Innovative method of culturing bdelloid rotifers for the application of wastewater biological treatment

This study aims to establish a simple and efficient method for the mass culture of bdelloid rotifers, which is the basis for the application of bdelloid rotifers as biological manipulators to improve wastewater biological treatment performance. A common bdelloid rotifer, Habrotrocha sp., in a wastewater biological treatment system was selected as the culture target. Rotifers fed on flour could reproduce faster than those fed traditional food such as Chlorella vulgaris or mixed bacteria. As a rotifer food, flour has the advantages of simple preparation, effortless preservation, and low cost compared to live Chlorella vulgaris or mixed bacteria, so it is more suitable for the mass culture of rotifers. The optimal rotifer culture conditions using flour as food were also studied. According to the experimental results, the recommended rotifer culture conditions are a flour particle size of 1 µm, a flour concentration of 6 × 106 cell/mL, a temperature of 28°C, a pH level of 6.5 and salinity of 100–500 mg/L. In addition, the sludge volume index in the sequencing batch reactor (SBR) with the addition of cultured rotifers was 59.9 mL/g at the end of operation and decreased by 18.2% compared to SBR without rotifer, which indicates that the cultured rotifers still retained the function of helping to improve sludge settling. This function may be related to the rotifer’s role in inhibiting bacteria from producing loosely bound extracellular polymeric substances in the SBR.