Use Of A Segmented Ceramic UF Membrane To Pretreat Cooling Tower Blowdown ZLD System
By By Brian L. Wise, Stanton Smith, PhD and Mark Waer, PhD
In an effort to conserve water, a major power plant in the southwest USA built a cooling tower water blowdown (CTBD) treatment system consisting of electrocoagulation (EC), ultrafiltration (UF), and reverse osmosis (RO). Although the system reached the water quality treatment goals adequately, the UF membranes only lasted 3 years and the EC was abandoned because of costs and maintenance issues. Without EC in service at present, the silica is not being removed. This resulted in RO system recovery decline and shortened RO membrane life.
A service company began a pilot plant trial with its segmented ceramic monolith membrane using magnesium chloride and sodium hydroxide as pretreatment as an alternative to EC + Polymeric UF. In the pilot testing, silica was removed by an average of 80%. The ceramic membrane flux held stably at 100 to 130 gallons per square foot per day (GFD) (170 to 220 liters per square meter per hour [LMH]) without the need of high rates of crossflow, and with conventional flux maintenance using backwashes and chemically enhanced backwashes. This treatment process was shown to be stable over several weeks of continuous operation, and the membranes were thereafter fully recovered by conventional chemical clean-in-place.
This article describes the pilot testing results used and the conceptual design and operating cost estimates of the full-scale upgrade of the CTBD treatment plant, which benefits from the advantages of the novel ceramic membrane used in the process.
Industrial companies require clean water for cooling, boiler makeup, and a variety of manufacturing processes. One of the biggest industrial users is cooling water for thermoelectric power generation. With continued water scarcity issues in various parts of the world, industrial companies are increasingly making the effort to reduce their water footprint to mitigate risk. It is more common now for a power station to reuse treated municipal effluent water as makeup for cooling towers when access to the waste effluent is feasible. When reusing waste water from an outside source is not practical, many companies are now looking for ways to reduce and reuse water from internal sources. When considering areas to reuse water, cooling tower blowdown (CTBD) often emerges as a target application given the large volumes of water used.
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