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Significance Statement
Our research demonstrates that considerable improvement to raw water quality used to feed seawater reverse osmosis facilities can be achieved when using a subsurface intake system. Our review paper also clearly shows that the economics of using subsurface intake systems are favorable, despite the increased cost of construction. The decreased use of energy and chemicals in the pretreatment system more than compensates for the higher constructions cost, especially when viewing the full system within the context of a life cycle analysis (lower operating cost).
Since publication of our paper, we have completed additional research on facility planning methods to locate subsurface intake systems based on coastal geologic and water quality conditions (Desalination and Water Treatment 52, 2351-2361). We have completed an investigation of beach gallery intake feasibility in Florida (Desalination and Water Treatment 52(1-3) 1-8) and four investigations on the technical feasibility of using offshore seabed gallery intakes along the shoreline of the Red Sea (IDA Journal 4(4) 42-48; Desalination and Water Treatment 51(34-36) 6472-6481), Desalination and Water Treatment, doi:10.1080/19443994.2014.909630, Journal of Applied Engineering and Research, doi: 10.1080/2349676.2014.895686). We have two papers in review that demonstrate that induced aquifer flow into well intake systems can remove up to 100% of transparent exopolymer particles (TEP), nearly all of the biopolymer portion of natural organic matter, all of the algae, and up to 98% of the marine bacteria. All of these particles or substances are linked to membrane biofouling.
Our research is currently focused on the development of new designs and concepts that can be applied to any facilities with any capacity, rather than solely small and intermediate capacity systems. Our analysis shows that gallery intake systems are must suited for applications to mega-capacity seawater RO plants (over 100,000 m3/d). The seabed gallery intake at Fukuoka, Japan is currently the largest capacity gallery intake system with the intake capacity being 103,000 m3/d. This system has been successfully operating for 8 years without any cleaning of the upper surface of the gallery.
We believe that subsurface intake system in combination with other emerging technology can be used to significantly reduce the cost and environmental impacts of seawater desalination. The issue of impingement and entrainment that may have some effect on the environment is essentially eliminated.
Thomas Missimer can be contacted at tmissimer@fgcu or [email protected].
Journal Reference
Desalination, Volume 322, 2013, Pages 37-51.
Thomas M. Missimer, Noreddine Ghaffour, Abdullah H.A. Dehwah, Rinaldi Rachman, Robert G. Maliva, Gary Amy.
Water Desalination and Reuse Center, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia and
Schlumberger Water Services, 1567 Hayley Lane, Suite 202, Fort Myers, FL 33907, United States.
Abstract
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 seawater reverse osmosis 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.
