Gas Bubbling Assisted Direct Contact Membrane Distillation For High Salinity Water

Membrane distillation(MD)is a separation process that relies on the vapor pressure difference between the two sides of a hydrophobic membrane.Membrane distillation technology has high application potential in seawater desalination,concentrated brine treatment,etc.,with good effluent water quality,low operating temperature and pressure,small size of equipment,the use of solar energy and other clean energy,etc.However,the membrane distillation process has not been commercially applied,mainly due to the low membrane flux,the hydrophobic membrane used is faced with the problems of membrane fouling and membrane wetting.Therefore,improving the mass transfer process and scaling of membrane distillation has become a research hotspot in membrane distillation process.In addition to membrane modification,which has been studied by many scholars,the auxiliary process has attracted attention in practical application because of its simplicity and efficiency.In this study,gas bubbling was coupled to the direct contact membrane distillation(DCMD)process,and its influence on the performance of membrane distillation was studied,especially the enhancement effect of bubbling on the membrane flux and scale inhibition effect of membrane distillation when the intake solution was high concentration brine.In the experiment,the bubbling assisted DCMD process was optimized,including the optimized operating parameters and equipment.In terms of the enhancement effect on the membrane flux,20wt% Na Cl solution was taken as the research object.It was found that the bubble had a significant enhancement effect on the membrane flux in the process of membrane distillation to treat high brine,and the enhancement ratio could reach more than1.6.And through the optimization of operating parameters,it is found that the enhanced effect of bubbling is more obvious at higher inlet temperature and inlet concentration,but it does not increase linearly with the increase of inlet flow and inlet flow,but there is an optimal value of technical operation.Based on the experimental analysis,the treatment efficiency of bubbling coupled membrane distillation for concentrated seawater was studied.The simulated reverse osmosis concentrated water(reverse osmosis used for seawater desalination)and the actual concentrated seawater were selected to carry out operation experiments.It was found that bubbling could improve the recovery rate of water and reduce the concentration time.At the end of the experiment,tensile test was carried out on the film after the concentration experiment,and it was found that the mechanical properties of the film were not affected greatly after the introduction of bubbling.