Selective removal of rotifers in microalgae cultivation using hydrodynamic cavitation

Abstract

Rotifers in algal open ponds consume microalgae rapidly, eventually causing the pond to crash. Hydrodynamic cavitation (HC) has been suggested as a means of controlling rotifers, and its effect on Nannochlropsis salina was examined here. Rotifers were removed at a rate of 87% after a single pass of HC when the initial concentration was 1000 individuals/mL, and up to 99% after four passes, regardless of the initial concentration. The removal rate is expected to be higher than 96% with a single pass in an actual pond, as the rotifer concentration does not typically exceed 500 individuals/mL, even under favorable environmental conditions. At the same intensity of HC, the reproductive capability of N. salina dropped by 12–15% however, the growth exhibited a constantly increasing overall tendency. In addition, the applied HC process was found to be the most energy efficient approach among the existing physical methods for controlling zooplanktons, requiring 6 MJ of energy for treating 1 m