Biodegradation and removal of heavy oil using Pseudomonas sp. and Bacillus spp. isolated from oily sludge and wastewater in Xinjiang Oilfield, China

Abstract

Environmental pollution arising from massive production of oily sludge is a global concern. Microbial remediation is an emerging strategy for cleaning up oily sludge-contaminated sites, but it is still challenging to apply heavy oil-degrading bacteria across regions. The aim of this study was to ascertain the feasibility of biodegrading and removing heavy oil from oily sludge by the use of bacterial strains isolated from oily sludge and wastewater collected from Xinjiang Oilfield, Northwest China. The application potential of these bacterial strains for bioremediation of oily sludge-contaminated soils was also evaluated. A total of six oil-degrading bacteria were isolated, three of which showed excellent oil displacement activity (clear zone diameter: 20–23 cm). The three strains were tentatively identified as Pseudomonas reidholzensis (SB2), Bacillus megaterium (SB4), and B. tequilensis (WB1). In a single-factor experiment, the addition of co-substrates stimulated bacterial growth performance on oily sludge agar plates, and all strains formed the largest colonies (mean diameter >11 mm) with sucrose and glucose as co-substrates. Bacterial treatment led to effective biodegradation of heavy oil extracted from oily sludge within 30 days. When additional carbon source (glucose) and nitrogen source (yeast extract) were used, the degradation rate of extracted heavy oil by SB2, SB4, and WB1 reached 15.60%, 11.95%, and 18.43%, respectively. In the oil samples treated with SB2 and SB4, there was a noticeable decrease in the relative abundances of alkenes, cycloalkanes, isoalkanes, and aromatics, accompanied by a slight increase in the relative abundance of n-alkanes. The major oil components all decreased in WB1-treated oil samples. Under simulated conditions, 13.63%, 9.57% and 15.61% of heavy oil was removed from modified oily sludge by SB2, SB4, and WB1, respectively. The results demonstrate the potential of Pseudomonas sp. and Bacillus spp. as candidate strains for use in oily sludge bioremediation.