Study On The Removal Performance And Mechanism Of Orange Ⅱ By Activated Perdisulfate By Modified Sludge Biochar

Printing and dyeing wastewater has caused pollution to the surface water environment.Printing and dyeing wastewater and its by-products are difficult to degrade naturally in water,which is highly toxic and poses a great threat to the ecological environment and human health.Advanced oxidation technology based on perdisulfates（PDS）is a potential method to degrade dye wastewater because it can generate active oxygen species with strong oxidation ability.The key of persulfate oxidation technology lies in catalyst.Biochar is an excellent choice for non-metallic catalysts due to its environmental protection,large specific surface area and many active sites.This study adopts the environmental protection concept of"waste control waste",using municipal sludge as raw material to prepare original sludge biochar and modified sludge biochar,and activating PDS to remove orangeⅡ.The main research contents and results are as follows:（1）Raw sludge biochar and porous sludge biochar（BC,1/2KBC,KBC and 2KBC）were prepared under N₂atmosphere at 700℃by activation and carbonization at different KHCO3/municipal sludge mass ratios（0:1,1/2:1,1:1,2:1）.As the proportion of KHCO₃increased,the specific surface area of the modified biochar increased,and the specific surface area of KBC reached 259.2m²/g,much higher than that of BC（21.5m²/g）.Sludge biochar can effectively activate PDS to remove orange yellowⅡ,in which KBC/PDS system can achieve 97.3%removal rate in 105min.The p H value of the initial solution has obvious influence on the reaction system,and the acidic condition can increase the removal effect.Alkaline environment will inhibit the reaction.The results of radical quenching experiment and EPR test showed that although SO₄^·-and·OH participated in oxidative degradation,they were not the dominant factors.EPR test did not detect significant singlet oxygen（¹O₂）signal.The electrochemical test results show that the KBC/PDS system has obvious electron transfer process.The results showed that KBC/PDS system achieved the oxidative degradation of orangeⅡmainly through non-free radical pathway.According to the reusability experiment,KBC has good stability.（2）In order to improve the catalytic performance of porous sludge biochar,nitrogen doped porous sludge biochar（1/2NKBC,NKBC,2NKBC）with different urea/KBC mass ratio（1/2:1,1:1,2:1）was prepared by using urea as added nitrogen source.Fourier infrared spectroscopy（FTIR）and X-ray photoelectron spectroscopy（XPS）analysis results showed that nitrogen elements were successfully incorporated into porous sludge biochar,and marginal nitrogen（pyridine and pyrrole nitrogen）was the main nitrogen.FTIR analysis before and after NKBC application showed that-C=O was involved in the reaction.The catalytic capacity of NKBC/PDS system is superior to that of KBC/PDS,and the removal rate of 99.7%can be achieved within 90 minutes.The results of reactive oxygen species quenching experiment and EPR test showed that SO₄^·-and·OH existed in NKBC/PDS system,but they were not the main active species for oxidative degradation of pollutants.L-histidine had a significant inhibitory effect on the reaction system,and EPR test detected a large amount of ¹O₂in the reaction system,indicating that ¹O₂was the main reactive oxygen species of oxidative degradation in the reaction system.Electrochemical tests showed that electron transfer was another non-free radical pathway for oxidative degradation of orangeⅡby NKBC/PDS system.Therefore,the NKBC/PDS system mainly realizes the oxidation degradation of orangeⅡthrough non-free radical pathway.The stability experiment results show that NKBC also has good stability.（3）In order to further improve the catalytic performance and separability of nitro-doped porous sludge biochar,different mass ratios of Fe²⁺/ascorbic acid/urea/KBC were prepared by co-pyrolysis of ferrous sulfate（Fe SO₄·7H₂O）as iron source and urea as nitrogen source（5%:2.5%:1:1,10%:5%:1:1,20%:10%:1:1）.10%:5%:0:1)Fe-nitrogen co-doped sludge biochar（5%Fe@NKBC,Fe@NKBC,20%Fe@NKBC,Fe@KBC）.By XRD,XPS and other characterization methods,it is confirmed that the modification method of Fe-nitrogen co-doping doping iron in the form ofα-Fe₂O₃,α-Fe⁰into the modified biochar,and gives biochar rich nitrogen-containing functional groups,a large number of active sites and separation characteristics.The advanced oxidation system of Fe@NKBC/PDS was constructed and applied to the removal of orangeⅡ.The effects of different reaction conditions on the degradation of orangeⅡby Fe@NKBC/PDS were investigated and the optimal reaction conditions were selected.Under the optimal reaction conditions,the degradation of 50 mg/L orangeⅡwas up to 99.3%within 20minutes,showing high catalytic degradation ability,which was much better than NKBC/PDS and KBC/PDS systems.·OH,SO₄^·-and ¹O₂were confirmed as the three main reactive oxygen species in the process of Fe@NKBC activation of perdisulfide by radical quenching and electron paramagnetic resonance（EPR）tests,and electron transfer mechanism existed in the system.Based on the above conclusions,the modified sludge biochar-persulfate catalytic system provides a technical strategy for municipal sludge reclamation and dye wastewater advanced treatment.