In this thinking paper, which has been developed to reinforce the Water Services Association of Australia’s (WSAA) “all options on the table” approach for urban water supply options, our water resilience team considers the benefits of purified recycled water (PRW) for drinking.
The more detailed paper for download as a pdf uses Melbourne as an example of a city where PRW could provide financial benefits and water supply resilience. PRW is cost competitive, climate resilient, and a sustainable option with a relatively low carbon footprint compared to some other water supply options.
This paper intends to initiate an open conversation of PRW as a potential supply option for consideration for communities around the world seeking increased water security.
Water has a significant role to play in shaping cities where people who live, work, study and play, feel happy and healthy, and connected to their communities. This was evident in the 2000s when much of Australia was hit by the ‘Millennium Drought’ with the lowest ever recorded annual inflow to water storage in 2006/07.
Australia would continue to experience harsher droughts into the future due to climate change. Using Melbourne as an example, the Greater Melbourne Climate Projections conducted in 2019 (Clarke, 2019), projected that by 2050, the median total rainfall in Melbourne is projected to decrease by up to 20 per cent.
Meanwhile, the population of Melbourne is expected to increase from 4.6 million to almost 8 million in the next 50 years. This means that the current drinking water supply would struggle to meet demand, and utilising recycled water in its current capacity may not be sufficient or be a cost-effective solution to take pressure off the drinking water supply.
We need to think differently about how to create and manage more high-quality recycled water to achieve resilience, liveability, and productivity outcomes for cities like Melbourne, both in Australia and around the world.
Diversification of water supply sources is one important consideration. Having all options on the table would include PRW, which could be considered together with more familiar solutions such as desalination, recycled water, groundwater extraction and increasing dam capacity.
PRW is a proven safe and sustainable way to supplement drinking water supplies and would give communities the opportunity to reclaim water rather than discarding it, saving hundreds of Olympic size swimming pools of valuable water from going to waste each day.
The first step in the PRW process involves collection and treatment at a wastewater treatment plant (WWTP). From there, the treated effluent is transferred to a PRW treatment plant (PRWTP) for further treatment.
The PRWTP comprises multiple treatment process units combined in sequence to purify the treated effluent, creating a high-quality water product.
This high-quality water is PRW and is safe for drinking. For more cost-effective and equitable distribution, the PRW is often pumped to the nearest drinking water storage, such as a dam or reservoir, where it is stored, blended with other water sources, and re-enters the existing potable water system.
The development of a PRW scheme requires, at each step, both complex technical decisions and community engagement activities. Aurecon has undertaken at a strategic level, an investigation of how a PRW scheme could be developed for Melbourne, which is a large Australian city comparable to many major cities around the world in terms of population and water use.
By exploring these technical and social themes, a platform can be created for discussion with communities in any city of the potential benefits that PRW can deliver as a viable option to contribute to long-term water security. Melbourne already has rainfall independent supply through the Victorian Desalination Plant and therefore a PRW scheme could be considered in serval different scenarios such as an additional drinking water source or as a contingent drought response.
The PRW scheme that we use as our case study begins at Melbourne’s Eastern Treatment Plant (ETP). This wastewater treatment plant services a population of approximately 2.5 million people in Melbourne. The daily average tertiary treated effluent from the ETP is 380 megalitres per day (ML/d). This is a substantial volume of good quality effluent, readily suitable for PRW treatment.
Located at the ETP, a new purified recycled water treatment plant (PRWTP) would be constructed. This plant would include best-practice PRW treatment processes, such as ultrafiltration, reverse osmosis, ultraviolet advanced oxidation, and chemical disinfection processes.
Ultrafiltration and reverse osmosis are commonly used for desalination of seawater, however, in our case, they would be optimised specifically for PRW treatment.
In addition to these treatment processes, the PRWTP would leverage the existing ozonation and biological activated filters at the ETP as pre-treatment processes before ultrafiltration. These two processes provide additional barriers for pathogen and chemical removal.
The scheme would transfer PRW to Sugarloaf Reservoir. A new pipeline would be constructed to discharge PRW to the Yarra River, upstream of the Yering Gorge Pump Station from where the PRW would blend with river water and then be pumped into the reservoir.
Once the PRW enters Sugarloaf Reservoir, it would be blended with surface water sources and stored for a long period before being extracted and treated through the Winneke Water Treatment Plant (WTP) before supply to the drinking water system.
