5.1 What is disinfection?

Disinfection is the process of eliminating or inactivating pathogenic microorganisms, such as bacteria, viruses, and protozoa, in the wastewater to make it safe for discharge or reuse. Disinfection is a critical step in the wastewater treatment process, as it helps minimise environmental contamination and prevent the transmission of waterborne diseases that can occur via:

• Direct ingestion of untreated water
• Ingestion of aquatic food species infected with pathogens absorbed from contaminated water
• Invasion resulting from skin contact with contaminated water

Disinfection processes are generally applied at or near the end of wastewater treatment to the effluent that contains low concentrations of dissolved and suspended materials that could compete for active disinfection agents.

The need for disinfection should be evaluated on a case-by-case basis, considering beneficial uses and criteria. Disinfection should not be required when significant benefits are not demonstrated. Prospective disinfection benefits must be weighed against the environmental risks and costs.

Critical factors such as disinfection type, system configuration, contact time, conditioning and pre-conditioning criteria, power costs, maintenance requirements, and other aspects need to be considered when selecting a disinfection method.