Remediation of soils contaminated with used motor oil by biostimulation method

Abstract

Relevance. Disruptions in technological processes, along with leaks and spills at industrial facilities, result in soil contamination by petroleum hydrocarbons. When oil enters the soil, it reduces air and water permeability, leading to soil ecosystem degradation, including microorganisms and vegetation. Therefore, the search for effective and safe methods to restore contaminated soils is highly relevant. Aim. To investigate the potential for remediating soil contaminated with used motor oil through biostimulation, using sheep bone biochar and manure as biostimulants, and assess the impact of human intervention. Objects. Soil contaminated with used motor oil at the Ulaanbaatar locomotive depot. Sheep manure provided nutrients, while bone biochar improved air exchange. The experiment included four variants: control, biochar, manure, and their combination. Bioreactors were placed outdoors for 365 days, with one group regularly moistened and stirred, while the other remained untreated. Methods. Total petroleum hydrocarbons were determined by ultrasonic extraction; light and heavy hydrocarbons were analyzed by gas chromatography, and heavy metals were measured using optical emission spectroscopy. Soil characteristics were determined using standard methods in Mongolia. Hydrocarbon-oxidizing bacteria in the contaminated soil were assessed using a motor oil and gasoline (1:1) mixture as a carbon source. Results and conclusions. A 365-day biostimulation experiment on soil contaminated with used motor oil showed that treating control soil without additives resulted in a 6% increase in biodegradation, highlighting the importance of human intervention. Adding biochar and sheep manure improved biodegradation: biochar increased it from 13.4 to 18.9%, manure from 11.5 to 15.9%, and their combined use raised efficiency from 22.6 to 27.3%. Heavy fractions of used motor oil were biodegraded by indigenous hydrocarbon-oxidizing bacteria and turned into lighter fractions, especially with biochar (4.7% degradation). The best results were obtained with the combined application of biostimulants. For citation: Nomintuya A., Buyan Ch. Remediation of soils contaminated with used motor oil by biostimulation method. Bulletin of the Tomsk Polytechnic University. Geo Assets Engineering, 2026, vol. 337, no. 8, pp. 227–243. http://doi.org/10.18799/24131830/2026/8/5037