AWWA MTC57598

Seawater Reverse Osmosis (SWRO) desalination plants operating with surface open intakes require an efficient pretreatment to meet RO feedwater requirements. The objective of this study was to assess the performance of ultrafiltration (UF) pretreatment prior to RO for the treatment of high fouling potential surface seawater. A pilot plant equipped with Aquasource UF membranes was operated in dead-end mode directly on Gibraltar harbor seawater. The efficiency of UF pretreatment was evaluated against conventional pretreatment with respect to downstream RO hydraulic performance. Results of the study illustrated that UF pretreatment yielded a very good and steady quality permeate, having a lower SDI value than permeate produced by simple one-stage dual media filtration pretreatment. The principal seawater components responsible for UF fouling was identified as organic matter released by planktonic organisms. Use of low dose pre-coagulation upstream of UF helped to control this fouling potential, resulting in steady state hydraulic conditions and a low cleaning frequency. The performance of RO membranes downstream of UF were evaluated under higher recovery and higher flux rate operating conditions, to address the differential cost of UF as compared to conventional pretreatment, enabling SWRO plant design having reduced operating expenses and increased ease of operation. Includes 12 references, tables, figures.