The PRW scheme would incorporate multiple treatment barriers, monitoring and management systems to ensure that the PRW produced from the scheme is compliant with the Australian Drinking Water Guidelines (ADWG) and the Australian Guidelines for Water Recycling (AGWR) Phase 2 Augmentation of Drinking Water Supplies.
Furthermore, the PRW scheme would be benchmarked against international standards and water reclamation frameworks, such as those implemented in the USA and Singapore, to provide cross-checking and further surety in drinking water safety.
The proposed PRWTP would have a water recovery ratio of up to 80 per cent. This means that with a daily average feed of 380 ML/d, approximately 300 ML/d of PRW can be produced, which in turn equates to 112 GL of water supply per annum, or 27 per cent of Melbourne’s current annual drinking water usage.
The PRW scheme proposed by Aurecon’s water engineers would require a total capital cost of AUD$2.3 billion, which is split approximately 2/3 for treatment assets and 1/3 for transfer assets.
As a unit capital cost, this equates to AUD$7.4 million per ML of PRW production capacity. In comparison, according to the Victorian Government Department of Environment, Land, Water and Planning (2015), the Victorian Desalination Plant (VDP) cost AUD$3.5 billion in 2012 for 410 ML/d production capacity, equating to AUD$10.9 million per ML of production capacity, converted to 2021 costs.
Toowoomba and San Diego are often cited as examples of how public perception and political sentiment can influence acceptance of PRW. Toowoomba in Queensland attempted to develop a PRW scheme without an effective community engagement strategy resulting in strong community backlash. Like Toowoomba, San Diego in the USA experienced similar backlash and journalists coined the phrase “toilet to tap” and the synonymous gag reflex or “yuck factor”.
However, San Diego persevered and turned the situation around “through long and careful education and public communications” (WSAA, 2019). The city now has plans to supply up to 40 per cent of its water supply with PRW by 2035.
Seqwater in Queensland has been engaging with the community for several years to help understand acceptance of PRW. Seqwater has recently presented results showing that the community’s acceptance of PRW is increasing over time (Sims-Chilton et al, 2021). This has primarily been the result of a focused education program to improve water literacy on the urban water cycle and the role that PRW can play to provide water security.
There are now many more successful examples than there are failures of successfully improving community understanding and gaining acceptance of PRW schemes. The best local example of a successful community engagement program is in Perth for the Groundwater Replenishment Scheme. The approach to gain acceptance is well understood and, with a well-defined plan, has a very good chance of success.
The barriers to investigating more widespread implementation of PRW to improve water resilience in our communities are not technical but are more social and political. The water sector should start having the conversation with communities about PRW to have a chance of success.
We believe that PRW is a cost competitive, climate resilient, and sustainable option with a relatively low carbon footprint compared to some other water supply options. To demonstrate this, we have used Melbourne as an example for technical and cost analysis of a large scale PRW scheme.
This analysis showed that a PRW scheme located at the ETP, and supplying to Surgarloaf reservoir could provide up to 112 gigaliters of climate resilient water supply per annum at a competitive cost to desalination.
As our climate continues to change and populations are projected to continue to increase, it is essential to adapt our approach to drinking water systems. There needs to be a shift from the source of our drinking water to the quality of our drinking water.
The journey towards water resilience is not a race, but the time to start considering all the options, including PRW, and initiating inclusive discussions with our communities is now.
The views and opinions expressed in this publication are those of the authors and do not necessarily reflect the views, opinions or policies of Aurecon, its clients, or other organisations or bodies.
Darren Romain leads Aurecon’s Community of Interest focused on exploring water supply challenges and solutions in our urban environment. He has more than 25 years of experience in water treatment in Canada, Singapore and Australia covering the full asset lifecycle from strategy, planning, design, construction, through to commissioning and optimisation. Darren is passionate about creating conversations around alternative water supplies for our communities to ensure a sustainable future in a changing climate and increasing water demand.
William Wu is a Senior Water Engineer at Aurecon. He has experience in the planning, design, and optimisation of water and wastewater treatment plants. William has been involved in planning and design of purified recycled water schemes and has helped shape alternative water supply strategies for major water utilities in both South Africa and Australia.
Contributing Authors & Reviewers: John Poon, Andrew Chapman, Sam Corben, Eddie Bayne, Saanika Rana, and Meg Cummins.
Clarke JM, Grose M, Thatcher M, Round V & Heady C. (2019: Greater Melbourne Climate Projections 2019. CSIRO
This paper outlines the economic, social and environmental benefits that purified recycled water could bring to a community looking to improve its water security and resilience. It uses Melbourne, a city with decreasing predicted rainfall and an increasing population, as a case study.
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