Electrochemical disinfection of simulated ballast water on conductive diamond electrodes

In this work, the electrochemical disinfection with conductive diamond electrodes was studied to treat simulated ballast water. Artemia salina was used as indicator organism and Escherichia coli as indicator bacterium. The influence of salinity (3 and 30 g/L NaCl simulating brackish and ballast water, respectively), current density (up to 1273 A/m2) and operation mode (batch and single-pass) on inactivation and total residual chlorine production rates was investigated. An increase in salinity and current density generally had a beneficial effect on both rates. A. salina in ballast water was completely inactivated after 45 min of batch treatment at 255 A/m2 (corresponding to about 200 mg/L of produced chlorine) and this increased to 60 min in brackish water. A. salina, whose inactivation follows first order kinetics, was found to be more resistant to electrochemical disinfection than E. coli. The complete inactivation of E. coli was achieved in less than 5 min of batch operation at 127 A/m2, whereas the concentration of produced chlorine was less than 20 mg/L. Operation in single-pass mode was less effective for A. salina because it did not suffer mechanical stress, whereas E. coli inactivation occurred at low current densities and irrespective of the salinity due to both direct oxidation on the surface of conductive diamond anode and chemical reactions with chlorine species and/or reactive oxygen species.