A Brine Management Framework for inland desalination & PRW: Methodology, case studies and lessons learnt

Abstract

Interrelated issues, such as climate change and population growth, are driving society towards the utilisation of more saline water sources  (e.g. brackish groundwater or purified recycled water i.e. PRW) which require desalination. The resulting requirement for brine management is the most significant challenge relating to desalination for inland locations, such as regional cities and remote townships and the energy and resource sectors. Brine management encompasses the sustainable management of this brine within technical, economic and regulatory constraints. This ultimately requires the long-term disposal or beneficial use of the brine (and intrinsic salt) along with strategies which make this possible (e.g. brine minimisation, salt recovery, landfill, brine injection etc). 

This paper presents tools to facilitate the development of an effective and sustainable brine management strategy. It includes a comprehensive Brine Management Framework, featuring adaptive planning that addresses both uncertainty and risk. Additionally, it provides relevant case studies (covering coal seam gas produced water brine management, PRW brine and brine resulting from inland desaliantion for drinking water supply) and a compilation of lessons learnt.

Introduction

Climate change, population growth, water scarcity and worsening source water quality are among the interrelated issues that are driving society towards the utilisation of more saline water sources  (e.g. brackish groundwater) which require desalination; inclusive of treated sewage for purified recycled water (PRW). The resulting requirement for brine management is the most significant challenge relating to desalination for inland locations, such as regional cities and remote townships and in the energy and resource sectors (e.g. oil and gas, power, hydrogen, mining / critical minerals).

Brine, in the context of this paper and the water industry, refers to the salty liquid by-product produced from the desalination of surface water, groundwater, sewage effluent or industrial / resource sector sources. Brine management encompasses the sustainable management of this brine within technical, economic and regulatory constraints. This ultimately requires the long-term disposal or beneficial use of the brine (and intrinsic salt) along with strategies which make this possible (e.g. brine minimisation, transport, salt recovery and purification, landfill, brine injection, co-disposal etc). 

This paper presents tools to facilitate the development of an effective and sustainable brine management strategy. It includes a comprehensive Brine Management Framework, featuring adaptive planning that addresses both uncertainty and risk related to future solutions.

Additionally, this paper provides relevant case studies (covering coal seam gas produced water brine management, PRW brine and brine resulting from inland desaliantion for drinking water supply) and a compilation of lessons learnt.

Brine Management Framework Methodology

This section presents a proposed Brine Management Framework that enables straightforward and clear formulation and implementation of a sustainable brine management plan. This is summarised as a flowchart presented in Figure 1.

Figure 1 – Brine Management Framework

The proposed Brine Management Framework is as follows:

1. Determine the extent to which desalination is required. Identify alternative sources which do not require desalination or minimise desalination e.g. carbon-based advanced treatment instead of RO-based PRW. Demand management and water reuse are important methods which avoid or reduce the requirement of desalination. 

2. Establish the brine (and salt) composition and understand its physical, chemical and biological properties. This may include feed water sampling that enables desalination process simulation to determine brine composition. Speciation chemistry modelling of the brine also provides an understanding of the treatability of the brine and potential for salt recovery.

3. Identify a suite of beneficial-use and disposal routes for the brine or salt. Examples are shown in Table 1. Beneficial-use of brine or salt, although difficult from a technical, economic and market perspective, should be considered for every project as it is potentially the most sustainable method for mitigating the brine and salt problem (although the resources required to undertake this need to be considered) and introduces other circular economy benefits.

4. Determine how to deliver the brine (or salt) to the beneficial-use or disposal route through treatment or processing (e.g. brine minimisation using various technologies, brine or salt purification etc) and transport. Examples of brine treatment technologies are presented in Table 2. 

5. Remove disposal and processing / transport options based upon fatal flaws (e.g. technical readiness level not adequate). 

6. Develop brine management strategies that link together the brine or, ultimately, salt disposal route with the brine minimisation / treatment method with transport as required. 

7. Evaluate the brine management strategies in a holistic manner (i.e. technical, social, environment, regulatory and costs) on a whole of project basis (i.e. project delivery, operations and maintenance and end-of-life actvities) using various tools (e.g. water chemistry modelling, process simulation, lab or pilot testwork, engineering design, ecological studies, regulatory assessments, cost estimation including net present costs, multi-criteria analysis etc).

