Clonal variation in reproductive response to temperature by a potential bulking control agent, Lecane inermis (Rotifera)

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The novel idea of using rotifers Lecane inermis (Rotifera, Monogononta) as a tool to overcome activated sludge bulking generates an on-going need to study rotifer biology. The results of biological research on rotifers can serve to improve the method so that it can be most effective when applied in treatment plants. The aim of this study was to test the effect of temperature on four selected rotifer clones originating from different treatment plants. The rate of population development from a single individual (parthenogenetic female) during a 10-day experiment was measured at three temperatures: 8, 15 and 20 °C. The temperatures used reflect the annual temperature distribution in the majority of municipal wastewater treatment plants in the temperate zone. The growth rate coefficient (r) and doubling time (tD) were calculated for each clone. Under the most favourable conditions (20 °C), r values varied between 0.41 and 0.47 d and doubling time between 1.5 and 1.7 d. At a temperature of 15 °C, the doubling time was approximately two times longer (2.5–3.4 d). The strongest intraspecific variations were observed at the lowest temperature of 8 °C. At this temperature, one of the clones almost failed to proliferate, and another exhibited a doubling time of 7.9 d. The doubling times were a few times greater for the remaining two clones (60 d for Lk1, 33.3 d for Lk4). These results could be very useful in predicting the chances that the rotifers would survive in a biological reactor in a wastewater treatment plant at the temperatures used in these reactors.

Keywords: activated sludge, intraspecific variation, rotifers, sludge age, temperature

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