The Effects of Nitrogen Source and Supply on Bioventing of Gasoline Contaminated Soil

摘要

Soil remediation through bioventing is becoming a popular in situ technology for treatment of hydrocarbon contaminated soil. Bioventing removes residual contamination left by soil vapour extraction (SVE) using low or intermittent airflow rates to produce oxygen-rich conditions in the vadose zone. This promotes the growth of indigenous microorganisms which degrade the hydrocarbon contaminant, provided sufficient nutrients are available. However, there are major questions that remain to be answered, including the optimum soil moisture content, type and amount of nutrients necessary and means of producing these conditions in the field. Accordingly, respirometer experiments were conducted using gasoline contaminated soil from a site in Ontario, Canada. The experiments conducted were designed to determine the optimum C:N ratio and the optimum form or combination of nitrogen supply. The completed experiments gave an optimum biodegradation rate constant of 0.0806 d~(-1) for soil amended with ammonia at a C:N ratio of 10:1, and a moisture content of 15w/w%. Minimal acidification was observed at a C:N ratio of 10:1, indicating that it is unlikely that inhibition will occur at a ratio of 20:1. Accordingly, future experiments will investigate a higher nutrient application rate of C:N = 5:1. While the degradation results agree with literature data, the microbial enumeration tests indicate that the degradation may not necessarily be due to bacterial metabolism. Future experiments will attempt to determine the mechanism of degradation by isolating bacterial and fungal soil microorganisms and repeating the bioventing trials.