Maintaining access to a sustainable water resource is becoming increasingly difficult in the midst of the ongoing global water crisis, emphasizing the importance of investing in alternative resources such as desalinated water. Throughout history, the desalination industry has adapted to the specific needs of an era or different environmental conditions by incorporating cutting-edge technologies. The general theme of this paper is the past, the present, and the future of the desalination industry. As such, this research aims to examine the evolution of the desalination industry over time, understand its current state, and ultimately use this knowledge to highlight some important considerations for its future. This review highlighted the immense influence of the energy market on the prevalence of desalination technology in a given region and/or eras. The information gathered here indicates that other sectors, such as agriculture, may need to rely on this unconventional water supply in the future, but there are certain factors ranging from socioeconomic to environmental concerns that need continued and increased research to facilitate the long-term, sustainable development of this practice.
This study reviews the desalination industry's evolution over time, understands its current status, and depicts what could potentially be the future of this industry.
The prevalence of desalination technology in a given region or era is heavily influenced by the energy market, and other sectors such as agriculture may need to rely on it in the future, but further research is required to ensure its sustainable development.
Although the modern interpretation of desalination technology, at least within the context of global water resources management, is a topical subject with unexplored angles, the core idea behind this technology is by no means new or novel per se. As a matter of fact, this technology has been utilized in some capacity throughout the entirety of human history worldwide (Angelakis et al. 2021). As our needs evolved, desalination technology had to adapt accordingly. As a result, this technology has gone through an evolutionary process to best cater for these new, more intricate, and demanding water requirements.
Historically speaking, an attempt to desalinate water, as in separating the dissolved minerals and most notably salt from the water, had two general purposes; one being to salvage and extract the said minerals for their monetary values, and the other being to gain access to water resources with markedly better quality. Given the context of this paper, we exclusively explore the latter situation. As such, the term desalination, from this point onward, should reflect solely on this idea unless explicitly stated otherwise.
Amid the water crisis, primarily affecting semi-arid to arid regions, incorporating desalinated water to augment exhausted available resources has gained more traction in recent years, most notably in regions struggling with conventional water security (Ashraf et al. 2022; Tan et al. 2022). This paper reviews the rich history behind the desalination industry, glances at the current status of desalination, and briefly explores the contemporary technologies that are being used in modern desalination units. Lastly, the paper delves into the potential role of this industry in the grand scheme of water resources management. Our main objective is, through unveiling the evolution and current status of desalination technology, to gain a deeper understanding of how it can be utilized as a remedy to offset the ongoing water crisis.
AN OUTLOOK ON THE HISTORY OF THE DESALINATION INDUSTRY
Desalination has a long and illustrious history, with variants of this technology found in some of human history's earliest civilizations. Historians, for instance, have reasons to believe that Minoan sailors, the Bronze Age Aegean civilization in the Mediterranean, implemented the earliest crude adaptation of desalination idea in recorded history as early as 3200 BC to 1100 BC (Angelakis et al. 2021). In the East, reasonable evidence made historians speculate that the Persian Empire had been incorporating desalination in what is believed to be one of the oldest water supply networks in recorded history (Saatsaz 2020; Angelakis et al. 2021).
Just as significantly, these early primitive applications contributed to the discovery of some of the fundamental principles of desalination. The famous remarks attributed to the renowned Greek philosopher Aristotle (384–322 BC) are arguably the first recorded milestones to capture the true nature of salinated water in a theoretical sense (Kucera 2019; Angelakis et al. 2021). Not only was he able to capture the bare essence of desalination in the statement, ‘… salt water, when it turns into vapor, becomes sweet and the vapor does not form salt water again when it condenses’, he also noted that such transformation requires an exogenous driver when he wrote, ‘… the sun causes the moisture to rise; that is like what happens when water is heated by using fire’.
