Study On The Separation Mechanism Of The Trace Aniline Compounds In Nanofiltration

Nanofiltration separation technology has become a hot spot in water reuse, especially in mild contaminated water treatment. However, the separation mechanism in nanofiltration of trace environmental organic pollutants is not clear yet. There were few reports on the separation mechanism of the trace aniline compounds in nanofiltration. Therefore, our work focused on the separation mechanism of the trace aniline compounds in nanofiltration provess. The results of our work can improve the nanofiltration process in the trace organic compounds separation with the data support.There is a positive correlation between the absorbability of organic pollutants and irreversible fouling. Therefore, in this paper, we analyzed the isothermal adsorption models of the aniline compounds on nanofiltration membrane active layer through the static adsorption tests. It determined the basic performance parameters, the optimum operation conditions, and the main impact factors of the nanofiltration with the cross flow process. By the streaming potential unit, we also researched the trend of stream-potential change, Zeta potential before and after the membranes was fouled by aniline compounds. By using the Fourier infrared spectrum (FTIR); contact Angle meter and scanning electron microscopy (SEM), we measured functional groups on the membrane surface, contact angle, and morphology characteristics before and after it was fouled. Based on the above results, we analyzed the pollution characteristics of the anilines organics on nanofiltration membrane. Furthermore, we anayled the separation mechanism of the trace aniline compounds in nanofiltration by fitting non-equilibrium thermodynamic basic filtering model and checking the Spiegler-Kedem (S-K) and space steric hindrance joint model basing on the experimental data.The main results are listed as following:(1) Freundlich isothermal adsorption model is more adequate to represent the experimental behavior for the three membranes, which is mainly dominated by multilayer adsorption. Through analyzing by the SPSS, it was found that there was no relationship between the membrane features of the membranes and adsorption. The solution octanol coefficient and the solute adsorption had significant correlation. The solute hydrophilic had a more significant effect than the hydrophilicity of solute than that of membranes. (2) It was also found that the membrane flux of the solution increased with the operation preasure and the flow rate. The rejection of the solution increased initially and then decreased with increasing the operation preasure, whereas it decreased with increasing flow rate. There was a sieve effect on the nanofiltration membranes. The octanol coefficient and the dissociation constant of the solute are the main impact factors which influence the membrane flux and the retention rate.(3) In the filtration experiments, the adsorption effect on the surface of the membrane was weak, which could be neglected in the practical application. The flux of the solution was mainly affected by the combined effect of the hydrophilicity of the solutes and t the molecular weight cut off. The larger the dissociation constant leads to the greater the electrical charge of the membranes.(4) The charge on the membrane surface of the three nanofiltration membranes are all negative charge. Streaming potential absolute size and operating pressure is positive related, while the Zeta potential is opposite related. The rejection of the electrolyte solution and the surface electrical charge on the NFX membrane is positive related. The aniline compounds have no influence on the surface electrical charge of the NFX membranes.(5) The numerical values of the solute permeability and intercept coefficient calculated by using the non-equilibrium thermodynamics based model are partial small, which is suitable to apply in the explanation of trace aniline compounds separation mechanism. The solute parameters which were achieved by using S-K model coincide with the phenomenon of the experiments.