The currently persistent dry conditions in south eastern Queensland have prompted the restart of arrangements for the Western Corridor Recycled Water Scheme, which could supplement water supply through a purified recycled water process. In addition to the usual community concern with such a move, the COVID-19 pandemic has provoked some negative commentary on such schemes through both social and conventional media, largely driven by ignorance.
Professor Stuart Khan has addressed these concerns in an AWA webinar on the topic, examining in turn the effectiveness of the seven typical barriers between wastewater as it enters a modern STP to its being reused for potable consumption. These seven barriers are:
1. Source control (reducing pathogens introduced to the wastewater)
2. Wastewater treatment plant
4. Reverse Osmosis
5. Advanced oxidation (UV treatment)
6. Natural environment
7. Water treatment plant (treatment, disinfection and distribution)
Using published data (including very recent sources) on SARS-CoV-2 and its analogues, Stuart convincingly argued that at worst, the system would achieve a combined validated log reduction value (LRV) of at least 10 (based on the Australian Guidelines for Water Reuse) which is slightly lower than the LRV of 14 based on the WHO guidelines.
Australian testing to date has detected up to 1 x 10^21 RNA particles per litre of raw water (i.e. 2.1 Log RNA per litre) in wastewater. This represents an overestimate of the actual risk, as the detection of RNA does not imply the presence of live virus. However, even at these levels of live virus in wastewater, the Australian Guidelines for Water Reuse estimate of the combined 10 LRV for the barriers provides protection sufficient to meet health-based targets. As more SARS-CoV-2 specific research is published it is likely that the validated LRV will prove to be much higher, and thus the level of protection will be enough to manage even greater concentrations of live virus in wastewater.
In summary, the combined barriers are more than sufficient to manage the risk posed by SARS-CoV-2 in recycled water.
Professor Khan's presentation was hosted by the Australian Water Association and can be accessed from their website.
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