Despite the technological limitations of early civilizations, early applications of desalination allowed these communities to effectively expand their exploration horizons. For example, sailors used a primitive variation of desalination technology for centuries to avoid the problem of a lack of water supply on long voyages. A notable example is the Aphrodisias sailors, who resorted to heating seawater poured into brass vessels and used suspended sponges to absorb the evaporated water for later use around 200 AD (Kalogirou 2005). In fact, from the 15th to the 19th centuries, this practice persisted in maritime transport and was modified by acclimated individuals such as Sir Richard Hawking and Thomas Jefferson (Kucera 2019; Angelakis et al. 2021). It should be noted, however, that each ancient civilization had devised creative ways to implement the idea of desalination to make it more compatible with their unique environmental conditions. For generations, farmers on the northern coast of China, who faced dry and cold winters where the temperature could go well below zero, implemented an ingenious idea of directly introducing sea ice to their irrigation practice to help maintain the soil moisture (Angelakis et al. 2021). This could be the earliest primitive demonstration of what became known as cryo-desalination or freeze desalination (FD), a form of desalination that was formalized theoretically by the Danish physician Thomas Bartholin in 1680 (El Kadi & Janajreh 2017; Najim 2022).
It could be argued that the industrial revolution paved the way for the advent and, in turn, the prevalence of what can be seen as the modern era of desalination. The revolutionary tectonic technological shifts in the said period provided the means to implement this idea on a large-enough scale that would also be economically enticing. In fact, within the same time frame, the French physicist, Jean-Antoine Nollet, recognized for the first time the osmosis effect, a phenomenon upon which most state-of-the-art modern desalination facilities are built (Angelakis et al. 2021).
Although vague and contradictory information often makes it impossible to pinpoint some of the milestones in the history of desalination, many scholars believe that the world's first commercial traditional thermal desalination plant was built in Sliema, Malta, around 1881 (Tan et al. 2022). Similar establishments have been documented around the same time in Latin America, most notably on the Pacific coast of Peru, Bolivia, and Chile (Gabbrielli 2013). From the practical side of things, though, it was not until the late 1920s that we could see a drastic leap in the desalination industry. In 1928, however, the world's first land-based distillation plant, an elementary thermal desalination unit, was built in Curaçao, Netherlands Antilles (Brewster & Buros 1985; Lattemann et al. 2010). Working at full capacity, the said facility was to provide 60 m3/day of desalinated water for drinking purposes (Ophir 1991). By the early 1930s, Saudi Arabia also saw the potential in desalination and, in turn, started to invest in some of the earliest multi-effect distillation plants in the world (Reddy & Ghaffour 2007; Bharadwaj et al. 2008).
The need to access a reliable and stable water source in remote arid regions became an absolute priority during the Second World War. As such, this challenge was a driving force to push the industry to transform desalination into a convenient solution to the challenge of water scarcity, at least for drinking and potable water requirements. During this period and up until the 1980s, thanks to legislative movements such as the saline water act, the United States established its role as a leading pioneer for this technology as it started to invest considerable public funding to study, explore, and advance the general practice of desalination (Cywin & Finch 1960; Kucera 2019). Due to the rapid progress in the desalination industry at that time, the Middle Eastern nations, in particular, were quick to recognize the potential of this technology to remedy their notorious water scarcity issues. For instance, Qatar commissioned a desalinated plant in 1954 (Boussaa 2014). The first multistage flash (MSF) distillation plant was built in Kuwait, another Middle Eastern nation, around 1957 (Al-Wazzan & Al-Modaf 2001).
By the 1960s, European nations with water scarcity started to entertain the idea of incorporating desalinated water to meet their ever-increasing demand in the municipal sector. Spain was the first nation to commit to this technology by building the first desalination plant in Europe and 24th in the world in 1964 (Gómez-Gotor et al. 2018; Villar-Navascués et al. 2020). The said plant was installed in Lanzarote, the Canary Islands, as a mechanism to cope with the region's arid climate. By the 1970s, more desalination plants were gradually added to the water supply network of the island. However, at that point in time, the primary purpose of desalination was to address domestic water demands (Zarzo et al. 2013). In 1987, however, the strategic importance of the agriculture industry paved the way for installing the first desalination plant in the islands solely dedicated to providing water for irrigation purposes (Martínez-Alvarez et al. 2016). This transition toward incorporating desalination in the water management schemes, perhaps out of necessity, slowly but surely took over the world, to the point that by the 1990s implementing desalination to meet municipal demands practically became a common practice in most water-challenged regions (Lattemann et al. 2010).
