Effect of bioclogging in porous media on complex conductivity signatures

Abstract

Flow through sand columns inoculated with Pseudomonas aeruginosa were used to investigate the effect of bioclogging on the complex conductivity and flow and transport properties. Complex conductivity (0.1–1000 Hz), the bulk hydraulic conductivity (K), volumetric flow rate (Q), dispersivity (D), and microbial cell concentrations were monitored over time. Environmental scanning electron microscope images of the sands were obtained at the end of the experiment. Bioclogging resulting from increases in microbial cell concentration and the production of exopolymeric substances (EPS) had a large impact on the imaginary conductivity (σ″), K, Q, D, and porosity (Φ). Changes in electrical and transport properties developed in three stages: an initial stage 1 with no significant changes in all measured parameters (Days 1–8), which we attribute to the reversible and irreversible attachment of microbial cells to the sand. In stage 2a (Days 9–16), bioclogging caused by the growth of biomass either as microcolonies filling pore throats and/or as uniform covering on the sand surfaces resulted in maximum decrease in Q and K, but with only moderate increases in σ″. In stage 2b (Days 17–24), significant production of EPS substances and increase in biofilm thickness resulted in a higher rate of increase in σ″ compared to stage 2a. In stage 3 (Days 25–32), biofilm growth reached a quasi steady state and insignificant changes are observed in all measured parameters. The results of this study suggest that σ″ can provide complimentary information in the assessment of bioclogging in porous media.