Multi-stage air gap membrane distillation reversal for hot impaired quality water treatment: Concept and simulation study

The major challenge of membrane distillation (MD) is the low gain output ratio (GOR) resulting from the high thermal energy requirement and the low water production. Here, the use of hot streams such as geothermal groundwater or produced water that are suitable to be treated by MD without the need for thermal energy input is discussed. Hot groundwater from the Northwest of Himalaya, India, is used as a case study. In this paper, we propose a novel multi stage air gap MD reversal design coupled with natural/forced cooling system. A 1-D rigorous simulation model is developed to estimate the performance of the proposed system. Water production capacity and GOR of various scenarios were estimated and reported. Based on our results, the increase in temperature difference between feed and brine discharge cooled down temperature can have a positive effect to improve both water production capacity and GOR. The increase of inlet feed flow rate increases the water production but not the GOR. The influence of increasing module width on water production and GOR is negligibly small. Results showed that the maximum GOR was about 3.89 without natural (passive) cooling system. Meanwhile, when natural (90%)/forced (10%) combined cooling system was applied, a GOR as high as 24.4 could be achieved.