UF membranes for RO desalination pretreatment

Development of an Environmental Impact Assessment and Decision Support System for Seawater Desalination Plants

“…UF/MF pretreatment was originally developed for highly polluted waste waters and has also become widely accepted for brackish waters today [50]. As a pretreatment to SWRO, it has long been considered as an expensive option that was only used as a last resort to deal with difficult source waters [54].…”

“…The type and amount of pretreatment depends on the intake water quality and the desalination process. As surface intakes have to cope with more variable water quality due to seasonal weather conditions and algae blooms, pretreatment is generally more complex and extensive than for sub-surface intakes, which can achieve a silt density index (SDI) < 3 with single stage sand filters (without coagulant) or with cartridge filters only [50].…”

“…CEB and CIP As mentioned in the previous sections, UF/MF membranes usually require three intermittent cleaning processes (Tables 6 and 7) to maintain permeability [22,50,132]: a frequent membrane backwash every 20-60 minutes for 1-2 minutes with filtered water to counteract the accumulation of suspended solids and bacteria, often enhanced with an air scour (AEB) to accelerate the removal of particles and foulants (short-term permeability maintenance), a chemically enhanced backwash (CEB) on a weekly or daily basis to restore the membrane's performance, using chlorine, hydrogen peroxide or chlorine dioxide, with acid and base conditioning (medium-term maintenance), cleaning in place (CIP) on a monthly basis or if severe fouling occurs using similar chemicals as for CEB at potentially higher concentrations (long-term maintenance).…”

“…Table 2 summarizes the pretreatment characteristics of the main pretreatment alternatives for SWRO, followed by plant-specific details for beachwells (Tables 3, 4), conventional pretreatment (Table 5), and UF pretreatment (Tables 6, 7). Table 2: Pretreatment options prior to SWRO [50,57].…”

“…Filters are backwashed with either filtrate or concentrate. The frequency depends on the quality of the raw water and is usually at least once a day [50]. The backwash is either discharged into the sea or dewatered, and the sludge sent to a landfill (cf.…”