Metabolism of waste engine oil by Pseudomonas species

Two bacterial strains phylogenetically identified as Pseudomonas aeruginosa strains RM1 and SK1 displayed extensive degradation ability on waste engine oil (SAE 40W) in batch cultures. Spectrophotometric analysis revealed the presence of various heavy metals such as lead, chromium and nickel in the waste engine oil. The rate of degradation of waste engine oil by the isolates, for the first 12 days and the last 9 days were 66.3, 31.6 mg l^-1 day^-1  and 69.6, 40.0 mg l^-1 day^-1 for strains RM1 and SK1, respectively. Gas chromatographic (GC) analyses of residual waste engine oil, revealed that 66.58, 89.06 % and 63.40, 90.75 % of the initial concentration of the waste engine oil were degraded by strains RM1 and SK1 within 12 and 21 days. GC fingerprints of the waste engine oil after 12 days of incubation of strains RM1 and SK1 showed total disappearance of C₁₅, C₂₃, C₂₄, C₂₅ and C₂₆ hydrocarbon fractions as well as drastic reductions of C₁₃, C₁₄, C₁₆ and PAHs fractions such as C₁₉-anthracene and C₂₂-pyrene. At the end of 21 days incubation, total disappearance of C₁₇-pristane, C₂₂-pyrene, one of the C₁₉-anthracene and significant reduction of C₁₈-phytane (97.2 %, strain RM1; 95.1 %, strain SK1) fractions were observed. In addition, <10 % of Day 0 values of medium fraction ranges C₁₃, and C₁₆ were discernible after 21 days. This study has established the potentials of P. aeruginosa strains RM1 and SK1 in the degradation of aliphatic, aromatic and branched alkane components of waste engine oils.