Fermentation Production Of Rhamnolipids And Study On Removal Of Copper Ions In Wastewater

Rhamnolipid is an important biosurfactant with promising applications.In response to the problems of low yield and product inhibition in rhamnolipid fermentation production,as well as the difficulty of treating heavy metal wastewater,this thesis provides a simple concentration method by using a fermentation-coupled foam separation device to lift product inhibition and later combines rhamnolipid biosurfactant as a foaming agent and adsorbent for foam separation with biosorption,thereby removing copper ions from wastewater.To improve the yield problem of rhamnolipids,the fermentation operation parameters of Pseudomonas aeruginosa,a rhamnolipid-producing bacterium,were optimized.A seven-factor,three-level orthogonal design was applied to the medium of Pseudomonas aeruginosa,and the optimal medium results were obtained as follows:glycerol 30.0 g/L,Na NO₃ 6.0 g/L,Mg SO₄ 1.0 g/L,KCl 1.5 g/L,K₂HPO₄ 2.0 g/L,Na₂HPO₄ 0.3 g/L,and Na Cl 1.0 g/L.The above parameters yielded an average of 13.76 g/L of rhamnolipid.The average yield of rhamnolipid was 13.76 g/L.The culture conditions of Pseudomonas aeruginosa were optimized by the response surface design method,and the obtained culture conditions were p H 7.49,inoculum 6.6%（v/v）,and temperature 36.0°C.Applying the obtained optimal medium and optimal fermentation culture conditions,the obtained yield of rhamnolipid was15.28 g/L,which was 57.39%higher than the yield before optimization.A fermentation-coupled foam separation device was designed for rhamnolipid product inhibition and recovery,and a spiral member was used to increase the liquid discharge for the foam separation process.The three operating parameters of the foam separation column with spiral members were optimized,and the recovery of rhamnolipids was 69.57%with an enrichment ratio of 4.25 when the liquid loading volume was 150 m L,the gas distributor aperture was 125μm,and the gas volume flow rate was 40 m L/min.The effect of the coupling start time point on the fermentation of rhamnolipids was studied,and it was concluded that from the fermentation to 45 h when the foam separation started,the yield of rhamnolipids reached 20.84 g/L than that without coupling.The yield of rhamnolipids reached 20.84 g/L,which was 13.22%higher than that without coupling.In order to achieve maximum removal of Cu²⁺from the wastewater,a method combining foam separation with biosorption was used.Firstly,rhamnolipids obtained from fermentation,as a foaming agent and adsorbent for foam separation,were used to adsorb 100 mg/L of Cu²⁺,and the removal rate of Cu²⁺reached 90.45%when at p H=5,rhamnolipid concentration of400 mg/L and gas flow rate of 150 m L/min.Next,the sterilized Pseudomonas aeruginosa cells were used as biosorbent for the adsorption of Cu²⁺in the residual solution of foam separation,and the optimal adsorption conditions were obtained as p H=5,the dosage of inactive Pseudomonas aeruginosa adsorbent was 2.5 g/L,and the optimal adsorption time was 30 min.The final Cu²⁺content in the wastewater was 0.48 mg/L.The combination of foam separation and biosorption showed a good removal effect of Cu²⁺.