Improving Fouling Indices Measurements and Modeling Their Relevance

Abstract

Reliable methods to predict feedwater fouling potential are important in preventing and diagnosing fouling at the design and operation stages of ultrafiltration (UF) and reverse osmosis (RO) plants, as well as monitoring pretreatment performance during operation. The desalination industry uses the silt density index (SDI) extensively to characterize feedwater fouling tendency. However, SDI measurements commonly lack the required precision, especially for high-quality pretreated waters, such as UF permeates. A novel performance model predicted how much transmembrane and feed-brine fouling will occur in the RO stage of a desalination plant based on SDI and modified fouling index (MFI) results. The SDI and MFI observations can now be translated into enhanced parameters that describe how much transmembrane and feed-brine resistance would be created by a certain fraction of water passing through the membrane. This article describes developments in the equipment and methodology used to measure fouling tendency of RO feedwater. Recommendations regarding the testing equipment and procedures are also provided.