Department of Water Management, Delft University of Technology, Delft, The Netherlands.
Department of Biotechnology, Delft University of Technology, Delft, The Netherlands.
Biotechnol Bioeng. 2021 Mar;118(3):1273-1285. doi: 10.1002/bit.27650. Epub 2020 Dec 25.
Biofilm and granular sludge processes depend on diffusion of substrates. Despite their importance for the kinetic description of biofilm reactors, biofilm diffusion coefficients reported in literature vary greatly. The aim of this simulation study was to determine to what extent the methods that are used to measure diffusion coefficients contribute to the reported variability. Granular sludge was used as a case study. Six common methods were selected, based on mass balances and microelectrodes. A Monte Carlo simulation was carried out to determine the theoretical precision of each method, considering the uncertainty of various experimental parameters. A model-based simulation of a diffusion experiment was used to determine the theoretical accuracy as a result of six sources of error: solute sorption, biomass deactivation, mass transfer boundary layer, granule roughness, granule shape, and granule size distribution. Based on the Monte Carlo analysis, the relative standard deviation of the different methods ranged from 5% to 61%. In a theoretical experiment, the six error sources led to an 37% underestimation of the diffusion coefficient. This highlights that diffusion coefficients cannot be determined accurately with existing experimental methods. At the same time, the need for measuring precise diffusion coefficients as input value for biofilm modeling can be questioned, since the output of biofilm models has a limited sensitivity toward the diffusion coefficient.
生物膜和颗粒污泥工艺依赖于基质的扩散。尽管扩散系数对于生物膜反应器的动力学描述很重要，但文献中报道的生物膜扩散系数差异很大。本模拟研究的目的是确定用于测量扩散系数的方法在多大程度上导致了所报道的变异性。颗粒污泥被用作案例研究。基于质量平衡和微电极，选择了六种常用的方法。进行了蒙特卡罗模拟，以确定每种方法的理论精度，同时考虑了各种实验参数的不确定性。使用基于模型的扩散实验模拟来确定由于六个误差源而导致的理论准确性：溶质吸附、生物量失活、传质边界层、颗粒粗糙度、颗粒形状和颗粒大小分布。基于蒙特卡罗分析，不同方法的相对标准偏差范围为 5%至 61%。在理论实验中，六个误差源导致扩散系数低估了 37%。这突出表明，现有的实验方法无法准确确定扩散系数。同时，由于生物膜模型的输出对扩散系数的敏感性有限，因此可能需要质疑将精确的扩散系数作为生物膜模型输入值的必要性。
