|Keywords (Extracted from title, table of contents and abstract of thesis)
oil degrading microorganisms, enhanced oil recovery, fermented sugar scum, fermented sugar foam, oil contaminated soil, bacillus, escherichia, enterobacter, arthrobacter, pseudomonas, biosurfactants, meor, hydrocarbon
In the present study, samples from different ecological sources were collected and screened for desired activity. Only samples of fermented sugar scum, fermented sugar foam and some samples of oil contaminated soil showed high gas production and hence were selected for further experimentation. Considering the bacterial counts, gas production, decrease in pH and quantity of oil consumed for the selection of ecological sources rich in hydrocarbon utilizing microorganisms, fermented sugar scum and oil contaminated soil were found to be the best sources for such bacteria. Results of experiments on Dhurnal Crude oil and Motor oil differ from each other only slightly. In case of Dhurnal Crude, high degree of all the parameters were observed as compared to Motor oil 30/40 PBS. The predominant bacterial isolates from the selected ecological sources were identified as Bacillus, Escherichia, Enterobacter, Arthrobacter and Pseudomonas. Bacillus was most commonly found in all samples, so further work was done on three strains of Bacillus (BS-l, BS-2, BS-3) and their mixture isolated from most active samples.
Gas analysis showed that four types of gases were produced. C02 was the major component produced by all the strains and mixed culture in a large quantity. The other three gases were N2' CH4 and C2H6' Growth and activity of bacteria are also dependent upon the amount and type of nutrients available to them. Best bacterial growth in sucrose mineral medium proved that these bacteria had already the capacity to use molasses as a sugar source. Comparison of crude oil and hexadecane was studied and it was found that hexadecane medium showed better bacterial growth and activity as compared to crude oil medium. A view of the overall results revealed that the strain BS-l was best among all the bacterial isolates and the mixed culture. All the parameters, i. e. bacterial growth, gas production, decrease in pH, oil consumption and biosurfactant production were found to be maximum in the case of strain BS-l. Effect of physical parameters (pH, temperature and NaCl concentration) on supernatant containing biosurfactants showed that BS-l produced more stable biosurfactants that showed better surface activity as compared to other strains and mixed culture. The GLC analysis of organic acids revealed that the maximum number of acids were produced by strain BS-l and mixed culture. The organic acids produced by three bacterial strains were Acetic, Butyric, Iso-butyric, Formic, Propionic, Isovaleric, Valeric, Iso-caproic, Caproic and Heptanoic acid. Similarly, the GLC analysis of organic solvents showed that the organic solvents produced by three bacterial strains and mixed culture were methanol, iso-propanol and acetone.
Biopolymers from three bacterial strains and their mixed culture were also isolated under anaerobic as well as aerobic conditions. Biopolymers produced under aerobic conditions were in greater quantity and were water soluble. Additional analysis by paper chromatography revealed that the biopolymers of bacterial strains and their mixed culture were made up of glucose and fructose.
Thermal analysis showed that the biopolymers of BS-2 and BS-3 were stable up to 470C while the biopolymers of BS-1 and mixed culture were stable upto 1120C and 1300C respectively. Viscosity of biopolymer solution and of saline biopolymer solution was also measured. All the biopolymers caused a significant increase in viscosity of water and saline solution.
The ability of gases, biosurfactant, biopolymers, organic acids and solvents producing bacteria to release oil from sandpack glass columns was also observed. Maximum residual oil recovery efficiency (ER) was exhibited by mixed culture which was 40.28%, followed by BS-1 (24.54%) and BS-2 (12.88%) with least residual oil recovery in BS-3 which was 0.38%. Similarly total oil recovery was highest in case of mixed culture (82.64%) followed by BS-1 (76.24%) and BS-2 (65.67%). Better oil recovery from these three strains and their mixed culture suggested that the bacterial strains can be considered for future MEOR studies on large scales and for field trials.