Ultimate Guide to Desalination
Table of Contents
Since 97% of the world’s water spans over 320 million miles of ocean water, that means there’s only 3% of freshwater for human consumption. However, two and a half percent of that water isn’t available. This lack of availability is due to water being in the atmosphere, glaciers, and polar ice caps. Other issues include that it’s too polluted or too deep beneath the earth’s surface.
Approximately one in three people have access to safe drinking water across the globe. However, in areas like Cape Town, Africa, four million people are part of the world’s most massive drought. That means, throughout the water crisis, those people were at risk of having no water. After taking drastic measures and implementing water restrictions, Cape Town pulled through and continues to thrive.
Water scarcity and global water crises are leading us to wonder if desalination could be part of the solution?
Why Don’t We Desalinate Ocean Water More Often?
With the water shortages occurring, it isn’t uncommon for people to wonder why we’re not using desalination more often. One of the main reasons why this isn’t happening is the amount of energy desalination requires. Because salt dissolves quickly in water, it’s difficult to break the chemical bonds it creates. The technologies and energy desalination requires are currently expensive.
Pinpointing the cost of desalination is challenging. The costs vary according to energy use, financial agreements, labor costs, land prices, and the water’s salt content. However, the estimated fees typically range between one and two dollars per cubic meter of ocean water desalinated. That’s typically how much water two average Americans use daily.
If you change the water source from the ocean to an aquifer or river, those costs drop to 20 cents per cubic meter. That means it costs less for farmers to use desalinated water. That tells us that it’s almost always cheaper to use freshwater sources than desalinated water.
The cost of using plants is another factor preventing us from using desalinated ocean water more often. On average, a desalination plant uses 15,000 kilowatt-hours of energy per one million gallons of water it produces. The cost of using desalination plants is not only monetary. During the process, ocean life and other small creatures can get sucked into the plant.
The price gap is improving, however. Experts believe these costs are going to continue dropping over time. The main reason is that technology makes desalination more cost-effective as other water technologies’ costs continue to rise. That’s attractive to areas where water shortages are occurring, like in California, for example.
How much of the world’s drinking water do we desalinate?
Fighting against water scarcity in the United States, and throughout the rest of the world, involves using some amount of desalination. Countries across the globe depend on plants and access to energy to receive clean water. Due to the complexities of water scarcity and climate change, many are unsure if desalination can solve the problem.
North America’s largest desalination plant is the Claude “Bud” Lewis Carlsbad Desalination Plant, located approximately 30 miles north of San Diego. In Huntington Beach, California, a second plant similar to the Carlsbad is under construction. When looking specifically at the United States, there are 49 municipal desalination plants in Texas. These plants process surface and subsurface brackish water. In San Antonio, you’ll find the country’s largest brackish water desalination plant.
With droughts and natural disasters occurring globally, that leads many to wonder how much of the world’s drinking water goes through the desalination process.
- Around 1% of the world’s drinking water has gone through the desalination process.
- Approximately 30% of the world’s irrigated areas suffer from issues with saline.
- As of 2016, there are 18,983 plants across the globe.
- During 2017, those plants produced 99.8 cubic meters of water daily.
- Today, over 300 million people worldwide get their water from desalination plants.
- Desalination costs have reduced as technology continues to evolve.
Civilizations have been converting ocean water into drinking water as far back as the Ancient Greeks. The desalination process has undergone many advancements compared to when people boiled salt water and collected the vapor in sponges 2,400 years ago.
So, What is Desalination?
When you hear the word “desalination,” it’s the process of removing minerals and salts from water. This process might occur for commercial, industrial, or municipal use. The feed water, or saltwater, might include brackish, industrial feedwater, surface water, wastewater, and well water. There are two primary desalination process technologies, which are thermal desalination and membrane desalination.
Because this process is expensive, it isn’t used for desalinating brackish water often. The process involves boiling saline water until it evaporates and then collecting that condensation. In doing so, the condensed vapor water is pure and leaves the salt behind.
The thermal desalination process can break up into several different types, including:
This process provides usable heat in dual-purpose facilities where power is available for desalination. These facilities typically produce energy solely to create potable water.
Pros of Cogeneration:
- Plants are easy to construct and run.
- Aside from conventional pumps, there are no moving parts.
- There’s a minimal amount of connection tubing.
- The feed water quality isn’t as important as when using reverse osmosis processes.
Cons of Cogeneration:
- Operating at a higher temperature causes scaling issues on tube surfaces.
- The process is energy-intensive, requiring both mechanical and thermal energy.
