Studies On The Production Of Biosurfactant And Its Role In The Biodegradation Of Organic Compounds

Biosurfactants were non-toxic, natural biodegradable products, offered the advantages of little environmental impact. Biosurfactants showed low critical micelle concentrations and high surface activities and were, therefore, promising substitutes for synthetic surfactants. Biosurfactants had the potential for enhancing the bioavailability and biodegradation of insoluble hydrocarbons. This paper aimed to contribute to the use of biosurfactants producing microorganism for the degradation of organic contaminants.The production of rhamnolipids by pseudomonas aeroginosa grown on water-miscible substrates glycerol was studied. To investigate the influences of cell concentration, carbon source concentration, nitrogen source concentration, etc. on the fermentation process, we ran fermentations with different feeding profiles. In a shake flask medium containing 3% glycerol and 4 g/1 nitrate, the biomass concentration reached a maximum of 4.08 g/1 after 60 h cultivation, a final concentration of rhamnolipids over 15 g/1 was reached, giving a production yield of rhamnolipids on glycerol of 0.35 g/g.Evidence indicated that cell growth rate could be enhanced by adding nitrogen source, and the carbon source was the limiting nutrient of the cell growth. The rhamnolipids were produced in a partly growth-associated mode. The glycerol was used in both cell growth and rhamnolipids production. An unstructured kinetic model for biosurfactant production was proposed. The model parameters were estimated using genetic algorithms, coupled with a Runge-kutta method for the interpretation of integral data. The correspondence between experimental data and model prediction was good. Analyzing the model, lower cell growth rate was favorable for rhamnolipids production. The specific rhamnolipids production rate reached a maximum 0.088 /h when the cell growth rate was 0.051 g/l/h.A fermentation using vegetable oils as sole carbon was established, the influences of oil volume percentage and the rotational speed of the shaker werestudied. Some important basic physico-chemical characteristics of the rhamnolipids were measured. Through analyzing the micellar formation, evaluating the emulsionfication ability and the pseudosolubilization ability of rhamnolipids. The rhamnolipids exhibited a low critical micelle concentration of 58 mg/1. Its miceller solubility ratio for the vegetable oil was 0.22 g/g. Its hydrophile-lipophile balance was in the range of 8-16. The emulsifying power and the stability of the whole broth were increased under the effect of rhamnolipids. When the oil volume percentage reached 10%, the emulsification capacity decreased. Some salt and hydrocarbon could reduce the CMC, leading to higher effectiveness of the rhamnolipids.Various bioreactor systems and impeller types were used in the heterogenous cultivation. Because of the problems with foaming caused by the biosurfactant during the process, the results of hydrocarbon biodegradation in the air-lift fermentators in consider were not perfect. Fluid dynamic and mass transfer characteristics of the stirred tank reactor were studied. The influences of operating conditions on mixing and mass transfer processes were researched. The foaming phenomenon limited the regulation of the air flow rate, so the stirring speed was the crucial operating factor for the volumetric oxygen mass transfer coefficient and the oil drop diameter, which was important for the microbial growth.The fermentation process for the biodegradation of hydrocarbon was investigated. The profile of biosurfactant production was typical of a secondary metabolite, since it was produced mostly during the stationary phase. It was considered that biosurfactant stimulated cell growth on oil by enhancing the dispersion and the solubility of hydrocarbon. The biodegradation was strongly influenced by the stirring speed and the oil volume percentage, so it was concluded that the oil droplet size was an important index, and the cell growth mainly occurred at the oil droplet surface.A mechanistic kinetic model...