Membrane fouling is the major problem that hinders the practical application of membrane bioreactor (MBR) systems. Since the MBR system includes living microorganisms and their metabolites, the fouling mechanism is even more complex than that of conventional membrane separation processes. This paper provides an improved understanding of the influence of filamentous bacteria on membrane fouling in microfiltration of activated sludge wastewater. In order to make clear the membrane fouling mechanism of filamentous bacteria, the physicochemical characteristics of sludge flocs, including extracellular polymeric substance (EPS), zeta potential, relative hydrophobicity (RH) and floc morphology were systematically investigated. The results showed that the sludge flocs with negligible filamentous bacteria led to severe membrane pore blocking, and the sludge flocs with filamentous bacteria created the formation of a non-porous cake layer on the membrane surface. The excess growth of filamentous bacteria resulted in much more release of EPS, lower zeta potential, higher hydrophobicity of sludge flocs and more irregularly shaped flocs, which did great harm to membrane filtration. The sludge flocs with a small quantity of filamentous bacteria had a positive effect on membrane permeation. It is important to control filamentous bacteria concentration in the operation of MBRs.

The membrane bioreactor (MBR) is an important process widely used in wastewater treatment. However, membrane flux declines rapidly due to membrane fouling, which limits the application of MBR. In order to alleviate membrane fouling, a precoated dynamic membrane (PDM) was studied systematically. The membrane module consisted of of 56-µm terylene filter cloth as the support membrane and powder-activated carbon (PAC) as the precoating reagent. The precoated dynamic membrane bioreactor (PDMBR) was used in municipal wastewater treatment practice. Meanwhile, from the viewpoint of retention capacity, flux recovery and alleviating membrane fouling, the suitable thickness of the PAC dynamic membrane was also investigated. The experimental results showed that the formation of PDM from PAC on a support membrane belonged to the cake filtering model, and the relationship of PDM resistance (Ra) and its thickness (D) was in accord with log-function; the suitable thickness was controlled around 0.3 mm. It was found that while the flux of PDM was kept at a high value, the operating pressure of PDM rose to 42 kPa after 43 days of stable operation of the PDMBR, and the removal efficiency of effluent COD and NH4+-N were as good as traditional hollow membrane bioreactors. Furthermore, the flux of the fouled membrane could be totally recovered just after being cleaned by brushing, and it did not consume any chemical reagents. Moreover, it was also found that the PDM could prevent biomass contaminations diffusing from the surface inwards by scanning electron microscopy (SEM).

向由孔径为56μm的普通工业滤布组成的膜生物反应器中投加不同量的粉末活性炭，对恒通量下的单周期运行情况进行了考察，并对被污染的动态膜表面和截面进行了扫描电镜观察。结果表明，较佳的PAC投量约为2g/L。在PAC投量为2g/L时，其运行周期（15d）为不投加PAC时（6d）的2.5倍，反应器中占优势的污泥平均粒径（100μm）也较不投加PAC时的（80μm）大。经扫描电镜分析可知，未投加PAC时膜孔隙间的凝胶层是造成膜污染的主要因素；投加2g/L的PAC时膜表面的滤饼层是造成膜污染的主要因素，其膜污染物易于清洗去除，经水力清洗和刷子刷洗后膜通量可基本恢复，再用0.5%的NaClO溶液浸泡12h后膜通量可完全恢复。

采用孔径56μm的工业滤布制作膜组件，以PAC作为预涂剂，组成预涂动态膜-生物反应器。对比预涂膜、未预涂膜和014μm中空纤维膜的污染物去除效果和膜污染状况。试验结果发现，预涂动态膜2生物反应器不仅污染物质去除效果更好，而且预涂膜可以防止污染物质与微生物向膜材料表面和内部扩散，从而减轻膜污染，运行1128h后，操作压力仅上升至6kPa，并且只需刷洗，膜通量就可以恢复，无须消耗化学试剂。

在膜生物反应器中，活性污泥在膜表面沉积形成滤饼层是造成膜污染的主要因素。采用扫描电镜和自动图像分析技术研究了膜过滤滤饼层的微观结构，并以分形理论和Darcy定律为基础，推导出用于预测膜污染滤饼层渗透性能的数学模型，验证了该渗透模型的可靠性，并利用该渗透模型进行了膜生物反应器中污泥浓度对滤饼层渗透性能影响的研究。结果表明，活性污泥颗粒沉积形成的柔性滤饼层具有明显的多孔结构，并且具有很好的分形特征；膜污染滤饼层的分形维数能够真实反映滤饼层的孔隙率大小；用该渗透模型得到的渗透系数K'可以作为有效预测滤饼层渗透 性能的参数；滤饼层渗透系数K'随污泥浓度的增大而递减，污泥浓度低于10000mg⋅L−1时，K'的变化趋势较小，污泥 浓度达到10000mg⋅L−1以上时，K'急剧下降。