2019 Volume 55 Issue 2 Pages 23-34
The Sludge Bioindicator is a simple tool to understand the treatment condition by making the use of characteristic of microfauna which is fluctuated according to the environmental change. Although the Sludge Bioindicator has been introduced in many wastewater treatment plants which adopt conventional treatment method, recently it has been reported that this Sludge Bioindicator is not accommodated to the advanced treatment. Dissolved oxygen （DO） concentration is suggested to be the reason for the difference in microfauna, though there are very few quantitatively studies on the effect of DO concentration on microfauna. In this study, to enhance the reliability of Sludge Bioindicator, relation between concentration of DO （7.2～0.2 mg/L, 8 phases） and micro fauna in activated sludge was examined.
As a result, it was cleared that microfauna varied with concentration of DO, instead the dissolved organic carbon removal ratio has not been changed. Mastigophora and Amoebozoa increased their cell densities in lower DO phase （2.4～0.2 mg/L） than higher DO phase （7.2～3.6 mg/L）. Although Metazoa preferred a more aerobic condition, Ciliophora appeared in wide range of DO. However, the aptitude for the low DO environment differed within the same taxonomic group.
The relation between the ratio of surface area to volume （S/V ratio） of microorganisms and DO level was also surveyed. It was cleared that microorganisms with higher S/V ratio （such as Mastigophora and Amoebozoa） tend to increase their cell density in the lower DO environment （R2 = 0.5434）. However, not all microorganisms showed this tendency, it is supposed that there are other factors will affect to the aptitude for the lower DO environment.
