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Desalination

Desalination is proven technology used globally to provide potable and industrial water supplies.

The two most widely used forms of water desalination are:

  • Seawater desalination using reverse osmosis (SWRO) and thermal desalination (distrillation) are proven processes used around the world.
  • Groundwater (or Brackish Water (BWRO)) desalination is used on saline waters from underground and is a common process to clean up groundwater.

Frequently Asked Questions (FAQ's)

Seawater Desalination (SWRO)

What is seawater desalination?

Seawater desalination turns ocean water into fresh drinking water by removing salt and impurities.

How is this process accomplished?

Historically, thermal distillation technologies dominated the market. These highly reliable and straight-forward systems have been in service with continuous technological improvement since the 1600's. However, they rely on a source of heat to work, which is typically fossil fuels. In use since the 1960's, by the 1990s, advances in membrane technology enabled the use of much more energy-efficient reverse osmosis (RO) techniques. Now, most ocean desalination projects use RO as the process to produce drinking water from seawater.

How does reverse osmosis (RO) work?

Under high pressure, fresh water is pushed through a semi-permeable membrane to separate salts and other impurities from the water molecules. The membrane allows only the small water molecules to pass through removing salt and other contaminants.

I often hear terms like brackish water, saline water, seawater and brine in reference to desalination. What is the difference between them?

These terms refer to broad classifications or degrees of salty water. For example, wastewater has about 1,000 milligrams per liter of minerals or salts. Ocean water, however, has 35,000 milligrams per liter of salts or minerals. Different sources of water have different levels of salts.

Desalting is taking the minerals and other constituents out of the salty water to make the water pure enough to drink. Membrane technology does this very effectively. The saltier the source, the more energy it takes to desalt the water. Thus, recycling waste water takes significantly less energy than desalting sea water.

Does drought affect the availability of water for desalination?

No. The desalination process is conducted in an enclosed, highly-controlled environment that uses an a functionally unlimited, local supply of seawater. It is unaffected by drought, snowpack, rainfall or other weather conditions.

Where else has desalination been successful?

Desalination facilities have been operating in arid coastal regions throughout the world for several decades. It is most common in the arid Middle East, where over 50 percent of global desalination capacity is concentrated. In addition, 17 percent of desalination capacity is in North America, and approximately 10 percent in each of the regions of Europe, Asia and North Africa. --- << This needs to be broken out as Ocean and Groundwater separate >> ---

Globally, more than 18,000 desalination plants operated in 150 countries produce more than 22,900,000,000 gallons of water for more than 300,000,000 people. Arid coastal regions throughout the world have been operating desalination facilities in for several generations. Over 50 percent of global desalination capacity is located in the Middles East. Roughly 17 percent is in North America, with roughly 10 percent in Europe, Asia, and North Africa. http://idadesal.org/desalination-101/desalination-by-the-numbers/

What kinds of improvements have taken place in RO technology?

The reverse osmosis membranes used today are more efficient, last longer, cost less and require significantly less energy than they did just a decade ago. There have been significant improvements in energy recovery technology, further reduceing power consumption. Desalination is now exponentially more efficient than earlier generations of reverse osmosis plants.

What is the quality of the water produced?

Desalinating water from the sea produces water of the highest quality that meets or exceeds all local, state and federal drinking water standards.

Why would an agency look to desalination when conservation efforts have dropped water usage significantly - are there studies that show water shortages in the future?

The decision to pursue desalination as a new water supply for a particular community will be based on several factors including climate resilience, projected growth and economics and reliable water supply during catastrophic events.

Climate change, higher temperatures, internal population growth, need to replace aging infrastructure, the need to return water to the environment, droughts, earthquakes and other factors tell us that we will need new, local and drought proof water supplies like desalination in the future to deal with these challenges.

The California Department of Water Resources projects that 500,000 AF per year of ocean water desalination capacity will be required to be produced over the next 20 years.

Water facilities take many years to develop, obtain approvals and construct. This means new facilities must be pursued years ahead of time to be operational by the time the water is needed.

Does an ocean water desalination project harm the ocean?

To ensure that ocean desalination facilities will be operated in an environmentally sensitive manner all desalination plants are subject to rigorous environmental review – including impacts to marine life. The State of California recently adopted stringent standards for desalination projects and technologies such as wedge wire screens and brine diffusers can be employed to protect virtually all adult and juvenile marine life. Any remaining impacts to microscopic marine life are typically addressed through environmental mitigation measures.

How will the desalted water be delivered to customers?

The desalted ocean water is potable water and can be put directly into the existing drinking water distribution system.

Where else is ocean-water desalination used?

Ocean water desalination is nothing new, Countries have been desalting ocean water since the 16th Century. Ocean water is used all over the world in 150 countries. It is used in Catalina Island, in Santa Barbara, on container ships, cruise ships, aircraft carriers, submarines and other ocean going ships.

The nations largest ocean water desalination plant – the Claude “Bud” Lewis – Carlsbad desalination plant began operating in December 2015. In 2017 Santa Barbara recently commissioned an ocean desalination project to supply 30% of their region’s water needs.

