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 Ca2+ binding with the organic foulants using the gradient diffusion thin-films (DGT) was proposed in this study. The DGT could effectively adsorb the Ca2+ binding with the sodium alginate via the chelation of the Chelex functional groups, and its adsorption amount of Ca2+ correspondingly increased as a function of the Ca2+ concentration in the feed solution. Owing to the extraction of Ca2+ 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 Ca2+ from the alginate-Ca2+ gel networks. The feasibility of fouling control strategy via in situ removing Ca2+ binding with the foulants in the fouling layer was demonstrated, which provides new insights into fouling control mechanisms during FO treating wastewater.