Fermentation Coupling Foam Separation Technology And Foam Separation Treatment Of Heavy Metal Ions Technology

Rhamnolipids,a biological surfactant,have the advantages of environmental friendliness and widespread use,but its low yield leads to the high cost.In this paper,the production of rhamnolipids was enhanced by the fermentation coupled with foam separation technology,and the excellent foaming property of rhamnolipids was used as an adsorbent to treat heavy metal wastewater.Firstly,in order to strengthen the fermentation of rhamnolipids,a new integrated fermentation and separation device was constructed to realize the continuous production of rhamnolipids.The results showed that the initial concentration of 1.25 g/L rhamnolipids had little effect on the growth of bacteria,and had a significant effect on the synthesis of rhamnolipids.Under the optimum experimental conditions of volumetric air flow rate 60m L/min,liquid capacity 100 m L,pore diameter of gas distributor 160μm,the recovery and concentration ratio of rhamnolipids were 75.15±2.3%and 4.83±0.14,respectively.The combination of foam fractionator and fermenter could produce rhamnolipids continuously.The results showed that the maximum yield of rhamnolipids could reach 16.46±0.49 g/L at the maximum synthetic rate of rhamnolipids.The yield was 32.63%higher than that of uncoupled operation,13.04%and 10.32%higher than that of other operations.Obviously,it was feasible to produce rhamnolipids by integrating fermentation and foam separation.Secondly,the technology of foam separation with rhamnolipids as a foaming agent and adsorbent was studied for the treatment of Cd²⁺wastewater.Rhamnolipids as an anionic surfactant,can form a stable complex with Cd²⁺by electrostatic attraction,which will have a high recovery rate after foam separation.At the same time,it was found that Cd²⁺can adsorb onto the foam in large quantities,and be separated from the wastewater.The results of single-factor experiment showed that Cd²⁺had a maximum removal rate of96.7±2.9%when the gas velocity was 250 m L/min,p H was 7,and the concentration of rhamnolipids was 1.3 g/L.Compared with the common chemical surfactants in the removal of Cd²⁺,rhamnolipids have a higher removal efficiency（96.7±2.9%）,which is 7.8%,10.3%and 13.1%higher than SDS,SDBS and CTAB,respectively.Finally,the foam separation technology for selective removal of mixed heavy metal ions was discussed.Cu²⁺,Cd²⁺and Pb²⁺were selected as heavy metal ions to be removed,and rhamnolipid was used as surfactant.The effects of rhamnolipids concentration,p H,volume flow gas rate and ionic strength on the removal and separation,and the mechanism of selectivity and removal were discussed.The best experimental conditions for the removal efficiency of three heavy metals were p H 7,gas volume flow 150 m L/min and surfactant concentration 1.0 g/L.The selective separation of heavy metal ions with rhamnolipids as surfactant and adsorbent demonstrated thant Cd²⁺and Pb²⁺had the best selectivity.