Herrling Maria P, Weisbrodt Jessica, Kirkland Catherine M, Williamson Nathan H, Lackner Susanne, Codd Sarah L, Seymour Joseph D, Guthausen Gisela, Horn Harald
Department of Wastewater Engineering, Institute IWAR, Technische Universität Darmstadt, Darmstadt, Germany.
Department of Water Chemistry and Water Technology, Engler-Bunte-Institute, Karlsruhe Institute of Technology, Karlsruhe, Germany.
Biotechnol Bioeng. 2017 Dec;114(12):2857-2867. doi: 10.1002/bit.26392. Epub 2017 Sep 4.
Mass transfer in biofilms is determined by diffusion. Different mostly invasive approaches have been used to measure diffusion coefficients in biofilms, however, data on heterogeneous biomass under realistic conditions is still missing. To non-invasively elucidate fluid-structure interactions in complex multispecies biofilms pulsed field gradient-nuclear magnetic resonance (PFG-NMR) was applied to measure the water diffusion in five different types of biomass aggregates: one type of sludge flocs, two types of biofilm, and two types of granules. Data analysis is an important issue when measuring heterogeneous systems and is shown to significantly influence the interpretation and understanding of water diffusion. With respect to numerical reproducibility and physico-chemical interpretation, different data processing methods were explored: (bi)-exponential data analysis and the Γ distribution model. Furthermore, the diffusion coefficient distribution in relation to relaxation was studied by D-T maps obtained by 2D inverse Laplace transform (2D ILT). The results show that the effective diffusion coefficients for all biofilm samples ranged from 0.36 to 0.96 relative to that of water. NMR diffusion was linked to biofilm structure (e.g., biomass density, organic and inorganic matter) as observed by magnetic resonance imaging and to traditional biofilm parameters: diffusion was most restricted in granules with compact structures, and fast diffusion was found in heterotrophic biofilms with fluffy structures. The effective diffusion coefficients in the biomass were found to be broadly distributed because of internal biomass heterogeneities, such as gas bubbles, precipitates, and locally changing biofilm densities. Thus, estimations based on biofilm bulk properties in multispecies systems can be overestimated and mean diffusion coefficients might not be sufficiently informative to describe mass transport in biofilms and the near bulk.
生物膜中的传质由扩散决定。人们已经采用了多种主要的侵入性方法来测量生物膜中的扩散系数，然而，关于实际条件下异质生物质的数据仍然缺失。为了非侵入性地阐明复杂多物种生物膜中的流固相互作用，应用脉冲场梯度核磁共振（PFG-NMR）来测量五种不同类型生物质聚集体中的水扩散：一种类型的污泥絮体、两种类型的生物膜和两种类型的颗粒。在测量异质系统时，数据分析是一个重要问题，并且已证明它会显著影响对水扩散的解释和理解。关于数值再现性和物理化学解释，探索了不同的数据处理方法：（双）指数数据分析和Γ分布模型。此外，通过二维逆拉普拉斯变换（2D ILT）获得的D-T图研究了与弛豫相关的扩散系数分布。结果表明，所有生物膜样品的有效扩散系数相对于水的扩散系数范围为0.36至0.96。如通过磁共振成像所观察到的，NMR扩散与生物膜结构（例如生物质密度、有机和无机物质）以及传统生物膜参数相关：在结构紧凑的颗粒中扩散受到的限制最大，而在结构蓬松的异养生物膜中发现快速扩散。由于内部生物质的异质性，如气泡、沉淀物和局部变化的生物膜密度，生物质中的有效扩散系数被发现具有广泛的分布。因此，基于多物种系统中生物膜整体性质的估计可能会被高估，并且平均扩散系数可能不足以描述生物膜及其附近区域中的质量传输。
