The Challenge
Recycled water is more and more frequently used for a wide variety of purposes, however current guidelines for its disinfection are based on the presumption that it will be used for human consumption. This means that disinfection techniques are expensive and must produce water of unnecessarily high quality because guidelines for recycled water intended for other uses are not available. This project investigated the use of chlorine and preformed monochloramine with the aim of establishing more cost effective guidelines for disinfecting recycled water intended for non drinking purposes.
The Project
Two human viruses; Coxsackie B5 and Adenovirus 2, known to be highly resistant to chlorine and monochloramine were selected as the test pathogens for this study. Handling, culturing and detection procedures for these viruses are already well established. The known high resistance of these two viruses makes them good test vehicles for establishing the effective disinfection concentrations for all human viruses commonly found in recycled waste water feeds.
A range of concentrations of chlorine and monochloramine were used to inactivate the test viruses under variety of conditions designed to replicate particulate and pH conditions typically found in wastewaters. Following disinfection under laboratory controlled conditions, the residual infectivity of the test viruses was determined using optimised cell culture conditions to demonstrate the activity of any remaining test virus. These results established the effective concentration levels for each of the two disinfection agents.
The Outcome
Effective treatment concentrations for chlorine were established for recycled water over a range of particulate and pH levels. These conditions simulate in the laboratory, the expected treatment conditions that will be normally encountered in treatment plants. The data generated within this project will be used to update the Australian Guidelines for Water Recycling for chlorine based disinfection processes. Significantly lower concentrations of chlorine are needed to achieve effective inactivation of human infectious viruses than were initially proposed by the Departments of Health in South Australia and Victoria. This opens the possibility for much more cost effective treatment of recycled water not intended for human consumption.
In contrast, the effective treatment concentrations established for preformed monochloramine were found to be high and difficult to achieve under actual wastewater treatment plant conditions. It is known that in situ formation of monochloramine is a more effective disinfection agent than preformed monochloramine. This now requires further investigation to establish the correct disinfection concentrations.
The new lower treatment chlorine concentrations established in this project offer potential cost savings to all recycling wastewater treatment plants using chlorination as the disinfection process, as significantly less chlorine can safely be used when the recycled water is not intended for drinking. In addition, risk management and safety for consumers when using recycled waters is improved, as a better understanding of the true rates of
inactivation of human pathogenic viruses is now available. New chlorine concentration guidelines will be integrated into the Australian Recycled Water Guidelines for use nationally.
