| The recycling of high-salty wastewater from coal chemical industry not only effectively alleviates the shortage of water resources in coal chemical enterprises,but also promotes the development of current environmental protection undertakings.At present,most of the zero-discharge treatment of coal chemical high-salty wastewater is concentrated on the membrane concentration,evaporation and crystallization process.However,the fouling problem of nanofiltration membrane equipment in this process not only seriously affects the long-term safe and stable operation of the process,but also extremely the land increases the economic cost of enterprises.For this reason,this article has launched a study on the fouling behavior and mechanism of nanofiltration membranes in the process of membrane concentration,evaporation and crystallization of high-salty wastewater from coal chemical industry.The main results obtained are as follows:Cyclohexanol is mainly adsorbed on the surface of the fouling layer by reducing the solubility of inorganic salts and the "competition and synergy" with APAM to further aggravate membrane fouling dominated by APAM.The electric neutralization and charge shielding effect of the cations in the feed solution reduce the repulsive force between APAM and the membrane.In particular,the coordination and complexation of Ca2+as a "bridge" between APAM-membrane and APAM-APAM makes the membrane flux drop faster and membrane fouling is more serious.Through the extended Derjaguin-Landau-Verwey-Overbeek(XDLVO)theory to calculate the contact angle measurement results obtained by different probe liquid measurements,,the AB interface energy between APAM-membrane and APAM-APAM increases from 22.60 mJ/m2 to 50.27 mJ/m2 and from 15.98 mJ/m2 to 47.49 mJ/m2,respectively.It can be seen that the composition of probe solution has a significant effect on the AB interface.The AB interface energy is an important part of the total interface free energy,so it has a significant impact on membrane fouling.In the calculation of the free energy of adhesion between APAM and membrane and the free energy of cohesion between APAM and APAM,the addition of cyclohexanol in the probe solution without CaC12 reduced the ratio of electron donor to electron acceptor from 3.00 to 2.12 and 4.86 decreased to 3.20.The addition of cyclohexanol in the probe solution containing CaCl2 increased the ratio of electron donor to electron acceptor from 4.51 to 6.62 and 2.20 to 3.26,respectively.It can be seen that in the probe solution cyclohexanol has a certain effect on the ratio of electron donor to electron acceptor at different interfaces.Polyaluminum chloride fouling always preferentially adheres to the membrane surface,and forms loosely adhered fouling on the membrane surface in the form of surface contamination.The membrane pores are always kept from being blocked under the erosion of the cross-flow shear force on the membrane surface,and finally the inorganic salt always maintains a high transmittance.Benzotriazole is mainly adsorbed on the membrane surface and the surface of the fouling layer to aggravate membrane fouling.The membrane surface fouled by benzotriazole is significantly denser,and the adhesion between the fouling and the membrane and the cohesive between the fouling and the fouling is also stronger,the fouling blocks the membrane pores,reduces the effective filtration area and makes more inorganic salts be intercepted.The research in this article provides a reference direction and theoretical support for the fouling prevention and fouling inhibition in the process of nanofiltration membrane in the process of treating coal chemical high-salty wastewater,and provides support and solutions for the development of related industrial wastewater treatment processes and the selection of membranes based on actual wastewater conditions.It also laid a foundation for the subsequent practical treatment of high-salty wastewater from coal chemical industry to reduce membrane fouling and related theoretical research. |
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