Elsevier

Science of The Total Environment

Volume 657, 20 March 2019, Pages 1343-1356
Science of The Total Environment

Review
The state of desalination and brine production: A global outlook

https://doi.org/10.1016/j.scitotenv.2018.12.076Get rights and content

Highlights

  • Unconventional water resources are key to support SDG 6 achievement.

  • Desalinated water production is 95.37 million m3/day.

  • Brine production and energy consumption are key barriers to desalination expansion.

  • Brine production is 141.5 million m3/day, 50% greater than previous estimates.

  • Innovation and developments in brine management and disposal options are required.

Abstract

Rising water demands and diminishing water supplies are exacerbating water scarcity in most world regions. Conventional approaches relying on rainfall and river runoff in water scarce areas are no longer sufficient to meet human demands. Unconventional water resources, such as desalinated water, are expected to play a key role in narrowing the water demand-supply gap. Our synthesis of desalination data suggests that there are 15,906 operational desalination plants producing around 95 million m3/day of desalinated water for human use, of which 48% is produced in the Middle East and North Africa region. A major challenge associated with desalination technologies is the production of a typically hypersaline concentrate (termed ‘brine’) discharge that requires disposal, which is both costly and associated with negative environmental impacts. Our estimates reveal brine production to be around 142 million m3/day, approximately 50% greater than previous quantifications. Brine production in Saudi Arabia, UAE, Kuwait and Qatar accounts for 55% of the total global share. Improved brine management strategies are required to limit the negative environmental impacts and reduce the economic cost of disposal, thereby stimulating further developments in desalination facilities to safeguard water supplies for current and future generations.

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.

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