UV Disinfection in New Zealand's Non-codified Regulatory Environment Using QMRA for Risk Assessment

This paper discusses an alternative, non-codified approach (as opposed to fully prescribed approaches) to wastewater effluent UV disinfection system design that allows for pragmatic, cost effective designs to be developed. New Zealand’s ‘effects based’ environmental legislation, as it applies to wastewater effluent discharges, provides for a license applicant to demonstrate the actual and likely effects (including public health) of their proposed activity and to propose measures to mitigate those effects. Quantitative Microbial Risk Assessment has increasingly become adopted in New Zealand as a means or a tool by which: a) the likely effect attributable to a particular activity in or near the environment, can be assessed, b) pragmatic discharge pathogen limits can be established, c) the disinfection system design parameters can be established d) systems developed can be tested and monitored for effectiveness. Significant savings can be made (but not always) and a fair outcome is typically achieved.