Printing And Dyeing Sludge Derived Biochar For Activation Of Peroxymonosulfate To Remove Aqueous Organic Pollutants:Activation Mechanisms And Environmental Safety Assessment

A large amount of printing and dyeing sludge（PADS）is generated during the treatment of printing and dyeing wastewater.PADS is classified as hazardous waste due to its high content of toxic organics and heavy metals,and its difficulty in disposal.Traditional sludge treatment technologies such as landfill and incineration not only take up land and produce dioxins,but also fail to resource the sludge.Pyrolysis technology can remove organic pollutants from PADS,stabilize heavy metals,and also use the complex components of PADS to form biochar containing rich functional groups.In this study,we prepared sludge-based biochar from PADS,investigated the effects of different pyrolysis conditions of dyeing sludge biochar on the catalytic effect of peroxynitrite（PMS）,explored the activation mechanism and main active sites of PMS activation by dyeing sludge biochar,and finally evaluated the environmental safety of dyeing sludge biochar.The main results are as follows.（1）Preparation of printing and dyeing sludge biochar using heteroatoms and oxygenated nitrogen-containing groups produced by the decomposition of complex components in PADS during high-temperature pyrolysis.The adsorption performance and activation performance of PADS biochar for PMS were significantly affected by the pyrolysis temperatures（400℃,600℃and 800℃）,but the effects of pyrolysis time（1 h,1.5 h and 2h）were not significant.The PADS biochar（BC-800-1.5）prepared at a pyrolysis temperature and time of 800℃and 1.5 h,respectively,had the highest adsorption and PMS catalytic performance,achieving 29%adsorption of bisphenol A（BPA）within 90 min and 99%removal of BPA by activated PMS within 20 min.（2）The effects of BC-800-1.5 and PMS dosing concentration,initial p H,natural organic matter humic acid HA and inorganic anions HCO₃^-、H₂PO₄^-and Cl^-on the catalytic performance of BC-800-1.5/PMS system were investigated by conducting experiments with different experimental conditions and influencing factors.The results showed that 0.7 g L^-1of BC-800-1.5 and 0.3 m M of PMS showed the highest efficiency of BPA removal for the BC-800-1.5/PMS system;the BC-800-1.5/PMS system maintained high BPA removal efficiency in the presence of a variety of natural organic matter or inorganic ions and could adapt to a wide range of p H in the environment.Thess indicated that the BC-800-1.5/PMS system has high interference resistance as well as stability.（3）The reactive oxygen species during BPA removal by BC-800-1.5 activated PMS were measured by free radical quenching experiments and electron paramagnetic resonance experiments.The results showed the presence of singlet oxygen（~1O₂）and a few superoxide groups（O₂^-·）in the BC-800-1.5/PMS system,and no other radicals were found.The pathway of PADS biochar（BC-800-1.5/PMS）activation of PMS degradation of BPA was revealed to be a non-radical electron transfer pathway dominated by singlet oxygen（~1O₂）.Then BC-800-1.5 before and after the reaction was measured by more in-depth characterization means such as FTIR,XPS,Raman spectroscopy,etc.,and it was compared that the structures of C=O,graphitic nitrogen and pyridine nitrogen on the surface of BC-800-1.5 before and after the reaction were reduced.It indicates that the main active sites of BC-800-1.5 are specific nitrogenous and oxygen-containing functional groups on the surface of biochar,such as C=O,graphitic nitrogen and pyridine nitrogen.（4）The heavy metal leaching experiments,polycyclic aromatic hydrocarbon extraction experiments and reproducibility experiments were conducted on BC-800-1.5 to study the heavy metal leaching of the solution after BC-800-1.5/PMS reaction at different p H and the heavy metal entry and exit of BC-800-1.5 according to the"Sulfuric acid nitric acid method","Horizontal shaking method"and"Acetic acid buffer solution method;the content of PAHs in BC-800-1.5 was detected;the performance of BC-800-1.5 activated PMS in removing BPA after three cycles was explored.The results showed that the leaching concentrations of seven heavy metals（copper,arsenic,zinc,chromium,nickel,cadmium and lead）of BC-800-1.5 in each use environment were in compliance with the Guangdong Province Comprehensive Wastewater Discharge Standard（DB4426-89）.The total concentration of 16 PAHs obtained by extraction in BC-800-1.5 was 209.185μg kg^-1,which was also in accordance with the European Biochar Fund regulations for superior biochar.BC-800-1.5 was activated by PMS to remove BPA after three cycles,and still could remove 74%of BPA within 30 min,with some reusability.These showed that the printing and dyeing sludge biochar BC-800-1.5 prepared by calcination at 800℃for 1.5 h meets the environmental safety standard and has some repeatability.