Biodegradation of Phenolic and Petroleum Wastewater by Isolated Bacillus cereus
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The thesis mainly focuses on the isolation of phenol-degrading bacteria from oilcontaminated sites and their application in the biodegradation of phenolic and petroleum wastewaters. Firstly, two potential phenol-degrading bacterial strains were isolated from two different site specific petroleum wastewaters and identified as Bacillus cereus MTCC 9817 strain AKG1 and Bacillus cereus MTCC 9818 strain AKG2, based on the 16S rDNA gene sequencing. In addition to the various morphological and biochemical characterizations, the optimum growth conditions and growth kinetics for both AKG1 and AKG2 were investigated. Next, biodegradation of phenol at various initial concentrations by isolated B. cereus strains were studied at their optimum physiological condition. The degradation kinetics revealed that the Haldane model fitted the experimental data fairly well. The phenol degradation mechanism in the isolated strains was also elucidated. Treatment of real petroleum wastewater samples, studied in batch mode by free cultures, demonstrated that coculture of the free cells (AKG1 and AKG2) was most efficient in removing COD, TOC and ammonium nitrogen. Probable identification of bio-degradation products was performed by liquid chromatography and mass spectroscopy. Also, an attempt has been made to probe the structural changes of bacterial cell membrane as a result of the bacterial adaptation to the toxic environment of the petroleum wastewater. The investigation with Ca-alginate immobilized AKG1 and AKG2 demonstrated enhanced tolerance of the immobilized cells to higher phenol concentrations (~ 2000 mg L-1). The storage stability of the immobilized strains and their potential application in repeated batch biodegradation has also been evaluated. Degradation kinetics indicated that phenol degradation by immobilized strains could well be fitted by Haldane model. Moreover, biodegradation of petroleum wastewater samples by alginate immobilized strains have been investigated and the reduction in COD, TOC and ammonium nitrogen level evaluated. The immobilized cells were found to be less effective than the free cell systems in treating petroleum wastewater. Finally, the fabrication and initial optimization of lab scale bioreactors for degrading phenolic and petroleum wastewater Ca-alginate immobilized Bacillus cereus (AKG1 and AKG2) were investigated. The performance of immobilized strains in phenol degradation in a packed bed reactor was studied and the combined effect of external mass transfer with biochemical reaction on the mass transfer correlation was determined in terms of Colburn factor (JD) and Reynolds number (NRe). Continuous biodegradation of the petroleum wastewater was carried out in re-circulated packed bed reactors by the isolated strains immobilized in either Ca-alginate beads or polyurethane foam (PUF) cubes. The biodegradation performances of both the immobilized systems demonstrated the excellent efficacy of the immobilized AKG1 and AKG2 strains in treating petroleum wastewater in continuous mode of operation. Continuous biodegradation of petroleum refinery wastewater in re-circulated fluidized bed reactors also demonstrated that the microbial treatment reduced the initial COD level and concentration of phenolic compounds efficiently...
Supervisor: Aloke Kumar Ghoshal