Lecane tenuiseta (Rotifera, Monogononta) as the best biological tool candidate selected for preventing activated sludge bulking in a cold season

Abstract

Rotifers in activated sludge reduce the quantity of dispersed bacteria, ingest filamentous bacteria, enhance flocculation and limit biomass production. Growth rates of rotifers are inversely correlated with temperature; thus, their density declines drastically in wastewater treatment plants (WWTPs) during the winter. The only species already demonstrated to be able to control bulking is Lecane inermis. However, they cease proliferation at 8°C. The goal of our research was to select other rotifers species whose growth rates at lower temperatures are sufficiently high to maintain a favourable density during cold seasons. We conducted selection experiments in the laboratory at temperatures reflecting the temperature distribution in the majority of municipal WWTPs in the temperate zone. In the first experiment, the general selection stage, we tested the influence of the temperatures 8, 15 and 20°C on competition among different rotifer taxa in sludge samples originating from different WWTPs. The rotifers best adapted to lower temperatures were found among the genera Lecane and Cephalodella. The second stage, focused on Lecane selection, showed that the genus Lecane was represented most abundantly by L. inermis and Lecane tenuiseta. At 8°C, only clones of L. tenuiseta exhibited positive growth rates. At 15°C, more selected clones were identified as L. tenuiseta than as L. inermis, but the r-value for L. inermis was higher. Our results suggested that L. tenuiseta is the best candidate for bulking control in cold seasons.