Application: Plant retrofit into existing granular filter media
Capacity: 50 MGD (187,500 m3/d)
Commissioned: March 2005
Location: Thornton, CO
OAKVILLE, ON, Canada, Jan. 23, 2006 -- Water quality was a major concern for the Columbine Water Treatment Plant (WTP), a large 30-million gallon per day (MGD) dual-media gravity filtration facility in the city of Thornton, CO.
The WTP draws its water from both the South Platte River and Clear Creek. With 10 to 15 wastewater treatment plants upriver, nitrates, total dissolved solids (TDS), and hardness are quite high by the time the water reaches the intake pipes of the Columbine WTP. In fact, at various times throughout the year, treated wastewater effluent can comprise up to 70% of the water flowing past Thornton.
The high degree of wastewater effluent in the source water needed an advanced treatment process to ensure that the City of Thornton receives the highest quality drinking water. Water managers decided that a retrofit strategy was the best way to meet the fiscal, technical, and performance requirements for the 30-year old facility.
For many conventional treatment plants, immersed hollow-fiber membrane cassettes can simply replace granular filter media in the existing basins. During the retrofit process, granular filter media are removed, piping is modified to accommodate the membrane system and increased flow parameters, and pumps and blowers are installed for permeate production, backpulse cleaning, and aeration.
A retrofit would enable the plant to quickly and cost-effectively increase both treatment capacity and water quality without building new structures for the process equipment. Municipalities benefit by avoiding large capital costs resulting from site acquisition and building construction, while dramatically improving water quality and increasing plant capacity.
Zenon ZeeWeed® immersed ultrafiltration membranes were selected to be retrofitted into existing filter basins based on the present worth cost evaluation, high value, and outstanding performance that the system demonstrated.
Process Overview
Raw water is pumped from the lakes and is pretreated by coagulation, flocculation, and sedimentation through four upflow solids clarifiers. From the clarifiers, the water flows to the ZeeWeed process tanks. Trains of membranes provide treatment for up to 50 MGD (187,500 m3>/d) of water.
Thousands of membrane fibers hang loosely in each membrane cassette and a slight vacuum is applied to the end of each membrane fiber to draw water through microscopic pores and into the hollow fibers. With a nominal pore size of 0.04 µm, the membranes form a physical barrier to suspended solids and provide greater than 4-log removal of pathogens such as Giardia and Cryptosporidium, and turbidity of less than 0.1 NTU. Rejected particles remain in the process tank and are discharged to reject equalization tanks. From these tanks, reject transfer pumps feed the water to the second stage filtration train.
The second stage, a 2.1 MGD train enhances the recovery of potable water from the river and is made up of five ZeeWeed® cassettes. The configuration enables the plant to recover more than 99% of potable water from the river and also substantially reduces the cost of raw water pumping.
UV disinfection and chlorination will be the final step of the treatment process before the water is released to the distribution system. Reject water from the second stage flows by gravity to settling ponds where it is held for a short time prior to flowing back to the first lake in the reservoir system.
For similar and other case studies, see: www.zenon.com/resources/case_studies/index.shtml.
Based in Oakville, Ontario, Canada, Zenon Environmental Inc. (www.zenon.com) is a world leader in providing advanced membrane products and services for water purification, wastewater treatment and water reuse to municipalities and industries worldwide. Canada's Top 100 Employers ranked Zenon in their top 100 list for the last six years.
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