Pretreatment
Reverse osmosis membranes are subject to fouling or plugging on the membrane surface. This can
decrease the permeate production capacity of the membrane or require an increase in operating pressure
(and subsequent energy) to overcome the fouling effect. As a result, virtually every membrane desalination
facility in the world (including SWRO) requires properly pretreated seawater. The pretreatment equipment
used in SWRO facilities is similar to what you would find at any other drinking water treatment facility
elsewhere and incorporates, individually or in combination: flocculation / sedimentation to remove
suspended material; dissolved air flotation (DAF) to remove potential algal biomass or potential
hydrocarbons; granular media filtration (GMF); and/or low-pressure UF or MF to remove suspended
particulate matter. The pretreatment energy requirements are comparable to any other surface water
treatment plant, and range from 0.9 to 1.5 KWh/kgal (293 – 489 kWh/AF). When compared to the energy
costs associated with the rest of a typical SWRO facility, pretreatment accounts for 8 to 12% of the total.