New water treatment technology helps alleviate climate-change driven drought
- Jan 28, 2022 12:15 am GMT
With climate change contributing to drought conditions all over the world, public water supply systems are struggling to meet demand. Membrion, a startup company in Seattle, is developing new water treatment membranes to enable these supply systems to tap into new water sources. One of the key features of Membrion’s innovation in membrane manufacturing, which it’s developing in partnership with a large multinational manufacturer, is that it’s expected to make desalination for some types of water more energy efficient than the current market leading technology. Although water efficiency will remain the number one technique for responding to drought, Membrion’s product has the potential to become an important tool in the drive to bring water services to the world’s growing and increasingly thirsty populations.
Feeling thirsty yet?
By the year 2050, due to climate change and population growth, five billion people worldwide will have inadequate access to water, according to a recent announcement from the UN World Meteorological Organization. Already, most of the Western U.S. is officially in unprecedented drought, and the United States Geological Survey forecasts that increased water demand, combined with climate change, will eventually stress water supply systems throughout most of the U.S.
As governments grapple with the growing gap between water supply and demand, the most economical and environmentally sound response is usually to ramp up efficiency efforts. Efficiency alone probably won’t be sufficient for long, and many municipalities will go searching for additional water sources.
With freshwater resources under pressure throughout the country, some public water systems will look to brackish water—surface or underground water that’s saltier than freshwater but not as salty as seawater. There’s more brackish water in the U.S. than freshwater, and sources have been identified in nearly every state. According to Greg Newborn, Membrion’s founder and CEO, “Leveraging brackish water supplies is going to be a must to combat climate driven droughts.”
Although sources are abundant, there are only a few hundred brackish water desalination plants in the U.S., out of its more than 148,000 public water systems. There are two primary reasons for such scarcity: the copious amounts of energy desalination plants require, and the hard-to-dispose highly-concentrated salty waste they produce. Membrion’s technology has the potential to mitigate these problems and enable more water systems to utilize brackish water.
The salt of the earth
Brackish water is defined as water containing salt and other minerals in concentrations ranging from 1,000 to 35,000 parts per million (ppm). Below that range it’s freshwater and above seawater. In general, the less salt in the water, the less energy required to remove it, which is why freshwater is the most attractive to process into drinking water, and seawater the least.
There are two primary technologies used to remove salt from brackish water: reverse osmosis and electrodialysis. Both rely on semipermeable membranes, thin sheets, usually made of plastic, filled with microscopic pores. For reverse osmosis, pumps pressurize the brackish water up to about 400 pounds per square inch (psi)—about a dozen times the air pressure in car tires—which drives water molecules across the membranes, leaving the salt behind. For electrodialysis, electric fields pull the salt ions out through the membrane pores, leaving behind freshwater.
Reverse osmosis is currently by far the dominant technology accounting for 80 to 90% of the country’s brackish water municipal desalination plants. But electrodialysis has the edge over reverse osmosis in some applications, and when combined with Membrion’s new membranes, has the potential to make it the clear choice in many more applications.
Just one word...ceramics
Founded in 2016, Membrion is the first company to make electrodialysis membranes out of ceramic instead of plastic. The company doesn’t actually use the same materials that are in your teacup. Industrial ceramics comprise materials that are both inorganic and non-metallic, and, like teacups, are known for being both hard and brittle.
To make its membranes, Membrion coats a piece of fabric with silica gel, the same chemical that’s contained within those desiccant packets you find in the bottom of vitamin bottles. That assembly is then dried in such a way that Membrion can control the size and distribution of the pores. For a product made from ceramic, these membranes are surprisingly flexible.
Because Membrion’s membranes are ceramic, they are tougher than conventional plastic membranes. They can handle wider temperature ranges, and are more resistant to corrosion and fouling. They’re currently used in the oil and gas fields, and in mining, where the conditions are too extreme for conventional plastic desalination membranes. In these applications, Membrion provides the membranes, which are then incorporated into electrodialysis equipment made by other companies.
