MINERALOGIC CONTROLS ON THE BIODEGRADATION OF HYDROCARBONS

While many petroleum-contaminated aquifers are amenable to bioremediation, efficiency is often compromised by slow biomass growth in conditions where nutrients and energy-efficient terminal electron acceptors are typically scarce. Microbial strategies that increase the bioavailability of these substances may enhance the viability of the native population or consortium, potentially stimulating growth and metabolism. In this study, we specifically examined the microbial release and utilization of phosphorus and iron from feldspars and manufactured glasses, and the subsequent impact on biodegradation of benzene and toluene. Laboratory microcosms containing P and Fe-bearing silicate rocks and glasses were inoculated with a native microbial consortium from a petroleum-contaminated, anaerobic groundwater and amended with benzene and toluene. The rate of substrate removal, biomass production and nutrient release was monitored over a 150 day period. Results show that microbial biomass increases in the presence of silicates containing trace phosphate mineral inclusions, suggesting that the cells can release and utilize silicate-bound P. Biodegradation rate, however, increased only in the presence of iron oxide inclusions within silicates, apparently stimulating the iron-reducing population responsible for degrading the compounds of interest. The highest rates of carbon removal were measured in microcosms with silicates containing both P and Fe. Silicates may be a convenient source of vital nutrients to microorganisms in nutrient-limited environments, providing essential substances to stimulate growth and metabolic activity. Therefore, intensive mineralogic characterization of aquifer sediment may be a valuable tool in assessing potential nutritional resources available to the native microbial consortium during intrinsic bioremediation.