Laboratory respirometry experiments were conducted on mixtures of soil and oily sludge to estimate biodegradation rates by CO2 production rates and determine optimum conditions for biodegradation of high-strength hydrocarbon waste products. These experiments were used to determine a suitable range of total petroleum hydrocarbon (TPH) concentration for biological treatment and to optimize for nutrient addition and moisture content. CO2 production rates from biological respiration of hydrocarbon-contaminated soil were maximized at concentrations of 3-9% TPH (30,00090,000 mg/kg TPH). CO2 production rates decreased dramatically at concentrations above 9% TPH, indicating that either these concentrations are lethal to microbes present, or this high sludge content inhibits aeration of the soils. Addition of 120 mg/kg nitrogen, 40 mg/kg phosphorous, and 40 mg/kg potassium to the soils resulted in a three fold increase in CO2 production rates. No significant increase in CO2 production was observed when the nutrient addition was increased to 240 mg/kg nitrogen, 80 mg/kg phosphorous, and 80 mg/kg potassium. Maximum CO2 production rates were observed at 15-20% moisture content. CO2 production rates decreased significantly at and below 10% moisture and at and above 25% moisture. Maximum CO2 production rates observed for soil with 50,000 mg/kg TPH, with added nutrients at optimum moisture content, were 30-35 μL CO2/g/hr. Assuming all CO2 was generated from hydrocarbon degradation, this maximum CO2 production rate corresponds to a hydrocarbon biodegradation rate of approximately 500 mg TPH/kg/day (assuming 100% respiration for a conservative estimate). If ideal conditions are maintained and rates of respiration remain high, clay soil contaminated with 60,000 mg/kg TPH sludge could probably be remediated in 2 months.


Civil and Environmental Engineering

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URL: http://digitalcommons.calpoly.edu/cenv_fac/87