Universitat Politècnica de València, IEC Group, Departament d'Enginyeria Quimica i Nuclear, Camí de Vera s/n, 46022, València, Spain; RWTH Aachen University, Chemical Process Engineering, Forckenbeckstr. 51, 52074, Aachen, Germany.
RWTH Aachen University, Chemical Process Engineering, Forckenbeckstr. 51, 52074, Aachen, Germany.
Water Res. 2018 Dec 15;147:393-402. doi: 10.1016/j.watres.2018.10.017. Epub 2018 Oct 10.
Fouling is one of the most pressing limitations during operation of membrane bioreactors, as it increases operating costs and is the cause of short membrane lifespans. Conducting effective physical cleanings is thus essential for keeping membrane operation above viable performance limits. The nature of organic foulants present in the sludge and the membrane properties are among the most influential factors determining fouling development and thus, efficiency of fouling mitigation approaches. The role of other factors like sludge viscosity on fouling is still unclear, given that contradictory effects have been reported in the literature. In the present study we use a new research approach by which the complex interplay between fouling type, levels of permeate flux, membrane material and feed properties is analyzed, and the influence of these factors on critical flux and membrane permeability is evaluated. A variety of systems including activated sludge and model solutions with distinct rheological behavior has been investigated for two membranes differing in pore size distribution. We present a novel method for assessing the efficiency of fouling removal by backwash and compare it with the efficiency achieved by means of relaxation. Results obtained have proven that backwash delays development of critical fouling as compared with relaxation and reduces fouling irreversibility regardless of fluid rheology. It was shown that backwash is especially effective for membranes for which internal fouling is the main cause of loss in permeability. Nonetheless, we found out that for membranes with tight pores, both relaxation and backwash are equally effective. The critical flux decreases significantly for high-viscosity fluids, such as activated sludge. This effect is mainly caused by an intensified concentration polarization at the feed side rather than by internal fouling events. However, membrane permeability has been proven to rely more on the permeate viscosity than on the feed viscosity: poor rejection of organic fractions showcasing high viscosity causes an acute decline in membrane permeability as a consequence of increased shear stress inside the membrane pores.
污染是膜生物反应器运行过程中最紧迫的限制因素之一，因为它会增加运营成本并导致膜寿命缩短。因此，进行有效的物理清洗对于保持膜运行在可行的性能极限之上至关重要。污泥中存在的有机污染物的性质和膜的性质是决定污染发展和污染缓解方法效率的最具影响力的因素之一。其他因素，如污泥粘度对污染的作用尚不清楚，因为文献中报道了相互矛盾的影响。在本研究中，我们使用了一种新的研究方法，分析了污染类型、渗透通量水平、膜材料和进料特性之间的复杂相互作用，并评估了这些因素对临界通量和膜渗透性的影响。我们研究了两种具有不同孔径分布的膜，包括活性污泥和具有不同流变行为的模型溶液在内的各种系统。我们提出了一种评估反冲洗去除污染效率的新方法，并将其与松弛法的效率进行了比较。结果证明，与松弛相比，反冲洗延迟了临界污染的发展，并降低了污染的不可逆性，无论流体的流变性如何。结果表明，反冲洗对于内部污染是渗透性损失主要原因的膜特别有效。尽管如此，我们发现对于孔径较紧的膜，松弛和反冲洗同样有效。高粘度流体（如活性污泥）的临界通量会显著降低。这种影响主要是由于进料侧的浓度极化加剧，而不是由于内部污染事件。然而，已经证明膜渗透性更多地取决于渗透物的粘度而不是进料的粘度：具有高粘度的有机部分的截留率差会导致膜渗透性急剧下降，这是由于膜孔内的剪切应力增加所致。
