Modeling of fouling considering behavior of EPS accumulated on membrane in MBRs

本研究从膜表面污泥中提取EPS，研究了膜通量变化与分子量分布变化之间的关系。EPS大于500，随着膜表面高分子量EPS的减少，膜表面的分子量增加，过滤阻力降低，表明高分子量EPS的分解对膜表面的过滤阻力有很大的影响。建立了EPS与膜表面分离的数学模型，并对EPS与膜表面的分离过程进行了模拟。建立了平板膜和中空纤维膜组件中膜上剪切应力与EPS剥离速率的关系模型。建立了平板膜组件中剪切应力与气泡流速的关系模型，中空纤维膜组件中膜内流速分布与气泡流速的关系模型，以及EPS分解速率与跨膜压力的关系模型。将膜表面的EFS分为高分子量（大于1000 kDa）、中分子量（100 k-1000 kDa）和低分子量（小于100 kDa）三种，并采用微分方程对各组分的变化进行了建模，其参数值由实验数据确定。实验结果与模拟结果吻合良好。实验结果表明，该模型是有效的。

In this research, EPS were extracted from sludge accumulated on membrane surface and relationship between change of permeate flux and change of molecular weight profile was investigated.EPS more than 500,000 Da increased on membrane surface and filtration resistance decreased with the decrease of highe-molecular-weight EPS on membrane surface suggesting strong influence of decomposition of high-molecular-weight EPS to smaller molecular weight substances on the performance of MBRs.A mathematical model was developed to simulate detachment of EPS from membrane surface. Relationship between shear stress on membrane and detachment rate of EPS was modeled for both of flat-sheet and hollow-fiber membrane modules. Relationship between shear stress and velocity of bubble flow was modeled for flat-sheet membrane module while velocity profile inside hollow fiber module and bubble flow velocity was modeled for hollow fiber membrane modules.Relationship between decomposition rate of EPS and trans-membrane pressure was modeled. EFS on membrane surface was categorized into high-molecular weight(more than 1000kDa), medium molecular weight(100k-1000k Da), and low molecular-weight(less than 100kDa) and change of each component was modeled using differential equations, whose parameter values were determined using experimental data. The experimental results were in good agreement with the simulation results using the developed model. Also permeate flux and the behavior of EPS was related using the model and experimental results suggested the validity of the model.