New approach for scaling control in forward osmosis (FO) by using an antiscalant-blended draw solution

In this study, a novel strategy for scaling control in forward osmosis (FO) by employing an antiscalant-blended draw solution is newly suggested. To evaluate its validity, an antiscalant-blended draw solution containing a mixture of NaCl and poly (aspartic acid sodium salt) (PAspNa) was examined by conducting FO experiments under gypsum scaling at various operating modes. Compared with a draw solution composed only of NaCl, the PAspNa-blended draw solution exhibited comparable water flux but significantly lower reverse solute flux. Gypsum fouling tests demonstrated that reversely flowed polymeric anions from the blended draw solution could effectively control membrane scaling, with a scaling inhibition efficiency comparable to that of the direct addition of PAspNa to the feed solution. Sodium hexametaphosphate (SHMP) was also assessed as another scale inhibiting chemical to verify this novel concept. Similar advantages were clearly observed with the SHMP-blended draw solution. The overall results demonstrated that this new scaling control strategy in FO could be extended to various antiscalants that are optimized for specific mineral scales, and thus potentially commercialized in real-world industrial applications, which is vulnerable to membrane scaling.