Volume 191 - Issue 4
Water recycling — forwards or backwards for public health?
Author: Peter J Collignon
Med J Aust 2009; 191 (4): 238-239. || doi: 10.5694/j.1326-5377.2009.tb02769.x
Published online: 17 August 2009
Published online: 17 August 2009
To the Editor: Recycling water from sewage into drinking water was recently discussed in the Journal.1 Although this is technically feasible, we need to be very wary. Such recycling is associated with very high ongoing monetary and energy costs, but, most importantly from a health perspective, is a “very high-risk”2 proposal that reverses 150 years of good public health policy of striving to keep sewage out of our drinking water supplies.
When we need to recycle water from highly contaminated sources, it is much safer to do so for industrial purposes using separated pipelines (as is done in Singapore and Brisbane). The most extensive scientific review on this issue concluded that putting it into drinking water should be a “last resort”, that
should be adopted only if other measures — including other water sources, nonpotable reuse, and water conservation — have been evaluated and rejected as technically or economically infeasible.3
Sewage contains very high concentrations of pathogens and drugs. Viruses (the most difficult pathogens to remove) can occur in concentrations higher than 106 per litre — orders of magnitude higher than in even the most polluted rivers. The technical and human performance needed to remove viruses safely will have to be proportionately higher than current practice — difficult to achieve, as we already have skills shortages. We would also need to ensure that the system will work all the time.
Reverse osmosis (RO) is the most effective way to remove viruses and drugs from sewage, and should remove virtually all viruses and drugs. Surprisingly, few in-use data are available to check this. RO membranes seem to leak. One study found that RO only removed 92% of antibiotics.4 Recent safety reviews, including an Australian review5 (based on the previous study3), showed viruses were still detected post-treatment at three of seven sites on some occasions. The calculated virus removal ranged from 87% to > 99.995%, which equates to a “log reduction” of 1 to 5. However, to produce safe drinking water from sewage, we need a consistent 9.5-log reduction for enteroviruses.2 Even Giardia was not always removed. This less than optimal performance was when the system was not known to be malfunctioning; lowered performance might occur as often as 5 days a year.6
Current surrogate testing (eg, organic carbon) can only detect a membrane leak (or bypass) of at least 1%, which is well short of meeting the 9.5-log reduction we need for virus removal and reasonable safety.2 We need real-time tests to show that there is adequate virus removal, rather than none at all or only becoming aware of a problem after processed but contaminated water is already in our reservoirs.
References
- Leder KS, O’Toole JE, Sinclair MI. Water recycling — forwards or backwards for public health [editorial]? Med J Aust 2009; 190: 293-294. 0_CHDHFFIE
- National Water Quality Management Strategy. Australian guidelines for water recycling: managing health and environmental risks (Phase 2). Augmentation of drinking water supplies. Canberra: Environment Protection and Heritage Council, Natural Resource Management Ministerial Council, and National Health and Medical Research Council, 2008. http://www.ephc.gov.au/sites/default/files/WQ_AGWR_GL__Augmentation_of_Drinking_Water_Supplies_Final_2008_05.pdf (accessed Apr 2009, link no longer available).
- National Research Council. Issues in potable reuse: the viability of augmenting drinking water supplies with reclaimed water. Washington, DC: National Academy Press, 1998. http://www.nap.edu/openbook.php?isbn=0309064163 (accessed Apr 2009).
- Watkinson AJ, Murby EJ, Costanzo SD. Removal of antibiotics in conventional and advanced wastewater treatment: implications for environmental discharge and wastewater recycling. Water Res 2007; 41: 4164-4176. 0_CBBFIDAE
- Khan S, Roser D. Risk assessment and health effects studies of indirect potable reuse schemes. Final report. Sydney: Centre for Water and Waste Technology, School of Civil and Environmental Engineering, University of New South Wales, 2007. http://www.lgaq.asn.au/lgaq/publications/Risk% 20Assessment%20and%20Health%20Effects%20 Studies%20-%20WSAA%20Version.pdf (accessed Apr 2009).
- Roser D, Khan S, Davies C, et al. Screening health risk assessment for the use of microfiltration-reverse osmosis treated tertiary effluent for replacement of environmental flows. Final report. Sydney: Centre for Water and Waste Technology, School of Civil and Environmental Engineering, University of New South Wales, 2006. 0_CBBGDHID