There are over 5,000 ocean water desalination plants of all sizes throughout the world with the largest facility in Saudi Arabia producing 232 million gallons (260,000 AFY) of fresh water a day.

Will the desalination water be safe to drink?

Desalinated water meets or exceeds all state and federal drinking water standards.

Does the desalinated water taste different from tap water?

There are many SWRO plants around the world and most say they can’t taste a difference. Thousands of visitors to the "Bud" Lewis Carlsbad desalination plant have tasted the desalinated water and some cannot tell the difference, and some can taste a difference and prefer the taste of the desalted ocean water.

** For these Desalination FAQ’s many thanks to the examples and background provided by West Basin, Poseidon, Deepwater Monterey and CalAm.

Seawater Desalination (SWRO)

What is Brackish water desalination?

Brackish or gound water desalination turns ground water that is not drinking water quality (high in salts or other impurities) into fresh drinking water by removing salt and impurities.

I often hear terms like brackish water, saline water, seawater and brine in reference to desalination. What is the difference between them?

These terms refer to broad classifications or degrees of salty water. For example, wastewater has about 1,000 milligrams per liter of minerals or salts. Ocean water, however, has 35,000 milligrams per liter of salts or minerals. Different sources of water have different levels of salts.

Desalting is taking the minerals and other constituents out of the salty water to make the water pure enough to drink. Membrane technology does this very effectively. The saltier the source, the more energy it takes to desalt the water. Thus, recycling waste water takes significantly less energy than desalting sea water.

How does reverse osmosis (RO) work?

Under high pressure, fresh water is pushed through a semi-permeable membrane to separate salts and other impurities from the water molecules. The membrane allows only the small water molecules to pass through removing salt and other contaminants. Brackish water RO takes less pressure than seawater RO because there is a lower concentration of salts.

What kinds of improvements have taken place in BWRO technology?

The reverse osmosis membranes used today are more efficient, last longer, cost less and require significantly less energy than they did just a decade ago. Today’s BWRO facilities are equivilant to recycled water facilities at sanitation districts.

Can the salt and minerals extracted be used?

Brackish water contains a variable amount of salt, usually less than one percent salt. The concentrated by-product (brine) from the desalination process contains two to three percent salt and 96 percent water. To recover the salt and minerals in the concentrated seawater, the remaining water would need to be evaporated. Either by using energy intensive distillation technology or by large surface salt ponds. There are some technological improvements in this arena and mineral harvesting may make economic or environmental sense in some circumstances.

Why would an agency look to ground water desalination when conservation efforts have dropped water usage significantly - are there studies that show water shortages in the future?

The decision to pursue desalination as a new water supply for a particular community will be based on several factors including ground water remediation, climate resilience, projected growth and economics and reliable water supply during catastrophic events.

Climate change, higher temperatures, internal population growth, need to replace aging infrastructure, the need to return water to the environment, droughts, earthquakes and other factors tell us that we will need new need new, local and drought proof water supplies like desalination in the future to deal with these challenges.

How will the water be delivered to customers?

The desalted ground water is potable – drinking - water and can be put directly into the existing drinking water distribution system.

Will the desalination water be safe to drink?

Desalinated water meets or exceeds all state and federal drinking water standards.

Glossary

Acre An acre is 43,560 square feet. There are 640 acres to the square mile.

Acre-Foot An acre-foot (AF) is one acre of water one foot deep. Thus, an acre-foot is exactly 43,560 cubic feet

CCF A CCF is one hundred cubic feet, which is a common billing unit in the western United States. The C comes from the latin "centum" meaning one hundred (Roman numerals). It is the same as an HCF.

CFS A CFS is a cubic foot or cubic feet per second. It is a common measure of water flow in larger quantities. A CFS is equal to 450 gallons per minute, 2 AF per day, 725 AF per year. Capacity rights in pipelines are often specified in CFS.

Cubic foot A cubic foot is a common unit of measure in the water business. At 12 inches on a side, it is simple and easy to understand and measure compared to a gallon, which is a legally-defined measurement of commerce equal to 231 cubic inches in the United States. A cubic foot is, exactly, 1728 cubic inches.

Cubic Meter is a cube one meter on a side. This is a common unit of measure for water outside of the United States. It is approximately equal to 35.3 cubic feet or 264 gallons.

Cubic Mile A cubic mile would be a cube one mile (5280 feet on a side). It is 3,379,200 acre-feet.

Gallon A gallon is defined as exactly 231 cubic inches, which is a box with inside measurements of 7 inches by 11 inches by 3 inches. Because the ratio of 1728 to 231 is not an even number, the conversion from acre-feet to gallons is not exact. An acre-foot is approximately 326,000 gallons.

HCF An HCF is one hundred cubic feet, which is a common billing unit in the western United States and is the same as a CCF.

Hectare A hectare is 10,000 square meters. It is 2.471 acres or about 108,000 square feet.

MGD is one million gallons per day. It is equal to 1120 AF per year.

