Activated Carbon Supported Nano-zero-valent Iron Induced Oxidation Reaction For The Treatment Of Pulping Effluent

Catalytic ozonation technology and catalytic persulfate oxidation technology have the advantages of high oxidation efficiency,strong adaptability and less secondary pollution,and have good application prospects in the field of effluent treatment.In this paper,activated carbon-supported nano zero valent iron catalyst(nZVI/AC)was successfully prepared by the carbothermal reduction method.The nZVI/AC catalyzed ozonation system and nZVI/AC catalyzed persulfate oxidation system were constructed respectively,which were applied to the advanced treatment of the secondary biochemical effluent of the bagasse pulp mill.The characterization of the nZVI/AC catalyst showed that the calcination temperature has a greater influence on the formation of active substances in the catalyst.When the calcination temperature was 600?,the iron element in the catalyst was mainly in the form of Fe₃O₄.When the calcination temperature was 800?,Fe₃O₄ could be reduced to zero valent iron by carbon.The catalyst contained a large number of microporous structures with a specific surface area of874 m²/g.Compared with activated carbon,the graphitization degree was lower and the number of active sites was higher.The nZVI particles were uniformly distributed on the surface of the activated carbon without agglomeration.Degradation experiments of p-chlorophenol showed that the optimal preparation conditions for the nZVI/AC used in catalytic ozonation were Fe(NO₃)₃ solution concentration0.4 mol/L,calcination temperature 800?,and holding time 3 h.Under experiment conditions of p H 9,gas flow rate 1 L/min,ozone concentration 25 mg/L,catalyst dosage 2.0 g/L,after 30minutes of reaction,the removal rate of COD_Cr reached the highest 62.5%,the final COD_Cr of the effluent was 105 mg/L,the final BOD₅ was 57.28 mg/L,and the colour was completely removed.In the fourth recycle test of the nZVI/AC,the removal rate of COD_Cr from the pulping effluent was reduced to 30.8%.This was due to the fact that the active material in the catalyst was oxidized and the specific surface area became smaller during the reaction.The free radical scavenging experiment initially showed that oxygen-containing free radicals dominated by HO·provide the main oxidation ability.After the reaction,the types and contents of organic matter in the pulping effluent decreased significantly.The optimum conditions of nZVI/AC catalytic persulfate for pulping effluent treatment were as follows:p H 5,sodium persulfate dosage 1.5 g/L,catalyst dosage 3.0 g/L,reaction time120 min.The CODcr removal rate of pulping effluent was 71.25%,chroma removal rate 96%,BOD₅/CODcr changed from 0.14 to 0.58,and the biodegradability was great.In the fourth recycle test,the removal rate of COD_Cr was still close to 50%.The oxidation ability of the reaction system mainly came from SO₄^·-and HO·,and the oxidation effect of HO·was more obvious.UV-vis and GC-MS analysis showed that persulfate oxidation process catalyzed by nZVI/AC could effectively degrade the pollutants in the pulping effluent and reduce the pollution load significantly.