced waste water treatment processes. The conventional immobilization technique, however, poses a problem with respect to mass transfer resistance for substrate and product molecules to the microorganisms inside immobilization gel matrices. The problem can be solved by utilization of functional gels as immobilizing media, which reversibly shrink and swell when external conditions change such as temperature, pH, and solvent composition. In this study, visible light-stimulus-responsive NIPA-CH (N-isopropylacrylamide-Chlorophyllin) gels were applied to examine a possibility of utilization in waste water treatment processes. The purpose of this study is to investigate physical properties of NIPA-CH gels such as swelling ratios, repetitive behaviors, and the influence of the swelling capacity on the immobilized microorganisms. The NIPA-CH gels showed sufficient swelling ratios under cyclic visible light stimuli, and it was suggested that the mass transfer of substrates would be enhanced by the shrinking and swelling effects of the visible light-stimulus responsive NIPA-CH gels.

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We examined phosphorus removal from small-scale domestic wastewater treatment system by means of an electrolytic bath. The electrolytic bath has electrodes of iron, and the wastewater treatment system has a biofilter. This method of removing phosphorus from the wastewater treatment system succeeded in removing more than 85% of the phosphorus while maintaining the Fe:P ratio at 1.5 and the polarity reversal period at 24 hours. And, this method offers high stability of phosphorus removal of more than six months. Moreover, compared with other methods, this method provides the phosphorus removal unit features a compact design and low running cost.
In view of these facts, we believe that phosphorus removal technology incorporating the electrochemical elution of iron can be provided for any wastewater treatment system.

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Assessment of environmental risk for many kinds of chemicals was studied on the survey in a model water area on sunny and rainy weather days during 1997-1999. Environmental risk, ecological risk and human health risk were assessed respectively. The relative ecological risk was indicated by the quotient of each environmental concentration with MTC (maximum tolerable concentration) calculated from the ecological effect data. Relative human health risk was also indicated by the water quality standards or the drinking water concentrations at 10^-5 carcinogenic risk level showed in IRIS database. As a result, although both of the relative risks for all tested chemicals were smaller than one at the upper stream in the river, the enlargement of the ecological risk contributed by nonylphenol was found at the lower stream on rainy weather days in particular. The emissions of chemicals contributed on these risks were characterized by the investigation on a branch and drainages flowing between the two sites on sunny days and primary runoff from elevated roads on rainy days.

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A model of TIN infiltration in sandy soil paddy fields was developed in this paper. It incorporates TIN uptake of fertilizer by paddy, denitrification, plankton growth, soil adsorption and desorption of fertilizer in paddy fields, decomposition of paddy litter, plankton and organic material in soil. The results calculated from the model were in good agreement with the measured values, which demonstrated that the model was useful in predicting the infiltration and runoff of TIN in paddy fields.
Runoff loading was derived from the model simulation (from Jun. 15 to Sep. 30). The infiltration loading was 3.06 g·m^-2, which was about 30.5% of the total amounts of input feritilizer (10.3 g·m^-2) for paddy.

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Ozonation of pentachlorophenol (PCP) with biological treatment were studied in distilled water (D.W.) and secondary effluents. Ozone was supplied into batch reactor at 6.25mgO₃·l^-1·min^-1 or 0.625mgO₃·l^-1·min^-1. PCP was easily decomposed by a few minutes-ozonation in D.W., but dissolved organic carbon (DOC) was not removed perfectly, even if 120 minutes-ozonation. PCP and the intermediates produced in an early stage of ozonation were not biodegraded. Improvement of biodegradability in PCP was required for at least 10 min of ozonation. One mg·l^-1 of PCP was ozonated in buffer solution and secondary effluents, which contained 18-28 times higher DOC than PCP. Decomposition rate of PCP in secondary effluents by ozonation decreased one third compared with that in buffer solution, however, PCP was decomposed selectively from many other organic matters in secondary effluents by ozone.

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Cross-flow microfiltration is one of the most promising solid-liquid separation processes, which can provide thorough separation with high rate.
A suspension to be filtrated is forced tangentially over a membrane surface to back-transport the filtered colloidal particles from it.
By the simulation with the rheological equation of activated sludge and the equation of the filtration with submerged membrane, suitable membrane module design was decided as the clearance in the flat-type membrane module having elements inside of 8 mm.
The Pilot-plant had been operated successfully for 6 months.

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