Abstract
In this study, ciliated protozoa Colpidium sp. and bacterium Enterobacter ludwigii isolated from a Johkaso were used to demonstrate the effect of protozoa for degradation of dissolved organic carbon in the biological wastewater treatment system. We examined changes of total organic carbon (TOC), dissolved organic carbon (DOC) and particulate organic carbon (POC) in concentration between the monoculture (E. ludwigii) and the mixed culture (E. ludwigii and Colpidium sp.) using modified Taub’s culture medium including peptone (200mg・l－1). In the monoculture system, 22.3mg－C・l－1 of DOC decreased for 2 days from the beginning of the culture. In this period, the average cell density of E. ludwigii was 3.9×108 CFU・ml－1. On the other hand, in the mixed culture system, 32.7mg－C・l－1 of DOC decreased in 2 days from the beginning of the culture. In this period, the average density of E. ludwigii was 2.9×108 CFU・ml－1. Consequently, the larger amount of DOC decreased in the mixed culture system than the monoculture system, though the cell density of bacteria in the mixed culture system is lower than that in monoculture system. Moreover, it was estimated that the rate in decrease of DOC per POC in the mixed culture system was 130 times of the rate in the monoculture system. From these results, it was strongly suggested that protozoa enhanced the activity of DOC degradation in the microbial ecosystem in the biological wastewater treatment system.
