The Study Of Sulfate-reducing Bacteria Combining With Biomaterials For Heavy Metals Effluent Treatment

With the development of modern industry and mining operations,the excessive exploitation and the unconscionable using of the resources,freewill voidance of the pollutant make the environmental the problems much more serious.Water heavy metals pollution was an especially serious problem due to the application of discharge of untreated industrial wastes from many process industries.Many heavy metal ions,such as arsenic,lead,mercury,chromium,copper,zinc and cadmium,have adverse effects on humans and the environment.Recently,the removal of heavy metals by bio-treatment has been identified as a promising alternative to traditional treatment techniques of physics and chemistry.This method including plant,animal,microbial treatment method,has high efficiency,low cost,biodegradable and minimization of chemicals.Sulfate reducing bacteria,that was a specific microbial group in biotreatment,has the potential to efficiently remediate heavy metals contaminated waste streams due to its unique reduction that can reduce sulfate to hydrogen sulfide.The remarkable adsorptive property of biomaterials,which were extensive source,renewable resources and environment friendly,were used as a practical material for limitless application.In this study,we systemically investigate this technology that combined sulfate reducing bacteria with biological materials to efficiently remove heavy metal from wastewater.The major works were done as follows:1.High metal tolerance of sulfate reducing bacteria had been acquired by increased the concentrations of heavy metals in the medium orderly.Their tolerance concentration of Cd²⁺?Cu²⁺?Zn²⁺were 250 mg/L,150 mg/L,150 mg/L,respectively.The high metal tolerance of Bacillus cereus has been obtained by the same way.Its tolerance concentration of Cd²⁺?Cu²⁺?Zn²⁺were 300 mg/L,150 mg/L,200 mg/L,respectively.2.The SRB-CCMKGM-Ni/Fe system,which was consisted of sulfate reducing bacteria,crosslinked carboxymethyl konjac glucomannan,Ni/Fe bimetallic nanoparticles,were established for wastewater containing cadmium treatment.?1?SRB can reduce sulfate into hydrogen sulfide,the latter can precipitate the dissolved heavy metals;CCMKGM were excellent adsorbent;Ni/Fe bimetallic nanoparticles,that were made by chemical synthesis,were used to reduce heavy metals from wastewater.Batch experiments were performed at different initial Cd²⁺concentration,pH and temperature to study the effects on the Cd²⁺removal and remaining SO₄^2-by all systems including SRB,CCMKGM,Ni/Fe,SRB-CCMKGM,SRB-CCMKGM-Ni/Fe,respectively.It was demonstrated that performance of SRB-CCMKGM-Ni/Fe system for Cd²⁺effluent treatment was much well than SRB,CCMKGM,Ni/Fe system.This system also enhanced Cd²⁺and SO₄^2-removal and increased SRB resistance to metals toxicity.At initial Cd²⁺concentrations in 200mg/L and 250mg/L,the removal rates of both of SRB-CCMKGM-Ni/Fe and SRB-CCMKGM were higher than 85%.Correspondingly,with the application of these systems,89.5%and 99.7%of Cd²⁺could be removed from effluent in 150 mg/L Cd²⁺,respectively.Comparatively,57.3%52.3%,58.9%were respectively acquired by SRB,CCMKGM,Ni/Fe system.It was implied that SRB immobilized on CCMKGM can greatly enhance Cd²⁺and SO₄^2-removal as well.Cd²⁺removal efficiencies and SRB activity increased greatly by Ni/Fe bimetallic particles.?2?The mechanism of removal of heavy metals by SRB-CCMKGM-Ni/Fe system was thoroughly studied by scanning electron microscopy?SEM?,Fourier infrared infrared spectrum?FTIR?,X-ray diffraction?XRD?and flame atomic absorption spectrum?FAAS?.It was demonstrated that the working principles of this system for removing heavy metals mainly included biosorption,chemical reduction and sulphate reduction.The results of SEM showed that the Ni/Fe nanoparticles were roughly globular with sizes of 40-80 nm.Contaminant oxidation by Ni/Fe nanoparticles appeared to increase production of reactive species such as hydroxyl radicals.The pictures of XRD indicated that the surfaces of SRB-CMKGM-Ni/Fe became coarse after reduction due to an abundant of small and irregular deposits.These deposits on the surface were Fe₃O₄,Fe₂O₃,Fe?OH?