Optimization of nitrogen for bioventing of gasoline contaminated soil

Bioventing is a promising in situ remediation technology for hydrocarbon contaminated soil. Using low airflow rates to produce oxygen-rich conditions in the vadose zone, and nutrient addition, bioventing stimulates indigenous microorganisms that degrade the hydrocarbon contaminants. However, several questions about bioventing remain to be answered, including the optimum soil water content, type and amount of nutrients necessary, and contributions of different microbes. Experiments were conducted using small-scale respirometers containing gasoline-contaminated soil from an active remediation site to determine the effects of soil water content, nitrogen content, nitrogen form, and the composition of the microbial population on the gasoline biodegradation rate. Results indicate that optimum bioventing conditions were 18 wt.% soil water content, C:N = 10: 1, using NH4+-N. A maximum first-order degradation rate constant of 0.12/d was observed. Biodegradation was limited at high C: N ratios by the availability of nitrogen and at low C: N ratios by acidification. It was also determined that aerobic bacteria were the dominant group responsible for biodegradation, with fungi playing a minor role.