DECREASE OF THE HYDRAULIC CONDUCTIVITY OF SAND COLUMNS BY METHANOSARCINA-BARKERI

The extent to which a methanogen can clog sand columns was examined: t wo permeameters packed with clean quartz sand were sterilized, saturat ed with water, inoculated with Methanosarcina barkeri and percolated u nder upward flow conditions. After approx. 5 months, the hydraulic con ductivity of the sand had decreased to 3% and 25% of the highest value s measured earlier. At that point, gas-filled regions in the sand were clearly visible through the transparent walls of the permeameters, an d methane bubbles were continuously released from the columns into the effluent. Scanning electron microscopy observations and biomass assay s indicated that cell mass accumulation did not contribute significant ly to the observed decrease of the hydraulic conductivity. This decrea se was therefore attributed to pore blocking due to the entrapment of methane bubbles.