USFilter picked for one of largest U.S. lime softening plants

The Metropolitan Utilities District of Omaha recently awarded USFilter a more than $6 million contract to provide clarification and dewatering technology for its new 100-million-gallon-per-day (mgd) Platte West Water Treatment Plant. As part of the contract, submittal and final design of the equipment will be conducted during the first three months of 2005....

WARRENDALE, PA, March 8, 2005 -- The Metropolitan Utilities District of Omaha recently awarded USFilter a more than $6 million contract to provide clarification and dewatering technology for its new 100-million-gallon-per-day (mgd) Platte West Water Treatment Plant. As part of the contract, submittal and final design of the equipment will be conducted during the first three months of 2005.

One of the largest lime-softening plants currently being designed in the United States, the plant will treat water from shallow wells along the Platte River using a lime softening and granular media filtration process from USFilter General Filter Products. Lime sludge from the softening process will be dewatered using two 300-ft3 recessed chamber filter presses from USFilter Dewatering Systems. While the dewatering installation marks the first such application for USFilter in the state of Nebraska, it is one of many USFilter filter presses installed for lime-softening sludge dewatering throughout North America.

Lime Softening Process
USFilter General Filter Products will supply six 125-ft octagonal Contraflo® solids contact units for the plant. Each unit will be capable of treating 17.3 mgd during full softening or 26 mgd if split lime softening treatment is used.

During the equipment procurement bid, equipment suppliers were required to submit information for painted steel and stainless steel options. Once the bids were received, the district and Omaha, Neb.-based HDR Inc., the consulting engineer for the entire project, evaluated the long-term cost-effectiveness of the options and selected a design with all submerged components constructed of stainless steel.

"The stainless steel option provides superior long-term corrosion resistance when compared to painted steel components," states HDR Project Manager Glenn Dostal, P.E. "After analyzing the life cycle cost of the equipment, we concluded future painting of steel components would outweigh the cost to purchase stainless steel construction materials."

To enhance the lime softening process, Contraflo units use a marine propeller that mixes previously formed lime sludge, treatment chemicals and raw water together. The marine propeller is ducted to the basin's bottom to re-circulate the heavy preformed solids that have settled to the basin floor. An inverted cone section in the basin provides reaction and flocculation time for the re-circulating water. As the water travels upward in the basin, the inverted cone provides a gradually reducing upflow velocity where solids settle out to provide a high clarity softened effluent.

Lime Sludge Dewatering
Capable of dewatering over 1 million gallons of lime softening sludge per week, the plant's two 300-ft3 recessed chamber filter presses will produce a cake that is more than 60% solids. The filter press, commonly called a "plate and frame," uses a feed pump to fill a series of filter plates that separate the solids from the liquid and produce a high solids cake. The filter presses are fully automated and include a state-of-the-art PLC system that controls the presses and various ancillary equipment.

According to Kevin Tobin, P.E., at Metropolitan Utilities District of Omaha, the utility considered several dewatering technologies during the initial stages of the project. The District selected USFilter Dewatering Systems' filter press because it produced the driest dewatered solids and the clearest filtrate. It was also the only technology that did not require polymer or other chemicals to dewater the sludge. Dewatering the sludge simplifies disposal, and replaces more traditional methods such as discharging the sludge to lagoons, a nearby river or a wastewater treatment plant.

Equipment delivery is scheduled for mid-2006, with plant start-up in late 2007.

USFilter Corp. (www.usfilter.com), a Siemens company, delivers cost-effective, reliable water and wastewater treatment systems and services to municipal, industrial, commercial and institutional customers worldwide. USFilter is part of Siemens' Industrial Solutions and Services Group (I&S), which provides innovative solutions and services designed to improve competitiveness in processing and manufacturing industries and in infrastructure. In fiscal 2004, I&S employed a total of 30,000 people worldwide and achieved total sales of US$5.74 billion.

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