The biotic community of the standard trickling filter and its accessory installations of the Okubo Camp of National Guards was studied. The points where the sampling was made are shown in Figs. 1-4. The biotic communities of all points were composed of relatively small number of species and predominated by large populations of few colony-forming species(Table 1). The characteristic colony-forming organisms may be important from the stand point of pollution biology. Judging from the species that appeared, the influent water to the trickling filter is β-polysaprobic, and filtrated water is regarded as intermediate between β-polysaprobic and α-mesosaprobic. These results are supported by the data of B.O.D. measurement. It is noteworthy that green algae such as Stigeoclonium sp., Hormidium sp., and Schizomeris sp., or diatoms, Pinnularia gibba var.(A), P. gibba var. sancta, P. gibba var. parva, P. gibba var.(B)etc., were found in large numbers at the sampling points interpreted as β-polysaprobic. It has been thought that these species, when found in large numbers, should indicate α-mesosaprobic or less polluted habitats, but the result obtained here shows that these algae can live in more polluted waters as well. The efficiency of sewage purification of the trickling filter examined is not so high as can be expected. This low efficiency may be due to insufficient volume of sewage to be filtrated. (The plant was originally planed for more quantity of sewage.)
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