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Microbial enhanced oil recovery (MEOR): kinetics of biodemulsification of simulated oil-water emulsion
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Biodemulsification has been recently receiving a lot of attention due to the environmental friendliness of the resultant microbial products commonly known as biosurfactants. It has the potential to address emulsion issues that challenge the petroleum industry which have been reported. However, it is not yet fully established due to high capital costs which continue to inhibit the full industrial application of this technology, more especially with the lagging literature. Thus, more studies are required that will positively contribute to the implementation of this technology despite current challenges. While many studies have been done, the kinetics of biodemulsification are yet to be fully documented in the literature. The aim of this study was to investigate the suitable carbon source and the effect of carbon source on the production of a B.licheniformis STK 01 biodemulsifier. Furthermore, to investigate the biodemulsification kinetics including the effect of temperature. Biodemulsification experiments were conducted by initially cultivating biodemulsifiers in conical flasks containing the growth media and the various carbon sources, in an incubating shaker operating at 37 °C and 160 rpm over a 48 hr period. The produced biodemulsifiers were then used for the various demulsification studies at 37 °C, over a 24 hr period. The simulated emulsions were produced in conical centrifuge tubes with the aid of Span 60 and Tween 60 surfactants. The study showed that all the produced B.licheniformis STK 01 biodemulsifiers possessed biodemulsifying capabilities but at different efficiencies. Motor oil proved to be the most suitable carbon source, resulting in a B.licheniformis STK 01 biodemulsifier that achieved 82,9% demulsification within 8 hrs. This is followed by diesel, paraffin, glucose, fructose and sucrose-cultivated biodemulsifiers with demulsification values of 73,7%, 61,9%, 52,9%, 45,1% and 44,7% respectively, thus, indicating the positive and significant contribution of insoluble carbon sources to the production of biodemulsifiers. The kinetics investigations revealed that B.licheniformis STK 01 biodemulsifiers cultivated on soluble carbon sources adhered to third order kinetics while insoluble carbon sources followed a first order. The biodemulsification rate constants, 𝑘, for soluble substrate glucose (𝑘𝑔), sucrose (𝑘𝑠) and fructose (𝑘𝑓) were determined to be 10×10−5 𝑑𝑚6/𝑚𝑜𝑙2𝑠, 5,029×10−5 𝑑𝑚6/𝑚𝑜𝑙2𝑠, and 9×10−5 𝑑𝑚6/𝑚𝑜𝑙2𝑠 respectively. The insoluble substrates motor oil (ko), diesel (𝑘𝑑) and paraffin (𝑘𝑝) gave the rate constants of 11,561×10−5 𝑠−1, 2,447×10−5 𝑠−1, and 2,245×10−5 𝑠−1 respectively. Finally, the relationship between the rate of biodemulsification of B.licheniformis STK 01 and temperature (37−67 ℃) was also investigated, assuming that the effect could be independently studied. The rate of biodemulsification was found to increase with the increase in temperature; this trend was depicted using the Arrhenius equation (𝑅2 value of 96,3%), with the corresponding Arrhenius parameters, namely activation energy and frequency factor as 70,88 𝐾𝐽/𝑚𝑜𝑙 and 14×106 𝑠−1 respectively. This study found that the carbon source used for the production of a biodemulsifier significantly contributes to its biodemulsification capability. It also found that insoluble carbon sources were the better carbon source option compared to soluble carbon sources and that the more complex the carbon source, the better the biodemulsifier produced. Furthermore, it found that the suitable biodemulsifier followed first order kinetics and the kinetic parameters thereof.