The Re-use Of Waste Frying Oil For Production Of Rhamnolipids Using Pseudomonas Aeruginosa Zju.u1M

As non-toxic natural biodegradable products with the advantages of little environmental impact, rhamnolipids with low critical micelle concentrations and high surface activities were therefore extensively used. Rhamnolipids had special potential applications in enhancing the bioavailability and biodegradation of insoluble hydrocarbons. Moreover, rhamnolipids could use the hydrophilic and hydrophobic carbon source as substrates, for an example, various vegetable oils and alkyl were used as substrates for production of rhamnolipids with the production of 5~100 g/L. However, the production is very low when use waste frying oil as substrates so that its process is not feasible for industrial scale. Therefore, the productivity of rhamnolipid at utilization of waste frying oil should be enhanced in order to extend this process to industrial level.This thesis was divided into four sections.In section 1, a new strain was isolated. Several candidate strains were isolated from local environment polluted by waste frying oil. Isolated strains were identified as P. aeruginosa after detection using microscope, CTAB (Cetyltrimethyl Ammonium Bromide) plate, product analysis. At last, a strain named P. aeruginosa ZJU.ul was chosen with the best production of rhamnolipids. When the initial concentration of waste oil was 4 % (v/v), the strain got a high productivity of 12.47 g/1. It was found that the isolated P. aeruginosa ZJU.ul averagely utilized the main components in waste oil according to the assay method by G\M analysis.In Section 2, U.V. mutation was conducted to improve rhamnolipid production. We obtained one U.V. mutation named P. aeruginosa ZJU.ul M after three runs of U.V. mutation. The production of rhamnolipid was improved to 24.61 g/1 from an original value of 12.4g/l. Furthermore, this strain had a good stability, which meets the requirment of the industrialization.In Section 3, the culture medium was optimized. We found out that the mutation strain also produced rhamnolipids best at the waste oil concentration of 4 %(v/v), which is same for its starting strain, P.aeruginosa ZJU.ul. For optimization, the concentrationof N> P^ Mg> Ca> Fe were investigated as the concerned compositions in the medium . After optimization, rhamnolipid production could reach 32.2 g/L, and almost 80% of waste oil was used.In Section 4, rhamnolipid was fermented in a bioreactor. A lot of foam caused by rhamnolipids during the fermentation inhibited oxygen transfer and tank pressure. A foam circulation system effectively eliminated the foam-induced problem. The strain rapidly grew with a short cell growth period. The production of rhamnolipid could reach 18.31 g/L and 24.61 g/L when fermentation with the normal culture medium and the optimized culture medium, respectively, both of which are much lower than those by culturing in shaking flasks. After analyzing the surfacial tensions of the serially diluted solutions of the crude extract of rhamnolipid and the cell-free culture broth, it could be found that rhamnolipid may be not the sole surfactant product in the fermentation.