Removal Of Heavy Metals And Typical Toxic And Harmful Organic Matter In Livestock Wastewater By NZVI/γ-Al₂O₃

Heavy metals and toxic and harmful organic matter widely exist in livestock wastewater,and the traditional biological treatment process is ineffective.And its environmental risks continue to increase and exceed the self-purification ability of natural water bodies,it also limits the sustainable development of the aquaculture industry.The nano-zero-valent iron（n ZVI）technology has attracted wide attention due to its advantages such as economy,high efficiency and environmental friendliness.But the phenomenon of agglomeration of n ZVI particles caused by the volume effect and surface interface effect is also caused and limit the development of this technology.Based on the current research,the magnetic nano-zero-valent iron-modified activated alumina（n ZVI/γ-Al₂O₃）composite materials were synthesized by chemical reduction method in aqueous solution with n ZVI being well-integrated on the surface and in the pore walls ofγ-Al₂O₃.The Zn（Ⅱ）,Cu（Ⅱ）,Cd（Ⅱ）,Cr（Ⅲ）,Mn（Ⅱ）and As（Ⅴ）isotherms and adsorption kinetics of n ZVI/γ-Al₂O₃ were analyzed,and their competitive and synergistic adsorption mechanisms for the heavy metals in a multicomponent system were also studied.And the degradation mechanism of Roxarsone（ROX）as representative of toxic and harmful organic matter that exist in livestock wastewater was also proposed,established a new technology of organic matter-heavy metal compound pollution treatment with strong adsorption and degradation ability and explored the reaction mechanism and degradation path of heterogeneous-Fenton-like technology to remove target pollution.The research results are as follows:（1）NZVI is loaded onγ-Al₂O₃,which not only overcomes the agglomeration of n ZVI particles caused by volume effect and surface interface effect,but also makes n ZVI still in a stable high surface energy state.n ZVI/γ-Al₂O₃ Composite materials have the advantages of high specific surface area,high reduction and high surface activity.NZVI penetrates into the interior ofγ-Al₂O₃ microspheres,so the recycled n ZVI/γ-Al₂O₃ composite material still has strong magnetism,and can be separated by applying an external magnetic field.（2）NZVI/γ-Al₂O₃ showed good adsorption performance for Zn（Ⅱ）,Cu（Ⅱ）,Cd（Ⅱ）,Cr（Ⅲ）,Mn（Ⅱ）and As（Ⅴ）in the single adsorption systems with saturation adsorption capacities of 53.0,74.9,114.7,99.1,42.9 and 80.4 mg/g respectively.There are competitive and synergistic adsorptions in the multiple heavy metals system.Under the optimized adsorption conditions with p H of 6.67,the adsorbent dosage of 0.5 g/L,and initial respective concentration of 10 mg/L,the removal rates of Cr（Ⅲ）,Cu（Ⅱ）,Zn（Ⅱ）,As（Ⅴ）and Mn（Ⅱ）are as high as 99.9%,99.9%,99.9%,99.9%and 81.7%,respectively.In addition,under the optimized condition,the equilibrium concentrations of them were lower than the limits of detection,while those of Mn（Ⅱ）and Cd（Ⅱ）were 1.9 and 6.4 mg/L,respectively.Synergistic adsorption between Zn（Ⅱ）and coexisting metal ions was observed in the multiple heavy metals system.However,competition adsorption from coexisting metal ions was detected for Cd（Ⅱ）with the removal rate of only 37.7%.With the help of ultrasound,the removal rate of heavy metals by n ZVI/γ-Al₂O₃ can be significantly improved,the adsorption equilibrium can be quickly reached,and the equilibrium concentration of Mn（Ⅱ）and Cd（Ⅱ）was reduced to1.2 and 1.8 mg/L,respectively.（3）Results revealed that the degradation of 100 mg/L ROX was best at the initial p H of3.21,H₂O₂ concentration of 10 mmol/L,and n ZVI/γ-Al₂O₃ catalyst concentration of 1 g/L.Under the n ZVI/γ-Al₂O₃/H₂O₂/ROX system,the primary reactive oxygen species·OH can be generated continuously and efficiently by building up the internal redox cycle of Fe⁰,Fe²⁺,specifically adsorbed on the surface of the catalyst by the adsorption specificity of Fe-As-Al and can migrate to the inside of the microsphere.Based on the research of intermediate products,the degradation mechanism of ROX in heterogeneous Fenton-like reaction was also proposed.With the help of ultrasound,the mineralization rate of ROX can be increased,and the As concentration in the system is less than 10μg/L.