Optimization of Diesel Oil Biodegradation by Response Surface Methodology and Immobilization Technique

Background: As a kind of hydrocarbon mixtures, diesel oil is mainly consisted of linear chain alkanes as a medium distillate of petroleum. The removal of diesel oil depends on several technologies not merely chemical or physical, but also biological methods, especially biodegradation. Method: Five microorganisms considered as the potential diesel oil-degrading bacteria were chosen for biodegradation experiment. Among these five microorganisms, D2 and D4 showed better removal efficiency of diesel oil with removal rate reached to 75.16% and 69.09%, respectively. Result: According to the test of 16S rDNA sequence, strain D2 and D4 were identified as Bacillus subtilis strain ATCC 13952 and Bacillus cereus AH676, respectively. After optimizing biodegradation condition of D2 mixed strains by using response surface methodology (RSM), the removal efficiency was promoted to 83.06%, with the optimal condition calculated as rotate speed 124 rpm, pH 7.1, temperature 37.0132;ƒ, and inoculum size 5.1% (v/v). Furthermore, immobilization technique was applied for improving the removal efficiency sequentially. Conclusion: Compared with free strains, the immobilized D2 mixed strains, embedded by the mixture of 4% (w/v) sodium alginate and 4% (w/v) polyvinyl alcohol (PVA), obtained a higher removal rate reached to 95.95% with no breakage and well permeability.