Evaluation of Pressure-Driven and Novel Membrane Processes for Treatment of Geothermal Brines

Abstract

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) as possible treatment technologies for cooling tower water. 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 NF pilot testing indicate that high quality water can be produced while operating at high fluxes using pressure-driven processes. DCMD pilot testing evaluated the treatment of superheated geothermal brines. Testing showed promising results with high operating fluxes, high quality product water, and also successful utilization of a waste heat. Finally, a preliminary cost estimate was conducted to evaluate the cost requirements for a full-scale system.