Identifying, Evaluating, and Implementing Antiscalants in RO Reuse Applications

Abstract

The Orange County Water District (OCWD) operates a 70-mgd RO system as part of the Groundwater Replenishment System (GWRS), an advanced wastewater purification facility. Each of 15 5-mgd RO units consists of a three-stage array, operating at 85 percent recovery. As part of the operating strategy, antiscalant and pH suppression are used to limit third-stage precipitation of sparingly soluble mineral salts. Identifying successful antiscalants is extremely challenging. A variety of antiscalants with varying chemistries and capabilities present opportunities for optimizing RO processes, pricing, dosage, and pH adjustment. Recognizing the potential savings in RO pretreatment chemical cost, OCWD began antiscalant pilot-scale trials in 2009. However, failure to identify an effective product led to the trial's cancellation. Concurrently, the GWRS RO facility began experiencing third-stage permeability loss in all 15 RO units because the antiscalant was ineffective. This article discusses fast-track testing to identify effective antiscalants, the evaluation process, steps taken to switch antiscalants, and RO performance and monitoring.