AWWA ACE61623

Cooling water recovery is becoming common place in the power plant design strategy due to environmental restrictions on discharges, limitations on water supply, and the need to expedite permitting of generation facilities. A conventional membrane process cannot function under high concentration of hardness, silica and other organic limitation. For treatment of cooling tower blowdown, the engineers provided softening micro filtration, followed by high recovery reverse osmosis for pre-concentration of the blowdown. Finally, the blowdown will be treated in an evaporation pond to achieve the zero liquid discharge objectives. The blowdown recovery is a membrane process with a modified pretreatment scheme to accommodate high concentrations of dissolved solids including silica. It has been commercially tested with silica levels in excess of 1600 ppm in the reject. Cooling tower blowdown recovery with the process is potentially more than 90% since the process is limited only by osmotic pressure. The process is also resistant to organic and biological fouling, which could potentially be present in the wastewater streams. The paper discusses the McClain Energy Facility, a new power plant in McClain, Oklahoma that utilizes the blowdown recovery process to treat high silica cooling tower blowdown and process wastewater. The high purity product water is recycled back to the cooling tower thus reducing the fresh makeup water requirement and reducing wastewater volume. The reject stream, which is about 10% of the original blowdown volume, is discharged to an evaporation pond. The design resulted in substantial savings in capital and operating cost in achieving Zero Liquid Discharge in addition to maximizing the reuse of raw water from a local wastewater treatment effluent. Includes table, figures.