Inactivation of Microcystis aeruginosa by continuous electrochemical cycling process in tube using Ti/RuO2 electrodes

Algae in waters often bring about influence in drinking water supplies. In this study, an electrochemical tube employing titanium coated with RuO2 as anode was constructed for inactivation of cyanobacteria (often called bluegreen algae) Microcystis aeruginosa. Suspensions containing M. aeruginosa (2-4 x 10(9) L-1) were exposed to current densities ranging from 1 to 10 mA cm(-2) in a detention time of 52 min. The variations of cell density, chlorophylla, optical density, pH, and conductivity were examined during the treatment. After 3.5 min the population of M. aeruginosa dropped rapidly and was reduced from 3 x 10(9) to 0.6 x 10(9) L-1 after 52 min at current densities from 5 to 10 mA cm(-2). The cell density and optical density of M. aeruginosa decreased proportionally to the current density and the detention time. Scanning electron microscopy investigation of algae revealed surface damage and apparent leakage of intracellular contents after electrochemical cycling process. Due to the damage of cells, the chlorophyll-a released from the cells was degraded by electrochemical oxidation. The removal rate of chlorophyll-a could reach 96% at the current density of 10 mA cm(-2). Electrochemical treatment caused minor variation of pH values and conductivity of the suspensions. After electrochemical cycling processes, the optical density at 680 nm of algal cell suspensions remained below 0.1 after 6 days, and it showed that cells had no potential to survive and grow. The results implicated that the inactivation of M. aeruginosa was successfully performed by the electrochemical treatment, and it made the algal cells lose ability to survive, demonstrating the potential of such an alternative process for efficient water purification.