Desalination 101: The basics

There are two main methods of desalination. The first is thermal-based distillation, where heat is used to boil seawater and remove salt in the process. This is the traditional method for desalination that¡¯s been used for centuries dating back to ships using desalination during long voyages. It is preferable to site these desalination plants near powerplants so they can leverage waste heat for the process.

The second main method of desalination is through reverse osmosis. The process of reverse osmosis involves pushing seawater through a membrane to separate water from its salt component. This is a fairly new technology as the first desalination plant to use reverse osmosis in the US was commissioned in California in the 1970s. It has become the trend in recent years because it is more efficient than thermal-based distillation. However, the process requires much more energy.

It's clear that we have proficient desalination technology at our disposal to produce clean drinking water. But the energy intense process typically results in large amounts of greenhouse gas (GHG) emissions. What if we were able to decarbonize the process?

Decarbonizing the desalination process

If the industry hopes to get the green light for more desalination projects, more effort will need to be put into reducing the carbon intensity of the process. This can be done in a few ways. From capturing carbon emissions, to reducing the carbon intensity of fuels with hydrogen, to implementing renewable energy sources, it will require an all-in approach to decarbonize the desalination process. Let¡¯s explore each of these concepts below.

• Carbon capture, utilization, and storage: One of the first ways we can reduce the emissions at desalination plants is by capturing the carbon before it gets released into the atmosphere. This is called carbon capture, utilization, storage (CCUS), and it can be implemented at desalination plants to demonstrate a commitment to limiting emissions. Even better, the captured carbon can be used for things like fertilizer production.
• Blending hydrogen: Another way to reduce the carbon intensity of desalination is by mixing hydrogen into the fuels we use to power the process. Hydrogen is the most abundant element in the universe. It also has several attributes that make it a great energy carrier. It is non-toxic, light, reactive, and does not emit any carbon dioxide upon combustion. By blending hydrogen into our fuels, we can reduce the carbon intensity by up to %20.
• Leveraging renewables: Perhaps the best way to decarbonize the process is by removing carbon from the equation all together. This is achievable through renewables like solar power, wind power, hydropower, biofuels, and more. The challenge here is that the desalination process requires a significant amount of energy¡ªand that would necessitate an incredible amount of wind turbines and solar panels to operate solely using renewable energy. An all-hands on deck approach is necessary.

Mitigating other environmental impacts

While decarbonizing the desalination process is sure to help sell these kinds of projects to the public, there are still other concerns from environmental advocates. It¡¯s not just about the intense energy use and carbon emissions that worry environmentalists¡ªthey fear other kinds of consequences as well.

One of the main concerns from the environmental community is a by-product of the desalination process: Brine. Brine is a sodium-rich residue that forms as the seawater breaks down into fresh water and salt. It must be properly treated and disposed of to avoid any damage to the environment. The good news? Brine can be used for things like food production and fertilizer, so there are benefits to brine as a by-product.

Another environmental concern is the intake of seawater from the ocean. Critics believe that these intake systems can potentially cause harm to underwater ecosystems and the species that reside there. There are similar concerns about the outflow of water back into the ocean. Is the water being treated responsibly? Or is there still some residual brine that could potentially damage the environment? These are questions that need answering before these types of projects can be successfully delivered.

Desalination in practice

There are currently more than 17,000 desalination plants around the globe. Most of them are located in the Middle East in countries like Saudi Arabia and the United Arab Emirates. This shouldn¡¯t be a surprise, as the arid region has virtually no fresh water sources¡ªat least not enough to sustainably serve the population. But it is somewhat surprising that out of all the desalination plants in the world, less than 200 of them exist in the US. That trend could likely change, particularly in the western US where droughts are becoming more frequent.

Let¡¯s start by looking in the Middle East, where desalination is an extremely common practice. The reason is simple: They need water¡ªbadly. They also have an abundance of energy as the region sits on massive oil and gas reserves. That¡¯s why thermal-based distillation makes sense in these areas. Why? Because desalination plants are placed right next to powerplants so they can leverage the electricity and waste heat to power the process. While this process is less efficient and more water is wasted, it does reduce the energy intensity.

Desalination projects can face more hurdles in regions where stricter energy use policies are in place. This is particularly true in states like California that have ambitious energy decarbonization targets. Desalination projects in the state face stiff push back from environmental advocates who believe these projects are not only just energy intensive, but also damage the environment in other ways. These include harm to ocean ecosystems, species habitats, and more. So, while decarbonizing the desalination process can help to relieve some concerns, there are still more roadblocks to successful project implementation in the US.

Providing safe drinking water while reducing carbon emissions

As we continue to navigate through the energy transition, we must understand two certain truths. We must continue to reduce the amount of greenhouse gas emissions being release into the atmosphere. And we also need water. Less than 3% of all of Earth¡¯s water is fresh water. So, if we can figure out a way to sustainably leverage seawater, we will be able to provide bountiful fresh water for communities in need.

Reducing the carbon intensity of the desalination process will help make these projects more achievable. And that will need to continue to be our focus as we combat the global water and climate crises.