In situ extracting organic-bound calcium: A novel approach to mitigating organic fouling in forward osmosis treating wastewater via gradient diffusion thin-films

Forward osmosis (FO) has gained increasing interests in wastewater treatment and reclamation. However, membrane fouling has become one major obstacle hindering FO application. A novel mitigation approach for FO membrane fouling via in situ extracting Ca ²⁺ binding with the organic foulants using the gradient diffusion thin-films (DGT) was proposed in this study. The DGT could effectively adsorb the Ca ²⁺ binding with the sodium alginate via the chelation of the Chelex functional groups, and its adsorption amount of Ca ²⁺ correspondingly increased as a function of the Ca ²⁺ concentration in the feed solution. Owing to the extraction of Ca ²⁺ from the fouling layer by the DGT, the FO membrane fouling was effectively mitigated evident by significant enhancement of water flux, and at the same time, foulants became easily removed by physical cleaning. The alleviation of FO membrane fouling by the DGT could be attributed to the fact that the structure of the fouling layer became more porous and looser after in situ removing Ca ²⁺ from the alginate-Ca ²⁺ gel networks. The feasibility of fouling control strategy via in situ removing Ca ²⁺ binding with the foulants in the fouling layer was demonstrated, which provides new insights into fouling control mechanisms during FO treating wastewater.