- Capital costs increase when adding more stages to improve the system’s efficiency.
Multi-effect distillation (MED)
This process involves evaporating water to remove the salt. During the 1980s, newer approaches came to fruition to help prevent scaling. The main reason for these innovations is because the systems could operate at a lower temperature.
Pros of Multi-Effect Distillation:
- It has a low operating cost because the distillation process can use waste heat.
- The feed water’s quality is less critical than when using reverse osmosis processes.
- It can operate at a lower temperature, which helps minimize tube corrosion.
Cons of Multi-Effect Distillation:
- There are high operation costs when waste heat isn’t available during the distillation process.
- During spray evaporation, the process is incompatible with higher temperatures due to issues with scaling.
Multi-stage flash distillation (MSF)
Multi-stage flash (MSF) distillation plants account for approximately 40% of the world’s desalinated water. The process involves pumping cold feed water through successively staged heating systems until it reaches the hottest stage. At this stage, low-pressure heating steam brings the water’s temperature above 100°C. That temperature, while the water is under pressure, starts the flash process. The water moves back through the previous stages and, throughout this process, vapor generates condenses and collects as distillate.
Pros of MSF:
- It’s possible to use the waste heat as a primary heat source.
- The process produces high-quality water containing as little as ten ppm.
- Water doesn’t require significant pre-treatment outside of filtration to remove solid substances.
- Higher operating temperatures help improve efficiency.
Cons of MSF:
- This process is considered energy-intensive.
- The MSF process requires both mechanical and thermal energy.
- Higher temperatures during operation could cause scaling issues.
- Higher temperatures could create corrosion, mechanical and thermal problems.
Solar water desalination
During solar distillation, a basin of ocean water has a curved or sloping transparent surface that absorbs solar radiation. The solar radiation causes the water to create condensation on the covering. Then, it’s collected and used for drinking water or other purposes.
Pros of Solar Distillation:
- The use of solar panels eliminates energy costs.
- The cost of solar panels is reducing.
- Because there are no mechanical parts, this is a low-maintenance process.
Cons of Solar Distillation:
- You must have a significant amount of space available.
- Due to the price of land, the initial investment is high.
- Some solar panel manufacturers are expensive.
Vapour compression evaporation (VC)
The VC process can be used as a stand-alone solution or in conjunction with other methods, like MED. The process involves heating the evaporating feed water coming from the vapor’s compression. A mechanical compressor and steam jet are two devices that condense the water vapor, so it generates enough heat to evaporate the ocean water.
Pros of VC:
- Small-scale desalination units benefit from the method’s simplicity and reliability.
- This process is efficient due to the low operating temperatures.
- Due to its low operating temperatures, risks of scale formation or tube corrosion reduces.
Cons of VC:
- It requires pre-treatment to prevent issues with the heat exchanger.
- Water must be kept at the right temperature to prevent corrosion.
- This process requires a large heat transfer area.
The membrane desalination process uses membrane applications to treat municipal water supplies. However, this process is also successful at beverage purification and chemical separations. Desalination plants typically use membrane technology when the water has a lower dissolved salt content. The main reason is that these processes are less energy-intensive than thermal processes that are equivalent.
Membrane processes produce freshwater by using a permeable membrane to move salt or water into two different zones with differing concentrations. We can divide the membrane desalination process into the following categories:
These systems use a permeable membrane to move salt from one side to another while under an electric potential. Typically, multiple electrodialysis cells are configured into what’s referred to as an electrodialysis stack. This stack forms multiple electrodialysis cells by alternating cation exchange and anion membranes.
Using electrodialysis technologies are gaining momentum in water resource management. The main reason is the possibility of recovering ions from steam concentrations and recovering and reusing the saline stream’s valuable compounds.
Pros of Electrodialysis:
- Electrodialysis has a short response time due to fast heat-up and cool-down.
- The membrane can withstand higher operating pressure.
- Compresses and stores hydrogen easier.
- It can operate under a broader range of power outputs.
- There are lower operational costs involved.
Disadvantages of Electrodialysis:
- Manufacturing costs are higher due to expensive components and materials.
- It can become damaged quickly due to overheating or cell design.
- Sensitive to dust, imperfections, and impurities.
The membrane distillation (MD) process separates two water solutions with differing temperatures using a micro-porous hydrophobic membrane. The membrane’s hydrophobicity prevents liquid from mass-transferring. As a result, it creates a gas-liquid interface.
Due to the vapor pressure difference resulting from the gradient temperature on the membrane, the water’s volatile components evaporate through the pores. The distillation side of the membrane contains non-volatile substances, including salts and water vapor. The supply-side has a further concentrated salt flow.