For the most part, the desalination industry underwent a series of technological advancements from the mid-1960s to the late 1980s. The most notable milestone in this chronicle evolution is the installment of the first commercial desalination plant in California that incorporated reverse osmosis (RO) technology in 1965 (Glater 1998; Kucera 2019). Though the idea has evolved immensely ever since, to this day, state-of-the-art RO technology remains one of the most efficient viable options to practice desalination on a large scale.
Gradually, desalination became an unconventional yet, formidable alternative water resource worldwide. As such, over the years, different nations, especially those with a history of water shortage problems, came on board with incorporating desalination in their general water management schemes. For instance, Israel, a country that constantly dealt with water deficit, installed their desalination plant to meet the ever-increasing municipal and agricultural demands in 1965 (Martínez-Alvarez et al. 2018). The Philippines is another example where desalination has been used since 2002, initially to support the needed feedwater for the power plants (Tan et al. 2022). Singapore, another region with notorious water availability challenges that had long relied on water imports from its neighboring country, Malaysia (Zolghadr-Asli et al. 2017), installed its first desalination plant in late 2005 (Tortajada 2006). In Algeria, currently the fastest growing desalination market in North Africa, the first seawater RO desalination plant came in line in 2008 (Lattemann et al. 2010).
A GLANCE AT THE CURRENT STAGE OF DESALINATION TECHNOLOGY
It should be noted that different technologies take different approaches to carrying out the desalination practice. While the end goals of these technologies are similar, there are notable differences between these technologies, such as in terms of the average energy consumption, the quality of intake and output water, and compatibility with different energy resources. How these technologies operate would determine why some stayed relevant over time and perhaps how the new alternatives are gaining more traction.
One of the most prominent practices in this industry is thermal desalination technology. The core idea behind thermal desalination is relatively simple; introducing thermal energy to the saline water would eventually turn it from a liquid to a gas stage. The most notable technologies that can be categorized as thermal desalination are multi-effect desalination (MED), MSF desalination, and vapor compression (VC) (e.g., mechanical vapor compression (MVC) and thermal vapor compression (TVC)).
The earliest commercial implementation of desalination was through MED. The desalination system is partly composed of effectively similar modules, in each of which the saline feedwater comes to contact with a series of heating tubes. As a result of this interaction, the water would transform into a gas stage. The vapor would then be used as an additional heating agent for the next module, enhancing the system's overall efficiency, as less heating needs to be induced to vaporize the saline water in the said stage. Modern MED plants typically have 8–16 modules (Shatilla 2020). Currently, the maximum capacity of MED units is approximately 15 MIGD (million imperial gallon per day), which equates to 68,190 m3/day (Al-Mutaz & Wazeer 2015; Scotney & Pinder 2022). The outlet water of each stage would be passed to the next module until, eventually, most water would be desalinated through evaporation, and the residual water from the last module would be considered brine. The main issue with MED is the fouling and scaling, which can be minimized with lower temperature evaporation (Shatilla 2020).
