A lab-scale reactor for the anaerobic ammonium-oxidizing (anammox) process was operated for the treatment of digester supernatant. In this study we used gel carriers with entrapped anammox bacteria to obtain a stable and high nitrogen removal performance. In continuous feeding tests, a stable nitrogen removal performance was observed and an average nitrogen conversion rate of 3.9 kg-N · m^-3 · d^-1 was obtained. A maximum nitrogen removal rate of 13.7 kg-N · m^-3 · d^-1 was confirmed in the high-loading test. After the stable nitrogen removal performance was observed, the operation of the reactor was stopped for one or three days and then restarted, in order to simulate a temporary process shutdown. The results of this test showed that our process can recover its performance immediately after a restart. The start-up period of this process was also evaluated under digester supernatant treatment. It was clearly shown that the anammox reactor using gel carriers can be started up within two months.

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The concentration of dioxins in the water of Lake Shimoteganuma, in which exceeded the environmental quality standard of dioxins (annual mean value: 1 pg-TEQ · l^-1, TEQ: toxic equivalency quantity) was exceeded from 2003 to 2007, was investigated. The neighboring lakes, Lake Teganuma and Lake Inbanuma, are shallow lakes like Lake Shimoteganuma. The concentrations of dioxins in the water of these lakes have not exceeded the environmental quality standard. When the result of the sediments of three lakes were compared, the proportion of fine sediment (<75 μm) of Lake Shimoteganuma was the smallest. However, the concentration of dioxins in fine sediment, which tend to float in water, was the highest. A water quality survey at defferent depths was performed. Because TEQ and iron (Fe) concentrations increased toward the bottom, it was surmised that Fe and dioxins were originated from the sediment. Only the TEQ of water near the bottom exceeded 1 pg-TEQ · l^-1 in August. However, the TEQs of all the layers exceeded 1 pg-TEQ · 1-1 in October. It seemed that admixture between deffernt depths was more common in October. Analyzing surface water quality from the inlet to the outlet of the lake, the concentration of dioxins increased with the concentration of chlorophyll-a, SS (suspended solids) and Fe in October. The rising widths of TEQ were 1.6 and 2.0 pg-TEQ · l^-1, respectively. By analyzing surface water quality for two years, TEQ was found to be over 1 pg-TEQ · l^-1 from summer to autumn on the whole. TEQ was below 1 pg-TEQ · l^-1 from winter to spring. The concentration 1,2,3,4,6,7,8-Heptachlorodibenzo-p-dioxin, which can be used as an estimate of TEQ, correlated with the concentrations of iron and chlorophyll-a in water of Lake Shimoteganuma.

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The River Uji merges with the R. Katsura and R. Kidu at the same point and then becomes the Yodo River. We observed the Yodo River every three days at three transverse points and the other three rivers weekly at their downstream points, and estimated the runoff loading balance of Cl^- during their flow downstream. The runoff characteristics of Cl^- in the rivers and the detailed input and output loadings during the flow of the rivers downstream were clarified. By computing the Cl^- loadings of the rivers outside of the observation periods using the regression equations between flow and loading, the mean Cl^- loadings for one year were estimated and compared with the total mean Cl^- loadings of the three upstream rivers and that of the Yodo River. By estimating the discharged Cl^- loadings for one year for the watersheds of the rivers using the statistical data of the consumption of salts and the watershed characteristics and by comparing the estimated values with the values due to the regression equations and observation data, it was confirmed that the basic discharged loading method of Cl^- can be applied to the analysis of the large watershed of the Yodo River.

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