8. Prepare a logical and explicit brine management plan based on a suite of high performing brine management strategies where a variety of solutions is important to mitigate potential risks. This approach should employ an adapative approach to quantify areas of uncertainty and proactively minimise the risk of failure for a range of different future conditions. The intent of this approach is to keep multiple options on the table and to identify the factors that would trigger a change of approach as new conditions develop. Examples of such changes include economic factors, increasing production (brine volumes), changes in brine reuse opportunities, etc. See Figure 2 for a simplified example of an adaptive pathways planning approach when applied to a complex brine management strategy for an inland desalination project.

Figure 2 – Example brine management plan including adaptive pathways (Visser and Pang, 2024)

In simple terms the proposed Brine Management Framework can be summarised as the development and evaluation of the following:

Brine Management Strategy = (Brine Disposal and/or Reuse) +  (Brine Minimisation / Treatment / Transport)

Table 1 – Examples of brine disposal and beneficial use routes

Table 2 – Examples of brine treatment technology

Case studies

The first case study presented here compares the application of the presented framework and all three case studies presented demonstrate the development of lessons learnt.  

Coal seam gas (CSG) industry

The coal seam gas industry in Australia, primarily located in southern and central Queensland with planned development in northern New South Wales, is a key export industry for Australia and a significant employer in the regional locations where they operate. To access the natural gas, the coal seam (located several hundred metres deep) needs to be depressurised by pumping the contained groundwater to the surface. The groundwater quality ranges from low to highly brackish water quality (2,000-20,000 mg/L TDS, typically 3,000-6,000 mg/L TDS) and according to the Queensland Government the yearly CSG water production rate from the Surat Basin in Southern Queensland is around 100-200 ML/ day (DERM, 2023). 

Over the last 20 years, the production of brine from the CSG industry has been one of the largest sources of inland desalination brine in Australia and may have resulted in bringing to the surface 5 million tonnes of salt (APPEA, 2018). Therefore, a significant amount of planning and development has been dedicated to mitigating its impacts (UQ, 2020). The authors’ experience of CSG-related water and brine management has been a major influence on the establishment of the Brine Management Framework proposed in this paper. To demonstrate the application of this framework, this paper details each step the CSG industry (with guidance from regulators) has taken to reach its current suite of solutions.

Step 1 – Determine whether desalination is required
Significant effort was made at the initial stages of the CSG industry to ensure that a sustainable water management approach was undertaken (UQ, 2020). Various solutions were explored for direct beneficial use (e.g. livestock watering, salt-resistant crop or tree plantation irrigation, aquaculture, dust suppression etc) and disposal (e.g. release, pond evaporation) to avoid desalination. It was evident that direct release or pond evaporation of CSG water was not acceptable in terms of environmental impact, regulation or social license. Therefore, the majority of CSG groundwater (i.e. medium to high brackish water quality) requires desalination to enable beneficial use due to soil chemistry and crop incompatibility with the untreated water. Generally, a small portion of non-desalinated groundwater can be used for purposes such as:
– Dust suppression locally (most CSG water)
– Livestock watering (low brackish CSG water)
– Crop or tree irrigation (low brackish CSG water with chemical amendment i.e. addition of hardness and sulphate to adjust the sodium adsorption ratio to prevent clay swelling) 

Step 2 – Determine brine composition
Once desalination was determined to be required for the majority of CSG water, the next step was to assess the composition of the brine produced. This is, to a degree, determined by the desalination approach employed, i.e. reverse osmosis (RO) will produce a different brine stream compared to electrodialysis reversal or continuous ion exchange. The two most common CSG industry desalination approaches are standard recovery RO and high recovery RO. High recovery RO typically employs softening (e.g. removal of multivalent metals and divalent hardness) and/or the use of sophisticated antiscalants to prevent membrane scale. The CSG brine chemistry is primarily a mix of sodium chloride and sodium bicarbonate with a small amount of impurities. The softening process removes multivalent impurities which are problematic for beneficial use of brine or salt and are at lower levels for high recovery RO brine. The tools used to determine the brine composition within the CSG industry included desalination process simulation/speciation chemistry modelling (e.g. EVS:Water Designer, OLI Stream Analyzer, PhreeqC) and sample analysis of brine resulting from laboratory trials, pilot trials, or existing desalination plants.

Step 3 – Identify beneficial-use and disposal routes 
A large array of beneficial-use and disposal routes for brine and salt has been investigated by the CSG industry (Brannock et al, 2011). The majority of options investigated are presented in Table 1 and have been investigated to varying levels of detail, ranging from desktop feasibility studies incorporating process simulation / chemistry modelling and Class V cost estimation, to pilot trials used to inform Front End Engineering Design (FEED) and Class II cost estimation and finally implementation. An example of an output from process chemistry modelling is shown in Figure 3, demonstrating that higher value sodium carbonate can be separated from sodium chloride at higher temperatures. 