Due to the said issues, from the late 1950s to the early 1960s, contemporary commercial desalination plants moved toward implementing the idea of MSF desalination (Kucera 2019). As the name suggests, similar to MED, MSF also consists of a set of stages. Each stage is, in effect, a chamber that suddenly drops the ambient pressure as the heated desalinated saline feedwater passes through, allowing the water to evaporate instantaneously. This process is called flashing, which the technology is named after. Each stage's outlet water is passed to the next at progressively lower pressures without adding extra heat. Modern MSF desalination plants typically have a primary heating chamber with additional 20–30 stage modules (Shatilla 2020). The total maximum capacity of these units is currently around 20 MIGD, which equates to 91,000 m3/day (Darwish 2014; Dehghan et al. 2022). While the vaporized water would be condensed into fresh water, the by-product of the last stage would be passed as the brine. One of the most notable differences between the MED and MSF desalination plants is the feedwater temperature required by these systems. The former technology operates at a relatively lower temperature (∼65–70 °C) compared to the latter case, where the usually higher temperature is required for the system to operate efficiently (∼90–110 °C). As such, MSF has often been considered a more energy-demanding desalination technology than MED (Baten & Stummeyer 2013). On the other hand, the fouling issue is less pronounced in MSF desalination plants, and the operation can be executed with minimum pretreatment requirements (Shatilla 2020). All in all, the high capital cost and energy requirements of MSF desalination plants notwithstanding, this is considered less complicated to operate compared to its predecessor, MED technology (Baten & Stummeyer 2013; Shatilla 2020).
Another thermal desalination technology that is primarily implemented in small- to medium-scale units is VC desalination. The idea behind this technology is rooted in the fact that gas compression would increase its pressure and temperature. As such, it is technically possible to utilize the latent heat rejected during condensation to generate additional vapor. In practice, there are two main approaches to implementing this technique for desalination, namely, MVC and TVC. The former units typically have a capacity within the 250–2,500 m3/day range, while the latter has a 500–20,000 m3/day range (Shatilla 2020). Thus far, this technology has yet to be commercially implemented in a larger-scale desalination process, such as in MED and MSF technology.
As a side note, it is worth remembering that corrosion of the carbon steel pipelines was a major concern for a long time when it came to thermal desalination units that worked with seawater. Consequently, until the early 1980s, thicker materials were used in MSF units to compensate for this issue, resulting in larger and heavier units. Introducing the stainless and duplex stainless steel, which in effect reduced the risk of corrosion substantially, allowed the construction of much lighter and smaller MSF units (Kucera 2019). It should be noted that by the 1980s, a revived interest in MED technology was reported, which can be primarily attributed to the lower operational costs of this technology compared to MSF units (Martínez-Alvarez et al. 2016, 2018).
Another practical approach to desalination is through a phenomenon technically referred to as the membrane process. The core idea behind the membrane process is to enforce the transport of a substance, say water, through permeable membranes against the potential gradient. Although the concept of the membrane process has been around since the mid-18th century, it was not until the 1950s that researchers started to use this idea and demonstrate its application using polymeric membranes. In the context of desalination, to this day, there are three known practical ways to enforce the membrane process, namely, pressure-driven, using an electric potential gradient, and finally, using a temperature gradient. Some of the most notable membrane process-based desalination units are RO, electrodialysis (ED), membrane distillation (MD), and FD.
By the late 1960s and the early 1970s, RO, a pressure-driven membrane process, started to show promising results as the next commercially viable option to replace traditional thermal desalination units (Lattemann et al. 2010). By the 1980s, sporadic and incremental improvements of the RO units, which mainly focused on enhancing the membranes' flux, rejection, and operating pressure requirements, turned RO into one of the most efficient technologies available for desalination. Although, from a practical standpoint, no major breakthrough has happened regarding the RO units (e.g., higher membrane selectivity with higher water flux and chlorine tolerance), ongoing research on incorporating nanotechnology (e.g., nanocomposite membranes) shows theoretical promise for the next generation of membranes (Palmer 2015; Kucera 2019; Sahu et al. 2023).
Another contemporary membrane-oriented desalination technology introduced in the early 1960s was the ED process. Though ED, a membrane process that is driven by the electric potential gradient, showed great potential when it comes to desalinating low brackish water, the energy consumption of the said units is far too great for them to be commercially viable to handle seawater treatments (Lattemann et al. 2010). An example of a thermally driven membrane process is MD. Though a promising technology, thus far, the application of this technology in practice has been limited to small- to mid-scale pilot studies and laboratory-limited studies (Zare & Kargari 2018).
