Control of gypsum-dominated scaling in reverse osmosis system using carboxymethyl cellulose

The mitigation of gypsum scaling on reverse osmosis (RO) membrane using carboxymethyl cellulose (CMC) as a green antiscalant was investigated in this study. Static test was conducted to pre-evaluate the inhibition performance and mechanism against gypsum scale using optical microscope and X-ray diffraction (XRD) as auxiliary analysis methods. The antiscaling effects in the RO system were investigated by flux change measurement and membrane surface observation. Results from the static test and RO operation indicated that a suitable degree of carboxymethyl substitution and an appropriate dose were both necessary for CMC to achieve satisfactory inhibition performance. Analysis from optical microscope and XRD showed obvious changes in crystal size and surface morphology of gypsum scales using CMC as antiscalant, which indicated that the effects of chelation, dispersion, and lattice distortion were all involved. In the RO operation, permeate fluxes in the presence of CMC remain relatively constant in gypsum-dominated solution compared with the sharp flux drop in the blank test. Coexisting anions, such as CO32- and PO43-, nearly had no influence on the antiscaling effect of CMC in the RO operation. Direct observation of RO membrane surface under scanning electron microscopy indicated that only a thin layer that contained few deposits was found when CMC was used. However, a thick crystal layer completely covered the membrane surface for the antiscalant-free test. Thus, CMC is an efficient and environmentally friendly antiscalant with remarkable potentials for membrane fouling control in RO operation.