Desalination is the process of removing salts and minerals from saline water, typically seawater, to produce freshwater suitable for human consumption or agriculture. This technology is an increasingly important strategy for addressing global water scarcity, particularly in arid coastal regions. However, the large-scale operation of desalination plants introduces several negative environmental consequences that affect marine ecosystems, the atmosphere, and coastal habitats.
Brine Discharge and Effluent Pollution
The most significant environmental challenge posed by desalination plants is the disposal of the waste product, known as brine. This effluent is a highly concentrated saline solution, often about twice as salty as the ambient seawater. The extreme salt concentration creates a dense plume that is heavier than normal seawater, causing it to sink and flow across the seabed.
This process leads to density stratification and the development of a hypersaline layer that smothers and alters the benthic ecosystem. Organisms sensitive to stable salinity levels, such as seagrasses and stony corals, can disappear entirely from the immediate discharge zone. Furthermore, the concentrated brine often contains chemical additives used during pre-treatment and cleaning phases. These chemicals include residual chlorine, anti-scalants, and anti-fouling agents, which can introduce toxic substances, such as heavy metals like copper, back into the marine environment.
The physical characteristics of the brine also cause harm beyond salinity and chemical content. Depending on the technology used, the brine may be discharged at an elevated temperature compared to the receiving water, creating a localized thermal plume. The dense, sinking brine plume can also deplete dissolved oxygen levels, leading to hypoxic conditions near the seabed. This combination of increased salinity, higher temperature, chemical pollutants, and reduced oxygen profoundly impacts the local biological community and translates into observable ecological effects throughout the food chain.
Impacts on Marine Life from Water Intake
The initial stage of the desalination process involves drawing massive volumes of seawater into the plant, resulting in the physical destruction of marine organisms. This harm is categorized into two distinct processes: impingement and entrainment. Impingement occurs when larger aquatic life, such as fish, crabs, and sea turtles, are physically trapped against the intake screens by the force of the flowing water.
Even if an organism is not immediately killed, impingement can lead to severe injury or exhaustion, making survival unlikely. To minimize this impact, the U.S. Environmental Protection Agency (EPA) recommends intake water velocity should be kept low, ideally no more than 0.5 feet per second. The second, more pervasive issue is entrainment, where smaller organisms pass through the protective screens and are carried into the plant’s treatment system.
Entrainment primarily affects plankton, fish eggs, and larval forms of invertebrates, which form the base of the marine food web. These minute organisms are killed by changes in pressure and velocity as they are pumped through the system, by heat applied in some thermal processes, or by chemicals used to disinfect the water. The annual loss of millions of these early-life-stage organisms can significantly impact local fish and invertebrate populations, disrupting the overall ecological balance near the intake.
Energy Demands and Climate Impact
Desalination is an inherently energy-intensive process, especially when using the prevalent reverse osmosis (RO) membrane technology. RO requires high hydraulic pressure to force water through semipermeable membranes, relying on large, electrically powered pumps. The energy required to produce one cubic meter of desalinated seawater typically ranges between 3 to 4 kilowatt-hours (kWh).
This high energy demand contributes significantly to the operating costs, often representing a majority of the total cost of production. When electricity is sourced from conventional power generation, such as fossil fuel power plants, the desalination facility results in substantial greenhouse gas (GHG) emissions. The release of carbon dioxide into the atmosphere contributes to global climate change.
The connection between the plant’s operational energy use and climate change creates a broader environmental context beyond local marine impacts. These GHG emissions exacerbate problems like ocean acidification and sea-level rise, which further threaten coastal and marine habitats globally. While providing a local water solution, the energy demands of desalination plants contribute to a worldwide environmental burden.
Coastal Habitat Disruption and Land Use
A desalination plant requires a substantial physical footprint, leading to the direct disturbance and permanent alteration of the coastal landscape. The construction phase involves grading and excavation for the main facility, as well as laying extensive infrastructure like pipelines and access roads. This activity can destroy sensitive coastal habitats such as wetlands, dunes, and mangrove forests, which serve as crucial nurseries and protective barriers.
The installation of intake and outfall pipelines causes significant disturbance to the seafloor and intertidal zones. This process involves the re-suspension of sediments, which can temporarily cloud the water and harm nearby marine life. Once operational, the permanent presence of the plant and its associated structures can fragment habitats and introduce visual and acoustic disturbances to the previously natural environment.