Zooplankton mortality in lake water treated by pulsed arc electohydraulic discharge plasma.

Zooplankton play a significant role in the quality of drinking and inland sources and as such are of great importance in ballast water treatment. In the past, chemical inactivation combined with filtration has been used to kill zooplankton; however, chemicals injected may result in secondary contamination of organic compounds in inland waters. In this study, zooplankton were killed with pulsed arc electrohydraulic discharge (PAED) plasma to prevent secondary contamination problems. The zooplankton species used was Daphnia magna (1.5 to 2.5 mm; mean length of 1.81 mm) and the treatment applied was 0.5 kJ/pulse PAED in a 3-L reactor. Experiments were conducted with pulse charging voltage from 2.3 to 3.8 kV, PAED electrode gap distances from 0.5 to 1.5 mm, and plankton concentrations from 10 to 100 animals/L. Exposure of zooplankton to 10-minute PAED treatment resulted in 84.7% mortality (mean of 10 trials) immediately after treatment, and 96.9% to 100 % after waiting for an additional 24 to 48 hours. Treatments with a single pulse or 1 minute PAED yielded lower mortalities. Mechanisms of PAED mortality of zooplankton will be discussed based on pressure wave and discharge parameters.