Biodegradation of diesel fuel in soil under various nitrogen addition regimes

Bioremediation is a growing technology for treating fuel-contaminated soils. Many biological, physical, and chemical parameters control the rate and efficiency of this process, including type and concentration of contaminants, temperature, oxygencontent, and nutrient status. This study investigated the effect that nitrogen sources and concentrations had on the degradation rate of diesel fuel in nutrient limited soil at two carbon-to-nitrogen ratios. The different sources of nitrogen studied were ammonium nitrate, ammonium sulfate, potassium nitrate, urea, and urea oligomers (control release fertilizer). Laboratory experiments were conducted on field-contaminated soil using sealed bioreactors at a controlled temperature of 25 degreesC. For both carbon-to-nitrogen ratios tested, hydrocarbon degradation rates were the highest for the ammonium sulfate (20:1 at 0.032 d(-1); 40:1 at 0.019 d(-1)) and urea treatments (20:1 at 0.025 d(-1); 40:1 at 0.011 d(-1)). A degradation rate correlation as a function of nitrate and ammonia concentrations was developed. The correlation suggests the occurrence of nitrate inhibition at elevated nitrate concentrations.