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Abstract
SWCC has initiated and developed NF membrane seawater pretreatment as a promising technique which can provide superior permeate quality for both membrane and thermal desalination processes. During last three years, intensive investigation was conducted on NF process resulting in increasing recovery up to 90% with 40% reduction in capital and operational costs. Thus, successful operation of NF process at such higher recoveries without injecting acid has raised another important aspect regarding alkalization of NF process to reduce boron content in seawater feed as an additional interesting achievement. Therefore, this paper presents the following investigation areas: first, testing the performance of three different NF membranes on removal of boron from seawater; second, alkalization of NF seawater pretreatment at different recovery ratios and feed pH and its effect on boron removal; third, problems encountered during alkalization of NF process and their remedies; fourth, performance of NF-SWRO configuration with NF membrane alkalization. Preliminary tests of three different NF membranes revealed that NF membranes of 18% salt rejection did not show any significant reduction in boron content even at feed pH 9·5. Whereas NF membranes of 25 and 35% salt rejection at feed pH 9·5 exhibited boron rejection of 29 and 46%, boron concentration in NF permeate reached about 3·4 and 2·6 mg L−1 respectively compared to seawater feed of 4·8 mg L−1. The operational results of 8-elements NF array for ∼4500 h at different recovery ratios (65% up to 85%) and feed pH (8·1–9·5) were presented and discussed. Results of NF-SWRO configuration indicated that with NF membrane alkalization boron content in RO permeate was 0·4–0·6 mg L−1 at 50% SWRO recovery and 15·9 L m−2 h−1 flux rate.
The existing research study confirmed that the alkalized NF membrane seawater pretreatment gives higher benefits in pretreatment stage (softening, partial desalination, boron removal and particulate removal) while operating SWRO at higher recovery and flux rate.
