ReviewThe state of desalination and brine production: A global outlook
Graphical abstract
Introduction
Rising water demands associated with population growth, increased water consumption per capita and economic growth, coupled with diminishing water supplies due to climate change and contamination, are exacerbating water scarcity in most world regions (Richter et al., 2013; Djuma et al., 2016; Damania et al., 2017). Recent estimates suggest that 40% of the global population faces severe water scarcity, rising to 60% by 2025 (Schewe et al., 2014). Furthermore, 66% of the global population (4 billion) currently lives in conditions of severe water scarcity for at least one month per year (Mekonnen and Hoekstra, 2016). These statistics demonstrate that “conventional” sources of water such as rainfall, snowmelt and river runoff captured in lakes, rivers, and aquifers are no longer sufficient to meet human demands in water-scarce areas. This is in direct conflict with Sustainable Development Goal (SDG) 6, aimed at ensuring the availability of clean water for current and future generations.
Water-scarce countries and communities need a radical re-think of water resource planning and management that includes the creative exploitation of a growing set of viable but unconventional water resources for sector water uses, livelihoods, ecosystems, climate change adaptation, and sustainable development (Qadir, 2018). Whilst water demand mitigation approaches such as water conservation and improved efficiencies can somewhat close the water demand and supply gap, these approaches must be combined with supply enhancement strategies in order to combat water scarcity (Gude, 2017). Such water resources conservation and supply enhancement strategies are already practiced in some water-scarce areas. However, expansion is required, particularly in areas where water scarcity and water quality deterioration is intensifying (van Vliet et al., 2017; Jones and van Vliet, 2018).
Among the water supply enhancement options, desalination of seawater and highly brackish water has received the most consideration and is increasingly seen as a viable option to meet primarily domestic and municipal needs. Desalination is the process of removing salts from water to produce water that meets the quality (salinity) requirements of different human uses (Darre and Toor, 2018). Seawater desalination can extend water supplies beyond what is available from the hydrological cycle, providing an “unlimited”, climate-independent and steady supply of high-quality water (Elimelech and Phillip, 2011). Brackish surface and groundwater desalination offers reductions in the salinity levels of existing terrestrial freshwater resources below sectoral thresholds (Gude, 2017).
The uptake of desalination has been substantial, but limited predominantly to high income countries (e.g. Saudi Arabia, UAE, Kuwait) and small island nations (e.g. Malta, Cyprus) with highly limited ‘conventional’ water resources (e.g. rainfall, snowmelt). However, reductions in the economic cost of desalination associated with technological advances, coupled with rising costs and the diminishing supply and security of “conventional” water resources, have made desalination a cost-competitive and attractive water resources management option around the globe (Ghaffour et al., 2013; Sood and Smakhtin, 2014; Caldera and Breyer, 2017; Darre and Toor, 2018). Nowadays, an estimated 15,906 desalination plants are currently operational, located in 177 countries and territories across all major world regions.
Realising the vast potential of desalinated water remains a challenge due to specific barriers, predominantly associated with the relatively high economic costs and a variety of environmental concerns (e.g. Einav et al., 2002; Roberts et al., 2010; Richter et al., 2013; Darre and Toor, 2018). Continued improvements in membrane technologies, energy recovery systems and coupling desalination plants with renewable energy sources provide opportunities for reducing the economic costs of desalination (Elimelech and Phillip, 2011; Pinto and Marques, 2017; Darre and Toor, 2018), whilst trends towards stricter environmental guidelines and permitting factors may cause the falling trend in desalination costs to slow, level off or reverse (Pinto and Marques, 2017). Regardless, continued reductions in the economic costs of desalination will be required for desalination to be considered a viable option for addressing SDG 6 in low income countries. Detailed evaluations of the challenges and opportunities associated with the economics of desalination are provided by Ghaffour et al. (2013) and Pinto and Marques (2017).
