The μ2M project on quantifying the effects of biofilm growth on hydraulic properties of natural porous media and on sorption equilibria: an overview

Abstract

The physical and chemical effects of bacterial biofilm formation upon hydraulic conductivity, mineral-solution interactions and the formation of biogenic mineral precipitates have been studied over a wide range of scales, from microscopic to macroscopic. Several novel pieces of equipment have been designed, constructed and commissioned in order to measure the physical effects of biofilms upon fluid flow through fractures and porous media, the overall effects of biofilm formation upon mineral surface reactivity, and the imaging and identification of mineral precipitates formed due to the presence of biofilm and bacterial cell surface polymers on a quartz surface. This paper presents an overview of key experimental methods and selected results; further experimental information is being published elsewhere.Biofilm formation within quartz sand in artificial groundwater resulted in a two orders of magnitude reduction in hydraulic conductivity under bench-scale constant head conditions. However, under quasi-environmental conditions within macroscopic centrifuge experiments, a reduction of 21% was measured, revealing differences in measurements and, hence, the value of the macroscopic experimental work in scaling from micro to macro.

Mineralogical comparisons of experimental results investigating the biological impacts on rock transport processes

“…At a larger scale, this could have significant implications for geological waste repositories by 85 sorption of contaminants onto biofilm or uptake of contaminants onto mobile microbes. Similar observations were made by Brydie et al 6 who found that the hydraulic conductivity, expressed by a change in effluent discharge flow rate, had significantly dropped after inoculation of bacteria within quartz sand packed columns 90 due to biofilm formation. Furthermore, in the studies described here new mineral phases may precipitate within the rock pore spaces from porewater fluids and may contribute to this reduction in hydraulic conductivity.…”

The role of biofilms in subsurface transport processes

“…Where conditions are suitable there is potential for biofilaments to establish (in a matter of days) causing pore blockages resulting in a decrease in permeability of the porous media and a change in the local fluid flow patterns. Extensive formation of biofilm reduces pore space, which can lead to eventual blocking of the pore system (Taylor and Jaffé 1990a;Taylor et al 1990) referred to as 'bioclogging' (Brydie et al 2005). Brydie et al (2005) observed a 70 % reduction in the permeability of sand due to bioclogging.…”

“…Extensive formation of biofilm reduces pore space, which can lead to eventual blocking of the pore system (Taylor and Jaffé 1990a;Taylor et al 1990) referred to as 'bioclogging' (Brydie et al 2005). Brydie et al (2005) observed a 70 % reduction in the permeability of sand due to bioclogging. Even greater permeability reductions (three orders of magnitude) were observed in earlier studies by Taylor and Jaffé (1990a).…”

“…via links to surface water; or via links to the repository components. Biogenic mineral precipitates and trapped mineral matter are much more chemically and physically stable than the biofilm, and can persist in the pore system long after the biofilm has decayed or been removed (Brydie et al 2005).Studies by Ferris et al (1999) with iron oxides and groundwater samples collected from the Äspö site looked at the extent to which dissolved metals sorbed into bacteriogenic iron oxides in a deep, hard rock groundwater environment. Results of metal distribution coefficients (K d values) showed K d values decreased with increasing iron oxide content which appeared to be influenced by the bacterial organic matter in the solids.…”

“…via links to surface water; or via links to the repository components. Biogenic mineral precipitates and trapped mineral matter are much more chemically and physically stable than the biofilm, and can persist in the pore system long after the biofilm has decayed or been removed (Brydie et al 2005).…”