Water Hunters

UNM researchers tap into technology to quench the world’s thirst

howe_thomsonCloudcroft, New Mexico is a Charming mountain town with A population of 750, A Ski area, the nation's highest golf course - and A serious water shortage. During winter, the town uses about 70,000 gallons of water daily. In the summer, the town's census soars, AS does the demand for water. In the summer of 2004, Cloudcroft's water shortage was so critical that the town had to truck 20,000 gallons of water in every day.

Cloudcroft is fixing its water shortage by building a novel water treatment plant that will supplement its existing water supply with recycled wastewater. University of New Mexico Regents Professor of Civil Engineering Bruce Thomson is a member of the New Mexico Environment Department task force working with Cloudcroft on the project. He is helping with treatment process selection and developing performance standards for the system. Those standards are critical given the negative perception of treated wastewater flowing from the town's taps. "We're shortening the distance from the discharge point to the intake point," explains Thomson. "The public is uncomfortable about the concept."

Cloudcroft's new system is actually a combination of two treatment processes, membrane bioreactor (MBR) and reverse osmosis (RO). MBR is a variation on conventional wastewater treatment that replaces standard clarifiers with a special membrane to remove bacteria. The conventional process removes 99% of the bacteria; MBR removes 99.9999%. The water from the MBR process then goes into an RO system, a high pressure treatment process that removes sodium, chloride, and other ions by forcing the water through a special synthetic membrane that allows water molecules to pass through but prevents most others from doing so. Water from this MBR to RO process will be almost as high quality as distilled water. Cloudcroft will store most of this treated water in a pond rather than pump it into a larger water source like a river or aquifer. "To the best of my knowledge, nobody in the U.S. has done anything like this," says Thomson.

New Sources, New Technologies

The water shortage in Cloudcroft is a snapshot of what's happening in communities across the Southwest, the nation, and the world. Fresh water resources are scarce and demand is growing. So researchers like Thomson are hunting for new ways to quench the world's thirst.

Kerry Howe, assistant professor of civil engineering and water treatment expert, is also on the hunt for water. Howe is studying new water sources and optimizing current water treatment systems. His research is funded by a contract from Sandia National Laboratories's Jumpstart Program. "Jumpstart finds technologies and people that are doing things that are not five or ten years out but that could be implemented a little faster," explains Richard Kottenstette, a member of the technical staff at Sandia National Laboratories and acting project manager of the Jumpstart Program. "Recently we've been looking at ways to ensure adequate supplies of water in the U.S."

Howe's research matches that goal. "One thing that we're trying to do is take water that you don't want to drink and make it water you do would want to drink," says Howe. The water in question is brackish (moderately salty) or saline (very salty), and it's plentiful. Ninety-seven percent of the world's water is saline. Experts estimate that brackish groundwater resources in New Mexico are three times greater than fresh water resources. How do you make salt water useful? Reverse osmosis is one answer. The process separates a feed stream into a product stream of potable water, and a waste stream, or concentrate that contains most of the salts. RO is used mainly in coastal communities but Howe is optimizing it for inland use. He's finding ways to increase the recovery rate, or the fraction of the total flow recovered for potable use. "If we go to a municipal reverse osmosis plant today, they might be running at a 70 percent recovery rate. What we're trying to do in the lab is to develop technology that would allow them to run at 90-95 percent recovery," says Howe.

To do that, he's controlling precipitation, or the point where minerals in the water turn to solids. Solids accumulate on the RO membrane surface and reduce the flow of water through it. In Howe's lab-based RO system, he adjusts flow rate, water velocity, and other conditions, so that minerals in the feed stream are concentrated just to the point of precipitation. When conditions reach that level, Howe sends a portion of the stream through another process where precipitation occurs. "We're trying to take something that would have happened within our reverse osmosis system and would have clogged the system and limited recovery, and we're putting in a separate process that will remove the solids separately," explains Howe. The process works. In a recent test, Howe operated his RO process for one week with a solution that was 100 percent supersaturated and experienced zero loss of flow.

