Effects of sodium dodecyl sulfate on forward osmosis membrane fouling and its cleaning

Effect of sodium dodecyl sulfate (SDS) on the fouling of a commercial aquaporin based biomimetic forward osmosis (FO) membrane was investigated. Increasing draw solution (DS) concentration and decreasing the cross-flow velocity could aggravate the membrane fouling, and the effect of the latter was greater than the former. SDS as a surfactant could wash away some sodium alginate (SA) and calcium chloride (CaCl2) which were adsorbed on the surface of the membrane. However, SA and CaCl2 tended to form irreversible fouling when SDS had already been on the membrane. When SDS + SA + CaCl2 was used as the feed solution (FS), SDS was first adsorbed on the membrane surface and then SA and CaCl2 interact with SDS; irreversible fouling was formed when the hydrophobic tail of the SDS was adsorbed to the SA, and reversible fouling was formed while Ca2+ (bridged with SA) was bound with the hydrophilic head of the SDS. Afterwards, the cleaning effects of HCl and NaOH solutions on the membrane fouling caused by SDS were studied. The initial normalized flux could be recovered to 0.88 using both methods. Cleaning with HCl solution could slow down the formation of membrane fouling, while cleaning with NaOH solution could damage the aquaporin in the active layer of the membrane.