Biodegradation of hydrocarbons as a mechanism of microbial enhanced oil recovery

Microbial enhanced oil recovery (MEOR) is one of the enhanced oil recovery (EOR) techniques that is applied to oil reservoirs after primary and secondary recovery techniques to increase oil production. The successful implementation of MEOR involves an interdisciplinary approach. This paper has focused on one of such approaches which is the bioengineering aspect of MEOR that is concerned with the quantitative description of microbial growth and yield factors. Early MEOR works have focussed on the use of external carbon sources i.e. carbohydrate nutrients to produce metabolites useful for oil recovery, using the petroleum hydrocarbons present in the reservoir as the carbon source for microorganisms can be essential in microbial enhanced oil recovery as this addresses some logistic problems encountered in adverse environment. The metabolites which are useful in MEOR techniques for oil recovery can be produced by growing the microorganisms on petroleum hydrocarbons. The microbial degradation of n-alkanes and some readily biodegradable substrate has been studied. A simple respirometric method has been developed to assess the biodegradability of these compounds. Initial experiments have been performed in small-scale laboratory bioreactors to determine hydrocarbon degradation rates through oxygen consumption data (under aerobic conditions) collected over a period of time. Analysis of initial kinetic parameters has shown that estimates of hydrocarbon biodegradation based on respirometry is very reproducible with some consistency in the data generated. It has been shown from calculated microbial growth rates that petroleum hydrocarbons can be utilized under aerobic conditions at reasonably rates. The biodegradation of petroleum hydrocarbons using nitrate as electron under anoxic conditions has also been studied.