Electric Assisted Coal-based Carbon Membrane Modified By Polyvinyl Alcohol For The Treatment Of Oily Wastewater

Oily wastewater has a wide range of sources and a large amount of discharge.If it is not properly treated and discharged into the environment,it will pose a serious threat to the natural environment and human health.Among them,emulsified oily wastewater is the focus and difficulty of treatment.In recent years,membrane technology has become a popular choice for the treatment of emulsified oily wastewater because of its simple operation and high efficiency.However,there have been some problems such as serious membrane pollution,unsatisfactory permeate flux and oil removal rate.In this study,coal-based carbon membrane was used as the base membrane,and superhydrophilic polymer（Polyvinyl alcohol）was used for hydrophilic modification.Based on the preparation of the best modified membrane,the good conductivity of coal-based carbon membrane was used to combine the hydrophilic membrane with the electric field assisted method to further improve the treatment performance of the membrane module.The modified membrane assisted by electric field shows excellent performance in the treatment of emulsified oil solution,which not only realizes the efficient removal of emulsified oil,but also has good oil pollution resistance.It provides a green,low-cost,efficient and stable method for the treatment of emulsified oil wastewater.The main research contents are as follows:（1）Polyvinyl alcohol（PVA）was used to modify the carbon membranes.The effects of four important preparation conditions on the hydrophilicity of the modified membrane and the performance of emulsified oil treatment were investigated.SEM,FTIR and XPS were used to characterize and analyze the changes of surface morphology and chemical functional groups before and after modification.It can be proved that there are covalent bonds between PVA and carbon membrane after modification,and PVA is firmly grafted on the surface of carbon membrane;The optimal modification conditions were determined as follows:PVA concentration 10 mg/m L,glutaraldehyde concentration 0.1 wt%,crosslinking temperature 70℃and crosslinking time 45 min.After modification,the hydrophilicity of the modified carbon membrane was significantly higher than that of the original carbon membrane.The contact angle of water in air decreased from 76.3°to 34.8°and the pure water permeation flux increased from 1865 L/m²·bar·h to 3185 L/m²·bar·h.The oil removal rate of 200 ppm emulsified oil solution was increased from 93.00%to 95.87%at the flow rate of 1.5 m L/min,which had good oil pollution resistance.（2）By applying electric potential on the membrane,the modified membrane has the dual functions of separating membrane and electrode,which further improves the treatment performance of the modified membrane and prolongs the service life.The results show that the best experimental conditions of applying cathode potential on the modified membrane are:voltage-3 V,electrode spacing 4.0 cm and electrolyte concentration（Na₂SO₄）0.1 mol/L.When the membrane module processes 200 ppm emulsified oil-water solution at a flow rate of1.5 m L/min,the membrane permeation flux could be kept at 89.66%of the initial permeability flux after 240 min operation,which was 1.85 times of that without power on,and the oil removal rate was 99.7%;The optimal conditions for the positive charge are:voltage+2 V,electrolyte Na₂SO₄ concentration 0.1 mol/L,electrode spacing 4.0 cm.Under the same process conditions,the membrane permeation flux can be maintained at 67.27%of the initial permeation flux after240 min operation,which is 1.39 times of that without electric charge,and the oil removal rate can reach 98.6%.It is found that the improvement of the processing performance of the membrane module under negative charge only depends on the repulsive force of the same charge.When the positive charge is applied,the oil droplets in oil-water emulsion are degraded by electrochemical oxidation on the membrane surface and in the pores.When the degradation rate is balanced with the membrane fouling rate,the permeation flux of the membrane is stable.In addition,the recovery and regeneration performance of the membrane module was further investigated,and the membrane fouling was analyzed.The results showed that the membrane modification and electrical assistance could effectively improve the reusability of the membrane module,and the combination of the two methods could further improve the oil removal and oil pollution resistance,inhibit the generation of irreversible fouling,and enhance the recovery and regeneration performance of the membrane module.