Construction Of Random Rough Membrane Surface And Its Relationship With Interfacial Interactions In Membrane Fouling

China is one of the countries with poor water resources in the world.With the rapid growth of the population and the development of industry,the shortage of water resources and water pollution have seriously restricted the economic development of our country.On the one hand,the human demand for water resources has remarkable growth,and on the other hand,the increasing water pollution has wasted a large amount of available water.Wastewater treatment and wastewater reuse is an important solution to solve water shortage Membrane bioreactor has widely applied to water treatment in many countries due to its excellent wastewater treatment performance.Membrane bioreactor(MBR)which combines biological process and membrane filtration has been widely used as a promising technology for wastewater treatment due to their multitudinous advantages such as high process efficiency,small footprint,low sludge production and relatively low costs.However,membrane fouling is a major obstacle to the wide application of MBR,which results in reducing membrane service time and increasing of maintenance and operational cost.There has been a growing interest in membrane fouling research.Therefore,it is very important to study the mechanism of membrane fouling in MBR operation and find the effective strategy for membrane fouling control.The research was based on a continuously operated MBR,deeply discussed the mechanism of membrane fouling.In this paper,the modeling of random rough membrane surface and sludge particles were investigated,the effects of involved parameters on the simulated surface morphology were also discussed.Thermodynamic interaction related with adhesive fouling in membrane bioreactor(MBR)was investigated based on XDLVO theory(extended Derjaguin-Landau-Verwey-Overbeek).The main results are presented as follows:(1)According to the AFM of membrane surface,Natural membrane surface was found to be randomly rough,and its height distribution obeys Gaussian distribution.A new method which combines spectrum method,Gaussian distribution and Fourier transform technique was deduced.Simulation of the rough membrane surface showed high similarity in terms of statistical roughness and height distribution between the simulated surface and the real membrane surface,indicating the feasibility of the new method.(2)It was found that,correlation length(l)and the number of superposed ridges(N)are key parameters affecting the simulated membrane surface morphology.The asperity size of the modeled surface increases,while the asperity density of the modeled surface decreases with l,indicating the important role of l in the simulated surface.The increase of superposed ridges can improve the accuracy of membrane surface and reduce the random error.This new method has evident advantages over conventional modeling methods.The proposed method for randomly rough membrane surface modeling could be potentially used to quantify the interfacial interactions between two rough surfaces,giving implications for membrane fouling mitigation.(3)The natural surface of a foulant bioparticle was found to be irregular and randomly rough.The majority diameter of sludge particles in volume are aroung 20 ?m.In this study,a new method which combines Gaussian distribution,Fourier transform,spectrum method and coordinate transformation was proposed to simulate surface topography of foulant bioparticles in a membrane bioreactor(MBR).The topography simulated by the new method was quite similar to that of real foulant bioparticles.(4)The simulated topography of foulant bioparticles was critically affected by parameters correlation length(l)and root mean square(?).the asperity density of the modeled surface increases with the increase of l;.High ? value tends to yield a sharp and intensive morphology;The larger segments set,the smaller surface roughness will be.The new method proposed in this study shows notable superiority over the conventional methods for simulation of randomly rough foulant bioparticles.The ease,facility and fitness of the new method point towards potential applications in interface behaviors and membrane fouling research.(5)Thermodynamic interaction related with adhesive fouling in a membrane bioreactor(MBR)was investigated in this study.Thereafter,surface element integral(SEI)method,together with composite Simpson rule and triangulation of Gaussian surface was proposed to calculate thermodynamic interaction.By using the unified method,quantification of thermodynamic interaction with a Gaussian membrane surface was realized for the first time to date.It was found that,in the short range of separation distance(0.158-4.0 rnm),EL interaction is repulsive continuously,while AB and LW interactions are attractive continuously.Meanwhile,AB interaction is more strengthened as compared with EL and LW interactions.It was also discovered that the strength of total interaction in smooth surface is over 10 times than that in rough surface which means membrane surface topography had profound impacts on thermodynamic interaction and adhesive fouling.The deduced method can be used to address impacts of various factors on thermodynamic interaction and adhesive fouling,pointing towards its potential widespread applications in interfacial and membrane fouling research in MBRs.