Characterization and biodegradability assessment of water-soluble fraction of oily sludge using stir bar sorptive extraction and GCxGC-TOF MS

Abstract

Percolation of water through oily sludge during storage and handling of the sludge can cause soil and groundwater contamination. In this study, oily sludge from a refinery was equilibrated with water to obtain the water-soluble fraction (WSF) of oily sludge. The WSF had dissolved organic carbon (DOC) of 166 mg/L. Human cell line-based toxicity assay revealed IC50 of 41 mg/L indicating its toxic nature. The predominant compounds in WSF of oily sludge included isomers of methyl, dimethyl and trimethyl quinolines and naphthalenes along with phenol derivatives and other polynuclear aromatic hydrocarbons (PAHs). Biodegradation of WSF of oily sludge was studied using a consortium of Rhodococcus ruber, Bacillus sp. and Bacillus cereus isolated from the refinery sludge. The consortium of the three strains resulted in 70% degradation over 15 days with a first-order degradation rate of 0.161 day−1. Further analysis of the WSF was performed using the stir-bar sorptive extraction (SBSE) followed by GCxGC-TOF MS employing a PDMS Twister. The GCxGC analysis showed that Bacillus cereus was capable of degrading the quinoline, phenol and naphthalene derivatives in WSF of oily sludge at a faster rate compared to pyridine and benzoquinoline derivatives. Quinoline, phenol, biphenyl, naphthalene, pyridine and benzoquinolines derivatives in the WSF of oily sludge were reduced by 87%, 92%, 88%, 77%, 40% and 62%, respectively with respect to the controls. The WSF of oily sludge contained, n-alkanes, ranging from n-C12 to n-C18 which were removed within 2 days of biodegradation.