Reverse osmosis desalination system and algal blooms part II: seawater intake technologies

Abstract

While thermal desalination processes require minimum pretreatment (mainly screening and chemical additions to prevent scaling), seawater reverse osmosis (SWRO) desalination plants require extensive pretreatment of the feedwater before entering the membranes. As the Arabian Gulf (AG) countries depend on seawater desalination, there is a strategic decision to move gradually to SWRO desalination technologies. The algal bloom (AB) events that have happened in the AG countries raise more concerns about seawater pretreatment. A seawater intake is a key limiting factor and is a real part of pretreatment for high performance desalination process. This paper (second part of a series of three parts) reviews several intake options and their effects on the quality of feed seawater and the major parameters causing membrane fouling, especially bio-fouling. These include the concentrations of algae, bacteria, total organic carbon, particulate and colloidal transparent exopolymer particles (TEP), and the biopolymer fraction of natural organic carbon. Several forms of algal organic matter (AOM) are produced by ABs with varying concentrations and include intracellular organic matter formed due to autolysis consisting of proteins, nucleic acids, lipids and small molecules; and extracellular organic matter formed via metabolic excretion and composed mainly of exopolysaccharides. Being comparatively large macromolecules, exopolysaccharides are most often insoluble in water. A significant fraction of these exopolysaccharides, known as TEP, are highly surface-active, sticky, and play a significant role in the aggregation dynamics of algae during AB events. This paper reviews the different seawater intake technologies and highlights advantages and disadvantages of each. It aims at recommending the best intake technology for the site-specific conditions of a given desalination project.