Seawater Desalination: Climate Change Adaptation Strategy or Contributor?

California’s Challenges: Water and Climate

Currently, no region in California has sufficient water to meet environmental habitat needs.[3] Additionally, demands for potable drinking water are increasing and will likely continue to increase given projections of population growth exceeding 600,000 people annually.[4] Compounding this problem, rising temperatures due to climate change threaten the Sierra snowpack, one of California’s vital sources of potable water.[5] The declining snowpack will likely strain California’s water system, making it difficult to retain enough water to meet the population’s needs during summer months.[6] At current GHG emission rates, spring and summer stream flows are predicted to decline by 20 percent before mid-century, and by about 50 percent before the end of the century.[7]

Water scarcity is particularly severe in Southern California, which receives only about one-third of the state’s precipitation but accounts for about two-thirds of the state’s water consumption.[8] While the region has historically relied on water imported from the Sacramento-San Joaquin Delta and Colorado River to meet its needs, these sources are potentially unreliable due to periodic droughts.[9] Additionally, water flowing to Southern California from the Sacramento-San Joaquin Delta has been reduced by restrictions on pumping, enacted to keep enough water in the rivers to protect endangered species.[10] With California’s population growing and climate change threatening to reduce the water supply, cities throughout California are pressed to find new sources of water.

California is the second highest emitter of GHGs in the United States, and approximately the twelfth highest emitter in the world.[11] In solving the water supply issue, California also has the opportunity to help curb climate change through reductions in GHG emissions and energy demand.

With water delivery and treatment accounting for nearly 20 percent of the state’s cumulative energy demand,[12] California’s current water management system is extremely energy-intensive. The state can achieve GHG emissions reductions by replacing existing water supply and treatment processes with more energy efficient alternatives.[13] To fight global climate change, California should reduce energy use in current water management, and prohibit building new energy-intensive water projects.

The Sierra Snowpack along State Route 431 in Washoe County, Nevada. The Sierra snowpack is a vital source of potable water for California. Photo credit to Ken Lund.

Desalination Technology and History

Desalination is the process of removing salt from water. This process has been around for centuries, and was first developed when salt, not water, was a precious commodity.[14] It can vary both in the technology employed and the type of water used as the input. Some technologies, such as thermal evaporation or distillation, mimic the natural hydrologic cycle to extract the salt from water.[15] Most modern desalination plants use membrane technologies, such as reverse osmosis, that mimic the biological process of osmosis.[16] Membrane technology is usually preferred over thermal systems because it typically has a lower capital cost, requires relatively less energy, and offers added benefits of removing microorganisms and organic contaminates.[17]

Desalination plants can process both seawater and brackish water, which is usually groundwater from fossil aquifers. Brackish water differs from seawater because brackish water has a lower salt content. Thus, it requires less energy and costs less to desalinate via reverse osmosis.[18]

Historically, desalination has been only a minor component of California’s water supply portfolio. Most of California’s existing desalination plants are small, producing between from 0.002 to 0.600 millions of gallons per day (MGD).[19] These plants are generally used for industrial processes and aquariums.[20] In 2002, due in large part to water supply demands, the California Legislature passed Assembly Bill 2717, which directed the Department of Water Resources to establish a Desalination Task Force (Task Force) to “make recommendations related to potential opportunities for the use of seawater and brackish water desalination.”[21] The Task Force estimated that desalination could contribute less than 10 percent of California’s water supply needs.[22] Nonetheless, it concluded that desalination could “provide significant value,” including providing additional water supply.[23] On the other hand, the Task Force recognized that the environmental impacts of seawater desalination could cause a “potential impediment.”[24]

In the nine years since Assembly Bill 2717 passed, privately held corporations and municipal water agencies have proposed new desalination plants.[25] Today, there are over twenty large-scale desalination plants proposed throughout California, ranging in capacity from 0.40 MGD to fifty MGD, with some plants possibly expanding up to eighty MGD.[26] The majority of proposed desalination plants in California plan to use seawater.[27]

Rows of filter tubes at the Ashkelon Desalination Plant in Israel, the world's largest reverse osmosis desalination plant. Photo credit to glichfield.

Seawater Desalination Promises and Realities

Promise of Drought Resistant Water Supply Brings Water Quality Concerns

Seawater desalination is an alluring adaptation strategy because it could provide a reliable, drought-resistant water supply to California’s many coastal regions, which have access to the Pacific Ocean.[28] Seawater desalination also has the potential to offer improved water quality compared to existing sources.[29] But these benefits do not come without a cost. Seawater desalination can introduce harmful chemicals and metals into the water it produces.[30] Additionally, source water drawn into the desalination plant could contain biological and chemical contaminants.[31] Contaminants of particular concern include endocrine disruptors, pharmaceuticals, and algal toxins.[32]

The Los Angeles Aqueduct, a major source of imported water for the city, running through Owens Valley in eastern California. Photo credit to calwest.

Unsupported Promises To Reduce Water Import Needs of Southern California

Desalination proponents contend that building new, large-scale seawater desalination plants in Southern California will reduce the need to import water from the Sacramento-San Joaquin Delta and Colorado River.[33] This is significant for two reasons. First, as mentioned above, these water systems are already stressed, and reducing the amount of water withdrawn from them would produce an environmental benefit. However, there are no enforceable mechanisms in place to ensure that new seawater desalination projects will offset imported water as opposed to just adding to total water supply. Without a concrete mechanism to ensure that desalinated water replaces imported water, this is an empty promise.

