Introduction
In the development of tactical water purification systems, as with most other evolving technologies, the U.S. Department of Defense (DoD) has increasingly utilized "commercial off-the-shelf" (COTS) products and components.
The COTS approach, set forth in the famed 1994 Perry Memo by then Secretary of Defense William Perry, recognizes that the military can often implement new technologies more quickly and cost-effectively by incorporating products developed, refined and proven in the commercial marketplace.
Driven by the war on terrorism and the deployments in Afghanistan and Iraq, the DoD has rapidly developed new tactical water purification systems that employ state-of-the-art, commercially-available ultrafiltration (UF) membrane technology, sometimes in conjunction with reverse osmosis (RO).
The new systems can be easily transported to remote locations and quickly set up to produce safe drinking water from almost any available raw water source, including highly-turbid water, seawater, and water with nuclear, biological or chemical (NBC) contamination. The systems are designed to provide potable water for missions ranging from the battlefield to humanitarian relief efforts around the world.
Transportable in a C-130 Plane
The U.S. Congress initiated the Expeditionary Unit Water Purifier (EUWP) program in 2003 with two principle goals:
•To stimulate discovery and invention in science and technology to push well beyond the present state-of-the-art in water reclamation, purification, energy and distribution technologies.
•To verify and validate the utility of emerging state-of-the-art science and technology in water purification systems for the benefit of both the military community and the federal and civilian community in keeping with "Dual Use" management objectives.
The first measurable objective of the program was to develop a transportable water treatment system that could be airlifted in a single C-130 transport plane and be quickly assembled to produce 100,000 gal/day of purified water from seawater.
Through extensive collaboration between Office of Naval Research, U.S. Army Tank Automotive Research, Development and Engineering Center, Naval Surface Warfare Center -- Carderock Division, and the U.S. Bureau of Reclamation along with industry experts, two first-generation EUWP demonstration systems have been built by Village Marine Tec, of Gardena, Calif.
The EUWP system consists of two skids that together can be airlifted in a single C-130 transport plane to provide potable water for reconstruction, humanitarian aid and disaster relief. The system can be set up in as little as eight hours, and is completely self-contained, requiring only diesel fuel to run power generators.
The 20' L x 8' W x 8' H skid containing a UF system can produce 200,000 gallons of drinking water per day from a contaminated water source, enough to support the needs of between 40,000 and 50,000 people. An identically-sized skid containing an RO system can receive pretreated water from the UF skid, and purify 100,000 gal/day when the source is highly turbid surface water or seawater, as well as feed water with NBC contamination. The system was benchmarked against the similarly-sized U.S. Army's Tactical Water Purification System (TWP) capable of treating 36,000 gal/day of freshwater and 28,000 gal/day of seawater.
Each EUWP uses 16 TARGA®-10 hollow fiber UF cartridges designed and manufactured by Koch Membrane Systems Inc., of Wilmington, Mass. The 10" diameter cartridges contain 35-mil hollow fiber membranes. The membranes and the cartridge housing are both composed of polysulfone, a high strength polymer thermoplastic noted for its excellent dimensional stability under a wide range of temperatures, and chemical stability when exposed to various types of cleaning chemicals that are used to maintain high productivity from the membranes.
The TARGA-10 operates at a low pressure, minimizing the electrical power demands on the portable generator. Moreover, unlike other UF membranes that use blasts of coarse bubble aeration during backflush to shake material loose, the TARGA-10 cartridge minimizes power requirements and noise because the system does not require large amounts of compressed air. Less compressed air means smaller compressors which results in space and power savings.
The EUWP systems were quickly put to the test. When Hurricane Katrina struck, the systems were undergoing final demonstration testing by the Bureau of Reclamation at the Brackish Groundwater National Desalination Research Facility in Alamogordo, N.M. Within days, a request came from the Mississippi Emergency Management Administration (MEMA) to send the unit to Biloxi to provide potable water to the Biloxi Regional Medical Center.
The EUWP arrived and was immediately set-up on the beach by engineers from the U.S. Department of the Interior's Bureau of Reclamation and U.S. Army TARDEC. A hose was dropped into the ocean, and within a matter of hours it was converting seawater into clean water suitable for use in the hospital.
Prior to Katrina, the EUWP system also passed another real-world test, purifying 250,000 gallons of water in three days at a remote U.S. Coast Guard station at Port Clarence, Alaska, after severe storms drove seawater into the reservoirs used to supply drinking water for the station. In addition to demonstrating the production capabilities, this deployment allowed the government to demonstrate the transportability of the system since it required flying it to a remote site via C-130.
Transportable in a HMMWV
The DoD has also utilized state-of-the-art membrane technology for its much smaller and more portable scale Lightweight Water Purifier (LWP). The compact LWP unit produces 125 gal/hour from fresh or brackish water and 75 gal/hour from saltwater (containing up to 45,000 mg/L TDS), sufficient production to support company/battalion-size units in the field.
The LWP, designed by Mechanical Equipment Company Inc., (MECO) of Sugar Land, Texas, is light enough to be carried by four soldiers and simple enough for two operators to set up and begin producing water in just 45 minutes. The entire system can be transported in the cargo space of a High Mobility Multi-Purpose Wheeled Vehicle (HMMWV) and in a single lift of a medium-lift utility or assault helicopter such as the UH-60 Black Hawk.
By utilizing UF membranes to pretreat water prior to processing by RO, this design replaces the Army's previous generation of portable water processing equipment that pretreated the RO feed water with multimedia filters (MMF) and disposable cartridge filters.
The MMF and cartridge filters posed several problems. They are capable only of removing suspended solids to approximately 1-5 micron, allowing contaminants such as bacteria and viruses to escape and cause early fouling of the RO membranes.
Another problem with cartridge filters is that they require frequent replacement, as often as every half hour. The problem is not only the labor involved in replacing the filters, but also the need to continually resupply consumable items. This can create a logistical challenge -- and be quite dangerous -- in remote locations and under combat conditions.
The ultrafiltration process in the new LWPs avoids the need to replace and resupply disposable filters, since the UF cartridges can be cleaned and reused. Each LWP system employs three ROMIPURE® ultrafiltration cartridges. The ROMIPURE cartridges are also COTS products supplied by KMS and are widely used in industrial water purification applications.
The 5" diameter ROMIPURE cartridges contain the same 35-mil hollow fiber polysulfone membranes as the much larger TARGA-10 cartridges used in the EUWP. The UF membrane pores have a 100,000 Dalton nominal molecular weight cut-off (MWCO), and consistently produce filtrate water with less than 0.1 NTU, a more than tenfold improvement compared to multimedia 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 U.S. Army awarded MECO an exclusive multi-year contract for 400 of the LWP units, and about half of the units have already been delivered, some of which are in use in Iraq and Afghanistan.
Commercial Off-the-Shelf Membrane Technology
The EUWP and the LWP exemplify the benefits of the COTS procurement process. By incorporating UF hollow fiber membrane technology from the commercial market, the DoD and its collaborators and suppliers were able to design and build high-performance mobile purification systems on an aggressive schedule. The ROMIPURE and TARGA-10 hollow fiber membrane cartridges have been tested in some of the most demanding industrial applications, and the DoD was able to successfully build its new generation of mobile water purification systems around these commercially available, off-the-shelf components.
TARGA and ROMIPURE are registered trademarks of Koch Membrane Systems Inc. in the United States and in other countries.
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