Glycerol as a potential solution for rotifer protection against predatory fungi in wastewater treatment

Rotifers are key organisms in activated sludge, as they are able to increase flocculation, improve effluent quality and control activated sludge bulking caused by the overgrowth of filamentous bacteria. Unfortunately, their populations are endangered by predatory fungi, which are surprisingly common in wastewater treatment plants (WWTPs). Looking for a remedy, we found that glycerol could impair the condition of rotiferovorous fungi while posing no threats to rotifers. We conducted experiments on the effects of glycerol at concentrations ranging from 0.005 % to 0.1 % on the growth rate of predatory fungi and rotifer survival in the presence of fungi to determine whether glycerol could be applied as protection for rotifers in the case of fungal infection in WWTPs. Our results showed that glycerol negatively affected both Zoophagus and Lecoophagus fungi. In both cases, the number of rotifers surviving in the presence of predatory fungi was much greater after glycerol addition. In the case of the mature mycelium of Zoophagus, the number of active rotifers was more than ten times greater at 0.005 % glycerol and 25 times greater at 0.1 % glycerol. In the case of Lecophagus, the number of active rotifers was almost two times greater at 0.005 % glycerol but almost six times greater at 0.1 % glycerol. Our experiments shed new light on the possibility of using rotifers for bulking control even when activated sludge is infected by predatory fungi. Moreover, it is another, beside improvement of nutrients removal, potential advantage of glycerol application in WWTPs.