Biodegradation of used engine oil in a wastewater sludge-amended agricultural soil

Abstract

Soil contamination by used engine oil is a common occurrence in most developing countries. This has been shown to have harmful effects on the environment and human beings at large. Used oils are considered to be hazardous waste materials. These are composed of toxic chemicals, such as heavy metals (which come from additives and wear and tear of engine parts), combustion products, light hydrocarbons, polar compounds, uninuclear and polynuclear aromatic compounds, resinous materials, and organometallic compounds. Some of these pollutants are carcinogenic in nature. The objective of this study was to evaluate the effects of used engine oil (doses of 0.5% and 5%) with hydrocarbon pollution on total petroleum hydrocarbon (TPH) removal from soil and determine the fate of TPHs at different temperatures (18 degrees C and 28 degrees C) during an incubation period of 240 days. The possible use of wastewater sludge as a biostimulating agent in used engine oil-contaminated soils was also evaluated. The results of 240 days of incubation indicated that TPH removal percentages in used engine oil-contaminated+sludge amended soils at 18 degrees C were 68% and 66% for doses of 0.5% and 5%, respectively. Incubation at 28 degrees C resulted in higher TPH removal with values of 56% (dose of 0.5%) and 74% (dose of 5%). Based on the first-order kinetics model, the high dose (5%) of used engine oil-contaminated soil amended with wastewater sludge showed the highest biodegradation rate of 0.00562/day and half-life of 123.13 days at the end of the incubation period at 28 degrees C. These rates were significantly higher than those of the control soil (0.00366/day and 189.01 days).