Submerged membrane distillation for inland desalination applications

Submerged vacuum membrane distillation is an alternative to conventional membrane distillation configurations which offers lower energy consumption and higher thermal efficiency. The feasibility of a submerged vacuum membrane distillation system for inland desalination was investigated. Relatively similar flux could be achieved compared to cross-flow vacuum membrane distillation, but a lack of agitation led to a faster rate of wetting. Transverse vibration was applied to limit crystal deposition on the membrane surface. While an increase in permeate flux was observed, scaling was not significantly reduced. Further attempts at scaling mitigation with periodical air backwash and aeration suggested that bubble generation may lead to more crystal deposition on the membrane when using a mixed feed solution containing sparingly soluble salts. © 2015 Published by Elsevier B.V.

In comparison to conventional cross-flow configurations, submerged VMD distillation offered lower energy consumption while achieving relatively similar permeate flux. However, scaling remained an issue. The application of transverse vibration in submerged VMD did not significantly limit salt crystal deposition, but did increase permeate flux by up to 21%. Long-term operation indicated that while submerged VMD coupled with transverse vibration consistently produced higher flux for both single and mixed salt feed solutions, wetting occurred at a faster rate compared to when agitation was not present. This was attributed to changes in the structure of the scaling layer on the membrane. The implementation of periodical air backwash and A aeration in conjunction with transverse vibration showed that bubble generation in mixed feed solutions containing sparingly soluble salts may encourage scaling in submerged VMD. Further investigation on the effects of bubbling in membrane distillation is required to verify this.