Study on reduction of calcium sulfate scaling in membrane distillation by pulse flow assisted

Abstract

Membrane distillation as an emerging heat-driven membrane technology that has attracted a lot of attention in the treatment of high-salty wastewater in recent years. However, the industrialization of membrane distillation has been hampered by membrane fouling. In this study,calcium sulfate scaling was alleviated by introducing pulsed flow field assisted direct contact membrane distillation. The effects of pulse duration and pulse frequency on fouling mitigation and flux enhancement were discussed, respectively. The results showed that under the condition of pulse duration of 0.5 s and pulse frequency of 5 min-1,the membrane distillation flux still maintained more than 70% of the initial flux after 20 h of operation, and the flux intensification ratio was close to 1.3. The morphological analysis of the membrane surface after the experiment also showed that the membrane surface under the optimal pulse condition had less fouling,and the membrane structure could still be clearly observed, while a large amount of calcium sulfate crystals accumulated on the membrane surface under steady flows. Further analysis showed that compared with the steady flow condition, the pulsed flow could promote the homogeneous crystallization of calcium sulfate,and the calcium sulfate crystals could be removed by the formed membrane surface shear force and membrane vibration.

Keywords

• membrane distillation
• pulsed flow
• calcium sulfate scaling
• homogeneous crystallization