GHD, 145 Ann Street, Brisbane, QLD, 4000, Australia.
A research project was undertaken to assess in objective scientific, economic and social terms, the potential place of direct potable reuse (DPR) in Australia, in the spectrum of available water supply options (ATSE, 2013). This project sought to place water recycling for DPR in context among other water source options, including indirect and non-potable reuse, and to identify barriers specific to direct potable reuse in Australia and how they can best be overcome. The project objectives intended that the outcomes will serve as a roadmap to facilitate the deployment of recycled water for DPR in the event that it becomes a necessary water supply option in various regions around Australia.
A qualitative stakeholder survey was undertaken for the purpose of identifying the range of potentially significant issues that would need to be addressed in order to make a comprehensive assessment of the benefits and risks of implementing a DPR project in Australia.
In all, 80 survey responses were received from a variety of industry bodies, academic organisations, State Government departments and agencies, health regulators, drinking water providers/managers, local government associations, local governments, Commonwealth Government departments and agencies, interested individuals, and private companies. Efforts were made to acquire the views of a diverse range of stakeholders, including those known to be vocal opponents to previous potable water recycling proposals in Australia.
Many of the respondents to the qualitative survey presumed that DPR may differ significantly, in terms of energy requirements, costs and lifecycle impacts, compared with alternative water supply strategies. In order to explore these presumptions, a lifecycle-based engineering assessment was commissioned (GHD, 2013).
Four hypothetical options were defined for alternative water supply to an urban city at a coastal location in Australia as described below. The nominal total capacity of treatment and delivery systems for all options was an average of 120 ML/d of product water or at least 40 GL/annum.
OPTION 1: Seawater (SWRO) desalination -- Producing product water that is fed into an assumed pre-existing potable water distribution system of the hypothetical city
OPTION 2: Indirect Potable Reuse (IPR) - Advanced water treatment, followed by recycling via a regional impoundment or 'environmental buffer' (e.g. dam) that serves as raw water source for conventional potable supply to the hypothetical city.
OPTION 3: Direct Potable Reuse (DPR) - Advanced water treatment, followed by recycling via a local reservoir that forms part of the conventional potable supply distribution system to the hypothetical city.
OPTION 4: Dual Pipe Reuse - Advanced treatment of secondary effluent from a modern wastewater treatment plant, producing recycled water of suitable quality for non-potable uses (e.g. toilet flushing and outdoor uses such as of exterior surfaces, irrigation of gardens, parks, golf courses and fire-fighting).
Results and Discussion
Two of the key questions posed in the stakeholder survey are presented below with a brief summary of the responses received.
Perceivable benefits of DPR:
Survey participants were asked "Can you identify any perceivable benefits of DPR (compared to IPR) that may apply in some (hypothetical) future circumstances? In other words, why might DPR ever be an idea worth considering above IPR?" A range of potential benefits for DPR was identified. These included potential cost savings, some of which were related to reduced energy requirements for transporting water. Improved flexibility was also proposed, including the ability to apply potable reuse in the absence of a suitable environmental buffer. Elimination of an environmental buffer was seen to have potential benefits to be derived from the maintenance of high quality water, produced by advanced treatment processes, without potential contamination from environmental sources. Notably, a number of respondents were unable to identify any particular benefits for DPR.
Perceivable obstacles to DPR:
Survey participants were asked "Can you identify any perceivable obstacles to DPR (compared to IPR) that may apply in some (hypothetical) future circumstances? In other words, why might DPR be less attractive or more difficult to implement than IPR?" The diversity of opinion about perceivable obstacles to DPR illustrates the complex interaction between the issues involved (e.g. health, safety, cost, and regulation), perceptions, and individual and group responses. A large number of respondents commented on the public's negative perceptions about consuming recycled water and the public's lack of confidence in the safety of treatment technologies or the trustworthiness of operators. Some respondents noted that these sentiments appeared to be shared by some policy makers, water managers, and regulators.
Hypothetical scenario comparative case study:
The hypothetical scenario analysis revealed that under some circumstances, many of the perceived benefits of DPR identified in the surveys, may indeed be significant. For example, DPR was shown to potentially have the lowest overall capital expenditure costs among the four options considered. Compared to IPR, major savings were achieved by the much reduced requirements for water transport via pipelines. Energy consumption for DPR was also shown to be reduced compared to seawater desalination and IPR. DPR was determined to have greater operational energy requirement compared to the non-potable dual-pipe water reuse scenario. These variable energy requirements were translated almost directly to relative operational costs for the four options, with DPR having the second-lowest operational costs after dual-pipe water reuse. The major disadvantages of the dual-pipe reuse option were the relatively high material use and high initial capital costs.
Potential benefits of DPR, relative to IPR, are likely to be highly case-specific. However, in some circumstances they may be expected to include significantly reduced energy requirements, reduced construction costs and reduced operational costs. DPR may also provide an opportunity to allow potable reuse in situations where a suitable environmental buffer is not available for IPR. Potential obstacles or disadvantages for DPR, relative to IPR, are primarily related to public perception and acceptance.
1. ATSE (2013) Drinking Water through Recycling: The Benefits and Costs of Supplying Direct to the Distribution System, Australian Academy of Technological Sciences and Engineering (ATSE). ISBN 978 1 921388 25 5.
2. GHD (2013) ATSE Australian Water Recycling Centre of Excellence Study: Financial and Life Cycle Inventory Analysis of Alternative Water Supply and Recycling Options in Australia. GHD, Brisbane.