Microbial Bioremediation of Spent Engine Oil: Current Advances, Challenges, and Future Directions

Abstract

The extensive pollution of soil and water by spent engine oil (SEO) presents a considerable environmental hazard, especially because of its poisonous and recalcitrant characteristics. Traditional remediation approaches typically fall short in managing these toxins successfully, leading to an increased interest in bioremediation as a sustainable option. This review aims to compile current achievements/advancements in the microbial bioremediation of SEO, with emphasis on the effectiveness of several bacterial and fungal species in degrading the hydrocarbons in SEO under diverse environmental settings. Various studies published in the last decade (accessible via Google Scholar, Google, Scopus, and PubMed), reporting on microbial degradation rates on SEO, the impact of environmental conditions, and the efficacy of microbial consortia were objectively selected and analysed. Key findings showed that various genera such as Alcaligenes, Acinetobacter, Bacillus, Candida, Flavobacterium, Pseudomonas, and Rhodococcus were the most commonly reported microorganisms with potential SEO remediation because they have been reported to significantly degrade and used hydrocarbons in SEO as an energy source. Notably, Pseudomonas alcaligenes and Klebsiella aerogenes exhibited significant degradation rates of SEO, up to 68%, over 21 days under optimal conditions; Acinetobacter, Bacillus, Micrococcus, Flavobacterium, and Pseudomonas were found to exhibit a total hydrocarbon reduction of 86.7% over 60 days; while species like Ochrobactrum thiophenivorans were found to effectively degrade waste lubricating oil. However, there are significant differences in degradation rates among the reported species due to physiological factors such as temperature, pH, and available nutrients. Hence, it is inferential to conclude that microbial bioremediation shows promise in SEO management but its effectiveness is highly dependent on the type of microbial strain used and optimizing environmental conditions. Therefore, this review identifies several key knowledge gaps and proposed future research directions, such as the integration of bioremediation with emerging technologies to improve and ensure efficiency and scalability in real-world applications.