Novel Trends in Dual Membrane Systems for Seawater Desalination: Minimum Primary Pretreatment and Low Environmental Impact Treatment Schemes

Abstract

Early adopters of ultrafiltration (UF) technology for pretreatment in seawater reverse osmosis (SWRO) desalination plants have used membrane-based technology mainly for its ability to reliably treat difficult feedwater. Recently the drivers for adopting UF technology have changed, and more emphasis is put on environmental aspects, such as the ability to decrease chemical consumption and sludge quantities. In addition, there are signs UF pretreatment is becoming increasingly cost competitive. Often a case is made that integrated, or dual, membrane systems are less expensive than conventional schemes, because savings in the SWRO stage are greater than the cost increase attributed to UF. Sometimes a case is made that even a pretreatment system can be less expensive, which is especially true when a stand-alone UF unit (hence without extensive primary treatment) is compared to enhanced conventional pretreatment techniques that use extended primary treatment (chamber coagulation, clarification processes) and multiple stages of media filtration. This article focuses on more recent drivers for UF adoption, especially on treatment schemes that reduce costs by minimizing environmental impact and the use of primary treatment techniques.