₃,Cd⁰,CdO and CdS,that had been produced by oxidation-reduction reaction of Fe⁰,Ni/Fe and SRB.In FTIR analysis,the functional groups of SRB and CCMKGM,such as–NH_2,-NH,–OH,C=O,O–C–O and-CH,were involved in the biosorption process.Furthermore,the amides I,II and III band spectrum peaks changed significantly,which indicated that protonated amidos of amide in the protein could play an important role in the biosorption.In addition,CdS produced by this system can be further utilized to manufacture solar cells,photocatalysts,and pigment at lower costs than currently other used methods.This technology,that was simple process,low requirements for equipment,low cost,high efficient,has broad application prospect for removal of heavy metals wastewater.The adsorption materials utilized in this technology can be reused and naturally degraded.3.An novel cleanup biotechnology was established for removing cadmium,copper and zinc contamination,which was based on cooperation and coordination between bacillus cereus,camellia oleifera cake,sulfate reducing bacteria and flotation way.Three primary members were involved in this system:Camellia oleifera cake,either as sorbent or culture medium for microbe;Bacillus cereus,was as decomposers for camellia oleifera cake and absorbed for heavy metals;The SRB can reduce sulfate into hydrogen sulfide,the latter can precipitate the dissolved heavy metals.The initial concentrations of Cd²⁺,Cu²⁺,Zn²⁺in wastewater were 200mg/L,100mg/L,100mg/L,respectively.?1?The optimum conditions of camellia oleifera cake degradation by B.cereus were 48h,pH 7.0,37?,and 150rpm.At this time,the total number of bacteria increased to reach a peak?6.7×10⁶CFU/mL?,but the saponin concentration was only7.8%.?2?The treating compound heavy metals process through the synergy of sulfate reducing bacteria,B.cereus and camellia oleifera cake was investigated.The singe heavy removal capacities of this system were given as follows:Cd²⁺>Cu²⁺>Zn²⁺.This could be attributed to special metal bioreduction capacity of SRB.Compared to the single metal,these results in experiment indicated that both of the maximum removal effects and active biomass of microbe in heavy metal co-contaminants decreased due to the influence of three kinds of heavy metals on microorganism at the same time.To create a low oxygen and rich nutriment environment for SRB,the COC degradation promoted by B.cereus could consume some oxygen of the reaction system.The SRB reduced sulfate ions into hydrogen sulfide,the latter can precipitate the dissolved toxic metals.Therefore,biological reduction of B.cereus and SRB played significant roles in heavy metal removal.?3?The mechanism of removal of heavy metals was fully studied by flame atomic absorption spectrum?FAAS?,scanning electron microscopy?SEM?and X-ray diffraction?XRD?.After treatment,a large amount of sulfide?CdS,CuS,ZnS?and heavy metals compound on the surfaces of microbes and camellia oleifera cake particles were presented.The shapes of B.cereus and SRB were obviously changed due to heavy metal damage and reduction product.The surfaces of camellia oleifera cake particles acted as a substratum for microbial communities to form biofilms.Owing to oxygen consumption by aerobic B.cereus,biofilms are largely anaerobic on the camellia oleifera cake particles surface,which creates a niche for anaerobic SRB.Subsequently,reduction of SRB,which used hydrogen as electron donors,reduced heavy metals to metal sulphides.The latter were used to absorb the heavy metals.The heavy metal biosorption mechanism produced by B.cereus cells refers to cell surface adsorption,extracellular precipitation,and intracellular accumulation through special components.Thus,these results of experiment demonstrated that a fast biosorption process on the B.cereus cell surface was followed by a relatively slow bioaccumulation process inside the cell.?4?In flotation process,microbe and camellia saponins were as capturing agent for heavy metals,and many small bubbles could absorb the metals as well,which can significantly eliminate the remaining toxic heavy metals in the solution.The selective adsorption abilities of camellia saponins were Cd²⁺>Zn²⁺>Cu²⁺.Almost 100%residual heavy metals in solution of flotation column were eliminated in the process.After flotation,the absorbed metals on biomass of flotation column can be fully eluted by using 30 mL or 50 mL of 1 mol/L HCl.Moreover,the eluted biomass can be reused in a second biosorption-flotation cycle.This new intriguing treatment approach through the synergy of biomaterial and microbes could significantly contribute to metal removal in the future.