Potable Water Potable water is, literally, safe to put in a pot and use for human ingestion, bathing, etc. Another term is "drinking water".

Potable Water Reuse Potable Water Reuse is a process whereby highly treated recovered waste water is injected into the ground water table (indirectly reuse) or into the potable water systems (direct potable reuse).

Salinity and Salt Management FAQ's

When saline water is used to irrigate, salts will accumulate over time in the irrigated root zone as the water in the soil is removed by the plants and normal evaporation, leaving the majority of the salts behind. Salt accumulation is largely dependent on the salt load (or salinity) of the irrigation water. History records that the collapse of ancient Mesopotamia and other ancient societies was partly due to crop failure and the lack of salt management.

Salt and Nutrient management plans are mandated by the State of California’s Recycled Water Policy, adopted in 2009. The Policy encourages the use of recycled water from municipal wastewater sources as it becomes an increasingly important source of water for California. Recycled water, and other sources of water (like imported water, Ground water etc), contain salts and nutrients that must be managed to protect the water quality of the state’s groundwater basins.

How do you measure the salinity of water?

Salts in water can be measured by relatively simple methods. The longest used and simplest method is a calibrated float. It will float higher in a sample of saltier water and lower in less salty. The density or specific gravity is read directly on a scale. This tool is called a hydrometer and has been in use the 4th century. https://en.wikipedia.org/wiki/Hydrometer#Salinometer

Another method, suitable for electronic monitoring, is electrical conductivity (the reciprocal of electrical resistance) using an appropriate conductivity meter for the measurement. Another method involves weighing water in a weighing container, and evaporating the water, then re-weighing and determining weight/volume (by difference). This is a little tricky because a sensitive balance must be used, and high temperatures may volatilize some salts.

Why do we irrigate?

Irrigation is an ancient and important agricultural practice. Crop yields are higher under irrigation and less dependent on the effects of weather. While only 15% of the world's cultivated land is irrigated, it accounts for 35-40% of the global food harvest. Projected population growth rates for the next 30 years will require an increase in food production equal to 20% in developed countries and 60% in developing countries to maintain present levels of food consumption. Expansion of irrigated agriculture was in large part responsible for the "green revolution" in food production and will continue to play an essential role in providing the needed increases in food and fiber production, especially in developing countries.

What happens when you irrigate?

Irrigation inevitably leads to the salinization of soils and waters. In the United States yield reductions due to salinity occur on an estimated 30% of all irrigated land. World wide, crop production is limited by the effects of salinity on about 50% of the irrigated land area. In many countries irrigated agriculture has caused environmental disturbances such as waterlogging, salinization, and depletion and pollution of water supplies.

Where does all the salt come from?

Application of irrigation water results in the addition of soluble salts such as sodium, potassium calcium, magnesium, and chloride dissolved from geologic materials with which the waters have been in contact. The ions responsible for salination are: Na+, K+, Ca2+, Mg2+ and Cl. Evaporation and transpiration (plant uptake) of irrigation water eventually causes excessive amounts of salts to accumulate in soils unless adequate leaching and drainage are provided. Excessive soil salinity reduces yields by lowering plant stand and growth rate. Also, excess sodium under conditions of low salinity and especially high pH can promote slaking of aggregates, swelling and dispersion of soil clays, degrading soil structure and impeding water and root penetration. As the Na+ (sodium) predominates, soils can become sodic. Sodic soils present particular challenges because they tend to have very poor structure which limits or prevents water infiltration and drainage.

What problems does salinity cause?

Over the course of history, thriving civilizations declined in part due to their inability to sustain food production on lands that had been salinized. It is estimated that 10 million hectares are now being lost every year as a result of salinity and/or waterlogging. Increases in salt loading in water tables and downstream aquifers which causes regional salinization.

Why is research on salinity so important?

In the future, global food needs will continue to increase while the soil and water resources available for new crop production will be limited and of diminished quality. The need to protect soil resources as well as to conserve water will continue to increase. Water must be used more efficiently and its quality protected. World agriculture must expand its base of production and increase production on lands currently under cultivation. Appropriate management practices to control salinity must be implemented on irrigated fields, in irrigation projects, and for geohydrologic systems. In order to meet the ever increasing demands for food and using ever decreasing and more marginal soil and water resources, the nation and much of the world community will continue to look to the U. S. Salinity Laboratory for expertise and leadership in salinity and water quality research and applications to solve these problems.

What are Local agencies doing about salinity management?

As referred above – the state is requiring Salt and Nutrient Management plans for local basins. There are many local activities that are improving salinity issues. The Salton Sea Authority continues to work hard mitigating salinity issues in their area. The other local efforts like the Santa Ana Watershed association, CV-Salts, and the Bay Delta continue to work towards salinity solutions. Increasingly brackish and groundwater desalination are useful tools dealing with salt management.

The classic method of removing salinity from soils is by leaching. That is, applying excess irrigation to the soil and draining away the salts. To do this requires a lower salt source of water, and a means to drain away the saline water ultimately to the ocean.

Developed and maintained by California Advocates, Inc.