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Understanding flow and transport of bacteria in porous media is crucial to technologies such as bioremediation, biomineralization and enhanced oil recovery. While physicochemical bacteria filtration is well documented, recent studies showed that bacterial motility plays a key role in the transport process. Flow and transport experiments performed in microfluidic chips containing randomly placed obstacles confirmed that the distributions of non-motile bacteria stays compact, whereas for the motile strains, the distributions are characterized by both significant retention as well as fast downstream motion. For motile bacteria, the detailed microscopic study of individual bacteria trajectories reveals two salient features: (i) the emergence of an active retention process triggered by motility, (ii) enhancement of dispersion due to the exchange between fast flow channels and low flow regions in the vicinity of the solid grains. We propose a physical model based on a continuous time random walk approach. This approach accounts for bacteria dispersion via variable pore-scale flow velocities through a Markov model for equidistant particle speeds. Motility of bacteria is modelled by a two-rate trapping process that accounts for the motion towards and active trapping at the obstacles. This approach captures the forward tails observed for the distribution of bacteria displacements, and quantifies an enhanced hydrodynamic dispersion effect that originates in the combined effect of pore-scale flow variability and bacterial motility. The model reproduces the experimental observations, and predicts bacteria dispersion and transport at the macroscale. [ABSTRACT FROM AUTHOR]

Microbial-induced carbonate precipitation (MICP) in porous media is a two-step procedure: First, the suspension of bacteria is injected and some of the bacteria get stuck on the grains. The second stage consists in the injection of a calcifying solution that triggers the calcite precipitation and creates a calcite shell around the bacteria. In the present article, we describe a novel method to measure the adhesion rate of Sporosarcina pasteurii bacteria on sandstone and that, additionally, allows to obtain information about local position of the calcite crystals on the sandstone grains. The method is based on the detection of the crystals developed on grains placed inside a microfluidic cell. The potential of the technique was evaluated and demonstrated by studying the influence of the injection time and ionic strength on the adhesion rate and on the spatial distribution of the crystals. The values of the adhesion rates are in good agreement with values determined using column experiments. We find, for example, an increase in the adhesion rate with the NaCl in solution, with a rate of the order of 0.005 min - 1 for a concentration of 3 g/L. with a maximum of 0.03 min - 1 for experiments realized with a salt concentration of 20 g/L. Our work shows it is possible to use small volumes of fluid to determine quantities accurately, such as adhesion rate or crystals spatial repartition, avoiding the waste of a large quantity of fluids. The method also opens the possibility to screen different fluid compositions and flow conditions to optimize the MICP process. [ABSTRACT FROM AUTHOR]

Suspending self-propelled “pushers" in a liquid lowers its viscosity. We study how this phenomenon depends on system size in bacterial suspensions using bulk rheometry and particle-tracking rheoimaging. Above the critical bacterial volume fraction needed to decrease the viscosity to zero, ϕc ≈0.75%, large-scale collective motion emerges in the quiescent state, and the flow becomes nonlinear. We confirm a theoretical prediction that such instability should be suppressed by confinement. Our results also show that a recent application of active liquid-crystal theory to such systems is untenable. [ABSTRACT FROM AUTHOR]

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