In search of clean water, scientists are improving desalination technology

Drought and climate change are impacting water supplies around the world. But desalination — pulling fresh, drinkable water from saltwater— can offer some relief.

Desalination technology has existed for a while; dry countries like Israel, Saudi Arabia and Spain have used it for years. Most desalination technology uses a lot of energy and leaves behind a toxic byproduct: all the salt extracted from the water. Scientists and entrepreneurs are working to improve its capabilities, from moving the process offshore to running mobile desalination hubs on solar power.

One of those entrepreneurs is Robert Bergstrom, CEO of OceanWell, based in California. The company is testing desalination pods at a reservoir near Los Angeles. Eventually, the pods will go into the ocean to create fresh water.

“We're a small startup team that is set out to develop an extremely eco-friendly desalination system of a new type,” Bergstrom said. “We call it submerged RO, for reverse osmosis.”

Reverse osmosis is the process of removing salt from the water by pushing it through a membrane. Once the desalination pods are placed in the ocean, the process is passive, Bergstrom said. Because of the lower pressure in the well, the ocean water naturally flows into the pod. But to get in, it has to go through a salt-excluding reverse osmosis membrane.

“We had the insight that the sea will do the work for us if we put the equipment in the right place and design it correctly,” Bergstrom said.

OceanWell’s system also requires much less electricity than desalination processes on land. Plus, it cuts down the briny byproduct created in traditional desalination. When desalination is done on land, questions abound about what to do with that leftover, salty brine. But Bergstrom doesn’t have that same concern.

“First, we don't really concentrate the brine. It is not nearly as strong. Instead of close to double salinity to the ocean, which is standard for traditional desalination, ours is only five to 10% greater salinity," Bergstrom said. “We don't discharge it close to the bottom. We are about 50 feet above the ocean floor with our pod. And above that, we are discharging the brine through a riser to get up to ocean currents so that there is no possibility that the brine can create a problem.”

At this stage in the development of these pods, each one can process one million gallons of water per day, Bergstrom said.

Some water districts in California are interested in OceanWell’s technology. Bergstrom said pumping drinking water to a large, coastal city like Los Angeles would have a reverberating impact. Right now, Los Angeles gets its water from several sources, including the drought-stricken Colorado River.

“If we can completely meet the needs of Los Angeles, the water that they are taking from those areas doesn't have to be transported at all, or it can be transported to other places that don't have an ocean that they can tap into," Bergstrom said.

For areas farther inland that rely on groundwater, desalination technology can also help curb water shortages. In New Mexico and West Texas, for example, some underground water is too salty to drink. But researchers at the Massachusetts Institute of Technology have been testing a process to address that problem.

Amos Winter is a mechanical engineer at MIT who specializes in water scarcity issues. Winter has been working on a system that uses solar power without batteries. Though reverse osmosis is the desalination industry standard, Winter’s work uses a technology called electrodialysis.

“It can vary its flow rate and its salt extraction rate in sync with the sun, and that's important because the sun's not always shining,” Winter said. “We don't have to store energy in batteries to always run the system at a constant power level. So, when it's really sunny out, we make water really fast. When it's maybe cloudy out, we make water more slowly. In comparison, reverse osmosis — which is the industry standard — has to run at a pretty steady power. So, you have to store energy in the middle of the day in batteries, so you can run it at night or in the morning.”

Winter said this technology can reach more people facing water shortages than seawater desalination could.

“The majority of water you find in the ground around the world is salty,” Winter said. “The reason we use solar power is that most people around the world are going to be resource-constrained. They may have lower income levels or not have access to grid electricity. So, our technology makes desalination much more accessible in all areas around the world.”

Winter said his team is already looking to apply its technology at a large-scale municipal water utility in Texas. Texas relies on its own power grid, not buying electricity from surrounding areas. During the summer, much of that energy is used up by air conditioning, so there’s less available for desalination, Winter said.

“Our technology uses less energy than [reverse osmosis],” Winter said. “We can use a cheaper source in renewable-powered energy, and we can increase robustness by supplementing the grid with a renewable source.”

Traditionally electrodialysis has been more expensive than reverse osmosis. But Winter said that because electrodialysis produces less brine as a byproduct and doesn’t rely on the electrical grid, the extra cost might balance out with reverse osmosis.

“In the future, our technology should become more and more competitive,” Winter said.

Peter O'Dowd and Chris Bentley reported, produced and edited this interview for broadcast with Catherine Welch. Grace Griffin adapted it for the web.