Study And Application Of Forward Osmosis Membrane Distillation Coupling Process In The Treatment Of High Salt Organic Wastewater

For the high salt organic wastewater with large discharge in industrial production and serious pollution to the natural environment,it is very important to treat salt and organic pollutants before discharge.As a new membrane separation water treatment technology,forward osmosis membrane distillation（FO-MD）coupling technology has the advantages of good effluent quality,low energy consumption and recyclable resources.It has a broad application prospect in the field of wastewater treatment.However,there are mainly problems of salt accumulation and membrane fouling in forward osmosis and membrane distillation,which will lead to the continuous decline of water flux and treatment efficiency.Therefore,this paper first explores how to prepare high-performance forward osmosis membrane;Then,the membrane was applied in the FO-MD coupling process,and the effects of operating parameters such as solution flow rate,draw solution concentration and draw solution temperature on the water flux of the two processes were explored,and the optimal operating parameters were determined;Finally,a new water treatment equipment based on fo-md coupling process and driven by light energy is developed,and the performance of the equipment to treat high salt organic wastewater under the optimal parameters is studied.The main achievements are as follows:（1）Polyacrylonitrile（PAN）porous positive osmosis initial membrane and alkali treated modified membrane were successfully prepared by phase conversion method.Then,a variety of characterization and testing methods were used to study the morphology and physicochemical properties of the two membranes.It is found that the modified membrane has stronger hydrophilicity and salt rejection than the initial membrane,but the water permeability is weaker.In addition,compared with commercial cellulose acetate membrane（CTA）,both porous membranes showed excellent salt accumulation mitigation effect and anti-pollution ability.（2）For the FO-MD process of treating high salt organic wastewater,a single factor gradient experiment was carried out to explore the effects of the changes of solution flow rate,draw solution concentration and draw solution temperature on the water flux of the two processes.It was found that the water flux in the forward osmosis process increased to a certain extent with the increase of draw solution concentration,temperature and flow velocity,and the draw solution concentration had the greatest effect on the water flux;The water flux in membrane distillation increases with the increase of the temperature and flow rate of the extract,but decreases with the increase of the concentration of the extract.In addition,this study comprehensively analyzes the change curve of water flux and determines the optimal operation parameters.（3）Through the combination of photothermal photoelectric technology and FO-MD coupling technology,a new membrane separation water treatment equipment driven by light energy is prepared,and the continuous treatment experiment of high salt organic wastewater is carried out based on the determined optimal operating parameters.It is found that the water flux in the process of forward osmosis and membrane distillation will change with time,but finally reach the flux balance in about 7 hours,and the water flux at the balance is about 16.6 L/（m2·h）.The FO-MD coupling process effectively isolates the inorganic salts and organics in the feed liquid,and the produced distilled water can be recycled directly through the reclaimed water system.In addition,through the balance calculation of the water volume and energy consumed in the treatment process,it is found that the water treatment equipment can maintain the balance between supply and demand in the operation process.To sum up,the experimental results not only provide an important theoretical basis for the industrial development of FO-MD coupling technology for the treatment of high salt organic wastewater,but also the new membrane separation water treatment equipment developed based on this technology has been proved to be an effective way to effectively treat high salt organic wastewater.