Figure 3 – Process chemistry modelling examining potential salt recovery (Brannock et al, 2011)

The need to examine a range of beneficial-use and disposal routes has been guided by regulation where, in the case of the Queensland gas industry, a hierarchy for the management of saline waste needs to be followed, which prioritised beneficial use over disposal routes (DES, 2012). A discussion of the selection process and eventual general industry brine management approach is provided in Step 8 (DERM, 2023).  

Step 4 – Determine how to deliver the brine (or salt) to the beneficial-use or disposal route 
Several beneficial-use and disposal routes identified by the CSG industry required a significant amount of treatment, brine minimisation and processing (e.g. selective salt recovery, zero liquid discharge etc) and transport (e.g. transport of salt products to overseas markets, pipeline to the ocean, pipeline to an injection well-field, transport to landfill etc) and were found to be a significant contributor to whole-of-life costs and cost sensitivity (Brannock et al., 2011). The majority of treatment approaches presented in Table 2 were investigated by the CSG industry. 

Step 5 – Removal of disposal and processing / transport options based upon fatal flaws 
To simplify the process of establishing a full brine management solution (i.e. linking together a disposal route and the methods to get there), several options were removed before further analysis by the CSG industry. Many of the treatment / brine minimisation technologies listed in Table 2 were removed due to low technology readiness levels (i.e. not sufficiently mature for the CSG industry timeline). Various disposal options were removed either due to not being technically feasible (e.g. brine injection studies, including large scale trials, did not identify any locations that were technically feasible) or because they were deemed to have significant social licence barriers (e.g. ocean outfall) (UQ, 2020).

Step 6 – Develop brine management strategies 
The CSG industry, from the commencement of the CSG export industry planning stages, with guidance from the Queensland regulators, understood the need to develop a holistic solution for brine that includes ulitmate disposal (or beneficial use) of the salt (UQ, 2020; DES, 2012). 

Step 7 - Evaluate the developed brine management strategies in a holistic manner
The CSG industry has undertaken significant effort evaluating the various brine management strategies with $100M of research and development and strategic planning work having been undertaken (APPEA, 2018). An array of tools and approaches were employed with the majority listed in the Brine Management Framework Step 7 being employed. Selective salt recovery (SSR) (i.e. beneficial use of salt) was deemed to have several issues with the following barriers being cited: lack of proven examples, external SSR consortia unable to provide guarantees and SSR solutions producing significant waste streams requiring disposal (UQ, 2020). Therefore, the current default approach for the industry is to crystallise the salt and encapsulate in a landfill or “salt encapsulation facility” (SEF) (DERM, 2023). Currently most of the salt is stored within large evaporation ponds as brine. As stated, this dissolved salt will be crystallised later and disposed of in a landfill or SEF. Various approaches exist to crystallise the salt including large footprint solar salt pans and thermal crystallisers (Brannock et al., 2011); each has their own advantages and disadvantages. It is anticipated that the SEF approach will not preclude opportunistic salt recovery at a later date.

Step 8 - Prepare a logical and explict brine management plan
Each CSG industry proponent has been required via various regulatory processes to develop and report on their proposed brine management plans (DERM, 2023). A peer review by The University of Queensland (UQ) concludes that the “Queensland CSG industry has undertaken appropriately detailed assessments of the leading brine disposal options” (UQ, 2020). However, it is also stated that although the industry’s selection of SEF is appropriate, it should continue to investigate other management options such as selective salt recovery (DERM, 2023). It is also suggested by the authors of this paper, that implementation of Adaptive Pathways Planning would provide a clear plan to deal with the continued future uncertainty outlined in the UQ report (e.g. What happens if SSR becomes feasible? What happens if SEF crystallisation is very challenging in practice?).

Inland desalination for drinking water (Australia)

Approximately 20 years ago, a township in regional inland Australia was forced to supplement its water supply with desalinated brackish groundwater in response to diminishing yields from their existing water sources (river water and shallow alluvial groundwater) during regular hot dry periods and a growing population. 

This case study has been assembled from publicly available information only (i.e. council and state government tender requests, council budget reports, conference papers, a book subsection and news releases) and demonstrates the common issues that often arise for inland desalination projects, be it desalination for drinking water supply or desalination for the resources sector. In summary, it shows what might occur if not following a robust approach which the Brine Management Framework proposed here attempts to provide. The most common misstep experienced is the lack of a well-defined (possibly well understood) sustainable long term disposal route for the brine or salt thus capturing the entire project cycle. 

