In the Mekong watershed, the lives of numerous children are lost as a result of waterborne infectious diseases. To achieve socioeconomic development in this region, it is necessary to construct a water utilization system that minimizes infectious risk on the basis of reliable risk evaluation. We have performed questionnaire surveys to clarify the types of drinking water available and detected bacteria that indicate fecal contamination in drinking water in Laos, Cambodia, Vietnam and Thailand. The types of drinking water (i.e., tap water, bottled water, river water, well water and rainwater) available in the Mekong watershed depend on geographic conditions, such as access to a water supply and rivers, and household income. On the basis of the observed characteristics of water utilization, a risk evaluation model for waterborne infectious diseases was developed using a geographical information system (GIS). In the model, the watershed was divided into a 1-km² grid, and the types of drinking water available were determined in each grid cell. The prevalence of contamination with indicator bacteria in each type of drinking water was also estimated on the basis of the results of field surveys. It was estimated that 12 million cases of diarrhea occur annually in the Mekong watershed. To reduce the number of diarrhea cases, it was effective to promote the use of rainwater for drinking in the rural area.

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Micropollutants contained in leachates from the Nonthaburi open dump site in Thailand were investigated. The leachate contained as high as 5 mg · l^-1 of bisphenol A and 0.06 mg · l^-1 of toluene, while the concentrations of these compounds in the leachate from the Nakornpatom engineered landfill adjacent to the Nonthaburi site were between 1/100 and 1/1000 of those in the Nonthaburi site. It is suggested that the heat generated by the biodegradation of wastes promoted the release of the micropollutants from plastic wastes in the solid waste disposal site.

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To understand the behavior of waste degradation in landfills and landfill stabilization in tropical and subtropical climate zones, eubacterial community analysis using waste landfill leachate was conducted. Waste landfills in Thailand, Vietnam and Japan were investigated of the bacterial communities. The waste landfills in Hua Hin (Thailand) and Go Cat (Vietnam) had high concentrations of organics in the leachate and organics in these high amounts of gas generated, indicating the active degradation of organic waste, as well as the disposal of large amounts of landfills. The landfills in the Japanese subtropical zone were suggested to be under going a comparatively stable degradation because of the long — term use of the landfill and the preliminary mineralization of landfill materials. All the bacterial communities isolated from observed in the landfills showed the existence of bacteria phylogenically related to Firmicutes and Bacteroidetes, indicating a highly reducing condition of the waste layer in the landfills. On the other hand, bacteria related to CFB (Cytophaga-Flexibacter-Bacteroidetes) group and ε-Proteobacteria were specifically detected from the Hua Hin landfill and Go Cat landfill but not from the Japanese landfills. The presence of these bacterial groups indicates the regional specificity of waste degradation in landfills under active degradation. Some common bacterial groups such as γ-Proteobacteria in the Hua Hin landfill and Japanese subtropical landfills were also found, suggesting certain similarities between these landfills.

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Dissolved humic substances in the river waters of Sanjiang Plain, which has undergone a land-use change from wetland marsh to cultivated land, were studied by three-dimensional excitation emission matrix spectroscopy and high-performance size exclusion chromatography to characterize the dissolved organic matter in the river systems. River water samples were collected at 14 points from nine rivers in the summer in 2005. Fulvic like fluorescence maxima were detected for the river waters at an excitation wavelength (Ex.) in the range of 315-335 nm and an emission wavelength (Em.) in the range of 410-430 nm and at an Ex. in the range of 235-260 nm and an Em. in the range of 410-440 nm. The relative fluorescence intensity of fulvic like materials in the river waters from wetlands in the August samples was lower than those of the September samples, but that of the river waters from the cultivated area was higher than those of the September samples. The fluorescent properties of humic substances can be divided into three groups on the basis of river water pH, the relative fluorescence intensity of fulvic like materials and its peak positions. These groups correspond to the land-use types such as wetlands, dry lands and their mixture in the watershed of rivers.

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In this study, we determined the dissolved ion concentrations of surface water and groundwater in areas of salinated land in northeastern Thailand to evaluate irrigational water resources. The concentrations of nutrient and heavy metals were measured at 35 points in July 2006 to investigate their changes in distribution. Seasonal variations were measured at 10 points between July 2006 and July 2007. In area A, which is a hilly groundwater recharging area, the ion concentrations in both ponds and wells were sufficiently low, making water in this area good for irrigation water. In area B, which is a medium-hilly residential area, the ion concentrations in a few wells were high and fluctuated seasonally, so care is required if water in this area is to be used for irrigation. In area C, which is a marshy area with groundwater discharge, the chloride concentrations were so high that the use of water in this area is limited to paddy rice cultivation. Further research on the analysis of changes in the aquatic environment is required, since the number of livestock shows an increasing trend and the lifestyle of people living around the studied areas is changing drastically.

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The characteristics of abnormal-water-quality-change detection were investigated using image analysis based on an activity decrease in medaka (Oryzias latipes). The activity of the medaka was quantified by analyzing the blocks' number at which the change in the life span of medaka was observed and its duration, and the alarm of accidental water quality change could be accurately sent in a short time for practical use on the basis of an activity decrease in medaka, although the detection time was extended slightly compared with that of the conventional method based on an abnormal reaction of medaka. The alarm condition was investigated for typical contaminants at various concentrations. From the results, this image analysis method was effective, particularly for the abnormal-water-quality-change detection of industrial wastewater containing a high concentration ammonia or phenol and of municipal sewage containing LAS.

