Abstract
The distribution of biofilm thickness on individual sand grains in a two-dimensional sand-filled cell maintained under anaerobic conditions was investigated. The cell was inoculated with a mixed microbial culture fed with methanol. Concentrations of biomass attached to the sand and suspended in the water in the cell were determined by protein analysis. The biofilm thickness on individual sand grains was investigated with confocal laser scanning microscopy (CLSM), and was found to follow a normal distribution with a mean range of 59–316 μ and standard deviations of 30–77 μ. The bulk average permeability reduction factor is 8. To investigate the implications of the variability of biofilm thicknesses, four models were used to calculate reductions in porous media permeability. Taylor’s model predicted a reduction by a factor ranging from 14 to 5,000 (from minimum to maximum mean biofilm thickness). Vandevivere’s model predicted a reduction in permeability by a factor ranging from 769 to 3,846 (from minimum to maximum mean biofilm thickness). Seki’s model did not give physically meaningful results in this study. Clement’s model predicted reduction by a factor ranging from 1 to 1.14 over the range of biomass levels observed in the cell. Data on the statistical and normal distributions of biofilm thickness in porous media, and assessment of their implications with respect to different permeability models, could lead to better understanding of the extent of bioclogging associated with field implementation of bioremediation of contaminants in aquifers.
Résumé
La distribution de l’épaisseur du biofilm sur les grains individualisés de sable dans une cellule bidimensionnelle remplie de sable maintenue dans des conditions anaérobiques a été étudiée. La cellule a été inoculée avec une culture d’un mélange microbien nourrie avec du méthanol. Les concentrations de la biomasse attachée au sable et en suspension dans l’eau au sein de la cellule ont été déterminées par analyse de la protéine. L’épaisseur du biofilm sur les grains individualisés de sable a été étudiée avec un microscope confocal à balayage laser (CLSM), et suit une distribution normale avec une moyenne comprise entre 59–316 μ et un écart-type de 30–77 μ. Le facteur moyen de réduction de la perméabilité est de 8. Pour étudier les implications de la variabilité des épaisseurs du biofilm, quatre modèles ont été utilisés pour calculer les réductions de la perméabilité dans un milieu poreux. Le modèle de Taylor prédit une réduction d’un facteur compris entre 14 et 5000 (du minimum au maximum de l’épaisseur du biofilm moyenne). Le modèle de Vandevivere prédit une réduction de perméabilité d’un facteur compris entre 769 et 3846 (du minimum au maximum de l’épaisseur du biofilm moyenne). Le modèle de Seki ne fournit pas de résultats significatifs du point de vue physique dans cette étude. Le modèle de Clement prédit une réduction d’un facteur compris entre 1 et 1.14 pour toute la gamme de niveaux de biomasse observés dans la cellule. Les données sur les distributions statistiques et normales de l’épaisseur du biofilm dans les milieux poreux, et l’évaluation de leurs implications en considérant différents modèles de perméabilité, pourraient conduire à une meilleure compréhension de l’étendue des colmatages d’origine biologiques associés à la mise en œuvre sur le terrain de techniques de remédiation biologique des contaminants dans les aquifères.
Resumen
Se investigó la distribución del espesor de biofilm en los granos individuales de arena en una celda bidimensional con relleno de arena mantenida bajo condiciones anaeróbicas. La celda se inoculó con un cultivo microbiano mixto alimentado con metanol. Las concentraciones de la biomasa unida a la arena y suspendida en el agua en la celda se determinaron por análisis de proteínas. El espesor del biofilm en los granos de arena individuales se investigó con microscopía confocal por barrido láser (CLSM), y se encontró que sigue una distribución normal con una rango medio de 59–316 μ y desviaciones estándar de 30–77 μ. El factor de reducción de la permeabilidad media es 8. Para investigar las consecuencias de la variabilidad de los espesores del biofilm, se utilizaron cuatro modelos para calcular las reducciones en la permeabilidad de los medios porosos. El modelo de Taylor predice una reducción por un factor entre 14 y 5000 (desde el mínimo al máximo espesor medio del biofilm). El modelo de Vandevivere predijo una reducción de la permeabilidad por un factor que varía desde 769 hasta 3846 (del mínimo al máximo espesor medio del biofilm). El modelo de Seki no dio resultados físicamente significativos en este estudio. El modelo de Clemente predijo una reducción por un factor comprendido entre 1 y 1.14 sobre el rango de los niveles de biomasa observados en la celda. Los datos sobre las distribuciones estadísticas y normales del espesor del biofilm en medios porosos, y la evaluación de sus consecuencias con respecto a los diferentes modelos de permeabilidad, podrían conducir a una mejor comprensión de la magnitud de la obstrucción biológica asociada con la aplicación sobre el terreno de la biorremediación de contaminantes en los acuíferos.
