Analysis on functions of micro-animals in the detritus food webs of biological wastewater treatment systems.

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In this study, it aimed to clarify the relations between the microbial ecosystems in biological wastewater treatment systems and its purification functions for waste water. Some bacteria were isolated from Johkasou systems, which are typical on-site biological domestic wastewater treatment facilities in Japan, and the isolated bacteria were identified by sequences of 16SrRNA. Some appropriate bacteria (Serratia marcescens etc.) were selected, in order to study on the function of microbial ecosystems for the wastewater treatment process. Moreover, it was shown that the T-RFLP method was a useful molecular biological tool for the analysis on complex microbial ecosystems in wastewater treatment systems.The mixed culture experiments with aquatic rotatoria, Philodina sp. and isolated bacteria from some Johkasous were performed. It was shown that Philodina sp. was very effective to make high transparent water by the filtration effect and the coagulation effect of Philodina sp.. Moreover, we obtained the result that mineralization of organic carbon under the condition of predation for bacteria by Philodina sp was faster than it under the monoculture condition of bacteria. Also, total amount of decreases of DOC and TOC was enhanced by the existence of Ciliata T.thermophila. in the mixed culture system with bacteria as a microcosm system with a simple detritus food web structure. On the other hand, the numerical analysis of a simple predator-prey model drew out the result of contradiction to our experimental results. That is, our experimental results strongly suggest that existence of predator such as protozoan and/or metazoan increase the activity of bacteria for decomposition of organic matter, because the simple predator prey interaction between bacteria and protozoa only causes decrease of bacterial population as decomposer of organic matter.