Study On The Mechanism Of Fe~0 Modified Anaerobic Granular Sludge In Treating Sb(Ⅴ) In Water

Antimony（Sb）is a toxic and harmful substance that exists in large quantities in the global environment.my country is rich in antimony resources.At the same time,large-scale antimony mining pollutes the surrounding environment of the mining area and poses a great threat to human health.Therefore,it is urgent to control antimony pollution.The traditional antimony pollution control methods have many drawbacks,and the use of anaerobic biological methods to control antimony pollution has the advantages of high antimony removal efficiency and low cost of treatment,so its application in the treatment of antimony polluted wastewater has attracted much attention.In this paper,the anaerobic granular sludge in a self-cultivated and stable ascending anaerobic sludge bed reactor（UASB）was used as the inoculum material to cultivate zero-valent iron（Fe⁰）modified anaerobic granular sludge.The physicochemical properties of anaerobic granular sludge before and after Fe⁰ modification were characterized.The effects of granular sludge dosage,temperature,p H value,interfering cations and other factors on the antimony removal performance of granular sludge in different systems were studied,the static and dynamic adsorption tests and thermodynamic models were used for fitting calculation.At the same time,various modern characterization methods were used to study the adsorption and removal effect and influencing factors of Fe⁰ modified anaerobic granular sludge on Sb（Ⅴ）in water adsorption mechanism.The conclusions of the study are as follows:1.The UASB reactor,which is self-cultivated in the laboratory and runs stably,is used as the experimental device.The inoculum amount of sludge is about 1.35 L,the operating conditions of the UASB reactor are controlled,the p H is set to 6.5～7.8,the reaction temperature is 35±1℃,and the CODcr concentration of artificial water distribution is4000～5000 mg/L,m（COD）:m（N）:m（P）≈200:5:1,hydraulic retention time（HRT）was 24 h,UASB was successfully started after 60 d incubation,and the removal rate of COD from Fe⁰modified anaerobic granular sludge was about 88%,indicating that Fe⁰ modification has little effect on the normal operation of UASB.2.The SEM,FT-IR and XRD characteristics of Fe⁰ modified anaerobic granular sludge and ordinary anaerobic granular sludge were compared and analyzed.The results show that the surface pores of the Fe⁰modified anaerobic granular sludge increase,and there are multiple lump-like adhesion protrusions.These changes can provide more adsorption sites for the adsorption process of the granular sludge and enhance its adsorption capacity.FT-IR analysis shows that the granular sludge contains abundant functional groups,and polysaccharides play an important role in Fe⁰modified anaerobic granular sludge,and the changes of other groups in the modified anaerobic granular sludge are not obvious.XRD characterization showed that some iron oxide peaks appeared in the modified anaerobic granular sludge,indicating that the added Fe⁰ was oxidized and precipitated on the sludge surface.Fe⁰ modified anaerobic granular sludge has four main crystal structures,namely Fe₃O₄,Fe₂O₃,Na₄Si O₄ and Fe OOH,while the main phase of ordinary anaerobic granular sludge is Si O₂.XRD results show that Fe⁰ modification has a great influence on the performance of anaerobic granular sludge.3.The experimental study on the adsorption performance of Fe⁰ modified anaerobic granular sludge found that at p H 5.8,the dosage of granular sludge was 3.0 g/L,and the temperature was 35°C,Fe⁰ modified anaerobic granular sludge had an effect on Sb.（Ⅴ）has the best adsorption effect.The adsorption processes of Sb（Ⅴ）and Sb（Ⅲ）by anaerobic granular sludge in different systems fit well with the Langmuir model,and the correlation coefficient R² is high.The 1/n values in the fitting of the Freundlich model were all greater than 0 and between 0 and 1,indicating that the two groups of granular sludge had good adsorption affinity for pollutants.The pseudo-second-order kinetic model has better fitting effect on the adsorption behaviors of the two groups of anaerobic granular sludges for the removal of Sb（Ⅴ）and Sb（Ⅲ）,indicating that the adsorption behaviors of the two groups of granular sludges for antimony are mainly chemical adsorption.And Fe⁰ modified anaerobic granular sludge EPS（Extracellular Polymeric Substances）of different components TB-EPS（Tightly Bound EPS）,LB-EPS（Loose Bound EPS）and sludge core iron content are higher than ordinary anaerobic granular sludge.4.After adding a certain concentration of Sb（Ⅴ）ions to the influent,the highest removal rates of Fe⁰modified anaerobic granular sludge and ordinary anaerobic granular sludge to the original sewage COD were 92.37%and 88.76%,indicating that the Sb（Ⅴ）in water is well tolerated.Fe⁰modified anaerobic granular sludge showed high removal efficiency of Sb（Ⅴ）in the early stage of antimony addition,and the highest removal rate was 99.5%,which was much higher than the highest removal rate of Sb（Ⅴ）by ordinary anaerobic granular sludge（61.3%）.It shows that the granular sludge modified by Fe⁰ has a higher removal efficiency of antimony.The removal effect of different components of granular sludge（LB-EPS,TB-EPS,mud core）on Sb（Ⅴ）was LB-EPS<TB-EPS<mud core.In the process of removing Sb（Ⅴ）from water by Fe⁰modified anaerobic granular sludge,the biomass binding amount is larger than that of ordinary anaerobic granular sludge,and the biomass sedimentation amount is roughly the same as that of ordinary anaerobic granular sludge.5.The two groups of anaerobic granular sludges before and after adsorption of antimony both contained abundant organic functional groups,among which polysaccharides and proteins participated in the adsorption process of antimony by Fe⁰ modified anaerobic granular sludge,while the protein in ordinary anaerobic granular sludge EPS played a more important role than polysaccharide in the adsorption process of Sb（Ⅴ）.The adsorption phase of Sb（Ⅴ）in water by ordinary anaerobic granular sludge is Si O₂,while Fe⁰ modified anaerobic granular sludge has more Fe Sb₂O₄ diffraction peaks after adsorbing Sb（Ⅴ）,indicating that the iron-antimony co-precipitate is formed after the complex reaction between Sb（Ⅴ）and iron ions in the granular sludge,which is the main reason for the adsorption and removal of antimony from Fe⁰ modified anaerobic granular sludge.