Microalgal exopolymeric substances fouling in submerged vacuum membrane distillation and its mitigation via enhanced air bubbling

This work aims at studying the fouling behaviour of submerged vacuum membrane distillation (S-VMD) in desalinating the algal-blooming seawater. A dynamic microalgal fouling phenomenon and its mitigation via air bubbling was investigated over the time. At the early stage of S-VMD operation, the precipitation of inorganic salts on the membrane surface was responsible for initiating the flux decline. In the later stage, significant amounts of EPS surrounding the microalgae cell aggregates were precipitated on the inorganic scalants and further increased the membrane fouling rate. Based on the exopolymeric substances (EPS) extraction analysis, hydrophilic polysaccharides as a result of the aggregation of microalgal cells was firstly observed, followed by dominating protein fouling over the long run S-VMD operation. Excreted proteins increased the hydrophobicity of the EPS by reducing the surface charge, thus leading to a strong hydrophobic interaction with membrane surface at the 60 h of S-VMD operation. Compared to the non-bubbling S-VMD system, the system subjected to 0.167 m/s air bubbling showed superior and stable flux performance with lower extent of fouling.