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

本研究从膜表面堆积的污泥中提取EPS，考察了膜通量的变化与膜表面分子量分布变化的关系，发现随着膜表面高分子量EPS的减少，膜表面EPS>50万Da，过滤阻力减小，说明高相对分子质量EPS向小分子物质的分解对膜生物反应器的性能有很大影响。建立了平板和中空纤维膜组件的膜剪应力与EPS分离率的关系模型。对于平板膜组件，模拟了剪切应力与气泡流速的关系；对于中空纤维膜组件，模拟了中空纤维组件内部的速度分布和气泡流速；模拟了EPS的分解速率与跨膜压力的关系。将膜表面的EFS分为高分子量(大于1000 kDa)、中分子量(100k-1000kDa)和低分子量(小于100 kDa)，并用微分方程法模拟了各组分的变化，并用实验数据确定了其参数值。实验结果与所建模型的模拟结果吻合较好。利用该模型对渗透通量与EPS的行为进行了关联，实验结果表明了该模型的有效性。

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.