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In Japan, customers' concerns about chlorinous odour in drinking water have been increasing. One promising approach for reducing chlorinous odour is the minimization of residual chlorine in water distribution, which requires stricter control of organics to maintain biological stability in water supply systems. In this investigation, the levels and seasonal changes of assimilable organic carbon (AOC) and its precursors in drinking water were surveyed to accumulate information on organics in terms of biological stability. In tap water samples purified through rapid sand filtration processes, the average AOC concentration was 174 microgC/L in winter and 60 microgC/L in summer. This difference seemed to reflect the seasonal changes of AOC in the natural aquatic environment. On the other hand, very little or no AOC could be removed after use of an ozonation-biological activated carbon (BAC) process. Especially in winter, waterworks should pay attention to BAC operating conditions to improve AOC removal. The storage of BAC effluent with residual chlorine at 0.05-0.15 mgCl2/L increased AOC drastically. This result indicated the possibility that abundant AOC precursors remaining in the finished water could contribute to newly AOC formation during water distribution with minimized residual chlorine. Combined amino acids, which remained at roughly equivalent to AOC in finished water, were identified as major AOC precursors. Prior to minimization of residual chlorine, enhancement of the removal abilities for both AOC and its precursors would be necessary.

The factors influencing the activities of extracellular ligninolytic enzymes synthesized by white rot fungus,Phanerochaete chrysosporium , were investigated by batch culture experiments. The LiP activity was maximal under the nitrogen-sufficient condition, compared with the activities under both conditions of the nitrogen-limited and nitrogen-excess. The manganese-dependent peroxidase (MnP) activity was highest under nitrogen-limited condition. Veratryl alcohol was found to be the most important substrate enhancing lignin peroxidase (LiP) activity in carbon-limited medium. The decolorization of azo dye (Reactive Red 22) by P. chrysosporium in the presence of both LiP and MnP under carbon-limited condition was greater than that in the presence of MnP under nitrogen-limited condition. Two chlorinated substances (2,6-DCP and MCPA) were degraded under conditions of nitrogen-limitation and notrogen-sufficiency. The azo dyes were also decolorized by the crude extracellular ligninolytic enzymes from P. chrysosporium.

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