Experimental Study On The Treatment Process Of Multicomponent Heavy Metal Wastewater Using Micellar-enhanced Ultrafiltration

Micellar enhanced ultrafiltration is a new and highly effective method for the treatment of heavy metal wastewater by combining the technique of surfacant and ultrafiltration.Synthetic surfactants can easily cause secondary pollution in the process of use.In this paper,we propose the use of an environmente-friendly and biodegradable biosurfactant—rhamnolipid,as a substitute for synthetic surfactants.The effect of micellar enhanced ultrafiltration on the retention of heavy metal ions and the permeation flux of ultrafiltration membrane were investigated,the optimal operating conditions were determined,and the competitive adsorption of heavy metal ions with rhamnolipid was observed.The critical micelle concentration(CMC)of rhamnolipid was 0.16mmol/L,when the concentration of rhamnolipid in solution reaches 0.16mmol/L,then the rhamnolipid molecules can aggregate to form micelle in theory.At this time,the micelle begins to adsorb heavy metal ions.The results showed that heavy metal ions have been retained even the concentration of rhamnolipid was lower than CMC.The results showed that the retention rate of heavy metal ions was related to the concentration of rhamnolipid,the standing time(the mixing time of rhamnolipid and heavy metal ions),the pH value and the concentration of heavy metal ions in wastewater,while has nothing to do with the Transmembrane Pressure(TMP).The optimal operating conditions for MEUF removal of heavy metal ions were:the molar ratio of rhamnolipid to copper,zinc,nickel ion was 3:1,and the molar ratio of cadmium was 5:1,TMP was 20kPa,standing time was 2 hours,pH value was 6-8.Permeate flux of ultrafiltration membrane was only related with the TMP of the system.The permeate flux of the membrane showed a linear relationship with the TMP in a certain range of pressure.When the TMP exceeded a certain value,the permeate flux of the membrane did not increase obviously,tending to a constant value.When the TMP was 20kPa,the permeate flux of ultrafiltration membrane is stable at 140?150L/m2·H.Rhamnolipid exhibited excellent performance in the treatment of copper,zinc,nickel,cadmium and lead ions in micellar enhanced ultrafiltration,where the rejection rate were morethan 95%,and the lead ion rejection rate was more than 99%while the chromium ion rejection rate was under 30%.Rhamnolipid showed a preference in the solublization and adsorption of heavy metal ions,where the priority order was Pb2+>Cu2+-Ni2+>Zn2+>Cd2+>Cr6+in this experiment.