“Desalination in the Middle East”, Harvard International Review

The number of seawater desalination plants have grown rapidly in the last decades. At present, there are an estimated 16,000 desalination plants globally. These discharge 142 million cubic meters of hypersaline brine daily, or 51.8 billion cubic meters of brine annually. Brine disposal has been a known issue for decades. However, with the acceleration of desalination plants in even regions like Palestine, the widespread adoption of desalination has thrown seawater salinity bands into disarray. In January 2023, the UN published a report titled “The state of desalination and brine production: A global outlook“ that was accompanied with a complementary press report titled “UN Warns of Rising Levels of Toxic Brine as Desalination Plants Meet Growing Water Needs”.

55% of global brine is produced in four countries. These are Saudi Arabia (22%), UAE (20.2%), Kuwait (6.6%) and Qatar (5.8%). The gulf states, facing acute water stress but having abundant oil and energy resources, adopted desalination early. Using Saudi Arabia as a case study, the country established a general department for desalination within the Ministry of Environment, Water and Agriculture in 1965. The country's first batch of desalination plants followed shortly: Al Wajh and Duba in 1969, Jeddah in 1970 and Khobar in 1973.

Desalination Desalination uses two main types of technologies. The first is thermal desalination whereby water is heated, before condensing in a cooling chamber to form desalinated water. The remaining hypersaline solution is known as brine. Thermal-based plants were common in the last century, whereas reverse osmosis type plants only became more common in the recent two decades. The result is a concentration of Middle Eastern plants which operate using thermal desalination technologies. The type of processing matters because thermal processes produce four times as much brine as membrane processes. In addition, the ratio of desalinated water to brine is not ideal, with 1.5 liters to 2 liters of brine produced per 1 liter of desalinated water.

Effects of Brine Brine causes ecological devastation, especially to marine life, many of which are sensitive to freshwater-to-salt water ratios. Certain species such as oysters and molluscs are also unable to physically swim to a less hypersaline zone. Research by Observatoire Océanologique Européen on Red Sea coral (Stylophora pistillata) show that rates of photosynthesis and respiration falls by as much as 50% when salinity levels are raised from 38 psu to 40 psu. A practical salt unit (psu) is benchmarked at 1g of salt per 1000g of water. The corollary is that most Red Sea coral reefs will die if salinity is kept at 40 psu or more for a sustained period. Other species, such as the Indo-Pacific Humpback Dolphin (or Hong Kong pink dolphin) are able to stay in mixed zones where freshwater meets saltwater, but typically are not able to traverse beyond the mixed zone. In addition, thermal desalination discharges large quantities of brine that is much hotter than ocean temperatures, in turn causing the oceans to warm. In areas outside the Middle East, increased sea temperatures have recorded decimation of entire catches of species. For instance, at Sendai Bay in Japan’s Pacific coast, ocean warming has been linked to sand lances’ decrease in population. Sand lances are susceptible to high temperatures and burrow into the sand in summer and lie dormant. However, ocean warming extends the period of dormancy, making them smaller and weaker resulting in fewer adults are spawning. Surface temperature of Japan’s waters has increased by 1.19 degrees over the last 100 years. In comparison, thermal desalination operates at 100 degrees celsius (boiling point of water). The temperature of the discharge varies by plant, but could potentially be up to 99 degrees celsius.

In addition, an increase in salinity affects what is industrially known as the quality of feedwater. Thus, less saline feedwater utilizes less energy and has a higher conversion ratio to clean water. In simpler terms, the dumping of brine at industrial scales back to the sea increases localized salinity, especially if not dispersed, and it creates a negative feedback loop where desalinating that saltier seawater is more energy intensive and less efficient. At present, the Gulf seas are now 25 percent saltier than typical seawater, in part due to brine release and in part due to natural weathering events such as in the Red Sea where saltwater from the Indian Ocean flows north where it evaporates and cools. This has the effect of raising its salinity and density.

Solutions

Various solutions have been touted, with limited practicality. Variations of the traditional sailors’ condensation bowl and tilted lid have been made, including Abu Dhabi-based startup Manhat that scales the traditional bowl into a large floating device or MIT’s free-floating desalination unit that has a similar set up with an additional multilayer evaporator that traps heat so as to boost its overall passive desalinating efficiency. The issue is that it requires a lot of sea space and has an impractical passive desalination rate of 1.5 liters of freshwater per day per 2.25 square meters. MIT’s produced 5 liters of freshwater per daytime hour per square meter. Considering each person uses between 50 to 100 liters of freshwater a day, both rates are untenable and not suitable for commercial production.

Future of Desalination: A Hybrid Solution However, one major flaw in Manhat’s and MIT’s free floating design is that it floats in the ocean, where temperatures are low. A quick fix to the desalination process can reduce energy usage and increase desalination efficiency, with the added bonus of cooling the Middle East. In particular, the Middle East contains large swathes of unused desert land. The temperature of the Red Sea is around 22 degrees celsius while the temperatures of the Gulf of Aqaba hovers between 20 to 30 degrees celsius. The latent heat capacity of water for vaporization is 2257.06 kJ/kg whilst the specific heat capacity of water is 4,182 kJ/kg. At average temperatures of 38 degrees celsius to 54 degrees celsius in the desert, there would be up to 40 percent increased efficiency in passive desalination if the Middle East were to place similar passive desalination devices on its large swatches of arid desert. In simpler terms, the device is not in a 22 degrees celsius cooling bath and heats up till 54 degrees celsius before being piped in as feedwater. It also passively desalinates nominal amounts of freshwater prior to being piped into a commercial plant as feedwater. Thus, water needs to be heated from 54 degrees celsius (for another 46 degrees celsius) instead of heating from 22 degrees celsius (for another 78 degrees celsius whilst losing heat to the surrounding seawater). In urban heat island effect studies, it is known that large bodies of water have an effect of cooling the surrounding region. Thus, this may have the effect of cooling the desert and reducing diurnal temperature swings as well. The same infrastructure can be replicated to become inland salt farm crystallizing pools, thereby resolving the issue of brine hypersalinity.