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Effect of the biogenic precipitation of calcium carbonate on bacterial transport in sand columns

Prediction of bacteria transport to riparian shallow groundwater is very important to prevent the pollution of water resources by coliform bacteria. The objective of this study was to investigate the effectiveness of microbially induced calcium carbonate precipitation (MICCP) in reducing bacteria (Escherichia coli and Pseudomonas fluorescens) transport. To perform the MICCP process, air-dried sterile sand was poured into polyvinyl chloride (PVC) cylinders (4.8 × 14.92 cm) and incubated for 3 days in the presence of Sporosarcina pasteurii (~108 Cell g−1sand), urea and CaCl2 (1.5 M). A pulse (0.1 pore volume (PV)) of bacteria suspension (108 CFU mL−1) was added on top of the sand columns (MICCP treated and control) and leaching experiments were followed at steady-state, saturated flow condition. Culturable bacteria were determined in the leachate and the sand extracts (resident bacteria) by colony count method. The MICCP treatment reduced saturated hydraulic conductivity (Ks) value 3.9 times compared to the control and thereby reduced bacteria leaching. Bioprecipitated calcium carbonate in MICCP columns increased bacteria straining compared to control columns especially in surface layer (0-3 cm). MICCP process increased filtration coefficient (λf), and relative adsorption index (SR), and decreased maximum depth of bacteria transport (Zmax). The average (Cav) and cumulative cell density (Ccum) of both bacteria passed from the MICCP column decreased around 3.9-fold compared to the control. Overall, the MICCP process has potential in bacteria filtration in the porous media reducing the risk of groundwater pollution.

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