An investigation of oxygen limitation in microcosm models in the bioremediation of a typical Niger Delta soil ecosystem impacted with crude oil

Abstract

Oxygen was investigated as a limiting factor in the bioremediation of a typical Niger delta soil impacted with crude oil under laboratory simulation conditions. Temperature, pH, moisture content and nutrients (N.P.K. 15: 15: 15) were maintained at optimal levels. Surfactant (S400) was added to aid emulsification of oil. Addition of hydrogen peroxide every four days and tilling were effected in some setups for enhanced oxygen supply. Hydrogen pyrogallol was added to create an anoxic environment in one set-up (experiment 4). Neat soil was used in the control experiment to avoid exogenous carbon sources. The bioremediation process was monitored for 50 days by periodic (10 days) measurements of oil and grease (O&G) and total organic carbon (TOC) levels. Enumeration of total heterotrophic bacteria, total hydrocarbon-utilizing bacteria, sulphate reducing bacteria (SRB) and nitrate utilising bacteria was done. The highest percentage loss in oil and grease level (>80%) and total organic carbon level (>95%) were recorded in the set-up treated with hydrogen peroxide and tilling. This set-up also recorded the highest titre of hydrocarbon-utilizing bacteria. Sulphate reducing bacteria and nitrate utilising bacteria were enumerated in the anoxic experiment 4. Experiment 3 (treated only with crude oil) recorded 57.7% hydrocarbon loss. This was attributed to remediation by natural attenuation processes. Aerobic bioremediation was estimated to be about 30 percentage points above anaerobic bioremediation. Aerobic degradation was found to be at least 30% more effective than anaerobic degradation. A combination of all possible aeration techniques is recommended for enhanced bioremediation.