Sulfolane degrading bacteria from petrochemical plant: activated sludge enrichment, isolation and characterization

Sulfolane is extensively used as an extractive solvent in sour-gas processing plants in the petrochemical industry. After repeated use, deteriorated sulfolane becomes corrosive and may leak into the environment to threaten aquatic and terrestrial organisms or cause shock loading of wastewater treatment systems. It is therefore important to remove sulfolane from the environment and maintain stable wastewater treatment efficiency. To address this issue, bioaugmentation provides a solution by adding specific microorganisms into the biological treatment system to speed up the contaminant degradation rate. Isolation of microbes capable of degrading target contaminant is key point. Understanding the physiological characteristics of isolated microbes is indispensable for subsequent successful applications. In this study, sulfolane degrading bacteria from the activated sludge of a petrochemical plant were enriched using 200-1000 mg L-1 sulfolane and then isolated. After confirming their sulfolane degrading ability, sulfolane biodegradation was then investigated under various pHs, sulfolane and sulfate concentrations. Enrichment could enhance the sulfolane degrading rate of the mixed culture from 3.9 to 7.1 times. Three strains (strain Y-a, Y-d and Y-f) capable of degrading sulfolane were isolated. The degrading microbes were identified as Cupriavidus sp. using 16S rDNA sequencing. Sulfolane concentration biodegraded by strain Cupriavidus sp. Y-d at pH of 7-9 was 1.40-1.45 times higher than that at pH of 6. The optimal pH for strain Cupriavidus sp. Y-d to degrade sulfolane was 8. When increasing the sulfolane concentration from 500 to 2000 mg L-1, the specific growth rate and specific substrate utilization rate increased from 0.19 to 0.48 d(-1) and 0.48 to 0.59 d(-1), respectively. Strain Cupriavidus sp. Y-d was capable of degrading 2000 mg L-1 sulfolane. Sulfate concentrations higher than 2511 mg L-1 had a negative effect on sulfolane biodegradation.