The primary brine management approach for this case study is the use of large evaporation ponds to seemingly indefinitely store the RO reject or brine from the desalination plant. The evaporation ponds continue to be intermittently expanded (i.e. additional ponds) and need regular refurbishment (e.g. replacement of liners). It is the authors’ opinion that there is a range of issues that the local council is exposed to due to this approach, including the increasing need for more land (which may become restrictive given its location relatively close to existing development) and the potentially very large end-of-life costs that have not been accounted for (i.e. there is a lack of a publicly stated explicit strategy to manage the salt within the ponds). 

Based on available public information regarding the township’s desalination plant capacity and feed salinity, it is estimated that over 20 years approximately 50,000 tonnes of dry salt will be produced. If salt extraction, processing (e.g. dewatering), transport, landfill gate fee and landfill level were to cost $200-500 per dry tonne (the higher range being more realistic based on recent project experience), the cost every 20 years for salt disposal would amount to $10M to $25M. This salt disposal cost is approximately the same as a new desalination plant of 3-4 ML/d capacity or the cost of approximately 20 hectares of evaporation ponds which were initially built (and expanded since). Further, it is noted that these costs exclude the means of salt production which may require a thermal crystalliser (including pretreatment), or large footprint purpose built solar salt pans in addition to the existing storage ponds. 

The scenario outlined in this case study (i.e. brine management largely limited to evaporation ponds without a disposal route) is not uncommon in Australia or elsewhere and demonstrates the legacy issues that occur in the absence of well-considered brine management planning.

Inland production of PRW (United States)

Several inland townships and cities located in Australia, such as Canberra and Blacktown, are investigating the future potential to augment drinking water sources with purified recycled water (PRW) (ABC News, 2024; Sydney Water; 2025). Although the uptake of PRW in Australia has been slow since the Millenium Drought 20 years ago, it has accelerated in the United States. PRW is now an important source of water for several locations in California, Colorado, Arizona, Nevada, Oklahoma and Texas; outside of California these primarily cover inland locations (see Figure 4). The uptake of PRW is largely driven by drought and population growth but also nutrient discharge limitations (IWA, 2022).

Figure 4 – USA locations using purified recycled water for drinking (WSAA, 2019)

Most PRW plants in the US (similar to Australia) are based on RO which results in a brine stream that is brackish in quality with elevated concentrations of problematic constituents (e.g. nutrients) and emerging contaminants (WRF, 2015). The typical approach for disposing of PRW RO brine at an inland location is local waterway release, which has many challenges with respect to regulations relating to a range of contaminants. This sometimes leads to the need for additional and complicated treatment e.g. in the case of the South East Queensland Bundamba AWTP, moving bed bioreactor (MBBR) is employed to reduce nitrogen nutrient levels. Other approaches such as deep well injection, evaporation ponds with landfill, sewer and land application have largely been ruled out due to technical and cost challenges or have a limited number of scenarios where issues are avoided (e.g. local geological strata that allow high injection rates into a deep well with minimal impact) (WERF, 2015).

Therefore, due to the difficulties and costs associated with disposing of PRW RO brine, including stricter discharge limitations, many utilities are looking towards strategies that do not use reverse osmosis and therefore desalination (WRF, 2020). For PRW at inland locations, US utilities are looking to employ carbon-based advanced treatment (CBAT), such as biologically active filters (BAF) and advanced oxidation. CBAT is not a new technology and has been employed in Namibia’s pioneering direct potable re-use (DPR) programme in Windhoek and has been used in Australia for non-potable purposes (van Leeuwen et al, 2003). In an important move which supports this technology, CBAT has recently been approved for DPR by Colorado’s key regulator for drinking water (WateReuse Colorado, 2023). 

However, a key issue arises for CBAT in that it does not remove the majority of the salinity, which may lead to increasing salinity within the urban water supply and collection system (IWA, 2022). To address this, approaches that involve softening have been proposed to reduce the amount of salinity and prevent the continual cycling up of salts. The waste stream is typically a concentrated (yet smaller volume) ion exchange regenerant liquid waste and/or lime softening sludge depending on the technology employed. This approach reduces the amount of cycling up of salinity in the system but will always result in some increase of drinking water salinity depending on the relative size of the existing non-PRW drinking water treatment plant/s to the PRW plant. Additionally, monovalent ions, which are not removed via softening processes, may also continue to cycle up. Therefore, care needs to be taken in the application of such processes.

