Research On Characteristics And Sorption Properties Of Extracellular Polymeric Substances (EPS) From Bacillus Vallismortis Under The Stress Of Zinc And Copper

As a new type of biological adsorbent,extracellular polymeric substances(EPS)has widely caused attentions for its great potential of heavy metal sorption.However,investigation on the influence of heavy metal on EPS was rarely reported in the open literature.Bacillus vallismortis is an aerobic heterotrophic bacteria screened in our laboratory pilot study,which has been found to be efficient in degradation of aniline(a kind of sandbergerite collecting agents).Wastewater in mineral processing is complex industrial wastewater that contains both heavy metals and refractory organic pollutants,and the interaction between heavy metals and microbial can not be ignored.For better understanding of interaction between heavy metals and EPS,the influences of Zn(?)and Cu(?)stress on the production,component changes and sorption properties of EPS were experimentally investigated.The characteristic of Bacillus vallismortis EPS under stress was analyzed by using SEM,FTIR,3D-EEM and XPS.Meanwhile,the EPS after the stress was used as the adsorbent of heavy metals and their adsorption capacity and adsorption behavior were studied.The main conclusions were listed as follows:1.Results showed that the EPS was harvested in stationary phase in the presence of Zn(?),and the production increased to 100.84 mg/g VSS under 12 mg/L Zn(?)exposures.Zn(?)promoted to produce polysaccharides and proteins,the former increased more.EPS was harvested in exponential phase under stress of Cu(?)and the production could reach as high as 60.65 mg/g VSS under 6 mg/L Cu(?)exposures.The stress of Cu(?)improved the production of extracellular proteins.2.As can be seen from the SEM results,the thickness of sticky material on the surface of the strain was increased after stress.3D-EEM results showed that the stress of metal caused tryptophan,tyrosine,portion of humus and fulvic acid increased.In addition,a kind of fulvic acid was found in Zn-EPS instead of Cu-EPS.3.Analysis of FTIR and XPS indicated that the types of EPS functional groups remained the same after stress but the relative concentrations of functional groups was improved by changing components.Stress of Zn(?)led portion of carbon chain in EPS break up and C combined with O/N so as to produce more C=O and amide group.In addition,the relative content of C-OH was increased.Cu(?)led portion of C-O generate to C=O and-OH.C-N and R2-NH in protein had also increased.All the augment of groups above could improve complexing capacity for EPS and metal.4.Influence of temperature on adsorption of three EPS was not obvious and the adsorption of Cu-EPS would slightly decline due to low activity of protein at high temperature.Adsorption of EPS before/after the stress increased with the increasing pH and Zn-EPS was more sensitive to pH might due to the higher content of extracellular polysaccharide.Three EPS went through the process of rapid adsorption,slow adsorption and adsorption equilibrium during adsorbing Zn(?)and Cu(?).The adsorption kinetics were conformed to level 2 dynamic model.The experimental data fitted very well with both Langmuir model and Freundlich model.The fitting coefficient showed that the adsorption capacity sequences of Zn(?)and Cu(?)were Zn-EPS>Cu-EPS>Control-EPS and Cu-EPS > Control-EPS > Zn-EPS,respectively.In general,adsorption capacity of EPS increased after the stress.5.The functional groups of three EPS were roughly the same,including hydroxyl,amide,carboxyl and C-O-C.Adsorption capacity of Zn-EPS and Cu-EPS were concerned with the affinity and content of functional groups.Specific EPS was produced by Bacillus vallismortis under stress of Zn(?)and Cu(?),providing a wide range of applicable combination point for metal ion and improving the capacity of removing heavy metals significantly.