Oxygen Consumption as a Measure of Oil Impacted Soil Treatability

We know petroleum hydrocarbons degrade in soil via chemical, physical, and biological pathways. Innovative remediation technologies enhance degradation by one or more pathways e.g., in-situ and ex-situ. The typical goal of degradation is to achieve the applicable regulatory criteria. Some, State Agencies, e.g., Louisiana, Texas, require oil total petroleum hydrocarbon (TPH) contamination levels be reduced to ≤10,000 mg/kg. However, other agencies, e.g., New Mexico and California, require oil contamination levels reduced to <1,000 mg/kg. Even 100 mg/kg is not uncommon, e.g., Los Angeles, County, CA. Microbial populations and substrate availability often limit biodegradation at petroleum hydrocarbon levels <1,000 mg/kg. Conventional laboratory biodegradation microcosm studies require an inordinate amount of time to evaluate petroleum hydrocarbon treatability (as measured by loss of analyte) and even more time to optimize treatment parameters that facilitate or improve kinetics (lower half-life values). Two studies discussed here demonstrate the utility of oxygen consumption respirometry in evaluating oil impacted soil treatability. In the first study, oxygen consumption rates were measured after a 1-week incubation period at varying TPH levels (5800 and 1000 mg/kg), carbon:nitrogen (C:N) ratios (100:1 and 25:1), and manure content (0, 0.5, 1.0 and 5.0 percent). Results showed TPH and C:N ratios significant at < 1 percent level and manure significant at < 5 percent level. The second study, a longer-term study (132 day) showed oxygen consumption resulted from degradation of gasoline range (GRO) and diesel range (DRO) fractions of TPH. These studies provide a means of evaluating treatability of low concentrations of petroleum hydrocarbon and a method for assessing treatment options that are passive in nature, but less destructive to the environment.