Biodegradation of Petroleum Sludge by Methylobacterium sp. Strain ZASH (early view)
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A bacterium was isolated from sludge-contaminated soil in a petroleum refinery and tested for its ability to degrade aliphatic hydrocarbon compounds present in petroleum sludge. The isolate was grown on minimal salt media agar supplemented with 1 % (w/v) petroleum sludge. The isolate was tentatively identified as Methylobacterium sp. strain ZASH based on the partial 16s rDNA molecular phylogeny. The bacterium grew optimally between the temperatures of 30 °C and 35 °C, pH 7 and 7.5, 0.5 and 1.5 % (v/v) Tween 80 as the surfactant, and between 1 and 2 % (w/v) peptone as the nitrogen source. The constants derived from the Haldane equation were ?max = 0.039 hr-1, Ks = 0.385 % (w/v) total petroleum hydrocarbons (TPH) or 3,850 mgl-1 TPH, and Ki =1.12 % (w/v) TPH or 11,200 mgl-1. The maximum biodegradation rate exhibited by this strain was 19 mg l-1 hr-1 at an initial TPH concentration of 10,000 mg l-1. Gas chromatography analysis revealed that after 15 days the strain was able to degrade all aliphatic n-alkanes investigated with different efficiencies. Shorter n-alkanes were generally degraded more rapidly than longer n-alkanes with 90% removal for C-12 compared to only 30% removal for C-36. The addition of sawdust did not improve bacterial degradation of petroleum hydrocarbons, but it assisted in the removal of remaining undegraded hydrocarbons through adsorption.
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