Ranking agro-technical methods and environmental parameters in the biodegradation of petroleum-contaminated soils in Nigeria

A combination of experimental cells consisting of some agro-technical methods aimed at accelerating the biodegradation of petroleum contaminated soils were evaluated in order to ascertain the relevance of these methods and the relative attention due necessary soil environmental parameters. The methods of treatment involved the variation of tilling, watering and nutrient application, plus biopile and phytoremediation treatments. In the experiments described, petroleum contamination of soils was simulated under field conditions, the remedial treatments were then utilized for clean up. Analysis of soil parameters after a six-week study period showed an increase in total heterotrophic bacteria (THB) counts across all the treatments, with THB counts increasing with increment in soil nutrient level and initial concentration of the contaminant. The total hydrocarbon content (THC) analysis, based on a performance index introduced in this study, indicated that on the average, the variation of nutrient application, tilling and watering facilitated the attenuation of THC at the rate of 429.4 mg/kg day, 653.2 mg/kg day, and 327.5 mg/kg day respectively. While the combined effect of various levels of nutrients, tiling and watering performed at the rate of 558.7 mg/kg day, biopile and phytoremediation treatments recorded 427.9 mg/kg day and 489.3 mg/kg day respectively. These results imply that though nutrient application, watering and other factors affect the biodegradation process, frequent tilling for maximum oxygen exposure is the most important factor that affects the biodegradation of petroleum-hydrocarbons in tropical soils.