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Industry News

U.S. Army Deploys New Water Purification Technology
By John McArdle
May 20, 2009
  E-mail article
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Wilmington, MA -- The United States Army is utilizing state-of-the-art membrane water purification technology to support highly mobile military operations and humanitarian missions. Mechanical Equipment Company Inc. (MECO), of Sugar Land, Texas, has designed a Lightweight Water Purifier (LWP) that can be easily transported to remote locations to produce safe drinking water from almost any available raw water, including highly-turbid surface water, brackish water and seawater. Additionally, the LWP is also capable of purifying water contaminated with nuclear, biological and chemical warfare agents.

The new LWP is light enough to be carried by four soldiers and simple enough for two operators to assemble and begin producing water in just 45 minutes from a water source such as a river, lake, pond, or ocean. The entire system can be transported in the cargo space of a HMMWV and by a single haul of a medium-lift utility or assault helicopter such as the UH-60 Black Hawk.

In the past, desalination systems had been designed for conventional seawater salt concentrations of 35,000 ppm, however in the Middle East, the salinity is much higher. It is 45,000 ppm in the Arabian Gulf, and in "waterholes" in the desert it can reach 60,000 ppm. MECO specifically tests each LWP to verify that it meets this 60,000 ppm requirement, enabling the systems to treat any water, anywhere in the world.

The compact LWP unit will produce 125 gallons per hour (gph) from fresh or brackish water and 75 gph from seawater, sufficient production levels to support company/battalion-sized units in the field. The exact number of people that the LWP unit can sustain in the field is proportional to the water consumption scenario. For example, if the unit is used solely for drinking water, it will be able to support many more soldiers than if it is used for general purposes such as cooking, cleaning, showers, or laundry.

Evolution of Portable Water Treatment

Water filtration technology has evolved significantly since MECO began designing and manufacturing transportable water treatment systems for the U.S. military more than sixty years ago. In fact, the original thermal desalination systems used by the Marine Corps in the invasion of Iwo Jima employed MECO’s patented vapor compression technology.

The new LWP combines two types of membrane filtration: ultrafiltration (UF) membranes pretreat the water prior to processing by reverse osmosis (RO) membranes. This design replaces the Army’s previous generation of portable water processing equipment, which pretreated the RO feed water with multi-media filters (MMF) and disposable cartridge filters.

The MMF and cartridge filters posed several problems. Fundamentally, they were only capable of removing suspended solids between approximately 1-5 microns, allowing some particulate breakthrough and causing quick fouling of the RO membranes.

The other problem was that the cartridge filters required frequent replacement, as often as every half hour in some cases. This problem extended beyond the labor involved in replacing the filters. More importantly, the continual re-supply of consumable items can be a logistical challenge – and quite dangerous – in remote locations and under combat conditions.

UF Pretreatment of RO Feed Water

The UF membrane process in the new LWPs eliminates the need to replace and resupply disposable filters. Each system employs three Romicon® Romipure® ultrafiltration cartridges from Koch Membrane Systems, Inc. (KMS), of Wilmington, Massachusetts, USA.

The 5-inch diameter cartridges contain hollow fiber membranes with an internal diameter of 35-mil. The membranes and the cartridge housing are both composed of polysulfone, a high strength polymer thermoplastic noted for its excellent chemical stability under a wide range of temperatures.

The Romipure UF membranes have a 100,000 Dalton nominal molecular weight cut-off (MWCO) that consistently produces filtrate water with turbidity of less than 0.1 NTU, a more than ten-fold improvement compared to MMF and cartridge filters. The UF membranes remove turbidity, suspended solids, bacteria and other microorganisms from the feed water that can foul the downstream RO membranes. The higher quality filtrate water prolongs RO membrane life and dramatically extends the time between RO cleanings, regardless of the feed water conditions.

The UF pretreatment not only serves to limit fouling of the RO membranes, but the Romipure cartridges also have important features that limit and counteract their own fouling. The hollow fiber cartridges operate from the inside to the outside during filtration (see Figure 1). The feed water (retentate) flows through the center of the hollow fiber, and the filtered water (permeate) passes through the fiber wall to the outside of the membrane fiber. The tangential flow of the retentate sweeps across the membrane surface and continually acts to limit membrane fouling.

Source: http://www.kochmembrane.com/

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