Biomineralization Of Pb(?) By Hyperthermophile-Thermus Thermophilus FAFU013 And Its Application For Pb(?) Passivation In Sewage Sludge Composting

Sewage sludge contains a large amount of heavy metals such as lead,which greatly limits the utilization of sludge.Biomineralization of Pb2+and other heavy metal into thermodynamically stable,extremely insoluble minerals with low mobility and bioavailability by microbe is rergarded as one of the most effective methods for heavy metal remediation in soil as well as sludge.It has been reported that some microbes would participate or accelerate the transformation of Pb2+ from mobile species into very stable minerals.However,most of them were mesophilic bacteria(optimum growth temperature<40?),and could not grow in the environments with high temperature(such as composting or hyperthermophilic composting).In this study,we isolated a hyperthermophile FAFU013 from hyperthermophilic sludge compost samples,studied the adsorption and metallogenic mechanism of Pb2+ by FAFU013 under hyperthermophilic conditions,and explored the passivation of Pb2+ in high temperature compost with hyperthermophilic bacteria.Our study provides a new way to solve the problem of heavy metal pollution in sludge compost,which is of great practical significance to the recycling of sludge.The main conclusions are listed as follows:1.Isolation and identification of hyperthermophile FAFU013 which could mineralize Pb2+.Gram staining and microscopic observation showed that FAFU013 was gram-negative bacteria.16S rDNA identification and DNA hybridization indicated that FAFU013 was Thermus thermophilus(T.thermophilus)and named T.thermophilus FAFU013.2.The strain FAFU013 has a strong capacity of Pb2+ biosorption.The maximum Pb2+ biosorption capacity of FAFU013 was 115 mg/g.Adsorption kinetics and isotherm analyses showed that the adsorption of Pb2+ by FAFU013 met the pseudo second order kinetics and Freundlich isotherm fitting,suggesting that Pb2+ biosorption of FAFU013 was based on the multi-layer chemical adsorption occurring on the non-uniform surface.Zeta potential,FTIR analysis and shielding experiments of functional groups indicated that the rapid and effective uptake of Pb2+ by FAFU013 was attributed to the synergy of electrostatic attraction and chelating activity of functional groups on bacteria.Additionally,the competitive biosorption experiments of coexisting ions suggested that FAFU013 also had strong Pb2+ biosorption capacity though in the presence of high concentration coexisting metal cations.3.Scanning electron microscopy couple with energy dispersive X-ray spectroscopy(SEM-EDS)was used to study the surface morphology of FAFU013 after Pb2+ biodsorption.The lead-containing granular sediments was observed on the surface of bacteria.X-ray powder diffraction(XRD)and high resolution transmission electron microscopy couple with energy dispersive X-ray spectroscopy as well as selected area electron diffraction(HRTEM-EDS-SAED)confirmed that these sediments were pyromorphite(Pb5(PO4)3Cl)crystal minerals.Further studies suggested that metabolism process or proteases of bacteria might play an important role in Pb2+ biomineralization.Moreover,Pb2+biomineralization mediated by FAFU013 could not be affected in the presence of coexisting metal cations.4.Lead-containing sludge was selected to simulate the process of hyperthermophilic sludge composting,and the effect of FAFU013 on the evolution of heavy metal speciation during sludge composting was investigated.The results showed that FAFU013 obviously reduced the content of bioavailable Pb2+ by 17.64%after the composting,while the residual Pb2+ content increased by 15.74%.In addition,the FAFU013 also had different degrees of passivation effect also could be observed on heavy metals such as Ni,Cu,and Zn during composting with inoculating FAFU013.