Saturated Hydraulic Conductivity Reduction Caused by Aerobic Bacteria in Sand Columns

Abstract

Bacterial reductions of the saturated hydraulic conductivity, Ks, of natural porous media have been traditionally associated with the development of anaerobic conditions and the production of large amounts of extracellular polymers by the bacteria. Various researchers have also reported that these reductions occur predominantly at or very near the surfaces of injection of nutrients within the porous media. Attempts to describe mathematically the resulting clogging process have, in the past, been based on the assumption that bacterial cells form impermeable biofilms uniformly covering pore walls. A series of percolation experiments was carried out to determine the extent to which an obligately aerobic bacterial strain, Arthrobacter sp., is able to clog permeameters filled with fine sand. A second objective was to elucidate the mechanism(s) responsible for this process. The experimental results indicate that strictly aerobic bacteria are able to reduce Ks by up to four orders of magnitude. Rapid reductions in Ks are associated with the formation of a bacterial mat at the inlet boundary of the sand columns. When the colonization of the inlet is prevented, clogging proceeds within the bulk of the sand at a noticeably slower rate. Under O2‐ or glucose‐limited growth conditions, this decrease in Ks within the sand does not appear on scanning electron micrographs to be caused by exopolymers, which are entirely absent, but rather seems to be due to the presence of large aggregates of cells that form local plugs within the pores. Under conditions of severe N limitation, the same mechanism seems to be largely responsible for the observed clogging, in spite of the production by the cells of extracellular substances, visible under light microscopy and on scanning electron micrographs. In all cases, the coverage of the solid surfaces by the bacterial cells is sparse and heterogeneous, contrary to the basic tenets of the biofilm model.

Processes in Microbial Transport in the Natural Subsurface

“…The primary differences between these two descriptions is that the structured models have the potential to represent the influence of biofilm structure on mass transfer (both diffusion and convection within the fluid and biofilm phases) and on momentum transfer (i.e., the change in permeability due to reduction in the pore volume), whereas unstructured models do not. Typically, structured biomass models are represented as either (1) continuous biofilm on the solid surface [182,183] or (2) discontinuous patchy film [123,175,187]. As discussed by Baveye and Valocchi [142], there has been perhaps too much emphasis on making the distinction between the two kinds of models rather than focusing on the fundamental transport and reaction processes that apply to the biofilm system (the early debate regarding the appropriateness of the various conceptual models is reflected in the exchanges of [141,142,157,186]).…”

“…However, a quantitative foundation for understanding microbial processes in porous media may best be achieved through structured models explored at the pore-scale. Recently, several studies have used volume averaging to formally upscale the processes of mass transport and reactions in biofilms [36,[132][133][134][135], and experimental work is beginning to be conducted to expose the structure of biofilms within experimental systems [34,123,136]. Continuing investigations such as these may help to refine our understanding of the role of biophase structure in the subsurface.…”

Effect of treated wastewater on soil chemical and physical properties in an arid region

“…Xantholagis and Wallender (1991) reported that the final infiltration rate decreased when using wastewater from a tomato paste factory in a furrow irrigation system. Vandevivere and Baveye (1992) applied the wastewater on a sand column and reported that aerobic bacteria decreased the saturated hydraulic conductivity more than 4-times, particularly in the upper zone near the soil surface. Vinten et al (1983) studied the influence of wastewater suspended materials on hydraulic conductivity and reported that the hydraulic conductivity in silty loam was reduced in comparison with sand and sandy loam soils.…”

Impact of water quality, cultivation, and cropping systems on infiltration and physical properties of an arid clay soil

“…Siegrist (1987) suggested that accumulation of suspended solids at the soil surface caused diminution of soil pore-size via two mechanisms: partial retention of dissolved organic matter (DOM) and swelling and dispersion of clay particles. Additionally Vandevivere and Baveye (1992) suggested biological partial pore clogging through increased biomass amount (mainly algae, bacteria, and their products) in TWW. Moreover, organic matter (OM) in TWW tends to complex soluble Ca 2+ and Mg 2+ ions thereby increasing SAR of irrigation water and subsequently soil solution (Metzger et al 1983;Nelson et al 1999).…”