Impacts of silica on the sustainable productivity of reverse osmosis membranes treating low-salinity brackish groundwater

Silica and silicate precipitation as limiting factors in high-recovery reverse osmosis operations

“…One would expect that the growth of the aluminosilicates on top of the accumulated seeds (Fe(III) oxide colloids) is much more extensive at high than at low recovery, leading to a larger observed particle size and this indeed seems to be the case (Figs. [6][7][8][9]. Colloidal fouling will not form a solid layer on the membrane, but if a sufficient amount of crystallization takes place inside the colloidal cake layer, it is possible to obtain dense silica deposit layers (at least on a local scale).…”

“…The presence of silica complicates desalination processes because of its high scaling potential [4][5][6] and the intricate chemistry of silica adds to the complexity of this problem. Silica has a low solubility of about 117 ppm in water at a pH of 7 and a temperature of 25 1C.…”

Foulant characterization and distribution in spiral wound reverse osmosis membranes from different pressure vessels

“…Moreover, silica fouling also frequently occurred in groundwater desalination plants [32]. Since membrane fouling has been strongly affected by the physicochemical properties of the membrane module as well as operation conditions, the fouling propensity of each plant could be different even though operated using an identical feed water source.…”

Desalination of geothermal waters using a hybrid UF-RO process. Part II: Membrane scaling after pilot-scale tests

“…Scale formation is a complex phenomenon involving both crystallisation and transport mechanisms. Thermodynamically, crystallisation or precipitation of calcium carbonate (CaCO 3 ), calcium sulphate (CaSO 4 ·H 2 O), barium sulphate (BaSO 4 ), strontium sulphate (SrSO 4 ), silicates (SiO 2 ), calcium phosphate (Ca 3 PO 4 ) or aluminosilicates (Al 2 SiO 5 ) becomes possible when the activity of ions in solution is above their saturation limit and the solution is supersaturated [1][2][3][4][5][6][7]. This phenomenon often occurs as a result of concentration polarisation taking place.…”

“…In this process the concentration of the salts is supersaturated at the membrane surface even though the bulk concentration may still remain unsaturated or under-saturated. Depending on process conditions and the type of membrane module, scale formation occurs by two crystallisation pathways [1,2,4,8,9]: (1) surface crystallisation (which occurs due to the lateral growth of the scale deposit on the membrane surface);…”