High-performance Fermentation And Application Of Rhamnolipid

Rhamnolipid is a versatile biosurfactant possessing excellent surface/interfacial activity and additional ecological features such as low toxicity and environment-friendliness,and can be potentially applied in the environmental,pharmaceutical,food,and agricultural fields etc.However,the industrial applications of rhamnolipid have rarely be reported yet.The main reason for this situation should be due to the high costs on production of rhamnolipid and the lack of the suitable application field.Generally speaking,the high cost on the production of rhamnolipid are caused by:1)small-scale of upstream fermentation with low-yield,2)costive downstream separation due to complexicity and solvent-waste.In addition,the application of rhamnolipid presents poor economical competition in the fields where chemical surfactants can be traditionally applied.Hence,this study will try to reduce the cost of rhamnolipid in production by focusing various approaches from the upstream to the downstream processing.One is the use of mechanical methods to control the foam which is the critical barrier for improving the fermentation scale and yield of rhamnolipid.The other is the development of the cost-efficient two-step ultrafiltration(UF)for separation of rhamnolipid.The application of rhamnolipid will be extended to the demulsification area and membrane cleaning where chemical surfactants show much limited treatment efficiency.This study,for the first time,applied the stop valve to control the extensive overflowed foam in the fermentation process.Under control by the stop valve in 10-L as well as in 500-L scale fermentation,the foam stream was significantly reduced by 70%-80%at the flow rate while enhanced to 30%-40%at the average water content,making the culture broth be timely pumped back to the bioreactor.This could largely reduce the volume of foam tank and the operation difficulty without showing any detrimental effect on the cell and rhamnolipid production.Secondly,the two-step UF was used to separate rhamnolipid from the cell-free culture broth.By regulating pH,the ethanol dose was reduced by half while the rhamnolipid recovery rate/purity were both enhanced to over 90%.In the first UF(UF-1),the rejection of rhamnolipid increased to 98%under regulation of pH down to 5,while the increase of pH to 9 in the second UF(UF-2)could not only improve the permeation of rhamnolipid but also reduce the ethanol dose from 50%to 30%.PSU-g-PEG membrane presented excellent anti-fouling properties in view of following aspects:1)the water flux of PSU-g-PEG could be totally recovered by the common cleaning after whatever UF for 1 h or 7 h;2)the PSU-g-PEG membrane can be reused without reducing the membrane performance.Thirdly,this study for the first time investigated the novel applications of rhamnolipid in demulsification and membrane cleaning.As found,rhamnolipid under alkaline pH presented high demulsification activity on the W/O type emulsion such as destabilizing the waste crude oil to recover 98%of crude oil,while rhamnolipid under acid pH benefited the demulsification of O/W type emulsion such as separating 70%of water from the floated oily sludge.Moreover,rhamnolipid cleaning could largely remove the protein foulant from the membrane and recover 95%of water flux.Overall,it seems that rhamnolipid presented much superior performance on these applications than chemical surfactants and showed great potential on the industrial application.In conclusion,the industrial application of rhamnolipid has been improved via mechanically controlling the severe foaming in the fermentation process,establishing cost-efficient separation process and expanding the new application fields.