Comparative Study of Bacterial Response to Nutrient Amendments and Hydrocarbon Removal through Leaching During Remediation

Introduction: Hydrocarbon pollution is of global concern because of it deleterious effect on the environment and on biodiversity. This study investigated the percentage of hydrocarbon loss through leaching during remediation and how organic-based nutrients impact leaching and the rate of hydrocarbon degradation.

Methods: The investigation involved both microbiological and chemical methods. Total petroleum hydrocarbons (TPH) and polycyclic aromatic hydrocarbons (PAHs) was monitored using Gas chromatography – Flame ionization detection (GC - FID). Other physicochemical parameters analysed included, total organic carbon, nitrate, phosphate and the soil pH. Bacterial monitoring was based on a culture dependent assessment of both heterotrophic and hydrocarbon utilizing bacteria. The nutrients used as biostimulant were: soy bean waste, poultry droppings, NPK and a combined treatment of all nutrient sources.

Results: Initial concentrations of TPH and PAHs in the oil-polluted leachate were 2648.3 mg/l and 6320 mg/l respectively while the baseline TPH concentration in the polluted soil was 48, 501 mg/kg. The baseline pH of 7.6 was optimal for microbial multiplication, however nutrient concentrations of nitrate (1.39 mg/kg) and phosphate (2.16 mg/kg) was low.HUB counts in the contaminated leachate was 8.5 x 10⁶ (cfu/ml) while that of the pristine soil was 6.1 x 10⁶ (cfu/ml). Approximately 6% of TPH and 6.7% of PAHs was lost through leaching from across all the setups during remediation. Nutrient amendment had no direct or significant (p ≤ 0.05) effect on the rate of hydrocarbon loss via leaching. Treatment C had the fastest rate of hydrocarbon loss (0.0207 d^-1) while the least rate of TPH removal (0.0144 d^-1) was observed in the unamended control. Analysis of variance revealed there were significant differences (p = 0.001) in HUB counts between the nutrient amended treatments and the unamended control treatment. Also, HUB counts significantly correlated (p = 0.05 and R = - 0.83) with TPH removal in all the nutrient amended treatments

Conclusion: The findings from this study will be useful in designing greener remediation strategies and for predicting loss of hydrocarbons via leaching during remediation.