Chemical Engineering Professor Partners with Water Agencies on Desalination Research

Improved Reverse Osmosis Membranes Hold Potential for Inland Water Use

Date: May 11, 2004
Contact: Marlys Amundson ( marlysa@support.ucla.edu )
Phone: 310-206-0540

Southern California consumes more than 250 million gallons of water per day for irrigation, laundry, drinking, bathing and other uses. Water is one of the largest industries in the nation – not only in terms of its market, but also in terms of treatment. It is a natural resource, but, like most synthetic chemicals, it goes through multiple chemical and filtration processes before reaching the consumer and it is a finite commodity.

(From left) Professor Yoram Cohen, Professor Julius "Bud" Glater, Eric Lyster and Andi Rahardianto.

“Water is not an unlimited resource,” explained chemical engineering Professor Yoram Cohen. “And water reclamation is a real issue for California and a prime opportunity for UCLA to make a positive impact.”

Southern California, which is essentially a desert, is especially concerned about the scarcity of water resources. In the last five years, there has been growing interest in water desalination through reverse osmosis membrane technology, a field pioneered by researchers in the UCLA Henry Samueli School of Engineering and Applied Science in the 1960s.

Cohen has embarked on a collaborative research project with the Department of Water Resources, the Metropolitan Water District of Southern California and others to advance reverse osmosis membrane desalination for cost-effective desalination treatment of agricultural drainage, Colorado River water and municipal wastewater. The goal of the Desalination Research and Innovation Partnership (DRIP) is to develop and demonstrate cost-effective water desalination technologies for inland use.

Among those that would benefit from the technologies advanced by DRIP is the San Joaquin Valley’s farming industry. One of the most productive agricultural areas in the country, the San Joaquin Valley is severely impacted by high levels of salt in the soil. Rough predictions show that by 2020, approximately 10-20 percent of the agricultural land in the region may need to be retired because of a build up of salts in the soil and groundwater.

The San Jaquin Valley is known as the "nation's salad bowl."

Researchers have known for more than 40 years that high salt levels would be a critical problem for agriculture. Early reverse osmosis membranes, however, required high water pressure for the desalination of agricultural drainage water to be effective, and were set aside in favor of other approaches.

Farmers have also implemented over-irrigation to wash away the salt with excess water, but had no way to store the hazardous drainage. If they moved the concentrate liquid into lagoons to allow the water to evaporate, they were left with high concentrations of selenium, which has a negative impact on wildlife and the environment. Another approach that had limited success was to plant and later harvest vegetation capable of absorbing some of the accumulated salts.

Improved reverse osmosis membranes, however, may prove to be a solution to treatment of agricultural drainage water. In the mid-1990s, Cohen and his team began a rigorous evaluation of a new generation of low-pressure reverse osmosis membranes able to operate in a pressure range of 100 to 250 psi. Typical water pressure in household taps ranges from 60 to 100 psi.

“Research in the area of membrane desalination is flourishing and the field is really coming of age,” said Cohen. “Whether they’re starting with groundwater or seawater, researchers around the country are pursuing economically feasible ways to create potable drinking water through reverse osmosis.”

It is not only agricultural areas that will benefit through better reverse osmosis membranes. DRIP technologies will also improve water supplies in urban areas.

One pressing concern in the Southland is the increasing salinity of the Colorado River, from which Los Angeles gets much of its drinking water. The standard for drinking water is no more than 500 milligrams of dissolved solids per liter, and the river is now reaching levels of 800 mg/l of dissolved solids. As an interim solution, water utilities are blending the river water with water from other sources to decrease the salinity, but in an era of scarce resources another solution must be found.

DRIP researchers are focusing their efforts on lowering the cost of desalination, which will expand available water supplies. Taking a three-pronged approach, Cohen’s group is investigating improved membrane surfaces, better operating conditions and additives to prevent or slow the build-up.

“This desalination program is an example of research at a university that will help the state solve a real problem. I feel particularly proud and fortunate to continue a legacy of research in reverse osmosis at UCLA. We’re continuing the pioneering work of Dr. Sid Loeb and Dr. Julius “Bud” Glater with more advanced tools and more pressing problems,” noted Cohen.

Removing the high levels of calcium and sulfates in groundwater through reverse osmosis will require intensive effort, especially as the team hopes to reclaim 95 to 98 percent of the water. This is a far greater rate of recovery than in desalination of seawater, which typically has a goal of 50 percent potable water recovery.

Los Angeles uses approximately 200 to 300 million gallons a day from the Colorado River. Even with a 98 percent recovery rate, there would be four to six million gallons per day of waste concentrate, which raises the issue of disposal. Members of DRIP are exploring possible disposal solutions and their potential impacts on the environment.

At UCLA, Cohen and his team are focusing on ways to improve water flow through the membranes by reducing mineral scaling. The concentration of dissolved ions near the membrane surface creates a build-up of crystallized salts that block the flow. With expertise in both surface sciences and surface nanostructures, UCLA researchers are well positioned to tackle this problem from multiple disciplines.

Cohen’s team is approaching the problem from several perspectives: development and improvement of membranes; reverse osmosis simulation studies to discover an optimal approach; and pretreatment through microfiltration or ultrafiltration. They are also examining processes that accelerate the precipitation of salts before they reach the membranes.

Researchers in Cohen’s lab are studying how surface crystallization is impacted by surface chemistry and topology, with the eventual goal of creating a membrane surface that is less prone to surface scaling. The team is creating new nanostructured surfaces and membranes to study in the lab. By developing surrogate surfaces under controlled conditions, they are able to isolate and study adhesion, how growth is affected at the nanoscale, surface features and surface chemistry.

“We’re fortunate in my research group to be able to work with Bud Glater, one of the original members of the team that developed the first practical reverse osmosis membrane,” explained Cohen. “He offers a tremendous perspective on the issues surrounding this area of research and provides a direct link to past research at UCLA.”

The partnership between UCLA and the water district agencies highlights the growing interest in reverse osmosis as a possible solution to the scarcity of available water resources.

“Five years ago, there was one student in the Engineering School studying desalination with low pressure reverse osmosis membranes. Now there are six PhD students involved in the area,” said Cohen. “They’re receiving funding for research and working closely with water agency personnel to solve real problems facing our community.”