| As a new process in the field of membrane separation,forward osmosis and membrane distillation have the characteristics of simple equipment,flexible operation,energy conservation and environmental protection,easy cleaning and excellent separation effect,and are used in many fields such as pure water preparation,seawater desalination and wastewater treatment.However,due to the different working principles of forward osmosis and membrane distillation processes,the feed liquid concentration effect and effluent quality of the two processes are also different.In addition to extracting the original components of the liquid,the positive permeated water will also be mixed with a little pollutants in the raw liquid,while the membrane distilled water is almost pure water,and the rejection rate of pollutants in the raw liquid can reach 100%on the premise that the membrane is not soaked.Based on the above characteristics of membrane distillation and forward osmosis process,as well as the high cost of ultra-high osmotic pressure treatment of high-salt wastewater,this paper adopts forward osmosis and membrane distillation two membrane treatment technologies to concentrate municipal wastewater and high-salt wastewater,and constructs a set of seawater of high-salt wastewater of municipal wastewater The high salt wastewater after forward osmosis treatment is further concentrated by vacuum membrane distillation technologyIn the forward osmosis part,firstly,high salt wastewater is used as the extraction solution to drive the treatment of municipal sewage,and then seawater is used as the extraction solution to drive the treatment of diluted high salt wastewater,which simultaneously realizes the concentration treatment of municipal sewage,the preliminary dilution of high salt wastewater and the desalination of seawater.The effects of membrane orientation and cross flow velocity on the flux of forward osmosis membrane were investigated.It was found that the water flux of PA-TFC membrane when the dense active layer was facing the solution to be treated was more stable than that when it was facing the extraction solution;When the cross flow velocity is 0.5 L/min,the water flux value is low and fluctuates greatly.When the cross flow velocity is 1 L/min and 1.5 L/min,the water flux value is similar and changes stably.Investigating the concentration and interception effect of municipal sewage and high salt wastewater,it is found that municipal sewage can be concentrated by 10 times,among which COD and TP can be concentrated by 6.68 times and 4.04 times respectively,and the interception rate is higher than 97%.TN and NH3-N can only be concentrated by about 2 times,and the interception rate is about 70%;High salt wastewater can be concentrated three times,the COD and cations in the wastewater are concentrated to about two times,and the interception rate is higher than 80%.In the membrane distillation part,the high salt wastewater after forward osmosis treatment is concentrated again by vacuum membrane distillation technology to recover the produced condensate.The effects of feed liquid side temperature,penetration side vacuum and feed flow rate on water flux and the final treatment effect of high salt wastewater were investigated.The results show that the water flux increases with the increase of feed liquid side temperature,transmission side vacuum and feed flow.Under the conditions of feed liquid temperature of 80℃,feed flow of 1.5 L/min and cold measurement vacuum of 0.085 MPa for 4 hours,the diluted high salt wastewater can be concentrated to 0.05 L.the water flux of membrane distillation and the quality of distillate are stable,and the salt rejection rate is always higher than 99.99%. |
