Characterization and Bioremediation of a Weathered Oil Sludge

Abstract

The feasibility of bioremediating a weathered petroleum sludge was studied both in the laboratory and in field composting. The sludge consisted of straight-chained alkanes ranging from C20 to C38, with a halogen content of 4.1% and a specific gravity of 0.91–0.92 (23–24 API). Twenty indigenous bacteria were isolated from the sludge and identified; all were mesophiles and grew with or without 3.6% sodium chloride. Nine bacteria used sludge as the sole carbon and energy source and were used in the feasibility and composting studies. The sludge-degraders reduced the total petroleum hydrocarbon (TPH) by 97.4% in 10 weeks in shake cultures with 46 µg/g; at TPH values of 4.1 x 104 and 1.0 x 105 µg/g the bacteria reduced the sludge by about 50% in two weeks and at 2.3 x 105 the sludge was toxic. There was no evidence that cometabolism occurred, and a surfactant did not enhance bioremediation. Piles composted with either sawdust or complete compost (composted agricultural wastes) as bulking agents were monitored by measuring the most probable numbers and TPHs through 24 weeks. The initial TPHs ranged from 3.1–3.6 x 104 µg/g, and the bioremediation rate and extent were better using complete compost (72–75% degradation) than with sawdust (56–58%). There was no measurable effect on bioremediation by augmenting with the sludge-degraders, and most probable numbers ranged from 105–106 cells g–1 soil in sawdust-bulked piles and 107–108 cells g–1 in complete compostbulked piles. After 18 weeks of composting, temperature means were significantly different in the two bulking materials (32°C in complete compost and 41°C in sawdust), but both were 41°C from weeks 19–24, during which time the bioremediation rate did not change in any pile.