Evaluation of Microbial Degradation of Crude Oil in a Polluted Tropical Soil

Abstract

This research is aimed at determining the growth and capacity of microorganisms to degrade crude oil following biostimulation
with NPK fertilizer and sawdust amendment. The contaminated soil was treated simultaneously with the nutrient amendment in treatments A, B, C, D, E, F, G, H and I and the population of microorganisms involved in the degradation of TPH monitored.
Optimum conditions for effective degradation of the contaminant were determined and the kinetics of the process evaluated. Physicochemical and biological parameters like soil pH, texture, total petroleum hydrocarbon (TPH), total nitrogen, total
phosphorus, hydrocarbon-degrading bacteria (HDB), and hydrocarbon-degrading fungi (HDF) in the native, control and treated
soils were analyzed using standard analytical method and procedures. The HDB/HDF population measured for TPH degradation
at intervals established the efficiency and kinetics of the bioremediation process. However, HDB growth rate in the treatments
were between 0.1840 and 0.1931. The utilization of nitrogen and phosphorus by microorganisms was between 81.5% and 92.8%.
TPH degradation in the treatments was between 98.14% and 99.05% and degradation rates between -0.0419 day-1 and -0.0479
day-1. However, optimum treatment was achieved in 105 days with an efficiency of 99.05% in the first-order kinetics at degradation constant of -0.0479 day-1, degradation half-life of 14.47 days, the microbial growth rate of 0.1921 day-1, and biomass doubling time; 3.61 days. Arousal of the population of indigenous microorganisms at the study site through the application of nutrients and a permeable medium resulted in massive biotransformation of the pollutants to non-toxic environmentally friendly forms.