Decrease of the hydraulic conductivity of sand columns by Methanosarcina barkeri

The extent to which a methanogen can clog sand columns was examined: two permeameters packed with clean quartz sand were sterilized, saturated with water, inoculated with Methanosarcina barkeri and percolated under upward flow conditions. After approx. 5 months, the hydraulic conductivity of the sand had decreased to 3% and 25% of the highest values measured earlier. At that point, gas-filled regions in the sand were clearly visible through the transparent walls of the permeameters, and methane bubbles were continuously released from the columns into the effluent. Scanning electron microscopy observations and biomass assays indicated that cell mass accumulation did not contribute significantly to the observed decrease of the hydraulic conductivity. This decrease was therefore attributed to pore blocking due to the entrapment of methane bubbles.