Application Of Biochar Immobilized Microorganism Technology In The Treatment Of Acidic Mine Drainag

Acid mine drainage（AMD）contains high concentrations of sulfate(SO₄^2-)and large amounts of ferric ion(Fe³⁺),which can seriously contaminate and damage the ecosystem if untreated and directly discharged into the environment.Therefore,it is crucial to explore a method to effectively remove SO₄^2-and Fe³⁺from AMD.Bioremediation is considered as an effective and green wastewater treatment method.However,microorganisms,when facing high loading shocks as well as high concentrations of pollutants,usually affect the activity of microorganisms or cause their death,which makes the application field and scope of bioremediation limited.To solve the above problems and maintain the activity of microorganisms,biochar-sodium alginate composites（BC-S）and biochar-microorganism composites（BC-M）were prepared by gel embedding method for simultaneous removal of SO₄^2-and Fe³⁺from AMD in this study.The effects of BC-M on the sorption process of SO₄^2-and Fe³⁺under different influencing factors conditions were investigated by batch adsorption experiments.Different adsorption models combined with FTIR,XRD and XPS characterization were used to investigate the adsorption behavior and mechanism of SO₄^2-and Fe³⁺by BC-M and the biotransformation of Acidithiobacillus ferrooxidans（A.ferrooxidans）in BC-M.Desorption experiments were then used to analyze the proportion of different removal mechanisms of SO₄^2-and Fe³⁺by BC-M.Finally,the reusability of BC-M and the application potential in actual AMD were evaluated by cyclic regeneration experiments and fixed bed column experiments,respectively.The main results are as follows:（1）The p H,cation exchange capacity and anion exchange capacity of BC-S increased with the increase of pyrolysis temperature.The specific surface area of RBC-S600 prepared from rape straw was relatively larger,which was more conducive to loading microorganisms and adsorbing pollutants.The Zeta potential of both the original biochar and BC-S decreased with the increase of solution p H.The bending vibration of amide Ⅲ bands C-N existed in BC-M（prepared from rape straw）,which illustrated that microorganisms had been successfully embedded in biochar.Through the three-dimensional fluorescence spectrum of BC-M（prepared from rape straw）,it was found that the fluorescence intensity of the solution increased with the increase of BC-M standing time,indicating that A.ferrooxidans generated extracellular polymers that facilitated interactions with contaminants.（2）When the pyrolysis temperature of biochar was 600℃,biochar:sodium alginate:bacterial suspension（w/w/v）was 0.25:1:20,the dosage of BC-M was 5 g/L and solution pH=3.0,BC-M prepared from rape straw and pig manure showed the best adsorption effect on SO₄^2-and Fe³⁺,respectively,with removal rate of 27.98%and 80.11%,respectively.The presence of PO₄^3-and HCO₃^-obviously inhibited SO₄^2-adsorption by BC-M,while the presence of NO₃^-and Cl^-had a small inhibitory effect on the adsorption of SO₄^2-by BC-M.The presence of Ni²⁺and Mn²⁺both promoted Fe³⁺adsorption by BC-M to different degrees,while the presence of Cu²⁺and Zn²⁺obviously inhibited Fe³⁺removal by BC-M.Humic acid and xanthohumic acid inhibited SO₄^2-adsorption by BC-M but promoted Fe³⁺removal by BC-M.（3）The different adsorption models combined with characterization analysis showed that the adsorption of SO₄^2-by BC-M was mainly heterogeneous physicochemical adsorption with monolayers,while the adsorption of Fe³⁺by BC-M was dominated by the chemisorption of monolayers.The adsorption of SO₄^2-and Fe³⁺by BC-M was mainly a non spontaneous endothermic reaction.The maximum adsorption capacities of BC-M（prepared from rape straw）for the co-adsorption of SO₄^2-and Fe³⁺were 32.85 and 63.53 mg/g,respectively.The effect of A.ferrooxidans on SO₄^2-and Fe³⁺was mainly through the biotransformation of SO₄^2-and Fe³⁺,adhesion of A.ferrooxidans and complexation of contaminants by the extracellular polymers they produce.The main mechanisms of BC-M for Fe³⁺were mediated by ion exchange,complexation and precipitation,whereas the removal of SO₄^2-was mediated by physical adsorption and surface precipitation.（4）After 5 regeneration cycles,BC-M could still maintain a good removal effect for Fe³⁺,and the removal percentage remained above 60.0%.The adsorption capacity of SO₄^2-decreased gradually with increasing cycle number.The cyclic regeneration of BC-M（prepared from rape straw）by co-adsorption for SO₄^2-and Fe³⁺indicated that BC-M were reusable and showed a simple and easy regeneration property.The dynamic adsorption effect of BC-M（prepared from rape straw）on SO₄^2-and Fe³⁺was the best when the dosage was 1.8 g,the fluid flow rate was 2.5 m L/min,and the initial concentration of pollutants was 400 mg/L.Compared with the static adsorption in actual AMD(54.35%and 83.71%removal for SO₄^2-and Fe³⁺,respectively),the dynamic adsorption efficiency of BC-M（prepared from rape straw）in actual AMD(35.60%and 63.45%removal for SO₄^2-and Fe³⁺,respectively)was lower.Overall,BC-M still had a good potential for application in actual AMD.