BIOFOULING POTENTIAL IN OPEN SEA AND ADJACENT BEACH WELL INTAKE SYSTEMS1

Intense solar radiation and elevated water temperature are characteristics of the Red Sea particularly in the southern part. These factors make coast water conducive to biological growth. Consequently, seawater reverse osmosis (SWRO) desalination plants sourced from open sea intake systems are subject to membrane fouling. Chronic membrane fouling in one such plant on the southwestern Red Sea coast of Saudi Arabia has necessitated the search for an alternative beachwell intake system. The beachwell system consists of three wells located within a distance of 20–30m from coast line and spaced about 75m from each other. Measurements of bacterial growth rates, bacterial biofilm formation, organic and inorganic nutrients were carried out in the beachwell water and compared to those of adjacent coastal seawater. Beachwells showed significantly higher bacterial growth rates and increased inorganic nutrient concentrations, but significantly lower biofilm formation and decreased organic nutrient concentrations than seawater. Therefore, presence of organic nutrients is a determinative factor in biofilm formation and subsequent membrane fouling. The present data indicate that feed water for the plant can be sourced directly from beachwells without significant fouling problems. On the other hand, well water also possesses characteristics which promote improved plant operation. These include reduced silt density index (SDI) values of less than one and a constant, favorable temperature of about 33°C