Department of Biotechnology, Faculty of Applied Sciences, Delft University of Technology, Van der Maasweg 9, 2629, HZ, Delft, The Netherlands.
Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600, Dübendorf, Switzerland; ETH Zürich, Institute of Environmental Engineering, 8093, Zürich, Switzerland.
Water Res. 2018 Nov 15;145:375-387. doi: 10.1016/j.watres.2018.08.036. Epub 2018 Aug 18.
Biofilm formation in membrane systems negatively impacts the filtration system performances. This study evaluated how biofilm compression driven by permeate flow increases the hydraulic resistance and leads to reduction in permeate flux. We analysed the effect of biofilm compression on hydraulic resistance and permeate flux through computational models supported by experimental data. Biofilms with homogeneous surface structure were subjected to step-wise changes in flux and transmembrane pressure during compression and relaxation tests. Biofilm thickness under applied forces was measured non-invasively in-situ using optical coherence tomography (OCT). A numerical model of poroelasticity, which couples water flow through the biofilm with biofilm mechanics, was developed to correlate the structural deformation with biofilm hydraulics (permeability and resistance). The computational model enabled extracting mechanical and hydrological parameters corresponding to the experimental data. Homogeneous biofilms under elevated compression forces experienced a significant reduction in thickness while only a slight increase in resistance was observed. This shows that hydraulic resistance of homogeneous biofilms was affected more by permeability decrease due to pore closure than by a decrease in thickness. Both viscoelastic and elastoplastic models could describe well the permanent biofilm deformation. However, for biofilms under study, a simpler elastic model could also be used due to the small irreversible deformations. The elastic moduli fitting the measured data were in agreement with other reported values for biofilm under compression. Biofilm stiffening under larger flow-driven compression forces was observed and described numerically by correlating inversely the elastic modulus with biofilm porosity. The importance of this newly developed method lies in estimation of accurate biofilm mechanical parameters to be used in numerical models for both membrane filtration system and biofouling cleaning strategies. Such model can ultimately be used to identify optimal operating conditions for membrane system subjected to biofouling.
生物膜在膜系统中的形成会对过滤系统的性能产生负面影响。本研究评估了透过液流动驱动的生物膜压缩如何增加水力阻力并导致渗透通量降低。我们通过计算模型分析了生物膜压缩对水力阻力和渗透通量的影响，并通过实验数据进行了支持。在压缩和松弛测试中，具有均匀表面结构的生物膜受到通量和跨膜压力的逐步变化。使用光学相干断层扫描（OCT）非侵入式原位测量施加力下的生物膜厚度。一种耦合生物膜力学与水在生物膜中流动的多孔弹性模型被开发出来，以将结构变形与生物膜水力学（渗透率和阻力）相关联。计算模型能够提取与实验数据相对应的力学和水力学参数。在升高的压缩力下，均匀的生物膜经历了显著的厚度减小，而仅观察到阻力略有增加。这表明，均质生物膜的水力阻力受由于孔隙关闭导致的渗透率降低的影响大于厚度减小的影响。粘弹性和弹塑性模型都可以很好地描述生物膜的永久变形。然而，对于研究中的生物膜，由于不可逆变形较小，也可以使用更简单的弹性模型。与其他报道的压缩下生物膜的弹性模量值一致，拟合测量数据的弹性模量。观察到并通过数值相关反比关系描述了在较大的流动驱动压缩力下生物膜的硬化，该关系将弹性模量与生物膜孔隙率相关联。这种新开发方法的重要性在于估计准确的生物膜力学参数，以用于膜过滤系统和生物污垢清洁策略的数值模型。这种模型最终可用于识别受生物污垢影响的膜系统的最佳操作条件。
