Biodegradation of semi- and non-volatile petroleum hydrocarbons in aged, contaminated soils from a sub-Arctic site: Laboratory pilot-scale experiments at site temperatures

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This study evaluates the feasibility of landfarming biotreatment of petroleum-contaminated soils obtained from a sub-Arctic site at Resolution Island, Nunavut, Canada, and evaluates the changes in composition of the semi- and non-volatile petroleum hydrocarbon fractions during the biotreatment. Pilot-scale landfarming experiments were conducted in a laboratory in soil tanks under temperature profiles representative of the 3-year site air temperatures in July and August where temperature varied uniformly between 1 °C and 10 °C over 10 d. The site soils were acidic and N-deficient, but contained indigenous populations of hydrocarbon-degrading microorganisms. Biostimulation with nitrogen and phosphorus nutrient amendments to achieve C TPH:N:P molar ratio of 100:9:1, and CaCO 3 amendment at 2000 mg Kg −1 for maintaining neutral pH, and periodic 10-day tilling, reduced total petroleum hydrocarbon (TPH) concentrations by up to 64% over a 60-day period. The rate and extent of semi-volatile (F2: >C10–C16) and non-volatile (F3: >C16–C34) petroleum hydrocarbon fractions in the landfarms containing higher initial TPH levels (∼2000 mg Kg −1) and lower TPH levels (∼1000 mg Kg −1) were compared. Significant biodegradation of the F2 and F3 fractions occurred in both of those systems. First-order biodegradation rate constants of up to 0.019 ± 0.001 d −1 were determined for the F3 hydrocarbon fraction and were similar to the F2 fraction biodegradation rate constants of up to 0.024 ± 0.005 d −1. Biodegradation profiles of the C14, C16 and C18 alkanes revealed that at TPH concentrations above 1000 mg Kg −1 these compounds are degraded concurrently, whereas below 1000 mg Kg −1 the higher-molecular weight alkanes are preferentially degraded. After the 60-day treatment period, the TPH concentration was approximately 500 mg Kg −1, and the residual TPH mass was largely associated with particles and aggregated particles with diameters of 0.6–2 mm, rather than the larger or finer particles and aggregates.