Fondly known as the blue planet, our home is 70% covered in water. This makes the fact that 20% of the earth's population doesn’t have access to clean water supply all the more shocking. The truth is, we only have access to a small fraction of the planet’s water. 2.5% of the water is freshwater, and much of this is stored in glaciers, leaving 1% of the world's supply ready for us to use. Water shortages are a serious threat to parts of the world where rainwater is sparse, leaving populations to rely on other means to gather water for drinking and sanitation.
Oceanwater is dense in salt and the saline heavy solution is not suitable for human consumption. This is where desalinisation comes in. The idea of removing the salt from the ocean water ready to send to homes makes a lot of sense at first glance. After all, it would open up a near unlimited source of water. The issue is more complex than the surface would suggest. The process is expensive, energy-intensive and has a knock-on effect on local ecosystems. This being said, for many parts of the world, the demand outweighs the potential drawbacks. This article will explore the issues surrounding the process and the question of whether desalination is the answer to worldwide water shortages.
Desalination (now referred to as desal) is widely used around the world. Each day, millions of gallons are pumped through desal plants to supply more than 300 million people with their freshwater. It’s widely used around the globe, with most of the world's desal plants being found in the middle east, but also widespread in China, Australasia, South Asia and the USA. Plants such as the Carlsbad plant in California are crucial to local populations. Carlsbad itself creates 10% of the freshwater that is used by the 3.1 million people in the area. In the Middle East, where nations are rich in energy-producing resources like oil but face a shortage of natural water supplies around them, the energy-consuming process is essential for water supply. The massive network of desal plants in Saudi Arabia contributes to 40% of the freshwater produced in the world, making them vital for life in the area. The cost of operating a desal plant has decreased by 50% in the last 30 years due to advancing technologies, making it a much more viable option economically.
Despite decreasing operational costs and advancing technology, there are some serious drawbacks to using desal as a blanket solution to global water shortages. Although technology is driving improvement, the amount of energy expended when operating a desal plant is still vast. the amount of energy expended does depend on the type of plant. There are two types of plant, a thermal desal plant or reverse osmosis (RO) desalination. Both use large quantities of energy, thermal to heat the water for the process, and the energy to power the pumps for the RO systems. As RO technology improves and the membranes become more efficient, less power is required to operate the RO systems. Most of the many desal plants in the Middle East run on the thermal model; the problem is these plants were incredibly expensive to set up, so replacing thermal plants with RO systems would be extremely expensive.
In addition to being less energy efficient, thermal which produces 25% freshwater to 75% run-off brine. In comparison, RO units produce a 50/50 ratio of brine to freshwater, making it much more efficient in terms of wastewater produced. With the number of thermal plants, more than half of the feed water used in desal is coming out as super saline wastewater, and the proper disposal of this by-product is what is affecting local ecosystems. The dense solution sinks and pools at the seabed and is toxic for any fish or sea life that comes in contact with it. Solutions to this include filtering the brine back through the seabed floor or mixing beforehand with seawater before its release. Another environmental issue involving desal is the contaminants in the feedwater. Agents are added to prevent clogging through the process, and when released in the brine, it can once again prove toxic to local ecosystems. The feedwater may also contain fish and other sea life that have been pulled in through the pumps. These fish are unfortunately killed in the process.
Despite the environmental issues involved, the readily available nature of ocean saltwater makes it a viable option. One way of improving efficiency is looking at the feedwater source. The process takes more energy the higher the amount of salt present in the saline solution, with oceanwater the higher estimate. Another option for feedwater sources is brackish groundwater with a lower ratio of salt. With less particulate to remove, less energy is wasted and less brine wastewater is produced. Overall, the question of whether desal can be a universal solution to water shortages can not be answered on a global level. It depends on locality. The availability of energy resources compared to water in the Middle East makes it vital for the local population, and the presence of brackish water in areas can lead to higher efficiencies if choosing to adopt desal. The answer boils down to whether there is a simpler and cheaper solution ready to go.