Kottenstette says that Howe's findings are important to the bigger picture. "This is an important step forward. This will go into our body of knowledge as to how these unit operations work in an actual desalination application," says Kottensette.

From Waste Stream to Revenue Stream

Howe is also tackling the challenge of waste stream disposal. Coastal RO plants simply dump their high-salinity concentrate back into the ocean. Inland communities have to find other cost effective, environmentally sensitive ways to dispose of huge volumes of concentrate.

That's why Howe is turning the concept of the waste stream on its head. "The overall goal is to actually take that waste stream and turn it into something you can sell," he explains. Howe and a team of students have conducted a nationwide inventory of the mineral content in ground waters. Depending on the region, waters contain high levels of silica, calcium chloride, calcium sulfate and other minerals. Each mineral has a market value that could be parlayed into an income stream. For instance, calcium sulfate is used to manufacture gypsum board for construction. Now Howe’s team is working with industries to turn waste streams into revenue streams.

The Arsenic Challenge

Calcium sulfate and other minerals have potentially lucrative second uses, but one common element found in ground water doesn't: arsenic. The toxin must be removed from water sources. Now, the EPA has lowered the maximum arsenic concentration in drinking water from 50 parts per billion to ten parts per billion, which adds to the arsenic removal challenge.

Large municipalities have the budget and technical expertise to remove arsenic from their water using a precipitation process. It's a greater challenge for smaller communities with smaller budgets. The most appropriate arsenic removal approach for small towns is often adsorption. In this process, water is passed through columns filled with an arsenic removal medium made of ferric oxide, which looks like coffee grounds. Arsenic forms chemical bonds with the ferric oxide which causes it to adsorb, or stick, to the medium's surface.

There are about a dozen commercially available adsorption media, and each works differently depending on the water source. By choosing the right medium, a community can maximize its arsenic removal process and save money. However, testing the efficacy of different media is prohibitively expensive and time-consuming for small municipalities.

Bruce Thomson has an answer. Last year Thomson unveiled a small, rapid process to test efficacy of arsenic removal media. His process, called Rapid Small Scale Column Testing (RSSCT), accelerates the standard testing process and costs less. Standard tests take up to a year, cost tens of thousands of dollars, and require columns that can be eight feet tall. RSSCT takes just weeks, costs about $10,000, and uses four-inch columns filled with finely ground adsorption media.

Thomson has already used RSSCT to test water for six New Mexico communities and expects that number to grow. "Over the next two or three years a couple dozen communities in New Mexico will want to do this testing with us," says Thomson.

Alicia Aragon worked with Thomson to develop the RSSCT procedure as a Ph.D student at UNM, and now uses the technology as a postdoctoral appointee in Sandia National Laboratories' Geochemistry Department. She uses RSSCT to evaluate arsenic treatment processes for communities in New Mexico and throughout the country. "I mimic the pilot studies with RSSCT and look at how the small scale test can predict the results of the pilot test," says Aragon. The pilot tests take up to a year to yield results; Aragon has hers in two weeks. So far, the tests are yielding the same results. "This is especially good for small rural communities and Indian reservations," says Aragon. "For them to quickly get results and know what's best for their water - that's going to help a lot."

Ironically, effective arsenic removal creates another challenge: how to dispose of arsenic-laden adsorption media. Once again, Thomson and Howe are searching for answers. Together they're studying what happens to the arsenic-laden wastes after disposal. "Once you collect this arsenic and put it all in one place, if it leaches off the media and gets into the groundwater, you create a whole new groundwater contamination problem," explains Howe. "Our new research may lead to decisions about what kind of landfills this media should go into."

Finding water sources, treating water, managing concentrates; it's a complex and vital cycle for every society. Howe and Thomson's research sustains the process and improves the outlook for the future. "We cycle things through our environment," comments Howe. "Our job as environmental engineers is to try to minimize the hazards associated with that and to maximize our use of those resources in an environmentally conscious way."