The accumulation processes of non-volatile organic acids were investigated in pure batch cultures of Chlorella vulgaris cultivated in the Chu medium and Microcystis aeruginosa cultivated in the Chu and MA medium, respectively.
Glycolic and oxalic acids accumulated in the culture of Chlorella vulgaris. The former acid mainly accumulated in the logarithmic growth phase, while the latter acid accumulated in the decrease phase.
The glycolic acid was the significant non-volatile organic acid in the culture of Microcystis aeruginosa, and accumulations of pyruvic, fumaric, oxalic and lactic acids were also determined at the end of experiment. However, these organic acids did not accumulated in the logarithmic growth phase of Microcystis aeruginosa cultivated in the MA medium with organic compounds.

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Factors affecting the gas-liquid oxygen transfer characteristics in the biofilter with total floor coverage aeration are experimentally investigated. A formula for estimating KLa in the biofilter packed with ceramic balls of 6-23 mm in diameter was obtained as functions of the packing material size and the microbial concentration in it. It was ascertained that an increase in the microbial concentration hinders the gas-liquid oxygen transfer rate in the biofilter, while the rate is considerably higher than that in the activated sludge aeration tank. The packing materials in the biofilter control the bubble size and the spiral liquid circulation rate caused by air-lift action. The maximum power economy of oxygen transfer in the biofilter is as high as 3 kg-O2 EkWh-1 provided that the microbial concentration is in the range of 2, 000-4, 000 g Em-3.

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The umu-test, which can detect the genotoxicity by the induction of error in the repair of damaged DNA, was applied to chemicals which are produced in the chlorination and ozonation processes.
In this research, 37 commercial chemicals were tested by the umu-test. When the retention time of the test strain with chemicals was 2 hours, the genotoxicity of the following organic chemicals were clearly detected with and/or without microsomal activation : m-dichlorobenzene ; 1, 2, 4-trichlorobenzene ; bromoform ; dichloroacetic acid ; trichloroacetic acid ; chloral ; formaldehyde ; ionone ; furfurol ; carvone ; glyoxal and acrolein. These dose response results are discussed and compared with results obtained in other bacterial assays.
Some of the selected organic compounds - chloroform, bromoform, trichloroethylene, acethyl acetone, acrolein, etc. - were identified as having genotoxicity which increased as the reaction time became longer values. From these results, it can be shown that there are different rate of transportation of chemicals across the cell membrane, the rate of damage and repair of DNA.

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