Silica mitigated calcium mineral scaling in brackish water reverse osmosis.

Although the autopsies of reverse osmosis (RO) membranes from full-scale, brackish water desalination plants identify the co-presence of silica and Ca-based minerals in scaling layers, minimal research exists on their formation process and mechanisms. Therefore, combined scaling by silica and either gypsum (non-alkaline) or amorphous calcium phosphate (ACP, alkaline) was investigated in this study for their distinctive impacts on membrane performance. The obtained results demonstrate that the coexistence of silica and Ca-based mineral salts in feedwaters significantly reduced water flux decline as compared to single type of Ca-based mineral salts.

Silica scaling of reverse osmosis membranes preconditioned by natural organic matter.

Reverse osmosis (RO) membranes were preconditioned in this study with humic acid, sodium alginate, or bovine serum albumin, and subsequently examined for silica scaling using the water matrix representative of concentrated brackish groundwater. The results suggested that water matrix combined with organic foulants affected silica scaling. High ambient pH favored the moderate silica ionization and thus the silica homogeneous polymerization to potentially form low molecular weight silica oligomers.

Dependence of initial silica scaling on the surface physicochemical properties of reverse osmosis membranes during bench-scale brackish water desalination.

Silica scaling of reverse osmosis membranes in brackish water desalination is less understood than hardness scaling due to the complex silica behaviors at the membrane/water interface. In this study, -COOH, -SOH, -NH and -OH functional groups were introduced onto polyamide membranes to create distinct surface physicochemical properties. The resulting membranes were further studied under similar scaling conditions to yield temporal flux loss data that were empirically interpreted by a logistic growth model.