Evaluation of First and Second Order Degradation Rates and Biological Half-lives in Crude Oil Contaminated Soil

Abstract

Aim: The aim of the study was to investigate crude oil degradation using first and second order kinetic models, microbial activity using dehydrogenase assay. Place and duration of Study: Department of soil science, University of Nigeria Nsukka, Enugu State from October 2015 to March 2016. Methodology: Characterisation and microbial analysis of Goat manure and crude oil contaminated soil were investigated. Dehydrogenase assay was used as a measure of microbial activity microbial count using Heterotrophic plate count was also investigated. Experimental data were fitted into both first and second order kinetic models and biological half-lives in order to evaluate the kinetic parameters and half-lives. Results: The physiochemical characterisation showed that Goat manure contained valuable sources of soil nutrient and organic matter, which enhanced the bioremediation process. The result obtained from the physiochemical characterisation of the control sample showed the inadequacies of soil nutrient in the crude oil contaminated soil. The microbial activity (DHA) indicated an increase in microbial activity in both the untreated crude oil contaminated soil and the Goat manure treated contaminated soil due to the presence of crude oil in the soil. Microbial count using heterotrophic plate count indicated that higher colonies were recorded in Goat manure. 70% degradation of crude oil was achieved on the 14th day of treatment, whereas only 21% was achieved in the control sample. The kinetic parameters obtained indicated that the first order kinetic model and biological half-life gave a better result (higher degradation rate and lower biological half-life) than the second-order kinetic model. Conclusion: In this study, we have shown that the bioremediation of COCS using GM as organic nutrient enhanced CO degradation. However, an increase in microbial count and dehydrogenase assay was observed in the GM treated COCS. The obtained kinetic parameter suggests that the first order kinetic model gave a better result (high degradation rate constant and lower biological half-life) for the studied CO degradation.