Reduction of hydraulic conductivity changes in an in-ground bioreactor

The biodegradation of dissolved naphthalene was studied in the laboratory, in preparation for a field-scale investigation of enhanced bioremediation in a permeable barrier. The laboratory experiments were performed, under water saturated conditions, in acrylic columns packed with silica sand. The sand contained 1% by volume of granular activated carbon (GAC). Naphthalene, nutrient, and nitrate solutions were pumped through, and concentrations and liquid pressures were monitored. One objective of the laboratory study was to determine if the decrease in hydraulic conductivity caused by microbial growth could be reduced. It was believed that biomass would attach preferentially to the small proportion of GAC added to the sand. Scanning electron microscope micrographs showing evidence of preferential attachment of biomass on the GAC are presented in this paper. A calculation indicates that the decrease in hydraulic conductivity could be less than 6%. Data gathered to design the field scale bioreactor and the design and assessment of the performance of the permeable barrier are presented elsewhere. Key words: hydraulic conductivity, biomass growth, in-situ bioreactor, granular activated carbon, naphthalene.