The purpose of the study is to clarify the conditions of the factors of denitrification which are necessary for an improvement of nitrogen removal efficiency in the circulated anxic-aerobic submerged bed process. The denitrification proceeds in the first anoxic reactor as well as in inner parts of the attached materials in the second aerobic reactor. 17 series of experiments were performed treating an artificial organic wastewater in the bench-scale pilot plants. The conditions of DO, ORP, and the C/N ratio which have been known to influence the denitrification efficiency were investigated. A little quantity of DO which is transported from the settling tank with the recirculation of nitrified effluent influences the denitrification in the first reactor. The optimum range of DO in the second reactor was below about 4mg·l^-1. The TOC/NO_x-N ratio was needed above 2 for the progress of denitrification in the first and second reactors. On the basis of those conditions, the appropriate conditions of design factors such as the recirculation ratio, the TOC loading rate and the HRT for the progress of denitrification were clarified.

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In order to evaluate the factors influencing nitrate concentration in groundwater under agricultural fields or rural settlements, properties of groundwater collected from 465 irrigation wells in Aichi prefecture, Japan was analyzed. Nitrate concentration levels depended on the land use, well depth, and oxidation-reduction potential (Eh) of groundwater.
Nitrate concentration in shallow groundwater with greater than 250mV of Eh were related to the land use of the surrounding area. Groundwater under upland field showed higher nitrate concentration than those collected from the sites of other land use types. Groundwater under rural settlements also showed a noticeably high nitrate concentration. Groundwater under paddy fields and forests were low in nitrate concentration. Nitrous oxide concentration was also high in oxic groundwater and significantly correlated with nitrate concentration, r=0.781.
The nitrate concentration levels of groundwater in which Eh value was≤250mV, did not noticeably increase regardless of land use type. Judging from the Eh level and the existence of denitrifying bacteria in most shallow groundwater, denitrification is considered to be an important factor for maintaining low nitrate concentration in anoxic groundwater.

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In the cross-flow ultrafiltration, effects of clay on the fouling due to organic substance were evaluated by fouling model materials and clay. Fouling model materials selected were BSA (Bovin serum albumin, MW68,000), Dextran (MW70,000), and humic acid (MW8,000-200,000) for larger size than molecular weight cut-off (MWCO50,000, polysulfone) and α-lactalbumin, Dextran (MW9,300) fulvic acid (MW8,000) for smaller size than that, and kaolin was selected as a clay material. The fluxes of BSA and Dextran (MW70,000) increased with an increase in the amount of kaolin, while the flux of α-lactalbumin, Dextran (MW9,300) did not increase with kaolin. The kaolin affected the flux decreased mainly more by adsorption and deposition (gel layer) on to the membrane surface than by the flux decline due to adsorption to the pore interior, but did not affect the flux decline that occurs by organic substance through the membrane pore. In contrast, the flux of humic substances decreased with an increase in the quantity of kaolin. The wasing recovery of flux with coexistence of kaolin was greater than that of fouling model material solution without kaolin.

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A release of phosphorus from calcium phosphate, iron(III) phosphate, and aluminum phosphate owing to the complex formation of their metals with fulvic acid was examined. Fulvic acid was extracted from lake sediments and treated with Amberlite XAD-8 resin. The non-adsorbed fraction of fulvic acid on the resin, which has highly Cu²⁺-complexing capacity, was used in this study, because the adsorbed fraction has only little Cu²⁺-complexing capacity as reported in our previous paper.
The non-adsorbed fraction was able to release phosphorus from calcium phosphate, but not from iron(III) phosphate, and aluminum phosphate. The application of X-ray analysis to the calcium phosphate indicated that the major component is hydroxyapatite. The stability constant of the Cu²⁺-fractionated fulvic acid was determined to be 2×10⁵ (log K=5.3) and the average molecular weight of the fulvic acid was 1,026.

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