14-02: Lessons Learned from a HERO-Based ZLD System

A critical topic that continues to be discussed at CTI meetings is the need for water conservation across a broad spectrum of industries and municipal applications. More and more, plant personnel are looking at cooling tower blowdown recycle and recovery as a method to conserve water. An emergency technology is water recovery based on the high-efficiency reverse osmosis (HERO) technology. This process includes ultrafiltration, softening, and reverse osmosis. However, the concentrating nature of cooling towers combined with chemical treatment programs subjects blowdown treatment systems to chemistry that may significantly influence performance. This paper examines lessons learned from HERO operation at a power plant in the Pacific Northwest. Difficulties included poor performance of an upstream multi-media filter, fouling of ultrafilter membranes from standard cooling tower treatment chemicals, and the somewhat belated realization that feed of a cationic polymer ahead of membrane systems is typically not a good idea. Also outlined is how improvement to the magnesium oxide feed system for a raw water clarifier significantly improved silica removal from the cooling tower makeup.