Another notable available technology for desalination is freeze-thaw desalination (Mao et al. 2023). Freeze-thaw desalination, also known as cryo-desalination or simply FD, is the process of excluding dissolved minerals from saline water through crystallization (Zambrano et al. 2018). Though the theoretical energy requirement of FD units is markedly lower than other alternative options (Ghalavand et al. 2015), and the risk of corroding pipelines are practically negligible (Williams et al. 2015), the costs of scaling this technology for practical uses is not reasonable yet (Babu et al. 2018; Montazeri & Kolliopoulos 2022). It is also worth noting that recent development in a hybrid electrochemical-based membrane, such as an ion exchange membrane, shows promising results for cost-effectively removing boron when combined with RO units (Jacob 2007; Swanckaert et al. 2022).
WHAT HOLDS FOR THE FUTURE OF THE DESALINATION INDUSTRY
As to where the desalination industry is headed in the future, one can, of course, only speculate, but based on how the technology has improved over the years, it would not be far-fetched to expect this technology to be one of the main ideas to augment water resources at least in regions that are now experiencing or are expected to battle with pronounced water scarcity issues. This argument stands to reason as it is in line with the growth rate of the desalination industry depicted in Figure 2. Obviously, continuation of this growth trajectory would rely heavily on various external and environmental factors and, as such, can and should be explored from different angles. That said, one cannot bring up desalination and not mention the economic aspect of this technology which, for the most part, is itself tied to the situation in the energy market, as this is, by nature, an intensive energy-driven technology. In the grand scheme of things, the energy market has proven to be inherently a volatile market (Salisu & Adediran 2020), and such energy market fluctuations can have notable impacts on the acceptability of this resource both in short- and long-term frames, as was the reported case in the Middle East around the mid-2010s. Based on available data, the rapid expansion of the desalination industry experienced a mild, temporary hiccup sometime around 2016, which, at least for a part, contributed to the downtrend in the oil market and how that negatively influenced the projected revenues in regions that relied heavily on these markets (Kucera 2019).
That said, renewable energy has become a viable option from the practical side to replace conventional energy resources. As such, over the years, it has secured a more significant portion of the energy market. In fact, from 2007 onward, renewable energy resources showed a steady monotonic upward trend, to the point that in 2019, they accounted for 26.49% of the world's total electricity generation (IEA 2021). This ongoing development in the energy market landscape could profoundly impact the desalination industry, as more countries could turn to this more environmentally friendly resource to fuel the desalination process. Saudi Arabia, for instance, made a conscious attempt to move toward powering desalination plants with renewable energy resources. In that spirit, they commissioned the construction of the world's first full-size solar-powered seawater desalination plant in 2015 (DeNicola et al. 2015), a project that has been up and running since late 2017. Australia is another notable example that has been working on a pilot case in Garden Island, south of Perth in Western Australia, to use a wave energy system for powering a desalination plant (Palmer 2015). From the environmental perspective, this switch could have huge implications as it can indicate a potential reduction in this practice's greenhouse gas (GHG) emissions. All that said, the answer to how relevant the overall costs of desalination would be in the acceptance and prevalence of this practice would be determined more than anything in a case-by-case situation. However, as the water shortage becomes a more pronounced and common phenomenon worldwide, it is plausible that the market value of conventional water resources would be affected to the point that desalinated water could be potentially perceived as a more economically viable alternative.