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Two methods for reducing the amounts of pesticides discharged from continuously irrigated rice paddies were evaluated by molinate and simetryn. The first method used a secondary outlet installed near the irrigation water inlet on the short side of an experimental paddy (0.5ha). The original outlet on the opposite side of the inlet was closed and pesticides were applied. Runoff from the secondary outlet began 1.25 hours after irrigation (1.7l·sec^-1) starting, and the pesticide concentrations were measured at the secondary outlet as well as around the midpoint of the long side of the paddy. The loads from the secondary outlet were 0.114g·ha^-1 of molinate and 0.035g·ha^-1 of simetryn, whereas the loads from the original outlet were estimated from the concentrations at the midpoint to be 5.48 and 1.44g·ha^-1, respectively, that is, a 98% reduction in the pesticide runoff load. In the second method, an experimental paddy (0.07ha) was irrigated for four days with 0.63l·sec^-1 after pesticides application. The drainage from this paddy was discharged through a secondary paddy (0.08ha). The inflows of molinate and simetryn to the secondary paddy were 477 and 83.0g·ha^-1, and the outflows were reduced to 257 and 32.8g·ha^-1, respectively.

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On the basis of hydrological processes in a well-characterized hillslope (0.65 ha), we analyzed the effects of flow paths on dissolved organic carbon (DOC) concentrations in a headwater stream (catchment area, 103 ha) during storm flow periods. In the hillslope, our previous findings of water flow paths and an analysis of the relationship between soil pore water pressure and hillslope discharge enabled us to classify the hillslope discharge representing water flow paths. During storm flow periods, the occurrence of upslope-derived water had the effect of keeping the stream DOC concentration low, reflecting that the DOC concentration of the upslope-derived water was very low. However, this effect was not observed during nonstorm flow periods, when the stream DOC concentration was nearly constant regardless of the occurrence of upslope-derived water. We inferred that the major reason that the effects of upslope-derived water on stream DOC concentration were different between storm and nonstorm flow periods was the difference in the timing of DOC export from a riparian area. We concluded that information on hydrological processes in hillslopes is helpful for elucidating the formation mechanism of stream DOC concentration in forested headwater catchments.

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It was proposed that ultraviolet(UV) irradiation could reduce nitrate to nitrite in an aqueous solution and that disodium ethylenediamine tetraacetate(EDTA) as an additive assists in the reduction of either nitrate or nitrite. The purpose of this study is to obtain basic data for a practical removal of nitrate and nitrite from industrial wastewater by UV irradiation. It was found that EDTA effectively removes nitrogen species at 1000-fold higher concentrations than the previous concentration examined by Takeda et al. and that glycine and glycolate are also very effective for the removal of nitrogen species. Glycolate was considered to be one of the decomposition products of glycine produced by UV irradiation. Both nitrate and nitrite from ammonium nitrate were completely removed by UV irradiation regardless of pH in most cases, when either of the additives was added with a molar ratio of about 1 to 1 as nitrate to a (N)-CH₂COO^-unit.

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To prevent the elution of lead from water pipes, the adjustment of the pH of purified water is effective. However, substantial data on the effect of pH adjustment on purified water are not yet available. Thus, to examine the effect of the pH adjustment performed by the Ushikubi Filtration Plant, the relationship between pH and lead concentration was analyzed from past data. As a result, the lead elution rate was found to decrease with pH adjustment; however, the rate also decreased year by year. Thus, the pH adjustment effect is still unclear. It was considered that faucets that elute a very small amount of lead in the same manner were distributed in Japan and that pH influenced such lead elution. Then, using the nationwide water supply statistics of 2003, the data of purified water quality were sorted into ten groups by pH, and mean lead concentration and lead detection rate were calculated for each group. As a result, relational formulae relating pH, lead concentration and lead detection rate were obtained. These equations will be useful for assessing the effects of decreases in lead concentration and lead detection rate induced by pH adjustment.

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The authors have been developing the establishment method of a phosphate ion removal, recovery and recycling system using a synthesized Mg-Al-Cl form hydrotalcite (HT).The powder form of HT, however, was not ideal for wastewater treatment because of its poor solid-liquid separating efficiency; thus, the authors have developed a HT-carrying fiber (HTCF). We have investigated practical ability by measuring the removal adsorption rate and breakthrough capacity of the HTCF for phosphate ions by a column method using a sample phosphate solution and secondary treated wastewater from a rural sewerage facility. It was found that, the breakthrough capacities of the HTCF were in the range of 28.72-30.68 mg-P·g^-1 in the case of using the sample phosphate solution, and in the range of 15.32-16.27 mg-P·g^-1 in the case of the secondary treated wastewater with the range of space velocities being from 1.5 to 6.0·h^-1. It was suggested that the decreased breakthrough capacities of the HTCF in the case of using the secondary treated wastewater were attributed mainly to HCO₃^- ions contained in the wastewater. However, the removal ability of the HTCF for phosphate ions in using actual secondary treated wastewater is sufficient, that is to say, it seems that the developed HTCF is a promising practical removal adsorbent for phosphate ions in wastewater.

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