Study On The Adsorption Of Typical Heavy Metals By Desulfovibrio Vulgaris And Extracellular Polymeric Substances

At present,the removal of toxic heavy metals from wastewater has become a top priority to avoid adverse effects on humans and the entire ecosystem.Microbial remediation is generally regarded as a hopeful treatment technology for heavy metal pollution due to its cost-effective and environmentally friendly characteristics.Extracellular Polymeric Substances(EPS)is a promising biosorbent,has received a lot of research in the field of heavy metal remediati ond bacterial cells is 64.477,136.697 and 44.432 mg/g.The aim of this study is to explore the fate and mechanism of biosorption of typical heavy metals by the Desulfovibrio vulgaris system(including bacterial cells and secreted loosely-bound extracellular polymeric substances(LB-EPS)and tightly-bound extracellular polymeric substances(TB-EPS)).Scanning electron microscopy revealed that the outer layer of Desulfovibrio vulgaris was covered with a layer of sticky,irregular and loose EPS.After the EPS was removed by physical or chemical methods,the surface of the bacteria became smooth;Four different methods were used to explore the best extraction method for EPS and found that the order extraction amount of EPS was:pure centrifugation(137.451±2.374 mg/L)>heating method(135.367±1.701 mg/L)>ultrasonic method(121.106±1.380 mg/L)>EDTA method(58.055±2.059 mg/L).After 240 minutes of contact time,the entire adsorption process reaches equilibrium,the equilibrium adsorption capacity of Cu²⁺on TB-EPS,LB-EPS and bacterial cells is 64.477,136.697 and 44.432 mg/g,respectively;The equilibrium adsorption capacity of Zn²⁺on TB-EPS,LB-EPS and bacterial cells is 52.927,75.832 and 25.511 mg/g,respectively;The equilibrium adsorption capacity of Pb²⁺on TB-EPS,LB-EPS and bacterial cells is 231.954,297.517 and 88.286 mg/g,respectively;Desulfovibrio vulgaris has the largest adsorption capacity for Pb²⁺,followed by Cu²⁺and Zn²⁺(Pb²⁺>Cu²⁺>Zn²⁺).The adsorption capacity of different components of Desulfovibrio vulgaris to metal cations follows the order of LB-EPS>TB-EPS>bacterial cells.It is worth noting that the adsorption contribution of EPS(including TB-EPS and LB-EPS)to Cu²⁺,Zn²⁺and Pb²⁺accounted for total adsorption capacity was 82%,83%and 86%,respectively.It can be seen that EPS(especially LB-EPS)plays a key role in removing Cu²⁺,Zn²⁺and Pb²⁺.The isothermal adsorption data of Cu²⁺and Zn²⁺on EPS are more consistent with the Langmuir model,while Pb²⁺is consistent with the Freundlich model.Through three-dimensional excitation-emission matrix(3D-EEM),scanning electron microscopy(SEM),attenuated total reflectance-Fourier transform infrared spectroscopy(ATR-FTIR)and synchronous fluorescence spectroscopy,it is found that the combination mechanism of EPS and Cu²⁺,Zn²⁺and Pb²⁺was mainly complexation and electrostatic interaction,and the aromatic protein substances and tryptophan protein substances in EPS play an important role in the binding process.