孔隙介质中生物膜空间分布及其对渗透性影响研究

孔隙介质地下水污染的生物修复过程中,微生物附着在介质颗粒表面,造成生物堵塞,影响生物修复的效率.对二维砂箱中的生物堵塞实验数据进行了统计分析,统计结果表明生物膜厚度在空间上服从正态分布.现有的定量刻画多孔介质生物膜与渗透率的模型一般均假设生物膜均质等厚地覆盖在颗粒表面,与实验结果不符.为探讨多孔介质中生物膜厚度变化对渗透率计算结果的影响,本文选择常用的Taylor模型中二大类六种模型进行比较分析研究.计算结果表明:生物膜厚度参数对模型计算结果影响显著,利用最小生物膜厚度计算得到的相对渗透率比利用最大生物膜厚度计算时的结果大1～4个数量级;不同模型对生物膜厚度参数的敏感性不同,其中Mualem模型最为敏感;Mualem Model利用平均值计算所得相对渗透率与实验测量结果相符,基于正态分布的生物膜厚度统计均值具有一定的代表性;Mualem模型更适用于计算孔隙介质中生物堵塞时对渗透率的影响.

A study of distribution of biofilm in porous media and its effect on permeability

Microorganisms built up on the grains of porous media under condition of ground water bioremediation, which resulted in bioclogging and impacted on the efficiency of bioremediation. The distribution of biofilm thickness on individual sand grains in a two-dimensional sand-filled cell was investigated. It followed a normal distribution. The existing quantitative models, which described the relationship between biofilm thickness and permeability, generally assumed that the particles were uniformly coated by biofilm with constant thickness. However, the assumption was not consistent with the experiments' results. To investigate the effect of the variability of biofilm thickness on permeability, six different Taylor's models were used to calculate reductions in porous media permeability as a function of biofilm thickness. The results indicated that the biofilm thickness had a significant impact on outcomes of the models. Reductions of permeability with the minimum biofilm thickness were 1~4 orders of magnitude greater than the relative permeability with maximum biofilm thickness by the Mualem model. Different models had different sensitivities to biofilm thickness. The Mualem model had the highest sensitivity among the six models. Permeability reductions predicted by the Mualem model with mean biofilm thickness were consistent with experimental measurements of reductions in permeabilities. Therefore, mean biofilm thickness might be a good representative for permeability reduction prediction. Mualem model was more suitable for calculating the change of permeability in porous media under condition of bioclogging.