Subsurface intakes for seawater reverse osmosis facilities: Capacity limitation, water quality improvement, and economics

• The use of subsurface intake types for seawater RO facilities was documented. • Feedwater quality improvements by using subsurface intakes were demonstrated. • Reduced environmental impacts using subsurface intakes were discussed. • Capacity limits on various subsurface intake types were assessed. • Life-cycle cost savings using subsurface intakes were preliminarily analyzed. a b s t r a c t a r t i c l e i n f o The use of subsurface intake systems for seawater reverse osmosis (SWRO) desalination plants significantly improves raw water quality, reduces chemical usage and environmental impacts, decreases the carbon footprint , and reduces cost of treated water to consumers. These intakes include wells (vertical, angle, and radial type) and galleries, which can be located either on the beach or in the seabed. Subsurface intakes act both as intakes and as part of the pretreatment system by providing filtration and active biological treatment of the raw seawater. Recent investigations of the improvement in water quality made by subsurface intakes show lowering of the silt density index by 75 to 90%, removal of nearly all algae, removal of over 90% of bacteria, reduction in the concentrations of TOC and DOC, and virtual elimination of biopolymers and polysaccharides that cause organic biofouling of membranes. Economic analyses show that overall SWRO operating costs can be reduced by 5 to 30% by using subsurface intake systems. Although capital costs can be slightly to significantly higher compared to open-ocean intake system costs, a preliminary life-cycle cost analysis shows significant cost saving over operating periods of 10 to 30 years. Seawater desalination is an energy-intensive and costly means of treating water to potable standards and has some environmental impacts. With the development of advanced membrane technology and energy recovery systems, the energy consumption and cost of seawater desalination have been significantly reduced over the past several decades [1]. However, membrane fouling is still a major problem at most seawater reverse osmosis (SWRO) facilities, which reduces operational efficiency and the life-expectancy of the membranes [2]. Complex and expensive pretreatment processes are commonly required to reduce the rate of biofouling and the frequency of membrane cleaning (Fig. 1). Possible environmental impacts associated with conventional open-ocean intakes, such as impingement and entrainment of marine biota, can also create large permitting costs and construction delays [3,4]. There are also environmental impacts associated with the use of chemicals to keep the intakes and …