Production And Application Of Rhamnolipids Using Waste Frying Oil As Carbon Source

As an important biosurfactant, rhamnolipids can effectively reduce the interfacial tension and has excellent emulsification ability. But its application has been restricted because of the relatively high cost and low yield in production. This paper aimed to reduce production costs via using cheap carbon source of waste frying oil and enhancing the rhamnolipid productivity of the selected strain. The direct use of the cell-free culture broth as crude rhamnolipid will further reduce the cost on isolation as well as purification of rhamnolipid. Its application has also been investigated in recovery of petroleum oil from oil tank as well as treatment of oily wastewater. The research will be introduced on detail as following:1) The previously obtained P.aeruginosa ZJU.u1M was selected as a starting strain for use of waste frying oil as carbon substrates. By UV mutation and breeding, the rhamnolipids production within 96 h of fermentation increased from 19.0 g/L to 27.2 g/L. With further optimization of the culture medium, rhamnolipid production continuously increased to 43.7 g/L which was double of the previous productivity. And the rhamnolipids productivity fluctuated between 38.5 g/L and 44.3 g/L with different batches of waste frying oil. When the fermentation was conducted in a 10L bioreactor, the rhamnolipid was accumulated to 35.7 g/L at 78 h of culture.2) As the iron overdose was presumed to explain the previously observed abnormal fermentation characterized by the white-color in appearance and low rhamnolipid productivity, its impact on rhamnolipid fermentation was investigated. It was found that the iron overdose at logarithmic growth phase inhibited the cell proliferation and rhamnolipids synthesis. But the iron overdose would enhance the rhamnolipids yield if it was added at stationary phase. It seems that the iron had a severe effect on rhamnolipid fermentation.3) By physico-chemical analysis of the cell-free culture broth, its main product of rhamnolipids were identified to be composed of mono-rhamnolipid Rha-C10-C10 and dirhamnolipid Rha-Rha-C10-C10 while it was proved to be of better interfacial activity and solubility enhancement than pure rhamnolipids. 4) The cell-free culture broth was used to recover the oil from the oil tank sludge in shaking flasks and compared with the three chemically synthesized surfactants including sodium dodecylsulfate, tween-80 and petroleum sulfonate. The cell-free culture broth performed superior to chemical surfactands in recovering oil from oil sludge due to a higher recovery effeeiency with a lower usuage. The effect of the operation conditions such as rhamnolipid dose, the combinational use with sodium and temperature on oil recovery were investigated. The oil recovery increased with the operation temperature and coexistence of sodium chloride. At the optimum operation with rhamnolipd of 340 mg/L, NaCl of 1 N and temperature of 30℃,92.4% of oil were recovered from oil sludge.5) The effect of the cell-free culture broth on treatment of oily waste water was conducted in aerobic active sludge system. It was found that the initial dosage of rhamnolipid at 45 mg/1 in a bench-scale active sludge system could greatly biodegrade fried oil to a low concentration of 65.4 mg/L. The removal efficiency in pilot study was much better with a low residual oil of 50 mg/L within 12 h of treatment. In biodegradation of petroleum carbonhydrates including crude oil and lubricating oil, their removal efficiency was enhanced to 60-90% at a increase by 3～4 times at even very low dosage of rhamnolipid (11.2～25 mg/L). Moreover, the rhamnolipid is biodegradable and thus environment friendly.Taken together, the enhanced rhamnolipid productivity together with the use of cost-effective waste frying oil as carbon source greatly facilitate the cost reduction on fermentation. The direct use of cell-free culture broth also save the cost on isolation of rhamnolipids, making it feasible in recovering oil from tank sludge or biodegradation of oily wastewater.