Tardigrades as potential bioindicators in biological wastewater treatment plants

Abstract The aim of this study was the evaluation of the relationship between the presence of tardigrades and various levels of sewage pollution in different tanks of a wastewater treatment plant. The study was carried out in the wastewater treatment plant located near Poznań (Poland) during one research season. The study was conducted in a system consisting of three bioreactor tanks and a secondary clarifier tank, sampled at regular time periods. The presence of one tardigrade species, Thulinius ruffoi, was recorded in the samples. The tardigrades occurred in highest abundance in the tanks containing wastewater with a higher nutrient load. Thulinius ruffoi was mainly present in well-oxygenated activated sludge and its abundance was subject to seasonal fluctuations; however, its preference for more polluted tanks seems to be consistent across the year. Although more detailed experimental study is needed to support the observations, our data indicate that T. ruffoi has a high potential to be used as a bioindicator of nutrient load changes.