The environmental impacts of seawater desalination units, like those of any other variation of wastewater treatment (Jokar et al. 2021), present pressing concerns that have been extensively studied and monitored over the years (Nasrollahi et al. 2023). One of the inherent challenges of desalination, for example, is the effective disposal of the by-product. The by-product can be brine water (concentrated seawater) and/or sludge, depending on the quality of the intake water and the technology used. Thermal and membrane-based desalination units produce brine. Sludge discharge is much smaller in volume and is mostly associated with RO units. Improper brine disposal can cause a variety of environmental issues, potentially endangering marine ecosystems such as seagrass meadows or benthic populations (Pistocchi et al. 2020). However, the severity of these issues varies from case to case, to the point where it can even be considered negligible in certain circumstances (Lattemann et al. 2010; McEvoy & Wilder 2012). Another notable environmental-related issue, particularly for thermal desalination, is rising seawater temperature near discharge zones (Kucera 2019). Needless to say, maintaining a sustainable practice that would secure the future of desalination technology would rely on mitigating and, ultimately, compensating for the impact by making environmental improvements/protections at other locations.
The advancement of desalination technology is another important factor that could ultimately shape the future of this industry. For the most part, however, this has not been a drastic and fast change, as the core technology in most modern desalination plants has stayed relatively similar since the late 1960s. In fact, most progress in the desalination industry can be described as a steady shift toward upgrading outdated desalination plants with state-of-the-art technologies such as RO desalination units. As of now, thermal desalination is the most common approach in the Middle East region, where energy prices are relatively reasonable (Kucera 2019). RO units, however, are expected to become the standard desalination practice in the future (Tan et al. 2022), which, as a more energy-efficient technology, can be seen as a making a positive contribution to global energy consumption. In the meantime, energy recovery devices (e.g., isobaric chambers and positive-displace pumps) and regular maintenance can be viable, practical options to maintain or even decrease the energy consumption and, in turn, offset the overall cost of desalination (Leon et al. 2021). Incorporating stem technologies, such as nanotechnology and nanocomposite membrane, is also a promising future direction, though thus far, scaling up these technologies to generate a commercially viable flux still pose some practical challenges (Palmer 2015; Kucera 2019).
In recent years, the desalination industry has grown steadily and gained traction as a source of unconventional water supply. If current trends continue, a tectonic shift may be on the horizon for various sectors that use or could benefit from desalinated water. Of course, the continuation of this trajectory, both on a global and local scale, is heavily dependent on a variety of factors. However, if programs such as AGUA in Spain and Israel's desalination master plan are any indication, other sectors in dry regions, particularly irrigated agriculture, may have no choice but to rely on desalinated water to deal with water deficit issues. However, this idea may bring to light new angles or amplify the negative effects of this practice. One of the most notable aspects of this would be the long-term effects of this practice on the environment, such as marine ecosystems and soil structures, as well as the agronomic effects, such as crop yield and quality, should the agriculture industry begin using desalinated water for irrigation. These are critical issues that require further investigation, possibly on a case-by-case basis. The overall cost of desalination is another factor that could continue to stymie the industry's growth. While the cost of desalinated water for domestic and municipal water demands can justifiably be offset through measures such as subsidies, for the most part implementation of desalinated water requires a clear economic justification. Although some industries are profitable enough to bear such high costs, the potential uses of desalinated seawater in agriculture and many other industries are currently very constrained. However, as access to traditional water resources becomes increasingly difficult, the idea of using desalinated water in other sectors has grown in popularity in recent years.
One of this study's most crucial findings was to demonstrate how the desalination industry is highly susceptible to the energy market’ behavior on both the regional and global scales. Of course, the first and most apparent implication here would be how this sector could influence the type of desalination utilized in a given region. The other implication was showcased by examples in the Middle Eastern market, where the growth of the desalination industry could even experience a temporary halt due to the function of the energy marker. With these in mind, observing this transition toward green and renewable energy-based desalination units, even in regions where traditional fossil fuel resources are not in short supply, can signal that the desalination industry may experience a shift toward more sustainability-oriented paradigms in upcoming years. Environmental and socioeconomic concerns are other pressing issues that need to be addressed and managed as this technology is scaling and plays a more prominent role in water resource management. At the time, it appears that regionally tailored remedies can put these problems at bay.
DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.
CONFLICT OF INTEREST
The authors declare there is no conflict.