Mixing Moves Osmosis Technology Forward0 pages

U.S. soldiers get drinking water via the first forward-osmosis membrane, made possible by high-shear mixing

By Doug Cohen, Charles Ross & Son Co.

CAPT. DAVE EATON COMMANDED A SIX-MAN Air Force unit during the recent invasion of Iraq. A few weeks after the invasion was launched, his unit took part in a joint operation with Army Rangers to capture an airfield in western Iraq. The operation was successful, and when the Rangers departed, Eaton's Air Force team stayed behind to secure the desert airfield and wait for more supplies.

When the supply plane failed to appear, the team realized it would not be receiving a delivery any time soon. The soldiers would have to hold the airfield and fend for themselves. Among other challenges and threats, Eaton knew his men would soon face a critical shortage of drinking water in the blistering desert heat. His solution was to supplement the small amount of water they had with their own urine.

He explained the plan to his team. "The guys looked at me sideways," Eaton says. They didn't know that he had brought along a new filtration device developed by Hydration Technologies (HTI), Albany, Ore.

The soldiers urinated into a common container into which Eaton tossed a sealed plastic sack that resembles a medical IV bag. As the soldiers watched, the bag spontaͭneously filled as water migrated through the walls leav׭ing impurities and poisons behind. They repeated this process for two weeks and held the airfield until follow-on forces arrived. The HTI filter was crucial to the unit's survival, Eaton says. "And [the water] tasted great!"

Many filtration and purification technologies are availͭable today, but virtually all of them suffer from a familiar set of disadvantages. Most require energy and mechanical parts to force liquid through a filter ͗ and energy is often in short supply during a crisis. Many such systems are complex and demand special training. Others require components that are delicate, not designed for rugged use, or too heavy to be considered portable.

Virtually all mechanical filters capture impurities and eventually clog. Ultrafine filters those that are designed to reject pathogens and extremely small impuri׭ties clog quickly when filtering turbid water.

Figure 1. A soldier puts an HTI X-Pack filter into a puddle. The membrane bag will fill with clean water via forward osmosis.

One alternative to mechanical filtration is chemical purification. But chemical treatments require precise dosages and exposure times, and can leave an unpleasant taste. They are also ineffective against threats such as chemical poisons, heavy metals and even some microor׭ganisms. Another critical disadvantage is that many chemical treatments are ineffective at purifying water that is extremely cloudy or turbid.

The one filtration concept that is free of all of these disadvantages is forward osmosis (FO). (See sidebar: "Forward Osmosis: How it Works.")

"The forward-osmosis concept has been around for years," says Robert Salter, CEO of HTI. "In theory, it looked like the perfect alternative to energy-reliant technologies ͗ mainly because it is so simple."

In Hydration Technology's FO filtration system, water diffuses into the bag when a generic sport-drink powder is in contact with the inner, clean side of the membrane. The process is spontaneous. It requires no energy, no moving parts and no special expertise. It won't clog in even the most turbid water (up to 1,000 Nephelometric Turbidity Units), because dirty water is

www.chemicalprocessing.com

October 2004 29