The shale gas revolution is leading to rapid transition from coal to natural gas in the power industry and also to significant expansion of other industries including petrochemicals. The shale gas revolution is leading to rapid transition from coal to natural gas in the power industry and also to significant expansion of other industries including petrochemicals. Many of these plants require high-purity water for steam generation and other unit operations. In addition, plant personnel are facing tighter guidelines on wastewater discharge quality and quantity. Membrane technologies have been leading the way with regard to makeup water treatment, and they are emerging as core components of wastewater treatment systems. This article examines direct applications of these technologies and includes several lessons learned. For years, clarification followed by media filtration was the common technique for removing suspended solids from makeup water. And indeed, modern clarifiers may still be quite appropriate in many situations, particularly where lime softening is needed. When suspended solid removal is the primary goal, the membrane techniques of micro- and ultrafiltration (MF and UF...