Do organic micropollutants pose a real risk in recycled water in South East Queensland?
Michael Lawrence, Julien Reungoat, Maria Jose Farre, Christoph Ort, Wolfgang Gernjak, Jochen Müller and Jürg Keller
Advanced Water Management Centre and The National Research Centre for Environmental Toxicology, The University of Queensland, Brisbane, Australia
South East Queensland (SEQ) is the fastest growing region in Australia, which, coupled with the worst drought on record, resulted in stored water supplies declining from 64% in April 2004 to less than 17% in August 2007. This has highlighted the need to secure the regional water supply and resulted in a $2.5 Billion AUD infrastructure project to diversify the drinking water supply by both closing the urban water cycle and seawater desalination.
The Western Corridor Recycled Water Project (WCRWP) is intended to supplement drinking water using a 7-barrier system to ensure the highest water quality is supplied to the SEQ population (as shown in Figure 1). This planned indirect potable reuse project purifies the treated water from wastewater treatment plants by microfiltration, reverse osmosis and advanced oxidation prior to supplementation of the water supply dams (an environmental barrier).
Figure 1: Conceptual diagram of the 7 barrier approach to the planned indirect potable reuse of water scheme in South East Queensland, courtesy of Queensland Water Commission.
In concert, these barriers are designed to prevent the infiltration of any contaminants from the wastewater into the drinking water supplies. The implementation of this scheme on such a large scale has provided numerous research opportunities, which are funded jointly by The University of Queensland (including both the Advanced Water Management Centre – AWMC – and the National Research Centre for Environmental Toxicology, EnTox), Veolia Water, Water Secure, and the Urban Water Security Research Alliance. The goals of the research are varied, but can be summarised as optimizing existing processes and/or investigating alternative technologies, monitoring and evaluating contaminants of concern and, where possible, developing strategies to further minimise or eliminate the identified risks.
WWTP Effluent Quality
Purified recycled water (up to 232 ML/day capacity) is manufactured from the effluent of 6 regional wastewater treatment plants. From a global perspective, the wastewater treatment plants (WWTPs) in SEQ operate at a very high standard. Over the last 15 years, there have been very strict regulatory limits placed on the discharge of nitrogen to Moreton Bay, resulting in significant upgrades to all major WWTPs. Coupled with the warm ambient temperatures (sub-tropical, 20-30°C) and long sludge age (typically > 15 days), these plants have been shown to be very efficient at removing many compounds (for example, endocrine disrupting chemicals, EDCs, which have removal efficiencies approaching or exceeding 98%).
As a result of the efficient wastewater treatment, relatively few micropollutants are detected in the inlet to the Advanced Water Treatment Plants (AWTPs). Chemical analysis of more than 250 organic micropollutants of concern typically result in only 20% of the micropollutants being detected above the analytical quantification limit. Further to this, the observed concentrations of compounds detected in these wastewater treatment plant effluents are often an order of magnitude lower than seen in other studies, for example in Europe.
Source Control
Nonetheless, despite the relatively low levels of micropollutants, one potential method of further improving the WWTP effluent water quality is to restrict the amount of these chemicals entering the WWTP by implementing better source controls. Research is currently being conducted to assess relevant point sources of micropollutants, for example hospitals, with a view to determining the feasibility (from economic, and as a proportion of total load standpoints) of treating the potentially higher pharmaceutical concentrations in these sources.
Advanced Water Treatment Process
The water enters the AWTPs and is treated by flocculation prior to microfiltration. There is little additional removal of the micropollutants detected at the inlet prior to the reverse osmosis stage. Following reverse osmosis, and throughout the remainder of the treatment plant (advanced oxidation, water stabilisation), the state-of-the-art analytical detection technique, including pre-concentration using solid phase extraction and liquid chromatography tandem mass spectrometry, are unable to find any of the incoming contaminants at quantifiable levels. Consequently, in the final purified water, no micropollutants are detected above regulatory limits.
Innovative Analytical Methods
Given such low levels of micropollutants in the inlet water, (and to investigate the possibility that unknown contaminants are present and posing risks), it has also become important to utilise bioassays to investigate human health and ecotoxicological risks posed by the recycled water. The bioassays have been used to investigate, amongst others, carcinogenicity, estrogenicity, and phytotoxicity. These bioanalytical tools are very sensitive, and have the advantage of evaluating the effects of all active compounds in the samples (i.e. including the combined effects of the many compounds that are not specifically targeted by chemical analyses), but to date, these tools are not viewed as a regulatory instrument.
Our results for an alternative treatment process utilizing ozonation and activated carbon adsorption indicate that the bioassays are consistent with chemical analyses, yet provide complementary information. The treated water does not illicit a significant response in the bioassays, as would be expected based on the results from the chemical analyses.
Alternative Treatment Processes
Alternative processes to those implemented in the advanced treatment plants are being investigated. One example is an ozonation/activated carbon treatment facility, which has demonstrated the production of high quality water. Of the initial 250 tested compounds, after ozonation and adsorption on activated carbon, only 10 compounds could be detected above the level of quantification. In all instances, these compounds were detected at concentrations several orders of magnitude below the guideline concentrations for recycled water for augmentation of drinking water supplies.
Reluctance to Use Recycled Water
Recently the major community concerns with respect to adding recycled water to drinking water supplies has not been based upon scientific research into water quality. Research demonstrates that recycled water treated using the 7-barrier system adopted in SEQ complies with all relevant standards and regulations for recycled water. Instead, there is resistance in some part of the community to accept this “new” source of water. A concerted media campaign, and a few vocal critics have elicited a negative community response, potentially delaying the introduction of recycled water into the drinking water supply.
Nonetheless, from a scientific standpoint, the addition of purified recycled water to the drinking water supply, based on our own research and similar studies elsewhere, does not appear to impose any additional risk, and an argument could be posed that the recycled water is of higher quality than the current conventional water sources.
From our perspective, we the authors believe, that more effective communication of the scientific research would assist in properly informing community stakeholders, and is imperative towards increasing acceptability of recycled water by the public at large. Recycled water is, but also has to be perceived, as a perfectly safe and valuable additional water supply for our growing population and a suitable strategy to reduce our dependency on rainfall as the major water source in the future.