Second, because importing water to Southern California requires a great amount of energy, decreasing the total amount of water imported to the region could reduce the amount of energy used for water supply, thereby reducing corresponding GHG emissions. But replacing imported water with desalinated water would not guarantee a reduction in GHG emissions because desalination plants are also extremely energy intensive.[34] Moreover, some desalination proponents argue they are not required to mitigate emissions associated with their energy use because they are not directly emitting GHGs. For example, Poseidon Resources Inc. argued that its proposed project in Carlsbad, California, would emit no GHG emissions and thus would not be subject to AB 32 requirements.[35] Nevertheless, the California Coastal Commission and State Lands Commission mandated a GHG mitigation plan as a condition of Poseidon’s permits and lease for the Carlsbad project.[36]

Reality − Large Energy Demand and Associated GHG Emissions

A serious disadvantage to seawater desalination is the amount of energy it requires. Seawater desalination is one of most energy intensive water supply option available.[37] Desalination systems using reverse osmosis technology require about 30 percent more energy than existing inter-basin supply systems delivering water to parts of Southern California.[38] Consequently, desalination would indirectly cause more GHG emissions than alternatives. Studies indeed show that extensive development of seawater desalination could lead to “greater dependence on fossil fuels, an increase in greenhouse gas emissions, and a worsening of climate change.”[39]

The cost of energy also makes desalination very expensive. In reverse osmosis plants, the cost of energy accounts for about 50 percent of the plants’ operating costs.[40] One proposed seawater desalination plant in the Camp Pendleton area in Southern California estimates that water produced by the plant would cost $2000 per acre-foot.[41] This is extremely high compared to the current cost for treated water in that area, which remains between $600 and $700 per acre-foot.[42]

The high cost of seawater desalination requires that the government heavily subsidize desalination projects in order to ensure projects are profitable. For example, Poseidon requested at least $530 million in tax-free state bonds for its Carlsbad project.[43] These public subsidies fund projects designed to generate profits for private companies. Poseidon originally projected a total cost of $270 million when it began the Carlsbad project in the late 1990s, but it now appears that it would cost at least twice that amount, with the public subsidizing the cost.[44] The high costs of desalination and the associated GHG emissions call for a serious look at alternative uses of funds. These subsidies could go to conservation measures or municipal water recycling programs that would provide at least the same amount of water at a lower cost and create jobs throughout the state.

A desalination intake pipe, which can pose serious risks to both large and small marine organisms. Photo credit to prilfish.

Reality – Impingement, Entrainment Harm Marine Life

Another disadvantage is that desalination plants using open seawater intakes pose a serious threat to marine ecosystems.[45] Open seawater intakes withdraw large volumes of water through pipes in the water columns of oceans, bays, and estuaries for industrial processes such as cooling power plants or supplying water for desalination facilities. Large organisms such as fish, marine mammals, and turtles are injured or killed when they become trapped or “impinge[d]” on the screens of the intake pipes.[46] Smaller organisms, such as plankton and larvae, pass through the screens but are killed as they become “entrain[ed]” in the desalination plants.[47]

For decades, California’s coastal power plants have used open seawater intakes for cooling systems known as once-through cooling.[48] Combined, these plants were permitted to withdraw over fifteen billion gallons of seawater per day,[49] killing an estimated seventy-nine billion fish and other marine life annually,[50] including threatened and endangered species, such as the Delta smelt.[51] State and federal agencies acknowledged that these power plants degrade marine life, impair coastal habitats, and contribute to declining fisheries.[52] To address this serious issue, the California State Water Resources Control Board passed a policy in spring 2010 to phase out the use of once-through cooling.[53]

Despite the fact that the use of open seawater intakes for once-through cooling will be phased out, thirteen of the twenty proposed desalination plants in California plan to use open seawater intakes to withdraw water, and ten of these will likely co-locate with existing power plants in order to share the intake pipes or take over the pipes if and when the power plants shut down.[54] If proposed seawater desalination plants utilize open intakes, they could perpetuate the destruction of marine life. Furthermore, allowing the proposed desalination plants to co-locate with power plants that use once-through cooling could potentially prolong the existence of these old, inefficient, GHG emitting power plants.

Reality – Renewable Energy Sources Could Reduce Emissions from Desalination Plants

One way to reduce the carbon footprint of seawater desalination is to utilize renewable sources, such as solar or wind power, to generate electricity needed to operate the plant. For example, one desalination plant in Perth, Australia, receives most of its electricity from a wind farm.[55] Requiring new seawater desalination plants to only use renewable sources of energy would reduce indirect GHG emissions related to the large energy demand of the desalination plants. If this requirement increased demand for renewable energy, it could also serve as an incentive to invest in more renewable energy production.

Renewable sources of energy, such as solar and wind power, help reduce the carbon footprint of seawater desalination. Above photo credit to Living Off Grid. Below photo credit to erikogan.

Copyright 2011 Angela Haren Kelley. All rights reserved.

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