A new Computational Fluid Dynamics (CFD) simulator for the ozone/UV process has been developed. The radical reaction model used in this simulator was validated by comparing both calculation and experimental results obtained from a completely stirred tank reactor system. Using this simulator, the distributions of relevant substances such as dissolved ozone, hydroxyl radical and organic compounds in the reactor can be investigated. The simulation results of the conventional ozone/UV reactor, i.e., the tube-type reactor where a UV lamp is inserted in parallel to water flow, showed that this conventional reactor is inefficient because hydroxyl radical concentration is high only at the inlet where ozonecontaining water flows in. Furthermore, the results obtained from the simulations with various UV intensity distributions of the lamp showed that the intensified irradiation around the inlet caused 20% improvement in the organic removal efficiency. Thus, the developed simulator is expected to contribute towards the optimization of the ozone/UV reactor for decomposing refractory pollutants.

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Changes in the toxicity in chlorinated water after chlorine addition were examined. For toxicity evaluation, the chromosomal aberration test and the transformation test were conducted as indexes of initiation activity and promotion activity, respectively, in the carcinogenesis process. Activity inducing chromosomal aberrations in chlorinated Lake Biwa water gradually decreased over time after chlorination. In contrast, activity inducing transformations determined by the two-stage assay gradually increased. Thus, toxicity that decreases or increases is present in chlorinated water. Furthermore, activity inducing transformations determined by the non-two-stage assay gradually decreased over time. This direction of change is opposite to that of activity inducing transformations determined by the two-stage assay and is consistent with that of activity inducing chromosomal aberrations. The drastic decrease in initiation activity detected as activity inducing chromosomal aberrations could be the main cause for the decrease in activity inducing transformations determined by the non-two-stage assay (an index of the sum of initiation and promotion activity). MX change was quantitatively consistent with those of activity inducing chromosomal aberrations and transformations determined by the non-two-stage assay. On the other hand, directions of changes in concentrations of typical by-products such as chloroform were consistent only with that of activity inducing transformations determined by the two-stage assay. Findings of this study suggest that MX is appropriate as an index for comparing the carcinogenicity of tap water near and far from a water purification plant.

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The influences of the transformations of dissolved organic matter (DOM) on the excitation-emission matrix (EEM) were investigated for the samples obtained from Hiroshima Bay, the rivers inflowing into the bay, sewage treatment plant, etc. and then subjected to photolysis and microbial degradation. We found that Peak6 of the EEM changed most markedly and that the difference in irradiation sources between sunlight and black light made negligible difference in EEM transformations. Distinct changes in EEM were not observed for the microbial degradation, except Peak4 for the samples characterized by prominent Peak4. The peak positions of EEM remained within ± 10nm through the transformation processes by photolysis or microbial degradation. The rate constants of RFI/DOC (relative fluorescence intensity divided by DOC) at Peak3, Peak4 and Peak6 exhibited positive values for photochemical degradation and on the other hand negative values for microbial degradation.

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Paenibacillus sp., isolated from sediment in the southern part of Lake Biwa, Shiga, Japan, was used for the acid fermentation of garbage. The fermentation characteristics of Paenibacillus sp. were discussed by comparing with those of themophilic bacteria and mesophilic bacteria and as a result high ability of VFAs fermentation by Paenibacillus sp. was exhibited. The suitable pH for Paenibacillus sp. was in the range from 5 to 5.5 for both acid fermentation and growth. In this pH range, the value of carbohydrate degradation rate constant was 5.7 (h·gATP)^-1, and the rate of VFAs production per carbohydrate unit was as high as approximately 0.9mg C-VFAs·(mg C-glucose-base)^-1. The degradation of proteins to NH₄⁺-N was not observed. Soluble carbohydrates at a concentration of 39,000mg glucose·l^-1 in garbage was degraded to produce VFAs of approximately 15,000mg C-VFAs·l^-1 at less than 1 day of HRT in continuous operation. It was confirmed by SEM observation that Paenibacillus sp. is maintain as the dominant species during continuous operation. From these results, Paenibacillus sp. may be used for the acid fermentation of garbage for the effective production of VFAs with low production of NH₄⁺-N.

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Nitrogen and phosphorus supplied from Sasagase and Kurashiki Rivers to Lake Kojima, Japan contribute to internal production of chemical oxygen demand (COD) in the lake. It is necessary to gather the information on their characteristics based on which we can decrease the COD value. Then, concentrations of nitrate (NO₃^--N) and phosphate (PO₄^3--P) were measured once a month at 21 sampling points along the rivers from Feb 2001 to Jan 2002. As results, the average concentrations of NO₃^--N and PO₄^3--P at most points in Kurashiki River were higher than those at each sampling point in Sasagase River. In addition, monthly concentration-changes of NO₃^--N and PO₄^3--P at each sampling point was as follows; 1) monthly changes in the NO₃^--N concentration were similar to those of PO₄^3--P at the sampling point where irrigation water was introduced in the summer, 2) the NO₃^--N concentration changed in inverse proportion to the PO₄^3--P concentration at the sampling points where phosphate was released from the sediments under the condition of low-dissolved oxygen in the summer, 3) monthly changes in the NO₃^--N concentration were independent of those in the PO₄^3--P concentration at the sampling point where it was affected by some non-specific sources.

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