Benefits of MD:
- MD has a lower working temperature and pressure.
- Lower energy costs.
- Less stringent mechanical properties.
- Separation can occur at temperatures well below the boiling point.
- Less susceptible to flux limitations.
Disadvantages of MD:
- It might not be feasible for industrial applications.
- Membrane pollution.
- Water loss due to polymetric membrane conduction.
- High thermal energy consumption.
- The high cost of membrane distillation modules is a burden for some plants.
Reverse osmosis (RO) is the most popular form of membrane desalination technology. During the reverse osmosis process, saltwater forces through a semi-permeable membrane. During that process, the salt separates from the water. Because reverse osmosis doesn’t use as much energy as thermal desalination, most new plants use this technology.
During reverse osmosis desalination, ocean water goes through a treatment process that removes impurities, oil, rubbish, seaweed, and more. After it’s free of organic substances, the treated water goes through reverse osmosis. During this process, the water moves into two separate streams. The first stream is for the brine, and the second is for the freshwater. Before returning into the ocean, the brine is diluted. That way, the high concentrations of salt doesn’t harm the ocean’s ecosystem.
Pros of Reverse Osmosis Desalination:
- The technology is cost-effective for providing clean and safe drinking water.
- The water is free from impurities, making it safe for cooking and making beverages.
- RO doesn’t use as much energy compared to other desalination processes.
Cons of Reverse Osmosis Desalination:
- The filtration process is slow.
- Clogging could occur more often, making these systems require additional routine maintenance requirements.
- This process produces a significant amount of wastewater.
Are There Negative Consequences with Desalination?
One of the most significant disadvantages of desalination is managing brine by-product. This by-product is the waste that is produced during the process. Desalination plants across the globe discharge up to 142 cubic meters of brine daily. That’s enough to cover the state of Florida beneath one foot of brine waste. Middle Eastern nations, including Kuwait, Qatar, Saudi Arabia, and UAE, are responsible for over half of the world’s brine waste.
Brine isn’t the only negative consequence of using desalination processes. There are also impingement and entrainment (I&E) impacts. I&E impacts are associated with operating open water intakes for ocean water desalination plants. When impingement occurs, that’s when organisms trap against the screens because they’re too large to flow through them. Entrainment occurs when passing through the plant’s intake and onward through the treatment facility.
Issues with I&E are plant-specific. The main reason is that there are plants that uphold environmental standards and, as a result, have low levels of I&E.
Can Desalination be a Solution to Future Water Crisis?
Over 300 million people worldwide depend on desalinated water daily. There are currently 150 countries using this process, which translates to 86.8 cubic meters of desalinated water production daily. When looking specifically at the United States, some argue that desalination isn’t the answer to future water issues. The main reason is that, over the next 20 years, the country’s population is expected to increase by 30%.
Compared to using freshwater sources, desalination is more expensive. However, companies across the globe are working on solutions to help cut these costs. Due to growing competition and investments in material supplier markets, this sector has been flexible regarding adjusting to efficient technological innovations.
For example, when desalination membranes are more precise, they increase efficiency and reduce costs throughout the process. With growing populations and recurring droughts in many regions throughout the United States, experts acknowledge desalination as part of the solution for helping to alleviate water resource stress.
Due to the high price of desalinated water compared to using freshwater, the consumer could see increases in municipal water pricing. However, that pales in comparison to the life-saving benefits desalination has during long-term water scarcity.
Ocean water is vast enough to support civilizations for thousands of years. That means the desalination process is a viable option to help solve the water crisis. Here are some of the ways the desalination process can help:
- Potable water is available without the stress of exhausting freshwater sources.
- Thousands of households can receive drinking water daily, thus creating a consistent service to everyone.
- There are advanced plants worldwide using reverse osmosis technology, which provides filtration for potable drinking water.
- Countries can depend less on natural resources, which, in turn, allows them to replenish them.
- Reverse osmosis technology allows industrial wastewater to be purified into safe drinking water.
Desalination provides resources to countries that do not geographically contain reservoirs and rivers. Thanks to the abundant supply of desalinated water, people can use it for agriculture and irrigation.
The process of removing impurities and salt from ocean water is referred to as desalination. The process involves pumping ocean water into a desalination plant where it passes through pre-treatment filtration. That process removes most of the water’s large and small particles.
While this process uses a significant amount of energy and currently costs a lot, newer technologies are helping to reduce these costs. If technology continues to improve and costs lower, then desalination can be an important part of the global water solution.