Desalination, the process of removing salt and other minerals from water, has become an increasingly necessary technology for providing potable water in water-scarce regions globally. By converting abundant seawater or brackish water into a usable freshwater supply, desalination plants offer a buffer against drought and increasing population demands. However, the environmental trade-offs associated with this technology are substantial and localized, raising concerns about its long-term ecological sustainability. Plant operations introduce specific physical and chemical stressors to marine environments and contribute to global atmospheric pollution.
Consequences of Brine Disposal
The primary localized environmental concern is the discharge of highly concentrated saltwater waste known as brine. This effluent is approximately twice as saline as the ambient seawater and is often returned directly to the ocean near the plant. Because the concentrated salt solution is denser than the surrounding water, it sinks rapidly to the seafloor upon discharge.
This rapid increase in salinity, often called “salinity shock,” is detrimental to marine life, particularly benthic communities living on the seabed. The brine stream also frequently contains residual chemicals used in the pre-treatment and cleaning phases, such as anti-scalants, anti-fouling agents, chlorine, and heavy metals.
The dense, chemical-laden brine accumulates on the ocean floor, potentially creating a localized hypoxic zone where dissolved oxygen levels are too low to support most marine life. Benthic habitats, such as seagrass meadows and coral reefs, are vulnerable to this impact, which disrupts the local food web. The discharge may also be warmer than the receiving waters, creating an additional stressor through thermal pollution.
Damage to Coastal Ecosystems from Water Intake
The process of extracting massive volumes of source water from the ocean poses a direct physical threat to marine organisms through the plant’s intake system. Desalination plants typically use open-ocean intakes, drawing in water at high velocities that injure or kill marine life. This impact is categorized into two distinct forms: impingement and entrainment.
Impingement occurs when larger aquatic organisms, such as adult fish, crabs, and sea turtles, are physically trapped against the intake screens by the force of the water current. Unable to escape, these animals are often fatally injured or suffocated.
Entrainment affects smaller organisms, including plankton, fish eggs, larvae, and small invertebrates, that pass through the intake screens. Once inside the system, these organisms are subjected to high pressures, extreme temperatures, and mechanical stress from the pumps and filtration systems, resulting in near-total mortality. The continuous removal of these juvenile and larval stages significantly reduces the recruitment of new individuals into local populations, disrupting the marine food web.
Operational Energy Demand and Emissions
A separate, global-scale environmental impact arises from the substantial energy required to operate desalination plants, particularly those utilizing Reverse Osmosis (RO) technology. The RO process is highly energy-intensive because it requires high-pressure pumps to force water through semi-permeable membranes, overcoming the natural osmotic pressure of the saltwater.
The specific energy consumption for modern seawater RO plants typically ranges between 3.5 and 4.0 kilowatt-hours of electricity for every cubic meter of freshwater produced. This high demand for power translates directly into a significant carbon footprint when electricity is generated by fossil fuels, which is the case for the majority of facilities worldwide.
This massive energy consumption links desalination directly to the emission of greenhouse gases, including carbon dioxide, a primary driver of global climate change. Furthermore, the need to power these facilities can necessitate the construction of dedicated power generation infrastructure or require significant upgrades to existing electrical grids. This dependence on pollutant-producing energy sources makes desalination an indirect contributor to global air quality issues and climate change.