摘要
本文研究了二维厌氧培养条件下砂箱中单个砂粒表面生物膜的厚度分布。砂箱中接种了混合菌种并注入甲醇作为营养。砂箱中砂粒表面生物量和水中生物量都用蛋白分析的方法测量。单个砂粒表面的生物膜厚度用共聚焦激光扫描显微镜(CLSM)测量,发现生物膜厚度服从正态分布且均值为59到316微米,方差为30到77微米。砂箱整体的平均渗透率折减系数为8。为了研究生物膜厚度变化的影响,本文采用了四种模型计算介质渗透率的减小。Taylor模型计算出的折减系数为14到5000(对应最小到最大生物膜厚度均值)。Vandevivere模型计算出的折减系数为769到3846(对应最小到最大生物膜厚度均值)。Seki模型对于本次研究未能算出具有物理意义的结果。Clement模型根据砂粒表面生物量计算出的折减系数为1到1.14。本文对多孔介质表面生物膜厚度数据进行了统计,发现其服从正态分布特征,并评估了不同渗透率模型的计算结果。研究成果会促进更好地认识污染含水层中采用生物修复时生物堵塞的影响程度。
Resumo
A distribuição da espessura do biofilme sobre os grãos individuais de areia de uma célula bidimensional cheia de areia mantida sob condições anaeróbicas, foi investigada. A célula foi inoculada com uma cultura microbiana mista alimentada com metanol. As concentrações de biomassa aderida à areia e em suspensão na água dentro da célula foram determinados por análise de proteínas. A espessura do biofilme sobre os grãos individuais de areia foi investigada com microscopia confocal por varredura laser (MCVL), e verificou-se seguir uma distribuição normal com uma gama média de 59–316μ e desvios-padrão de 30–77μ. O fator de redução de permeabilidade média é 8. Para investigar as implicações da variabilidade de espessuras de biofilme, quatro modelos foram utilizados para calcular reduções na permeabilidade em meios porosos. O modelo de Taylor previu uma redução por um fator variando de 14 a 5000 (de mínima à máxima espessura média do biofilme). O modelo de Vandevivere previu uma redução na permeabilidade por um fator que varia de 769 a 3846 (de mínima à máxima espessura média do biofilme). O modelo de Seki não deu resultados fisicamente significativos neste estudo. Modelo de Clemente previu redução por um fator que varia de 1 a 1.14 ao longo da gama de níveis de biomassa observada na célula. Dados sobre as distribuições estatísticas e normais de espessura de biofilme em meios porosos, e avaliação das suas implicações com relação a diferentes modelos de permeabilidade, podem levar a uma melhor compreensão da extensão da bio-obstrução associada com a implementação à campo de biorremediação de contaminantes em aquíferos.
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Funding for this research from US Dupont Company, and also from NSFC40872155 and 41472212, is gratefully acknowledged.
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Ye, S., Zhang, Y. & Sleep, B.E. Distribution of biofilm thickness in porous media and implications for permeability models. Hydrogeol J 23, 1695–1702 (2015). https://doi.org/10.1007/s10040-015-1306-6
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DOI: https://doi.org/10.1007/s10040-015-1306-6