Elucidating the impact of micro-scale heterogeneous bacterial distribution on biodegradation. (June 2018) - Schmidt, Susanne I.
Highlights: The heterogeneous micro-scale microbial growth in pores reduces bioavailability. This growth form can reduce degradation rates by up to an order of magnitude. Effective mass transfer rates for such limited biodegradation are derived. A conceptual approach how these results may be scaled up is provided for two substances: acetate and toluene. Abstract: Groundwater microorganisms hardly ever cover the solid matrix uniformly–instead they form micro-scale colonies. To which extent such colony formation limits the bioavailability and biodegradation of a substrate is poorly understood. We used a high-resolution numerical model of a single pore channel inhabited by bacterial colonies to simulate the transport and biodegradation of organic substrates. These high-resolution 2D simulation results were compared to 1D simulations that were based on effective rate laws for bioavailability-limited biodegradation. We (i) quantified the observed bioavailability limitations and (ii) evaluated the applicability of previously established effective rate concepts if microorganisms are heterogeneously distributed. Effective bioavailability reductions of up to more than one order of magnitude were observed, showing that the micro-scale aggregation of bacterial cells into colonies can severely restrict the bioavailability of a substrate and reduce in situ degradation rates. Effective rate laws proved applicable for upscaling when using the introduced effective colony sizes.