Targeted Regulation Of Sludge-derived Biochar And Its Activation Of Peroxymonosulfate To Degrade Toxic Organic Pollutants

Sewage sludge（SS）is an inevitable by-product in the municipal or industrial wastewater treatment processes,which has a large output.Disposing of large quantities of sludge in an economically and environmentally acceptable manner has become a vital issue in today’s society.Currently,the sludge pyrolysis process,which aims at the utilization of organic matter in sludge,can convert sludge into biochar with rich reactive sites and become one of the important approaches to resource utilization.Due to abundant functional groups and favorable porous structure on its surface,sludge-derived biochar（SBC）has been used as a non-homogeneous catalyst for peroxymonosulfate（PMS）-based advanced oxidation processes（AOPs）to realize the strategy of"waste to waste",which is of great significance for the sustainable development of social resources.Nevertheless,there are limitations to the use of SBC as a catalyst:lack of stability and reusability and unsatisfactory accessibility of catalytically active sites in its internal pores due to its complex compositions.To enhance the catalytic performance of SBC,it needs to be modified by physical or chemical modifications.Therefore,the diversified modifications to SBC in this project were carried out by the addition of transition metals,acid modification and co-pyrolysis of different biomasses,which aimed to enhance the catalytic performance of SBC by achieving（I）improving the specific surface area and pore structure of carbon-based materials,（II）increasing the degree of graphitization or defect structure of carbon,（III）enhancingπ-electron mobility through sp~2 conjugation,（IV）introducing new reactive sites and functional groups,（V）changing the electron density in local carbon atoms.The main research findings obtained are as follows:（1）A composite catalyst（FeOCl-SBC）was innovatively synthesized as an efficient activator for PMS to degrade Rh B in wastewater,which was obtained by impregnating FeCl₃·6H₂O and SBC.The addition of FeOCl triggered the increase of carbonyl groups（C=O）on biochar,which promoted the generation of reactive oxygen species（ROS）and accelerated the catalytic rate.Compared with SBC/PMS(0.0993 min^-1)and FeOCl/PMS(0.0215 min^-1)systems,the kinetic reaction rates(k_obs)of FeOCl-SBC/PMS(0.2107 min^-1)for organic pollutants were increased by 2.1 and 9.8 times,respectively.FeOCl-SBC/PMS system had a wide pH range（3.0～9.0）and maintained 85%removal rate after 10 reuses.C=O groups and Fespecies(Fe³⁺/Fe²⁺)played significant roles in the generation of singlet oxygen（~1O₂）and superoxide radical(O₂^·-)in FeOCl-SBC/PMS system.（2）Surface modification of sludge-derived biochar using Acetic acid（CH₃COOH）was performed to activate the SBC surface to generate more oxygenated functional groups（OFGs）.The acetic acid-modified biochar（ASBC-50）improved the efficiency of biochar-activated PMS in degrading organic pollutants by increasing the specific surface area and the number of-COOH functional groups.The ASBC-50/PMS system（99.2%）showed a significant improvement of nearly 20%in the removal of BPA compared to the SBC/PMS system（81.2%）.The ASBC-50/PMS system achieved more than 85%removal of BPA in a wide pH range（3.0～11.0）,and the removal efficiency still remained 99%after 6 recycles.OFGs（C=O/-COOH）played an important role as active sites in the production of ~1O₂ and O₂^·-.（3）A cost-effective and environmentally friendly biochar catalyst（BCs（9-1）-900）with high catalytic activity was prepared by co-pyrolysis of sludge mixed with sugarcane waste after ball milling for the activation of PMS to degrade Bisphenol AF（BPAF）.Compared with pure SBC-900,BCs（9-1）-900 had the advantages of higher graphitic carbon content,larger specific surface area and excellent electron-transfer ability,and thus it exhibited stronger catalytic degradation of BPAF.Under the conditions of using a small amount of PMS（50 mg/L）and catalyst（200 mg/L）,20 mg/L of BPAF can be completely degraded in less than 10 min;In a wide pH range（3.0～9.0）,BCs（9-1）-900/PMS system reached more than 95%degradation efficiency of BPAF within 10 min and was successfully used to catalyze the degradation of BPAF in real environmental water bodies and other organic pollutants.Persistent free radicals（PFRs）and oxygenated functional groups played an important role in this catalytic process,and the main catalytic mechanism of BCs（9-1）-900/PMS system was the non-radical pathway of singlet oxygen（~1O₂）and electron transfer.