Tailoring Water Permeance Of NF Membranes Based On Logistic Equation

Membrane separation technology is widely used in the field of water treatment,but membrane fouling restricts the further promotion of membrane technology.For this reason,membrane fouling has been studied by scholars at home and abroad.On the basis of previous research,a membrane fouling control model based on logistic equation was established.The influencing factors of membrane flux attenuation were investigated.Based on the principle of Fourier transform,Fourier transform is performed on the membrane flux attenuation curve,and the frequency domain characteristics of the membrane flux attenuation curve for different pollution types,different stages of the membrane flux attenuation curve and different pollutants are investigated.The changing law of membrane fouling was discussed.And based on the Fourier series,a model is established to realize the prediction of membrane flux.The main results were as follows:(1)The logistic equation is used to fit the membrane flux decay curve.A membrane fouling control model based on logistic equation was established.The model expression is:The model expression is simple.The experimental value and the model simulation value can fit well.After the significance test,the correlation coefficient R~2is above 0.95,indicating that the model has a good fitting effect.(2)The membrane fouling control model is used to fit the flux decay curves of different types of membranes.The influence of different pollutants,cross-flow rate,trans-membrane pressure drop,hydraulic conditions and other factors on the value of membrane flux decay rate k was investigated.And further research found that the smaller the membrane flux decay rate k value,the greater the membrane specific flux after filtration is stabilized.It is verified that the value of k in the logistic equation is the key factor to control membrane fouling.(3)Based on the fast Fourier transform,the membrane fouling characteristics of the four classic clogging models,namely the filter cake clogging model,the intermediate clogging model,the standard clogging model and the complete clogging model,are analyzed.The results show that the frequency spectra of the four models consist of a set of waves with the same frequency and different amplitudes.(4)Determine the periodicity of the membrane flux decay curve based on the Fourier period.The results show that the flux decay curve of the conventional continuous decay type membrane does not have periodicity.Therefore,the fast Fourier transform method was used to analyze the frequency domain characteristics of the membrane flux attenuation curve when the nanofiltration membrane filters BSA,SA,HA three characteristic pollutant solutions respectively.Studies have shown that the frequency composition of the three membrane flux decay curves is still the same,only the amplitude is different.(5)A prediction model based on Fourier series was established to realize the prediction of membrane flux.The maximum absolute error of this model is 0.08,and the minimum relative error is only 0.02%.And only a few series items are needed to achieve the desired prediction results.