Study On The Characteristics And Adsorption Properties Of Bacillus Vallismortis Sp.EPS Under Exogenous Sulfur Stress/Induction

Na₂S was used as a stress/inducer to regulate the components of Bacillus vallismortis sp.EPS,and EPS was used as an adsorbent to study the adsorption properties of Cu???and Zn???that as two typical heavy metals.The effects of Na₂S stress/induction on the components of EPS,especially the sulfhydryl protein were also investigated.The mechanism of the action of exogenous sulfur on Bacillus vallismortis sp.EPS was analyzed by means of SEM,3D-EEM,FTIR and XPS.The best adsorption conditions for Cu???and Zn???as well as their adsorption behavior were studied by using Bacillus vallismortis sp.EPS as heavy metal ion adsorbent before and after stress/induction.The main conclusions are as follows:?1?The growth of Bacillus vallismortis sp.was affected to a certain extent when it was stressed/induced by Na₂S of different intensities.In the range of stress/inducer intensity of5-80mg/L,the biomass dry weight of the strain reached the maximum value of 1.81g/L when the concentration of Na₂S was 20mg/L.The results also showed that the maximum EPS production of 105.58mg/g VSS coupling with doubled increase in protein in which the contant of-SH increased by 48.2%from 104.15 to 154.36?mol/L were recorded in the presence of 20mg/L Na₂S.The adsorption effect of Bacillus vallismortis sp.EPS on Cu???and Zn???is the most significant when the concentration of Na₂S is 20 mg/L..?2?The results of scanning electron microscopy?SEM?showed that there were more extracellular polymeric substances on the surface of the strain after the stress/induction of exogenous sulfur,which indicated that the stress/induction of exogenous sulfur could stimulate the strain to produce more EPS in a certain way,which increased the content of protein like substances in EPS and enhanced the binding ability with heavy metal ions.?3?The results of infrared spectrum showed that there were different functional groups in EPS before and after stress/induction,mainly reflected in the presence of characteristic peak containing-SH in S-EPS.The active groups of the two EPS in the process of adsorption of Cu???and Zn???are also different.The main groups involved in the interaction of Control-EPS and two heavy metal ions are C=O,C-N and N-H.The C-O group in polysaccharides also participate in the adsorption of Zn???.When S-EPS adsorbs two heavy metals,the main functional groups involved in the adsorption process are-SH,C=O and N-H/C-N.X-ray photoelectron spectroscopy?XPS?was used to analyze the main elements C,O,N and S in EPS.The results showed that the chemical forms of these four elements in EPS changed after exogenous sulfur stress/induction,which were mainly manifested in the partial carbon chain break,and then combined with O and N elements,and the existence of carbon-oxygen double bond and amide substances,that is,the concentration/number of C=O and C-O/C-N groups increases.An obvious S-element signal was detected in S-EPS and existed as a thiol containing-SH,while the S-element signal in Control-EPS was weak.?4?Bacillus vallismortis sp.EPS adsorption studies on Cu???and Zn???showed that the adsorption capacity of EPS on Cu???and Zn???increased with increasing p H before and after stress/induction,the adsorption capacity of EPS to Cu???and Zn???was less affected by temperature,and the adsorption capacity of EPS to Cu???and Zn before and after stress/induction was less affected by temperature.The adsorption process of???has a high fitting degree with Langmuir model and Freundlich model.Fitting Langmuir isothermal equation,the maximum adsorption capacity of S-EPS for Cu???and Zn???was1428.57mg/g and 979.09mg/g,respectively,which was better than that of Control-EPS.This is related to the difference of EPS components.The results of adsorption kinetics show that the process of adsorption of Cu???and Zn???by two kinds of EPS is more in line with the second-order kinetic model,which shows that the rate controlling step of adsorption process is chemical reaction and spontaneous endothermic reaction.?5?The existence of Cu???has a significant inhibitory effect on the adsorption of Zn???by S-EPS.When Zn???exists as a coexisting ion,the inhibitory effect on Cu???is not so strong.Compared with the adsorption of two metal ions by single system S-EPS,it can be concluded that when there are two metal ions Cu???and Zn???in the system at the same time,S-EPS will show better affinity for Cu???.