Understanding the interaction mechanism of algal cells and soluble algal products foulants in forward osmosis dewatering

Forward osmosis (FO) has increasingly been an energy saving technology in microalgae dewatering, whereas membrane fouling is still a major obstacle for FO application. To explore the fouling mechanism of algal cells and their organic matters during microalgal FO dewatering process, Chlorella vulgaris and Scenedesmus obliquus were adopted as algae species, and the algae-derived foulants including algae cells, soluble algal products (SAP) and algal broth were used as feed solutions. The water fluxes behaviors of algal foulants had been investigated, and the dissolved organic carbon (DOC), protein and carbohydrates proportions of the feed solutions were then characterized, followed by the scanning electronic microscopy (SEM) and the analysis of extended DerjaguinLandau-Verwey-Overbeek (XDLVO) theory for the FO membrane foulants. The results indicated that algal broth resulted in the fastest flux decline due to the combined fouling between SAP and algae cells. The competitive adsorption phenomenon between cells and SAP was found in C. vulgaris broth but not in S. obliquus, resulting in a high protein content loss in the feed solution of C. vulgaris. The fouling potential of those individual and combined feed solutions could be well predicated using the XDLVO theory, and the higher the interfacial energy, the faster the flux decline was found for both adhesion and cohesion stages. The findings improve the understanding of FO membrane fouling mechanism by micmalgae, indicating the selection of algae species for FO processes.

Automated summary

This study investigated the membrane fouling mechanism in microalgal FO dewatering process and found that algal broth resulted in the fastest flux decline. A competitive adsorption phenomenon between cells and soluble algal products was observed in the feed solution of Chlorella vulgaris. The XDLVO theory was effective in predication of fouling potential for individual and combined feed solutions.