Abstract
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.
Highlights
Waste engine oil is a brown to black oil removed from automobiles when oil is changed
It markedly differs from fresh engine oil as it contains minute quantities of additives and metallic salts. It contains higher concentrations of heavy metal contaminants that are dangerous to living organisms such as lead, zinc, calcium, barium and magnesium as well as lower concentrations of iron, sodium, copper, aluminum, chromium, manganese, potassium, nickel, and molybdenum resulting from engine wear (Mumford et al 1986; Vazquez-Duhalt and Greppin 1986)
Heavy metals content of waste engine oil Spectrophotometric analysis of the waste engine oil used in this study revealed the presence of various heavy metals such as lead, chromium, zinc, copper, nickel, manganese and iron, respectively (Table 1)
Summary
Waste engine oil is a brown to black oil removed from automobiles when oil is changed It markedly differs from fresh engine oil as it contains minute quantities of additives and metallic salts. It contains higher concentrations of heavy metal contaminants that are dangerous to living organisms such as lead, zinc, calcium, barium and magnesium as well as lower concentrations of iron, sodium, copper, aluminum, chromium, manganese, potassium, nickel, and molybdenum resulting from engine wear (Mumford et al 1986; Vazquez-Duhalt and Greppin 1986). There is serious environmental concern on the composition of the additives used in engine oil as some of them including zinc diaryl or diakyl dithiophosphates, molybdenum disulphide, heavy metal soaps and organometallic compounds, which contain heavy metals, are dangerous environmental contaminants (Vazquez-Duhalt 1989). Consequent upon this, the waste engine oil accumulates different contaminants such as fuel (petrol or diesel), water, antifreeze and insoluble particles, which principally originates from atmospheric dust, metals, metal oxides and combustion products (Vazquez-Duhalt 1989)
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