Experimental Evaluation of a New Compact Design Multistage Water-Gap Membrane Distillation Desalination System

Water desalination using the membrane distillation (MD) process is an emerging technique that has the potential for future commercialization. In this study, the performance of a new design multistage water-gap membrane distillation module is experimentally investigated for possible scaling up and commercialization. A new compact design is proposed for enhanced productivity, low energy consumption, and therefore low freshwater production cost. The variations of permeate flux, specific thermal energy consumption, gained output ratio, and production cost with the different operating parameters are studied. Besides, the impacts of having parallel and series flow arrangements among the module stages are investigated. Results showed that operating the multistage system at higher feed temperature increases productivity, reduces the specific energy consumption, and minimizes the water production cost. The parallel flow arrangement is slightly better than the series arrangement in terms of productivity. However, the series flow arrangement is found better in terms of energy efficiency. The best-achieved performance indicators are gained output ratio (GOR) of 0.49, specific thermal energy consumption of 1320 kWh/m³, and water production cost of 6 $/m³, which are very promising findings of the tested compact multistage water-gap MD system.