Disinfection of grey water

The reuse of grey water, for applications such as toilet flushing and irrigation, represents a potential sustainable solution to water shortages experienced by regions worldwide. Although reused grey water is not intended for potable use, the potential for transmission of waterborne pathogens by aerosol inhalation, topical contact, or indirect ingestion is a key concern for grey water reuse. This thesis explores the pathogen content of grey water and investigates pathogen removal through treatment and disinfection processes. The impacts of organic and particulate material in grey water on the efficacy of disinfection processes are investigated in depth. Grey water can potentially harbour a range of pathogenic microorganisms, with opportunistic bacterial pathogens in grey water indicating a particular risk of grey water reuse for the vulnerable members of society. The disinfection of grey water is therefore critical prior to reuse. Particulate material in grey water limits the efficacy of disinfection by chlorine, ultraviolet light, and origanum essential oil, by shielding microorganisms from the applied disinfectant. Microbial resistance to the disinfectants was linked to the particle size distribution of the grey water, with increasing particle size offering greater protection to associated microorganisms. Additional organic material was shown to reduce the applied disinfectant but no impact on microorganism resistance to disinfection was observed when a constant disinfectant dose was maintained. Treatment of grey water, targeting the removal of large particulate material, improves the efficacy of grey water disinfection, allowing compliance with stringent microbiological standards for urban water reuse.