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Evaluation of Pressure-Driven and Novel Membrane Processes for Treatment of Cooling Tower Water
AdvisorChildress, Amy E.
Civil and Environmental Engineering
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Cooling towers are an essential part of power generating facilities and require large quantities of water for continuous operation. To meet the high water demands, cooling towers use makeup water from various sources. Low quality makeup water leads to poor efficiency throughout the plant and large amounts of blowdown. This investigation evaluates pressure-driven membrane processes such as nanofiltration (NF) and reverse osmosis (RO) along with novel membrane technologies such as direct contact membrane distillation (DCMD) and forward osmosis (FO) as possible treatment technologies for cooling tower water. Results from bench-scale testing showed that all four technologies were able to effectively treat the cooling tower water. Membrane cleaning strategies were also explored for the NF/RO and DCMD systems. Results showed that, in most cases, the fluxes were recovered and the membranes maintained high rejection after cleaning. Pilot studies were conducted for approximately 300 hr using an NF system with ultrafiltration (UF) pretreatment; performance was evaluated at 30 and 60% water recovery. Results for pilot testing indicate that high quality water can be produced while operating at high fluxes using pressure-driven processes. Finally, a cost estimate was conducted to evaluate the requirements for a full-scale NF system to treat cooling tower waters. It was determined that membrane systems could possibly save $170,000 per year for a 100-MW facility depending on the cost of an alternative water source.