Transfer Simulation And Property For Treatment Of High-salinity Wastewater Of Membrane Distillation

Membrane distillation(MD)is a separation process that combines membrane technology with classical distillation,and can be applied to seawater desalination,wastewater concentration,ultrapure water production,food industry and other fields.MD has the advantages of high rejection,compatibility with low-grade heat and high system compactness.The process simulation of MD will help to explore the mechanism and potential applications.It also helps to optimize operating parameters,structure design,and the configuration of MD system.In addition,the study on the application and performance of MD for the treatment of high-salinity wastewater was relatively few.In view of this,transfer simulation and property for treatment of high-salinity radioactive wastewater of MD were carried out.Two basic configurations of MD,direct contact membrane distillation(DCMD)and air gap membrane distillation(AGMD),were chosen as the modelling processes.Some methods were presented for the calculations of the total gas pressure in the membrane pore,the thickness of condensate film,and the heat transfer in air gap.Further,programs were compiled to simulate MD process.And the influence of various factors,such as temperature,salinity,porosity and thickness of air gap,on process performance(such as flux,polarization coefficient,etc.)was investigated systematically.In DCMD,it was proved by experiments that the hot fluid can counteract the static pressure of the distillate side to cross the membrane and make entry into the other side,with the result that the mechanical energy in the distillate side increases due to the input of flow work.To put the energy to useful work,energy-saved DCMD(ES-DCMD)was developed and estimated.The simulation showed that the normalized energy saving of about 30% was achievable.DCMD was used to concentrate simulated samples of concentrated seawater and radioactive wastewater from nuclear components factory.The effects of temperature and salinity on flux and rejection were investigated.The temperature enhances the transfer but salinity is unfavorable.MD showed high rejection for the treatment of high-salinity wastewater.Except the volatile substances(ammonia),the rejection rate of conventional substances and the simulated radioactive elements(cobalt and uranium)was around 99%.SEM and EDS showed that scales were formed on the surface and inside the pores of the membrane used for long term,and the structure of membrane material also changed.There is possibility of fouling at low supersaturation even unsaturation.And membrane structures can also serve as the core of crystallization.It could reduce the risk of membrane fouling that removing nucleation sites before rapid crytalization,use of antiscalants and pretreatment when dealing with high-salinity wastewater.