Abstract
Soil pollution from spent engine oil is a serious ecological threat, containing toxic hydrocarbons, heavy metals, and car cinogens. Conventional disposal and accidental spills result in complex, intractable messes that defy natural breakdown, necessitating advanced biological cleanup methods. The goal of this study was to develop an effective biological remedy for oil-laden ground using freeze-dried beneficial microbes. Two bacterial species, Ochrobacterium intermedium LMG 3301 and Bacillus paramycoides MCCC1A04098, were isolated from contaminated sites and processed as individual and mixed freeze-dried solid inoculants. These inoculants were assessed in a soil microcosm comprising 1.5 kg of soil arti ficially contaminated with used engine oil as the main carbon source. Experimental findings, derived from a completely randomized design and a fractional factorial design, indicated that the bacterial consortium (O. intermedium along with B. paramycoides) provided the most effective treatment. Although O. intermedium alone achieved moderate success (12.05 ± 2.26%), a collaborative effort significantly improved the remediation, removing 55.12 ± 4.5% of total petroleum hydrocarbons from the soil after 84 days. Statistical analysis showed that higher levels of engine oil and protective agents were associated with decreased total moisture loss. On the other hand, a greater inoculum size was positively associated with oil degradation and higher moisture loss. These freeze-dried formulations demonstrated durability, retaining their ability to degrade oil in soil containing 4% oil for 12 weeks at room temperature. In summary, this study indicates that a freeze-dried mixture of bacteria provides an effective, scalable ex-situ biological restoration approach for rehabilitating environments heavily polluted by industrial lubrication waste.