The estimation of material mass in bodies of water such as lakes provides much information on water quality formation mechanism since it enables evaluation of mass balance in the body of water examined. However, such estimation is difficult, because water quality is not uniform and a precise water quality survey is actually difficult in a large lake. In this paper, mass estimation methods are proposed and compared with each other. In each method, material mass in Lake Biwa, Japan was estimated based on water quality data at 75 points in the lake. The spline technique that interpolates the concentration value in 500X500X1m-size mesh in the lake with a σ value of 0.3 was selected as the most suitable estimation method. Judging from the N/P ratio, mass values estimated by this technique were more reliable than those reported previously. Nitrogen and phosphorus are present in Lake Biwa at 7.6-13X10³ tonN and 190-340 tonP, respectively, and their averages in 20 surveys from 1995 until 2000 were 11X10³ tonN and 230 tonP, respectively.

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Biodegradable organic substances in Yodo River water, its coagulated water and the ozonated water were analyzed in terms of the concentration of assimilatable organic carbon (AOC), the apparent molecular weight and the E260 absorbability. The fundamental behaviors of AOC through coagulation and ozonation were investigated. Yodo River water contained a relatively high content of macro organic compounds (>5,000 Da) that did not exhibit E260 absorbing features. However, these compounds were not detected as AOC. Coagulation resulted in decreases in the concentration of AOC by up to 75%, due to reductions in the phosphorus concentration. During ozonation, the AOC concentration increased rapidly with the reduction of E260 and increased slowly following the change of some large molecular organic compounds to small ones. However, 30-50 % of AOC that could be increased through ozonation was reduced by pre-coagulation.
In addition, water samples prepared under the condition of different limiting substrates were subjected to AOC measurements and batch incubation tests for bacteria living in Yodo River. Experimental results indicated that the AOC concentration converted to acetate equivalent could not represent the concentration of the available carbon for assimilation. However, its apparent value was probably reflective of the growth potential of bacteria even under the phosphorus limitation. Thus, it was suggested that the apparent AOC concentration is a useful indicator for evaluating the regrowth potential of native bacteria in Yodo River.

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Two ELISA methods were investigated for the quantitative detection of viability and infectivity of Cryptosporidium parvum oocysts. One is to detect the sporozoites attached to the cell surface, and another is to detect the oocysts developing in host cell. It was thought that the former method, named “Fixed-cell” ELISA, could assess the viability of oocysts, and the latter method, named “Living-cell” ELISA, could assess the infectivity of oocysts. In both ELISA systems, the resulting optical density was related to the number of oocysts inoculated. Inactivation of oocyst by ultraviolet (UV) irradiation was evaluated using these two ELISA systems. One-log reduction in infectivity of oocysts was achieved by 10 mW·s·cm^-2 of UV irradiation. At this UV dose, no reduction in viability determined by “Fixed-cell” ELISA was observed.

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The objective of this study was to develop a regeneration system for GAC and a solvent for use in TCE treatment. Thus, we evaluated the characteristic of TCE desorbed from GAC by acetic acid solution, the degradability of TCE in acetic acid solution by ozone, and the adsorption performance of TCE for GAC regenerated by acetic acid solution. The conclusions obtained from this study are as follows: The amount of TCE desorbed from GAC increased with increasing concentration of acetic acid. Almost all TCE was desorbed by more than 50% acetic acid solution. TCE in acetic acid solution was effectively decomposed by ozone. The specific amount of TCE decomposition in acetic acid solution in relation to ozone consumption was 4.0-48.0% higher than that in pure water. The adsorption capacity of the regenerated GAC was the same as that regenerated with new GAC. This result indicates that GAC regenerated by acetic acid solution can be recycled for TCE adsorption.

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