Correlating scalants characteristic and air bubbling rate in submerged vacuum membrane distillation: A fouling control strategy

The feasibility of aeration for membrane scaling mitigation in submerged vacuum membrane distillation (S-VMD) system was evaluated. The effect of aeration rate in both intermittent and continuous modes were investigated. The flux decline rate due to fouling was reduced significantly with air bubbling. In the absence of aeration, larger salt crystals containing sodium chloride (NaCl) and magnesium sulphate (MgSO4) were deposited on the membrane. Continuous air bubbling at 30 LPM provides sufficient surface shear with noticeable reduction of sealants on the membrane surface. However, continuous bubbling at higher flow rate (60 LPM) caused rapid nucleation and smaller crystals on membrane that inferior the bubble scouring effect. Based on the theoretical analysis of hydrodynamic forces induced by the bubble flow, the net shear force generated by the bubbling at 60 LPM with velocity of 0.2 m/s (bubble size of 250-400 mu m) is not effective to remove particle that is smaller than 1.09 mu m. Continuous aeration at 30 LPM showed better cleaning efficiency and had almost constant specific energy consumption over long term operation. These results indicated that air bubbling is a feasible and effective method for alleviating membrane scaling in S-VMD system.