While the effluent pollutant loads of nitrogen, phosphorus, and COD from paddy fields are very important basic figures in a wide variety of environmental planning and research tasks, more reliable figures have been required. In this paper, the database of the pollutant load from paddy fields in Japan, established by the authors, is explained and the analytical results and future issues are presented. The database is based on the 72 references published since 1980s and it includes 467 data sets of the pollutant loads and information on the references, and investigation and farming conditions. The investigation of the irrigation season and the verification of the effects of the wide variety of improved farming methods during the irrigation season have been conducted in Japan. However, data for nonirrigation season and specific data obtained in paddy fields cultivated using variety of farming methods will be needed. The verification of the effects of the improved farming methods in the nonirrigation season and the development of the best management practices for the reduction of the pollutant load in the nonirrigation season are also required. The figures for phosphorus and COD adopted for the Seventh Total Water Pollutants Reduction Plan and the water conservation plan for selected lakes are much lower than the average values for by conventional farming methods available in the database. Therefore, the values for the Seventh Total Water Pollutants Reduction Plan will be revised referring to our database. The pollutant load from a paddy field cultivated by custom farming decreased with the decrease in the amount of fertilizer used. Thus, the recent data will be of great value. Other countries are facing a shortage of the data on pollutant loads in paddy fields. In the countries, there is a lack of experience in improving methods of farming to reduce the pollutant loads in paddy fields. Therefore, our database will be useful for other countries. The database is available on the web, and it is expected to contribute to future governmental and research activities.

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The effect of operating factors on the advanced oxidation performance of an electrochemical flow cell by the Fenton-type reaction of ferrous ion (Fe²⁺) and hypochlorous acid (HOCl) was discussed in this research. As a result of the research, the balance between the generation rates of Fe²⁺ and HOCl was found to be of critical importance in the overall current efficiency (CE) of the process. The linear velocity of flow water on the electrodes affected the CE through the change in diffusion flux. A rise in linear velocity enhanced the diffusion flux and CE, but extremely high linear velocity degraded the CE owing to reverse reactions on counter electrodes. An increase in iron concentration also enhanced the CE as a result of the enhancement of Fe²⁺ regeneration, but iron concentration greater than 27.5 mM deteriorated the CE because of the formation of a brown deposit on the cathode. The current density directly affected the balance between the Fe²⁺ and HOCl generation rates. The increase in current density enhanced the CE of HOCl production, but deteriorated the CE of Fe²⁺ regeneration. Accordingly, a decrease in the areal ratio of the anode to the cathode was effective in improving the overall CE.

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The purpose of our study is to evaluate the application of Biotope Sand (BTS) for controlling water bloom and water quality in a closed water area. BTS is a sand product recycled from waste casting. The field test utilizing BTS was demonstrated in a storage reservoir. BTS to be spread on floating water bloom and a filtering device with a BTS packed bed were introduced as two methods of BTS utilization. As a result, water bloom and water quality of the storage reservoir were improved within two years. The results suggested that the combination of BTS spreading and the filtering device caused the water bloom to settle, and the BTS filtering device contributed to water quality control. A laboratory-scale cultivation test using fish and aquatic plants was carried out to check the safety of BTS. As a result, it was confirmed that BTS has no negative effect on the growth of fish and aquatic plants. It was hypothesized that the existence of BTS promoted the growth of nitrite-oxidizing bacteria and inhibited the accumulation of nitrite.

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Chlorate and bromate were detected in high concentrations in outdoor pool water in the Tama area, Tokyo, in a survey of disinfection by-products. In order to consider the cause of such high concentration and a method of reducing the amounts of these compounds, we investigated the concentrations and variation of chlorate and bromate in pool water and in the sodium hypochlorite used in the pool facilities. In addition, our survey data of pool water and pool facilities were analyzed in detail. As a result of the investigation, it was found that there was no apparent difference in the quality of the sodium hypochlorite used in outdoor and indoor pool facilities; hence, another cause of the high concentration of chlorate in the outdoor swimming pool water was suspected. From the analysis of the correlation of the chlorate concentration and chloride ion concentration in pool water, it was shown that an overuse of sodium hypochlorite at more than the required amount for sterilization in outdoor pools is a possible cause. In order to reduce the chloric acid concentration in pool water, it may be effective to control the dose of sodium hypochlorite, on the basis of the chloride ion concentration as an indicator, and to dilute pool water by replenishing the water.

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