The safe disposal of effluent produced in the desalination process remains a particular concern and a major technical and economic challenge (Roberts et al., 2010). The desalination process separates intake water into two different streams – a freshwater stream (product water) and a concentrate waste stream (Wenten et al., 2017). The salinity of the concentrate stream depends on the salinity of the feedwater. As the vast majority of concentrate is produced from saline water (>95% from SW and BW sources), the term ‘brine’ is used throughout this paper. However, it should be noted that desalination plants operating with low saline feedwater types (e.g. RW, FW) produce concentrate with a lower salinity than typically associated with the term ‘brine’.
A desalination plant water recovery ratio (RR), defined as the volumetric processing efficiency of the purification process (Harvey, 2008), indicates the proportion of intake water that is converted into high quality (low salinity) water for sectoral use. The remaining water (calculated as (1 − RR)) is the proportion of intake water being converted into a waste (brine) stream, which requires management. For example, a desalination plant operating with a recovery ratio of 0.4 means that 40% of intake water is converted into product water, and by extension 60% of intake water is converted into brine. The RR of a desalination plant is dependent on and controlled by a number of factors (Xu et al., 2013). Different desalination technologies are associated with variations in RR, with membrane technologies typically associated with a much higher RR than possible with thermal technologies (Xu et al., 2013). The feedwater quality is also important, with it being much more difficult (and expensive) to operate desalination plants at a high level of water recovery when the feedwater salinity is high (Harvey, 2008).
With the aim of providing a global assessment of the research and practice around desalination, the objectives of this study are to: (1) share an insight into the historical development of desalination; (2) provide a state-of-the-art outlook on the status of desalination, considering the number of desalination facilities and their associated treatment capacity with regards to aspects such as geographical distribution, desalination technologies, feedwater types and water uses; and (3) assess brine production from desalination facilities and the management implications of the produced brine. This study therefore seeks to update the literature on the state of desalination in both research and practice, which is outdated. Furthermore, this study makes the first comprehensive quantification of the volume of brine produced by desalination facilities, employing a novel methodology that considers the efficiency of desalination plants based on both their operating technology and the feedwater type.
Section snippets
Desalination in research
A bibliometric analysis was conducted to evaluate the major research trends in the field of desalination. The Science Citation Index Expanded (SCI-EXPANDED) from the Web of Science Core collection was used for the time period 1980 to 2018. This study firstly categorises desalination publications based on major research theme (‘technology’, ‘environment’, ‘economic and energy’ and ‘social interests’). Subsequently, considering the ‘technology’ category, trends in research on specific
Research trends in desalination
Trends in the research history of desalination are displayed in Fig. 1. Approximately 16,500 publications were found to have been produced on the topic of desalination since 1980. Research in desalination has grown exponentially, with the total number of publications approximately doubling with each five-year period (e.g. ~5000 in 2010 to ~11,000 in 2015). The large majority of publications focus on technological aspects of desalination (e.g. 75% in 2005). As such, desalination literature
Discussion
Owing to recent, rapid developments in desalination research, the last comprehensive assessment (Tanaka and Ho, 2011) available in the academic literature is outdated. This study presents statistical analysis of the scientific literature covering an array of desalination topics since 1980, addressing a diverse range of social and technical aspects with respect to publication date, revealing patterns in publishing trends. Our findings suggest that research in desalination has increased
Conclusions & outlook
Against the backdrop of increasing global water scarcity, desalinated water is increasingly becoming a viable option to narrow the water demand-supply gap, particularly in addressing domestic and municipal needs. Desalinated water can substantially extend the volume of high-quality water supplies available for human use. A steady and assured supply of high-quality water is crucially important in an era when the world at large is embarking on the Sustainable Development Agenda to ensure access
Acknowledgements
This work is part of the UNU-INWEH's project on Unconventional Water Resources. UNU-INWEH is supported by the Government of Canada through Global Affairs Canada. Michelle van Vliet was financially supported by a Veni-grant (project no. 863.14.008) of NWO Earth and Life Sciences (ALW).
Conflicting interests
The authors declare no conflict of interest.
References (89)
- et al.
Brine disposal from reverse osmosis desalination plants in Oman and the United Arab Emirates
Desalination
(2001) - et al.
Brine utilisation for cooling and salt production in wind-driven seawater greenhouses: design and modelling
Desalination
(2018) - et al.