A tale of two technologies
To understand the impact Membrion’s membrane advancements could have, let’s first review how electrodialysis currently compares to reverse osmosis in three ways:
Energy. To desalinate a gallon of brackish water using reverse osmosis, on average, takes as much electricity as to run a 9 W LED bulb for an hour. Electrodialysis should be more energy efficient, given that it doesn’t require the high pumping pressures associated with reverse osmosis. In practice, though, electrodialysis systems are the most efficient technology only when purifying slightly salty water (1,000 - 3,000 ppm).
The reason for electrodialysis' limited energy advantage is that reverse osmosis uses pumping energy to force water molecules through membranes. When there’s more salt in the water, the pump only has to work a bit harder. In contrast, electrodialysis uses electric energy to draw salt ions through membranes. The more ions that have to be moved, the more electric energy it consumes.
Where there’s little salt in the water, electrodialysis consumes about 40% less energy to desalinate brackish water than reverse osmosis. Membrion’s Newbloom expects his company's new membranes will do even better, reducing energy consumption by as much as 60% compared to reverse osmosis.
Brine disposal. Desalination systems separate treated water into two streams: clean water, which is further treated and piped onward to users, and a highly concentrated brine stream. Brine disposal often accounts for about a third of the overall cost of running a brackish water desalination plant, and if not done carefully, can cause environmental damage.
A typical brackish water reverse osmosis system produces 1 gallon of brine for every 4 gallons of drinkable water produced. Electrodialysis systems produce less brine, even when treating heavily salted water — as little as 1 gallon for every 19 gallons of drinkable water. Less brine, even though it’s more concentrated, usually enables less expensive and easier disposal.
Fouling. The build up of minerals on membrane surfaces degrades the performance of desalination systems. Because they can reverse their electrical polarity, and drive unprocessed minerals off those surfaces, electrodialysis systems usually can go longer than reverse osmosis without being shut down for cleaning.
Add it all up, and electrodialysis beats reverse osmosis on brine disposal, fouling and energy consumption when desalinating slightly salty water. Reverse osmosis only has the edge when it comes to consuming less energy to desalinate moderately to heavily salted water.
If Membrion’s new product could enable electrodialysis systems to be more energy efficient over a wider range of salinity, they could gain market share, reduce energy consumption and enable more water supply systems to draw brackish water.
You can never be too thin
According to Newbloom, Membrion’s new membranes, which are expected to go into commercial production soon, will be about one-tenth as thick as the current market leading products. “That thickness reduction means that it takes less electricity to move ions across the membranes.” said Newbloom. He also claims that conventional membranes made from polymers can’t be made this thin because they “are delicate and break easily. Our more durable ceramic materials enable this ultra-thin performance.”
Newbloom claims that these new membranes will extend the salinity range over which electrodialysis desalination is more energy efficient than reverse osmosis up to 12,000 ppm, which covers most ground water sources. He also expects that electrodialysis systems equipped with super thin membranes will be able to “deliver up to 40% lower levelized cost (including first cost, energy, and brine disposal) than existing reverse osmosis technology for low salinity applications and up to 20% lower for high salinity applications.”
If Membrion and its partner can actually achieve these performance improvements, it’s likely that brackish water desalination would be used far more than it currently is.
Tackling the climate-change driven water crisis
Brackish water desalination is a valuable tool to increase freshwater supplies, not a silver bullet that will solve our climate-driven drought problems. We will also need innovative policies and technologies at every step of the water cycle, including more efficient irrigation technologies, a pricing and trading scheme to reallocate water from low-value to high-value uses, and standards for lower-volume indoor plumbing systems. Even when it’s part of the solution, brackish water desalination must be accomplished with great environmental sensitivity in order to avoid depleting and polluting the very estuaries and aquifers that make it available.
In the meantime, we can expect that when Membrion and its partner bring their new product to market, it will come up to speed quickly. Electrodialysis is a mature technology. Both Membrion and its partner are experienced in producing and distributing electrodialysis membranes. There is likely to be pent-up market demand for this product. With climate change likely to continue to put pressure on water supplies, it’s clear that water efficiency and treatment will spur innovative new technologies for many years to come.
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