Electron microscopic investigation of the bactericidal action of electrochemical disinfection in comparison with chlorination, ozonation and Fenton reaction

Laboratory experiments were carried out to investigate the mechanisms of electrochemical (EC) disinfection of artificial wastewater contaminated by Escherichia coli culture. Comparative disinfection tests with chlorine, ozone and hydroxyl ((OH-)-O-.) radicals produced by the Fenton reaction were also conducted. It was demonstrated that the EC process was highly effective for wastewater disinfection. Investigation with scanning electron microscopy (SEM) showed different appearances of damage to in the surface morphology and structure of the cells after different forms of disinfection. Substantial leakage of intracellular materials was found for the E. coli cells after EC disinfection, which was also observed for the cells treated by the Fenton reaction. However, such cell lysis was noticeable to a less extent for the ozonated cells and hardly noticeable for the chlorinated cells. Electron microscopic examination suggested that the cells were likely inactivated during the EC process by the chemical products with an oxidising power similar to that of hydroxyl radicals and much stronger than that of chlorine. The SEM results support the hypothesis that the predominant killing action of EC disinfection is provided by high-energy intermediate EC products. Therefore, in addition to electro-chlorination, the great capacity of EC disinfection may be attributable to the generation of short-lived germicidal agents, such as free radicals. (C) 2003 Elsevier Ltd. All rights reserved.