A Look At Desalination

By Hannah Ahern

Children often wonder how the world can lack safe-drinking water when there are oceans filled with endless blue. What they do not know about are the consequences consuming salt water can have on human health. On the American Museum of Natural History’s website, a researcher on the Q&A section answered a first-grader’s question regarding why humans cannot drink salt water, “If you drank seawater, the salt would get absorbed into your blood along with the water . That would make your blood too salty. So, your kidneys would have to remove the salt. But to do that they would need to use even more water!” In other words, the excessive level of chemical salts actually leads to further dehydration. It is only through a process called desalination that we can turn salt water into a safe-drinking water. 

Desalination as a Process

Desalination is the process that enables a separation of dissolved salts/other minerals from potable water. According to the CDC Safe Water Manual, “desalination is also effective in removing other chemicals like fluoride, arsenic and iron.” However, desalination’s ability to remove other chemicals relies heavily on which method the user chooses. Likewise, the aftereffects we see in the desalination process is dependent on the chosen method. 

While desalination technology is ever-developing, in general there are two types of technologies, thermal or membrane. According to the AWWA Manual, membrane-based desalination utilizes mechanical pressure, electricity, or concentration gradients as a means of accomplishing physical separation. On the other hand, thermal technology relies on evaporation of salt water, ultimately condensing and recovering the water vapor.

As the world water crisis deepens, desalination’s place in the future of safe-drinking water production grows increasingly crucial. In the case of America’s coastal populations, seawater desalination can potentially create enough drinkable water to support these entire communities. In order to understand this important concept better, let’s explore these technological processes. 

Thermal Technology

Before membrane desalination emerged, thermal technology was the only option to desalinate water before the early 1960s. Thermal technologies are based on the concept of using evaporation and distillation processes. Modern thermal-based technologies are mostly developed as dual-purpose power and water desalination systems. As previously stated, thermal desalination purifies water by heating the saline water and then collecting the resulting water vapor. Additionally, due to the high cost that goes into the process, thermal technology is mainly used in seawater desalination, as opposed to brackish (meaning water with less salt concentration than sea water) water desalination.

There are three main methods of thermal desalination: 

1. Multi-stage flash distillation
2. Multiple-effect distillation
3. Vapor-compression evaporation. 

To gain an overall understanding of these complex processes let’s take a look at distillation as an overarching technique. 

Distillation

An effective reducer of a wide range of drinking water contaminants, distillation can be enacted through both artificial or more mechanical means. For example, the United States Geological Survey portrays a simplified version of this process as listed below:

1. Dig a pit in the ground and place a bowl at the bottom of the pit that will be used to catch the condensed water. 
2. Cover the pit loosley with a plastic sheet (you can use stones or other heavy objects to hold it in place over the pit.) Be sure that the lowest part of the plastic sheet hovers directly over the bowl. 
3. Leave your water “trap” overnight and water can be collected from the bowl in the morning.

Furthermore, distillation is an essential scientific process in many different fields. According to researchers, there are three definitions of distillation as relevant to desalination. 

1. The heating and/or reducing pressure in a saline mixture which then transforms the liquid substance into vapor. All of this later condenses into drinkable liquid. 
2. The separation of fluids by utilizing the concept of “relative volatility.”
3. A “partial vaporization” caused by the heating of a liquid that relies on a different container to gather the condensed vapor. 

Membrane Technology

As defined prior, membrane-based desalination utilizes mechanical pressure, electricity, or concentration gradients as a means of accomplishing physical separation. According to a water research journal, “membrane treatment processes use either pressure-driven or electrical-driven technologies. Pressure-driven membrane technologies include reverse osmosis (RO), nanofiltration (NF), ultrafiltration, and microfiltration.” As for electrical-driven technologies, Electrodialysis (ED) is a popular electrically driven membrane process used to demineralize brackish water. As a means of understanding membrane technology in more detail, let’s explore one of the most detailed and advanced desalination systems in the world, and the method used in over 60% of facilities worldwide, reverse osmosis.

Reverse Osmosis

 This leading membrane technology forces sodium-containing water through a filter-like membrane, effectively trapping larger salt molecules while allowing smaller water molecules to pass through. Essential to understanding this process is the role osmosis, or the osmotic pressure  difference between saltwater and freshwater. Effective in desalinating both brackish water and seawater, reverse osmosis is a well-rounded practice for creating safe-water. However, important to note is that reverse osmosis requires energy to operate. Thus, while highly effective, the high cost of this method limits the production of reverse osmosis plants. 

Environmental Repercussions of Desalination Technology

Perhaps the biggest risk posed by desalination processes like reverse osmosis and electrodialysis is the often contaminant-continuing brine left behind in the water source. This phenomenon can be seen in how the California Coastal Commission denied a 2022 bid for a plant production plan “due to concerns about higher water rates, marine life loss, and impacts to poor households already living near industrial areas.” The area residents reportedly disliked the salty brine water left behind by the 100 million gallons of daily desalinated seawater. Ultimately, this brine water poses a dangerous risk to ocean life by depleting oxygen in the ocean.

Additionally, another important factor when discussing environmental repercussions of desalination is the vast amounts of energy it requires, which in some places is currently provided by fossil fuels. Researchers caution that there is potential for a “feedback loop” where greenhouse gas emissions increase alongside the need for fossil-fuel generated desalination practices. Furthermore, desalination’s future in fossil fuel generated electricity producers, like the Middle East, requires a great deal of caution when looking towards the future of desalination plant production.

Looking Towards the Future

All of this is not to say that the future of desalination technology dooms our environment.  Desalination supporters recognize the necessity to confront and solve these environmental problems tied to desalination technology. So while it is necessary to discuss the risks these desalination practices pose for our future, it is also necessary to recognize the ways in which researchers are working to solve these issues and innovate new ideas. 

Just one example of these innovations is the recent use of microbial desalination cells (MDCs), a technology which “harnesses the power of microorganisms to purify water while simultaneously generating electricity.” Another noteworthy positive trend is the more than half decrease of desalination cost throughout the last three decades. 

As humans on this earth, we must continue to innovate sustainable methods of water purification for the betterment of our planet. Desalination technology is just one of many innovations that represent the power of collaboration.

 If you want to learn more about progressive technologies like this and how they can aid in fighting the global water crisis, feel free to explore the Business Connect website. Be sure to shop for desalination filters on our website, as we offer various kinds of handheld and portable emergency desalination filters. 

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