Biocatalytic remediation of used motor oil-contaminated soil by fruit garbage enzymes

Abstract

This work was aimed to utilise biocatalysts―enzymes derived from organic wastes mainly comprised of fruit garbage for remediation of used motor oil-contaminated soils. The fruit garbage used were orange and watermelon peels, which were allowed to ferment for 90 days for the derivation of enzymes. The enzymes identified in the extract solutions of the fruit garbage were protease, catalase, lipase, and amylase. Soils collected from the uncontaminated field were amended with used motor-oil at 5% and 10% (w/w) contamination levels. The amended soils were allowed to homogenise for 2 weeks before the experiment. The enzyme working concentrations were derived from Design Expert 7.0.0. matrix for 5% and 10% used motor-oil contamination levels as 0, 1, 5.43, 7.75% and 10% for 5% used motor-oil contamination level and 0%, 1%, 3.28%, 6.62%, and 10% for 10% used motor-oil contamination level. The experiment was run for six weeks. The minimum and maximum of 47% and 58% removal of oil and grease by orange garbage enzymes were recorded at 5% and 10% contamination levels, respectively at the end of six weeks experiment. Similarly, 41% and 52% removal of oil and grease were achieved with watermelon garbage enzymes at 5% and 10% contamination levels, respectively. Also, 62% and 74% of oil was biocatalytically removed in terms of Total Organic Carbon (TOC) by orange garbage enzymes at 5% and 10% contamination levels, respectively. In contrast, watermelon garbage enzymes showed an overall TOC removal efficiency of 45% and 39% for oil contamination levels of 5% and 10%, respectively. The differences observed in the biocatalytic remediation activities of the applied fruit garbage enzymes might be due to the difference in composition of the garbage enzymes. However, despite the differences in their enzymatic compositions, it is evident that extract solutions of fruit garbage enzymes of both orange and watermelon have the potential to remove oil from soil and hence could be applied for biocatalytic remediation of oil-contaminated soils.