Bacterial Consortium-Mediated Hydrocarbon Degradation of Waste Engine Oils

Abstract

The automotive and industrial activities are considered one of the important sources of pollution with the increasing amount of WEO released to the environment. One of the ways to solve this problem is through bioremediation. It is, however, challenging since used engine oil contains complex hydrocarbon compounds and is toxic towards the environment and living organisms. Biodegradation by single species bacterium is limited to a small range of hydrocarbon compounds. Hence, a better strategy is to use a synergistic action of different microbial members in a consortium. Different waste engine oils from the motorcycle workshop (MW), urban vehicle workshop (UVW), and heavy vehicle workshop (HVW) were tested for degradation by a bacterial consortium culture. A two-level factorial design experiment was carried out to evaluate the effect of different WEO and nitrogen concentrations towards the growth of the bacterial culture and hydrocarbon degradation in shake flask fermentation. The bacterial consortium culture grown in mineral salts medium (MSM) supplemented with MW (Viscosity, 82 mPa.s) was shown to exhibit the highest biomass with 0.37 (OD600) with 8% (v/v) WEO and 5 g/L nitrogen from ammonium chloride (NH4Cl). Pareto chart of biomass with WEO and nitrogen concentration showed a positive effect for MW and UVW, while a negative effect for HVW which was presumed due to the toxicity, higher complexity of hydrocarbon composition and higher viscosity of WEO from heavy vehicles. Subsequently, GC-MS analysis indicated the degradation of various polyaromatic hydrocarbon (PAH) and BTEX compounds such as naphthalene, benzene, and toluene in the three WEO samples. Assessment of cell hydrophobicity of the culture grown on all three WEO exhibited high cell hydrophobicity, with HVW showing the highest cell hydrophobicity of 81%. This suggests that the bacterial culture altered cell hydrophobicity to facilitate hydrocarbon uptake.