Study On Preparation Of Forward Osmosis Membrane And Integration Process For Electroplating Wastewater Treatment

With the development of electroplating industry,electroplating wastewater containing numerous hard-degradable heavy metal ions is generating rapidly,direct discharge of which can cause serious harm to environment and public health.Quality of the product water treated by traditional methods cannot meet the increasing strict national discharge standards and reuse requirements.It is of great significance for the electroplating industry to explore a new practical and effective technology to reduce pollutant discharge and improve rate of electroplating wastewater reuse.Forward osmosis(FO)is a new membrane separation technology which is driven by the difference of osmotic pressure between the feed and draw solution.FO demonstrates potential application in wastewater treatment owing its advantages of high rejection of pollutants,low fouling tendency and high pollution reversibility.However,due to the serious internal concentration polarization(ICP)in FO membrane and the lack of suitable process for industrial applications are significantly hindered the industrial application of FO technology.To solve the above problems,in this paper,electrospun nanofibrous membrane with a unique interconnected pore structure,was adopted as the support layer which can effectively alleviate the ICP.Then the FO membrane was fabricated via interfacial polymerization.Using dopamine to modify the electrospun membrane could strengthen the binding force between the base film and the active layer resulting in a improvement of selectivity of the FO membrane.And the separation performance on simulated heavy metal wastewater was investigated.On the other hand,a pilot scale FO-RO-NF combination membrane process was constructed for advanced treatment of the actual electroplating wastewater.By optimizing the combination process parameters,the product water originated from electroplating wastewater could be reused for electroplating production line.The main contents include the following three aspects:(1)Study on TFC membrane based on ePAN support layer modified by polydopamine.A polydopamine(PDA)layer with superior adhesion can form on the surface of ePAN nanofiber through oxidation and cross-linking of dopamine and the TFC membrane was fabricated by adopting dopamine to modify the ePAN support layer.The chemical structure of PDA's contains numberous functional groups increasing the binding force between the support layer and the selective layer of polyamide.Compared the micromorphology and separation performance of FO membrane,there is typical peak valley structure on the polyamide layer and no obvious defects on the prepared membrane.and the membrane showed good stability in water system and the rejection of Cu2+ over 87%.The results confirmed that dopamine could increase the binding force between support layer and the active layer resulting in the improvement of selectivity.(2)Study on nTFC membranes based on ePAN support layer modified by polydopamine nanoparticles.The unique three-dimensional pore structure on the surface of ePAN easily cause defects on polyamide layer,while the modification of dopamine has no effect on pore structure of ePAN leading to a relatively low rejection of the prepared TFC membrane.Dopamine in alkaline solution through self polymerization and assemble can form polydopamine nanoparticles(nPDA).The nPDA was intercepted by the ePAN,and it would modifiy the three-dimensional pore structure of the ePAN surface.Increasing nPDA until the surface pore of the ePAN was completely covered,the morphology of polyamide layer formed on the surface of the ePAN support layer changes from nodular and small leaf-like structure to leaf-like structure.Compared with the TFC membranes,the rejection of nTFC membranes on Cu2+ had been greatly improved,meanwhile the water flux didn't show significant decline.The prepared nTFC membranes had a lower membrane structure parameters than that of the two commercial membrane(HTI-CTA and Oasys water-TFC)under the same test condition and calculation methods.(3)Study on pilot-scale advanced treatment based on commercial FO-RO-NF combination process.Taking the treatment on actual electroplating wastewater from an electroplating industrial zone of Ningbo as the research object.Investigate the factors affecting the system operation stability,water recovery rate,membrane fouling,the effect of cleaning,and the final water quality.The results showed that the water recovery rate of FO process was mainly affected by the concentration of the DS that provide by RO process.NF process could effectively control the concentration of pollutants in DS ensuring long-term operation stability of the membrane system.During one month continuous operation,system recovery is 84.6%,and the flux of FO process was remained 3.12 L/m2h.After the multiple membrane process,the removal efficiency of ammonia nitrogen,dissolved solids,COD were 97.4 ± 2.1%,99.6±0.19%and 96.4%,respectively.The concentrations of total Cr,Cr(VI),total Ni,total Fe and total Zn in product water were below the detection limit.And the average conductivity of product water was 48.2±25.2 ?s/cm,satisfying the standard reuse in electroplating production line.In this paper,a high-performance FO composite membrane was fabricated via IP process on the ePAN support membrane modified by PDA layer or nPDA formed through oxidation and cross-linking of dopamine;A feasible membrane combination technology for advanced treatment of electroplating wastewater had been developed,expanding the industrial application of FO technology.