Dow's Filmtec Group Offers a Low-Pressure Membrane for Potable Water Production
A new application area for water filtration is opening up with the Filmtec low energy (LE) reverse osmosis (RO) elements: 75-125 psig. The new elements of the TW30 filter series, which are typically sold as spiral-wound canisters, can save as much as 40 percent in electrical pumping energy costs compared with conventional elements that operate at pressures up to 225 psig. Dow (Midland, Mich.) introduced the series at the annual Water Quality Assn. Convention in Ft. Lauderdale, Fla. The mid-size RO elements are rated to provide a flow of 2,000 gal/d, with 99 percent salt rejection, at 25 degrees C and less than 125-psi operating pressure when total dissolved solids (TDS) are 2,000 ppm sodium chloride.
"These are Dow's standard LE test conditions," emphasized Kari Dawson-Ekeland, marketing manager for the company's Liquid Separations business unit. "In actual practice," she continued, "these elements can operate at even lower pressure with lower TDS feedwater. When the operating pressure can be lowered to as little as 75 psi, the elements will still provide excellent flow. These elements truly provide the best of both worlds by operating at lower pressure while providing great rejection and reliability."
A Dow spokesman said that the LE elements "do not represent new chemistry" in manufacturing the membrane, but rather an adjustment of the manufacturing process to increase liquid flux through the membrane, without causing reduction in water quality. An economic analysis of applications where electricity costs around 8 ct/kWh indicated that the element could save upwards of $400 annually-a one-year payback. Although many existing systems would probably require a replacement pump operating at a lower pressure, the energy savings achieved by the new low energy RO elements may justify the system modification, she said, especially in locations where electrical energy costs are a concern.
By Nick Basta
For more information, contact Dow Liquid Separations Products, P.O. Box 1206, Midland, MI 48641-1206. Tel: 1-800-447-4369