Developments in high recovery brackish water desalination plants as part of the solution to water quantity problems
Desalination
(2003) - et al.
Concentration of brines from RO desalination plants by natural evaporation
Desalination
(2005) - et al.
Performance and cost estimation of nanofiltration for surface water treatment in drinking water production
Desalination
(2006) - et al.
Preliminary results of the monitoring of the brine discharge produced by the SWRO desalination plant of Alicante (SE Spain)
Desalination
(2005) - et al.
Short-term effects of SWRO desalination brine on benthic heterotrophic microbial communities
Desalination
(2017) - et al.
Impact of the brine from a desalination plant on a shallow seagrass (Posidonia oceanica) meadow
Estuar. Coast. Shelf Sci.
(2007) - et al.
Technical review and evaluation of the economics of water desalination: current and future challenges for better water supply sustainability
Desalination
(2013) - et al.
Brine management methods: recent innovations and current status
Desalination
(2017)
Reverse osmosis desalination: water sources, technology, and today's challenges
Water Res.
Acid and base recovery from softened reverse osmosis (RO) brines. Experimental assessment using model concentrates
Desalination
Drought impacts on river salinity in the southern US: implications for water scarcity
Sci. Total Environ.
Assessment of desalination technologies for treatment of a highly saline brine from a potential CO2 storage site
Desalination
Economic analysis of desalination technologies in the context of carbon pricing, and opportunities for membrane distillation
Desalination
Being “green” in chemical water treatment technologies: issues, challenges and developments
Desalination
A 13.3 MGD seawater RO desalination plant for Yanbu Industrial City
Desalination
Electrodialysis of brine solutions discharged from an RO plant
Desalination
Operation and reliability of very high-recovery seawater desalination technologies by brine conversion two-stage RO desalination system
Desalination
Concentrating brine from seawater desalination process by nanofiltration–electrodialysis integrated membrane technology
Desalination
Pressure-driven membrane operations and membrane distillation technology integration for water purification
Desalination
The end of scarcity? Water desalination as the new cornucopia for Mediterranean Spain
J. Hydrol.
Seawater desalination for crop irrigation—a review of current experiences and revealed key issues
Desalination
Energy and greenhouse-gas emissions in irrigated agriculture of SE (southeast) Spain. Effects of alternative water supply scenarios
Energy
Techno-economic assessment and environmental impacts of desalination technologies
Desalination
Impact of land disposal of reject brine from desalination plants on soil and groundwater
Desalination
Comparative study of brine management technologies for desalination plants
Desalination
Pretreatment options for large scale SWRO plants: case studies of OF trials at Kindasa, Saudi Arabia, and conventional pretreatment in Spain
Desalination
Practice of water desalination by electrodialysis
Desalination
Desalination projects economic feasibility: a standardization of cost determinants
Renew. Sust. Energ. Rev.
Impacts of desalination plant discharges on the marine environment: a critical review of published studies
Water Res.
Uses of the reject brine from inland desalination for fish farming, Spirulina cultivation, and irrigation of forage shrub and crops
Desalination
Emerging desalination technologies for water treatment: a critical review
Water Res.
Desalination of brackish river water using Electrodialysis Reversal (EDR): control of the THMs formation in the Barcelona (NE Spain) area
Desalination
Physical water scarcity metrics for monitoring progress towards SDG target 6.4: an evaluation of indicator 6.4. 2 “level of water stress”
Sci. Total Environ.
Overview of seawater concentrate disposal alternatives
Desalination
Reverse osmosis applications: prospect and challenges
Desalination
Optimization of seawater RO systems design
Desalination
Development of lower cost seawater desalination processes using nanofiltration technologies—a review
Desalination
High water recovery with electrodialysis reversal
Impact of brine disposal from EMU desalination plant on seawater composition
Environmental assessment of brine discharge including wastewater collection in the Arabian gulf
Environmental effects of brine discharge from two desalination plants in Algeria (South Western Mediterranean)
Desalin. Water Treat.
Evaluation of a sequential biological concentration system in natural resource management of a saline irrigated area
Aust. J. Water Resour.
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