Design And Preparation Of Triple-layered Thin Film Composite Forward Osmosis Membranes And Its Application In Shale Gas Wastewater

As a new type of membrane separation technology driven by osmotic pressure,forward osmosis(FO)technology has attracted wide attention due to its advantages such as easy operation,environmental friendliness,and low pollution tendency.It is widely used in seawater and brackish water desalination,farming irrigation,drug separation and other fields.Polyamide composite(TFC)FO membranes have serious internal concentration polarization(ICP)problem in the actual application process,and the "trade-off" between the water flux and salt rejection of TFC membranes restricts FO technology in practical application.In addition,membrane fouling will also affect the performance of the FO membrane,shorten the service life of membrane materials,and increase cleaning and actual operating costs.To cope the above problems,this research uses carbon nanotubes(CNT)as the intermediate layer to prepare a high-performance thin film nanocomposite(TFN)FO membrane with a triple-layered structure,and systematically studies the application of FO in shale gas wastewater treatment and inorganic fouling in the FO process.The specific research content is as follows:The dopamine(DA)modified CNT dispersion was deposited on a polyethersulfone(PES)ultrafiltration support layer by suction filtration to construct an intermediate layer structure of the FO membrane.The graphitic carbon nitride(gCN)was acidified to prepare acidified graphitic carbon nitride(aCN)with excellent dispersibility and smaller size.The co-precipitation method was further used to generate silver phosphate(AP)particles on the surface of aCN,thereby obtaining aCN/AP composite nanomaterial with antibacterial properties.Disperse aCN/AP in m-phenylenediamine(MPD)aqueous solution to cause an interfacial polymerization(IP)reaction with trimesoyl chloride(TMC)solution on the surface of the CNT intermediate layer to form a polyamide(PA)separation layer,thereby obtaining a TFN membrane with a triple-layered structure.Using 1 M sodium chloride solution as the draw solution and deionized water as the feed solution,the water flux of the TFN-CNT6-aCN/AP0.5 membrane reaches 67.0 L·m-2·h-1,and the reverse salt flux less than 3.0 g·m-2·h-1.Taking bovine serum albumin and humic acid as model pollutants,the antifouling test was carried out.The TFN FO membrane showed good antifouling capacity.After the continuous 24 h fouling experiment,the fouling recovery rate of TFN-CNT6-aCN/AP0.5 membrane to bovine serum albumin and humic acid were 61.7%and 80.7%,respectively.In addition,the TFN FO membrane has excellent antibacterial properties against Gram-negative E.coli and Gram-positive S.aureus,with sterilization rates of 99.0%and 92.0%,respectively.In the process of treating actual wastewater with FO,inorganic fouling will reduce the water flux and shorten the lifetime of the FO membrane.In this study,FO membrane was applied to the treatment of shale gas wastewater.The FO membrane treatment experiments of simulated shale gas wastewater and actual shale gas wastewater were carried out respectively,and the influence of reverse salt diffusion on inorganic fouling on the membrane surface was systematically studied.Sodium chloride,sodium sulfate,and ammonium sulfate were selected as the draw solution,and the influence of calcium sulfate scaling on the surface of the forward osmosis membrane under different operating conditions such as temperature,flow rate,and membrane surface orientation were explored to determine the optimal operating conditions.Under the optimal operating conditions,the influence of reverse salt diffusion on barium sulfate scaling and the coexistence of barium sulfate scaling and calcium sulfate scaling was studied.In addition,FO application in the actual shale gas wastewater and the inorganic fouling in the actual process were analyzed,which provided theoretical and technical support for the FO treatment and resource utilization of shale gas wastewater.In summary,this article based on the bottleneck problem of FO membranes and prepared a triple-layered TFN FO membrane with high-selective permeability and excellent antibacterial and antifouling abilities.The FO technology was used in the treatment of shale gas wastewater and the inorganic fouling phenomenon during the treatment process were investigated,and the influence of reverse salt diffusion on the fouling of the FO membrane was revealed,which provided new ideas for the development and application of FO membranes.The idea promoted the development of membrane separation and membrane water treatment technology.