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.