Effect Of Denitrifying Bacteria On Transport Of Nanoscale Iron And Its Mechanism

As a widely concerned nanomaterial,nanoscale zero-valent iron(nZVI)is mostly used for in-situ remediation of groundwater due to its high reactivity and reducibility.In the study,denitrifying bacteria(HTB)was used as model bacteria,nZVI?chitosan-stabilized nanoscale zero-valent iron(CS-nZVI)and nanoscale zero-valent iron/copper(nZVI/Cu)bimetallic were prepared by liquid phase reduction method.The effects of denitrifying bacteria on the transport performance of nZVI materials in porous media under different conditions were studied by static sedimentation experiment and column transport experiment.The morphology of iron nanoparticles was characterized by transmission electron microscopy(TEM)and scanning electron microscopy(SEM),the oxidation products were characterized by X-ray diffraction(XRD)and Raman spectroscopy,and the mechanism of bacterial influence on the transport of nZVI materials was discussed from the aspects of bacterial pre-equilibrium pre-equilibrium simulation column,oxidation products and bacterial components.The main conclusions are as follows:(1)It was found by TEM and SEM that the synthesized nZVI,CS-nZVI and nZVI/Cu particles were spherical or ellipsoidal,and the nZVI and CS-nZVI particles changed to needle-like or flake-like after adding HTB,while nZVI/Cu changed little after adding HTB.Furthermore,the oxidation products of nZVI,CS-nZVI and nZVI/Cu were characterized by XRD and Raman spectra.It was found that the oxidation products of particles were mainly?-Fe OOH and Fe₃O₄/?-Fe₂O₃ after adding HTB.(2)In the presence of HTB,the stability of nZVI materials in suspension was enhanced,low concentration HTB promoted the transport of nZVI,CS-nZVI and nZVI/Cu in porous media,and reduced the deposition of particles,while the increase of HTB concentration inhibited the transport of nZVI materials.Under different particle concentrations,different concentrations of bicarbonate,and different p H conditions,HTB has different effects on the mobility of different nZVI materials.(3)The mechanism of HTB affecting the transport of nZVI materials was discussed in the following aspects.a.The bacterial solution pre-equilibrium simulation column experiment showed that the competition of adsorption sites of HTB on the surface of media was not the main factor affecting the transport of nZVI materials in porous media;b.Most of the magnetic oxidation products(Fe₃O₄/?-Fe₂O₃)were trapped in porous media,and the non-magnetic oxidation products(?-Fe OOH)had good mobility;c.Protein and polysaccharide enhanced the suspension stability of particles in solution,while protein promoted the transport of nZVI and CS-nZVI,and inhibited the transport of nZVI/Cu,in the presence of polysaccharides in solution,the mobility of three materials in porous media decreased.