Investigations on semiconductor sonocatalysis for the removal of pathological micro-organisms in water

Contamination of drinking water by bacterial pollutants is a major environmental problem. In the current study, the possibility of using zinc oxide-mediated sonocatalysis, as a potential advanced oxidation process for the removal of a major pollutant, i.e. Escherichia coli, is investigated. Critical parameters for optimum efficiency are identified. The organism deactivation is fully irreversible in the case of ZnO-mediated sonocatalysis. Scanning electron microscopy images show that morphological changes and cell-wall disruption of organisms are more in sonocatalysis compared to sonication alone. The deactivation is practically unaffected by initial pH in the range 5-9. Reactive oxygen species including in situ-formed free radicals play significant role in the deactivation. Sonoluminescence-induced photocatalysis is a major contributor in the disinfection process. A probable mechanism involving physical effects and semiconductor activation by ultrasound followed by the events leading to the deactivation of the bacteria is proposed.