Jitendra Sangwai

The present work investigates the reaction kinetics of biodegradation of waxy crude oil using Bacillus subtilis YB7, a thermophilic organism. Mathematical modeling of the reaction kinetics of microbial growth together with biosurfactant production and hydrocarbon substrate utilization have been attempted. Although various models, such as Monod's, Logistic, Tessier and Contois were investigated for substrate degradation and biomass production, and compared with the experimental studies, none of them could accurately predict the biosurfactant production in the presence of waxy crude oil. In this study, a new model, which is an extension of Monod's equation, has been developed to predict the observed values of biosurfactant production along with substrate degradation and biomass production in the presence of waxy crude oil satisfactorily. The proposed model has also been tested with various experimental studies carried out in the literature. The proposed model is observed to provide satisfactory model predictions when compared to other models available in literature. This shows that the proposed model can be used to study the reaction kinetics of all types of biodegradation studies to find the optimum parameters for maximum possible biodegradation of hydrocarbon substrates and production of biosurfactant. The positive values of activation energy observed in the study indicates that the process of biodegradation is an endothermic process. The negative values of entropy indicates that the reacting molecule underwent an internal rearrangement to give the activated complex, without a change in the number of molecules. It is believed that this study will be suitable for possible model development for biodegradation of hydrocarbons for oil recovery applications or bioremediation methods.

The study has been carried out to investigate the production of biosurfactant by a thermophilic strain of Bacillus subtilis on various hydrocarbon substrates, such as waxy crude oil, model crude oil and six long chain paraffins (C16H34 to C36H74) at 35, 50 and 75 °C. Model crude oil represents the mixture of the six long chain paraffins. The maximum biosurfactant production has been found to occur at 50 °C with n-hexadecane (C16H34) as a substrate. It has also been inferred that the physico-chemical properties of the biosurfactant is reduced with an increase in carbon number in the hydrocarbon substrate. Biosurfactant production is observed to be higher in the presence of waxy crude oil than the model crude oil, which is due to the presence of short chain paraffins with fewer carbon numbers in the former. B. subtilis in the presence of waxy crude oil has been observed to show high microbial adherence, improved surface tension reduction and emulsification activity, production of higher amount of biosurfactant 'surfactin', and improved biosurfactant stability upto 120 °C at 10 MPa, 10% (w/v) salinity and pH 8-14. This indicates the potential of microorganism in tackling oil-spill, wax degradation, flow assurance and enhanced oil recovery.

Most of the crude oil reservoirs in the world are getting matured leading to the increased production and deposition of long chain paraffins (wax) at subsurface and surface facilities creating a challenge for flow assurance and safer operation. Deposition of wax on the inner walls of the pipelines tends to decrease the flow of crude oil thereby causing billions of dollars of loss. This article reviews in detail about the various aspects of the microbial degradation of waxy crude oil, along with different mechanisms involved in the hydrocarbon degradation. In addition, the article acts as a guide to screen the microorganism suitable for different environmental conditions for their applications in pipelines, oil spill remediation and microbial-based enhanced oil recovery technique to waxy and heavy oil reservoirs for environmentally safe operation.

Marine and costal pollution has become a global concern in recent years due to the increase in intensity of contaminants in the marine environment. The release of crude oil in the marine environment during exploitation and transportation cause serious environmental pollution, owing to the presence of toxic organic compounds. Crude oil, which is the most predominant energy resource throughout the word is the complex mixtures of hydrocarbons including more than 70% of alkanes along with aromatics, naphthenes and resins. The long chain alkanes present in the crude oil remains persistent due to its non-volatile nature and pose a major menace to terrestrial and marine ecosystems. Biodegradation has emerged as a potential and economical technology for the restoration of oil spilled environment. It provides efficient, economical and environment friendly solution for on-shore and off-shore oil spill remedies. The present study investigates the degradation of crude oil using a biosurfactant producing microorganism 'Bacillus subtilis' to obtain maximum degradation. Bacillus subtilis isolated from polymer dump site, Chennai, India was used for the degradation of crude oil. Crude oil degradation and viscosity reduction was observed to be 80% and 60%, respectively, in 10 days. The high microbial adherence, surface tension reduction, emulsification activity, production of higher amount of biosurfactant, stability of the produced biosurfactant at extreme environment conditions, viscosity reduction and high rate of degradation indicates the potential of the microorganism for oil spill treatment.

Microorganisms play an important role in the formation of methane hydrate in subsea environment. Studies involving the effect of biosurfactants produced by microorganisms on methane hydrate formation kinetics are not well understood. The present work investigates the influence of cell free solution containing biosurfactant obtained during the cultivation of microorganisms on the formation kinetics of methane gas hydrate. Two microorganisms, viz., Pseudomonas aeruginosa CPCL and Bacillus subtilis YB7 have been used to produce biosurfactants namely, rhamnolipid and surfactin, respectively. The performance of the cell free solution containing various concentrations (200, 400, 600, 800 and 1000 ppm) of biosurfactant to form the methane gas hydrate was analyzed by adding it into the pure water system and compared with synthetic surfactant, sodium dodecyl sulfate (SDS). It has been observed that the introduction of biosurfactant into pure water system improves the formation kinetics of methane hydrate and reduced the induction time. Addition of 200 ppm of rhamnolipid solution in pure water system has resulted in 47.3% of methane gas to hydrate conversion with an induction time of about 0.23 h, whereas pure water showed 45.1% conversion with an induction time of about 5.77 h. The same concentration of surfactin and SDS have resulted in 42.7 and 33.3% of methane gas to hydrate conversion, respectively. Biosurfactants studied here shows efficient and better performance than their chemical counterpart, namely SDS. This study also provides information on the optimum biosurfactant concentration for the improved formation kinetics of methane hydrate. The results suggest that the utilization of environment friendly biosurfactant can be used as an effective kinetic promoter for the methane hydrate formation suitable for optimum storage and transportation of natural gases.

This study reports the production of biosurfactant from Pseudomonas aeruginosa and Pseudomonas fluorescens with waxes namely, n-hexadecane and n-eicosane as carbon sources. The latter organism produced 9.8 and 8.2gL-1 of rhamnolipid containing C8 and C10 fatty acid with n-eicosane and n-hexadecane as substrates, respectively, whereas, the former produced 5.7 and 11.5gL-1 of C10 and C12 fatty acids. Both the microorganisms were observed to degrade 85-90% of the waxes in one day and achieved very high cell surface hydrophobicity in a short period and indicates their ability of quick adherence to hydrophobic surfaces. The produced biosurfactant was stable upto 100°C temperature, 8MPa pressure, 20% (w/v) salinity and alkaline pH. Reaction kinetics was mathematically modeled using the Monod and Logistic growth model. The Logistic growth model was observed to fit the experimental values of biomass formed, biosurfactant produced, and the paraffins (waxes) degraded satisfactorily. The enhanced physico-chemical properties of biosurfactant with paraffin substrates, such as high bacterial adherence, wax degrading ability, emulsification activities, and surface tension reducing ability indicates the potential of these organisms in addressing oil spill, flow assurance and enhanced oil recovery process.