This case study describes a scenario where brine and waste management are largely avoided by using an alternative to standard desalination technology. This approach aligns with the Brine Management Framework proposed in this paper i.e. avoid or reduce desalination where possible.

Lessons learnt

Resulting from the collective experience of the authors, covering brine management projects in Australia, the Middle East, South East Asia and the United States, the following selected key lessons learnt are shared to assist future brine management projects:

• The whole-of-life cost of sustainable brine management often challenges the cost of the inland desalination project itself.
• Every brine management project is different due to differing water chemistry, project size and location.
• A brine management project does not finish with the storage of RO reject in evaporation ponds. A long-term sustainable solution is required for the intrinsic salt (i.e. beneficial use or disposal) otherwise the environment and future generations will pay the price.
• A suite of brine management strategies should be progressed to hedge risks. Adaptive Pathways Planning should be used to enable clear planning to deal with future uncertainty.
• High recovery RO (often including pre-softening) is currently the best method to reduce the costs of brine management for scenarios where brine minimisation is required.
• Once recovery limits of RO are reached, the most common technologies are evaporative technologies (e.g. pond evaporation or thermal evaporation), which are typically expensive (often challenges the cost of the RO plant itself).
• Minimising plant recovery can also be beneficial. Whilst it results in larger saline stream volumes, lower salt concentrations, can open up opportunities that would not otherwise be realised (e.g. crop irrigation).
• Deep well injection presents potential in specific locations but requires extensive investigations to derisk and typically significant regulatory hurdles.
• Government often needs to step in to provide regulation (e.g. salt trading scheme such as the Hunter River Salinity Trading Scheme in New South Wales, provide a hierarchy of management practices such as the QLD CSG industry) or incentivisation (e.g. funding) to ensure successful inland desalination and sustainable brine management.
• Beneficial reuse of brine as salt or other products is typically very challenging but should be considered for every project as it sustainably removes the salt risk from the location where desalination takes place. This assumes negligible impact from the salt recovery process itself which also needs to be considered (salt recovery may require significant resources).
• Salt recovery is challenging and expensive for a range of reasons, e.g. the requirement to separate salts and impurities with similar properties, the need to meet high purity specifications, salt markets that are often distant from the brine source requiring transport, local (sometimes distant) salt markets that can be swamped by a nearby source, and many products produced having cheaper and higher purity sources (e.g. lithium salars or spodumene).
• Salt recovery is typically successful if the brine stream is very pure, the market is close by (e.g. onsite production of chemicals) or if there is significant government support (e.g. Debiensko coal mine NaCl recovery etc.) (Ericsson and Hallmans, 1996).
  
  

Conclusion

Inland desalination has only occurred at a reasonable scale within the last 20 to 30 years, in Australia, the United States or elsewhere. We are yet to fully experience or understand the long-term cumulative effects of inland brine management. The impact of inadequate brine management may also exacerbate as inland groundwater desalination and production of purified recycled water (typically using RO) are predicted to increase in the coming decades due to a combination of traditional water source degradation and population growth. Therefore the detailed Brine Management Framework, case studies and the lessons learnt presented in this paper are intended to enable more efficient selection and comparison of sustainable brine management strategies.

The Authors

Dr Matthew Brannock
Matthew Brannock has 25 years of experience in the design of PRW, desalination & brine management systems within engineering consulting & academia. He has worked on brine projects for water utilities and energy and resource sector companies. Solutions covered high recovery RO, thermal concentration and crystallisation, salt recovery, brine injection, co-disposal, landfill etc

Daniel Visser
Daniel Visser is a Chartered water treatment engineer with experience encompassing planning, design and modelling, construction and commissioning advice, and troubleshooting for the municipal, mining, oil & gas, hydrogen and other sectors. He has experience with many technologies which for desalination projects includes reverse osmosis (SWRO, BWRO, HERO), electrodialysis and thermal desalination.

David Reynolds 
David is a process engineer with 10 years of experience specialising in advanced water and wastewater treatment including industrial applications covering CSG, energy, mining, desalination, brine, F&B and PFAS/PFOA remediation. He has extensive knowledge of RO and membrane systems in terms of undertaking performance testing and autopsies. David has worked with major desalination plants across Australia. 

Kieran Mitchell
Kieran has over 18 years in both water treatment and minerals processing industries covering both design and operational process roles. Kieran has recently lead projects focussing on desalination, demineralisation and cooling water for hydrogen production facilities along with treatment and management of brine and wastewater from CSG and industrial operations.

References