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CHAPTER
1
Introduction to Saline Water Pretreatment
1.1 Purpose of Pretreatment 1 1.2.3 Membrane Fouling and Flux
1.2 Membrane-Fouling Mechanisms 3
1.2.1 External and Internal Fouling 3 References 1.2.2 Concentration Polarization 4
Redistribution 8
10
OUTLINE
1.1 PURPOSE OF PRETREATMENT
As any other natural water source, saline water (e.g., seawater, brackish water) contains solids in two forms: suspended and dissolved. Suspended solids occur in a form of insoluble particles (particulates, debris, marine organisms, silt, colloids, etc.). Dissolved solids are pre- sent in soluble form (ions of minerals such as chloride, sodium, calcium, magnesium, etc.). At present, practically all desalination plants incorporate two key treatment steps designed to sequentially remove suspended and dissolved solids from the source water.
The purpose of the first stepdpretreatmentdis to remove the suspended solids from the saline source water and to prevent some of the naturally occurring soluble solids from turning into solid form, and precipitating on the reverse osmosis (RO) membranes during the salt separation process (see Fig. 1.1). The second stepdthe reverse RO systemdseparates the dissolved solids from the pretreated saline source water, thereby producing fresh low- salinity water suitable for human consumption, agricultural uses, and industrial applications.
Ideally, after pretreatment the only solids left in the source water would be the dissolved minerals, and as long as the desalination system is operated in a manner that prevents these
Pretreatment for Reverse Osmosis Desalination
http://dx.doi.org/10.1016/B978-0-12-809953-7.00001-2 1 Copyright © 2017 Elsevier Inc. All rights reserved.