The on-site purification system used is composed of an Electrodialysis Reversal (EDR) System and a Granule- Type Denitrification System. A pilot-scale experiment on using the on-site purification system was carried out for 14 months to investigate the characteristics of nitrogen removal from groundwater and the influence of the purification system on the surroundings. The results revealed the following : (1) Ninety-six kilograms of nitrogen was removed from groundwater in the examination area. (2) On investigation of the annual flux of nitrogen in the examination area in the same period, the calculated amount of nitrogen in flux in the examination area was 769kg as estimated by precipitation, fertilization, infiltration, denitrification and crop removal. As a result, 12.5% of infiltrated nitrogen was removed by the purification system. (3) The purification system did not affect the seasonal changes in chemical oxygen demand (COD) and the phosphorus (PO₄-P) concentration in the pond drain from the purification system. (4) It was observed occasionally that nitrous oxide (N₂O), an important greenhouse gas, was markedly produced in using the Granule-Type Denitrification System.

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The correlation of the mutagenicity of tap water with its raw water quality was studied in summer and winter using Salmonella typhimurium TA98 and TA100, in order to understand the difference in mutagenicity of municipal tap water from two different water supply systems. As a result, the mutagenic activity, TNVOX, MX and KMnO₄ consumption in tap water from the river water-line water supply system were higher than those from the lake water-line water supply system. The mutagenic activity of tap water from the river waterline water supply system was found to have a positive correlation with the TOC of its raw water. It was considered that existence of some precursors of by-products became mutagenic after chlorination and that mutagenic substances existed in river water. The mutagenic activity of municipal tap water from the lake waterline water supply system was highly negatively correlated with the volume of water reservoir. It was assumed that the markedly high mutagenicity was caused by the decrease in water volume in the reservoir owing to a drought. The ratio of the mutagenic activity of tap water per KMnO₄ consumption of raw water in winter was significantly higher than that obtained from the study of municipal tap water samples in summer.

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A subsurface flow constructed wetland (S.F.C.W.) with a zeolite substratum has been developed in Japan. It is characterized by the high removal rate of ammonium nitrogen due to its ion-exchange capacity. However, after saturation of zeolite with ammonium nitrogen, this rate rapidly decreases. Therefore, it is necessary to restore the ion-exchange capacity of the zeolite by removing the adsorbed ammonium nitrogen. In this study, we examined nitrification by microorganisms grown on zeolite for this purpose. We prepared zeolite with adsorbed ammonium and incubated it in secondary-treated wastewater of a rural sewage treatment plant. Nitrification activity was measured using zeolite incubated for different periods. The following results were obtained: 1) Nitrification activity was observed after only 10 days of incubation. 2) Nitrifying bacteria attached to the zeolite incubated in the secondary treated wastewater with organic matter. 3) Ammonium adsorbed to zeolite was metabolized by nitrifying bacteria and released into the medium. 4) Nitrification rate was estimated as 5.2×10^-3mg N·h^-1·cm^-3 zeolite after one month of incubation.

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A subsurface flow-constructed wetland (S.F.C.W.) with a zeolite substratum is characterized by a high removal rate of ammonium nitrogen due to its high ion-exchange capacity. However, after saturation of zeolite by NH₄⁺, the rate is markedly decreased. Therefore, it is necessary to restore the ion-exchange capacity of zeolite by removing the adsorbed NH₄⁺. We examined the possibility of restoring the ion-exchange capacity of zeolite by nitrification using two tanks with a continuous supply system for secondary treatment wastewater from a rural sewage treatment plant. In this study, water supply was stopped at night (21:00-6:00). The water in the tank A was retained at night and that in tank B was drained in order to supply oxygen in the tank and promote nitrification. The nitrification activity in tank B was higher than that in tank A. In tank B, NH₄⁺ adsorbed to zeolite was nitrified at night and a high concentration of NO₃-N was observed. This result shows that the ion-exchange capacity of zeolite is easily restored by nitrification, and which nitrification is promoted by water drainage from the tank when the water supply has been stopped. It is suggested that S.F.C.W. with a zeolite substratum extends the time to saturation by NH₄⁺.

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Izunuma & Uchinuma, designated as Wetlands of International Importance especially as Waterfowl Habitat, in the Ramsar Convention on Wetlands, are famous swamps visited by migratory birds. The level of the water pollution in these swamps has exceeded the environmental quality standards in terms of chemical oxygen demand (COD) (5mg·l^-1) for the last ten years. It is considered that the sediment removal from the bottom of these swamps is necessary in order to improve water quality and prevent shallowing. However, conventional methods of sediment dredging affect the ecosystem greatly, require a lot of time and are costly. Thus one of the authors, Shibasaki, suggested a more efficient plan, i.e., the sediment removal of employing the “resuspension phenomenon” resulting from gale force winds. In 2000 and 2001, two experiments based on Shibasaki's proposal were carried out in Izunuma & Uchinuma. About one-twelfth of the annual deposit of sediment was removed in the first experiment. It is clear that this “resuspension phenomenon” method is very effective in preventing the swamp from shallowing.

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A long-term pilot scale experiment was conducted to verify the phosphate removal ability of a prospective phosphate adsorbent prepared by baking volcanic ash soil mixed with iron (II) sulfate at 500°C. A tank packed with 300l of the adsorbent was placed in a municipal wastewater treatment plant. The adsorbent layer was backwashed for 3.5 minutes with air and water every day in order to prevent the adsorbent from becoming filled with suspended solids. Secondary effluent was supplied to the tank at a rate of 600l·h^-1. The average PO₄-P concentration in the influent was 1.35mg·l^-1, which was decreased in the μg·l^-1 order in the effluent after about 50 d. The concentration then started to increase very gradually after about 60 d, increased up to 0.5mg·l^-1 after 120 d, and increased about 1.0mg·l^-1 after 240 d.
An average of 3.30mg·l^-1 of suspended solids in the influent was almost completely removed from the effluent as a result of the daily backwashing. The pH of effluent was maintained at almost the same level as that of the influent throughout the pilot study. The PO₄-P removal ability was found to be unaffected by water temperature, indicating that the adsorbent would be useful in cold regions. The overall results of this pilot study show that baked volcanic ash soil is an effective medium for the removal of PO₄-P from secondary effluent in municipal wastewater treatment plants.

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