Preparation Of Municipal Sludge Biochar Cathode And Its Application In E-Fenton Technology

Water resources are an important resource for the healthy and sustainable development of human society.With the continuous advancement of industrialization and urbanization,a large number of organic pollutants are directly discharged into natural water bodies without proper treatment,resulting in serious water pollution.Urban sewage treatment plant is an effective way to slove the harmless treatment of urban domestic sewage,but the traditional sewage treatment process cannot achieve complete mineralization of organic pollutants.In addition,as an intensive industry,sewage treatment plants produce a large amount of municipal sludge every year in the world.The components of municipal sludge are complex and contain a large amount of toxic and harmful organic matter,heavy metal ions and microorganisms.Therefore,the disposal and resource utilization of sludge received extensive attention.In recent years,biomass carbon materials have received extensive attention in the environmental and energy fields due to their high specific surface area and tunable local charge distribution density.Sludge is a special biomass char precursor,which can be produced by high temperature pyrolysis,microwave pyrolysis and hydrothermal carbonization.Electro-Fenton technology is a new type of electrochemical advanced oxidation.This technology uses Fe²⁺to catalyze the electro-generated H₂O₂ on the cathode surface to·OH with high redox potential,thereby realizing the complete mineralization of organic wasterwater.The modification of carbon cathode has always been a major development direction of EF technology.Improving the performance of catalysts for electrochemical two-electron redox reaction by changing the pore structure and local charge density of carbon materials is one of the main directions of EF tevhnology improvement.Therefore,the preparation of a new and efficient 2e-ORR cathode material using municipal sludge as the precursor of EF technology cathode material is of great significance for the advanced treatment of organic wastewater and the recycling of municipal sludge.（1）Preparation of A²/O process activated sludge biomass carbon cathode and performance of EFA new type of EF cathode material was prepared by using ZnCl₂ to activate activated sludge at the inlet of Sanjintan secondary sedimentation tank at high temperature.The BET results showed that ZnCl₂ could promote the formation of mesoporous and microporous structures during sludge pyrolysis.It was found that when the ratio of activated sludge powder and ZnCl₂ was 1:1,its S_BET=433.84m²·g^-1,and the S_BET=88.05m²·g^-1 of biomass carbon obtained by direct high-temperature carbonization.The mass ratio of mud powder increases gradually,and the specific surface area decreases gradually.All electrode materials were tested by EIS,and it was found that the electrode impedance was greatly reduced after high temperature activation of ZnCl₂.The results of XPS analysis showed that with the increase of the relative content of ZnCl₂,the graphitized nitrogen gradually decreased,and the content of porphyrin nitrogen and pyridine nitrogen increased gradually.At the same time,the ratio of different oxygen functional groups also changed.It is inferred that the high temperature activation of ZnCl₂ not only increases the specific surface area of the material and enhances the mass transfer effect,but also exposes more ORR catalytic active centers.From the electrogeneration effect of H₂O₂,it can be known that the optimal potential of H₂O₂ electrogeneration decreased from-0.9V to-1.1V,but the cumulative concentration of H₂O₂ increased from 0.61mmol·L^-1 to 1.31mmol·L^-1 within 30 min.When 0.3mmol·L^-1Fe²⁺was added to the electrolyte,the degradation kinetic constant of 0.1mmol·L^-1 BPA was0.224min^-1.（2）Preparation and EF performance of biochar cathode from digested sludge in A²/O process.Digested sludge is sludge produced by digestion reaction.The digestion process is mostly used to remove nitrogen and phosphorus from organic wasterwater.It is generally believed that the nitrogen content in digested sludge is higher than other activated sludges.This chapter also uses ZnCl₂ high temperature carbonization digestion sludge to prepare biomass carbon cathode.The BET results showed that the specific surface area of the N0 material was 328.76m²·g^-1,and the specific surface area of the A2 material was 592.27m²·g^-1.With the increase of the relative content of ZnCl₂,the specific surface area of the digested sludge biomass char gradually decreased.The EIS test was performed on the N2 material and the result was 7.87 ohm.XPS analysis showed that the relative content of N species in the N2 material was 3.66%;the O content was relatively low,9.19%.This may lead to the relatively weak adsorption effect of N2 material on O₂.The H₂O₂ capacity of the digested sludge biomass char was tested.The results showed that after the pyrolysis of ZnCl₂,the optimal potential of H₂O₂ electrogeneration was reduced from-0.9V to-1.1V,but the cumulative concentration of H₂O₂ within 30 min was reduced from 0.44mmol·L^-1 rose to0.54 mmol·L^-1.When 0.3 mmol·L^-1 Fe²⁺was added to the electro-fenton system,the degradation kinetic constant of 0.1mmol·L^-1 BPA was 0.117min^-1,and the degradation kinetic constant of 50 mg·L^-1 X3B was 0.188min^-1.Finally,the degradation effect of EF on BPA was run on the N2 cathode in natured water,and the results showed that BPA could be rapidly degraded in boeh the Yangtze River water and the East Lake water.（3）Preparation and EF properties of oxidation ditch activated sludge biochar cathodeActivated sludge was collected from Wuhan Baoxie Sewage Treatment Plant as the precursor of biomass charcoal.The sewage treatment plant uses the oxidation ditch process to treat organic wastewater.Also using ZnCl₂ high temperature pyrolysis activated sludge,BET results show that B1 material has the largest specific surface area,414.35m²·g^-1.As the proportion of ZnCl₂ gradually increased,the specific surface area of activated sludge biomass carbon gradually decreased.The H₂O₂ electrogenerating capacity of the activated sludge biomass charcoal cathode in the oxidation ditch was tested.The results showed that the optimal potential of H₂O₂ production shifted to the negative potential after the activation of ZnCl₂,and the cumulative concentration of H₂O₂ increased from0.71mmol·L^-1 to 0.9mmol·L^-1 within 30 min.XPS analysis was performed on the B2material,which showed that its nitrogen and oxygen species were similar to those of A2.The impedance of the B2 material was characterized by EIS,and the fitting result was 7.03ohm.In the electro-fenton system,adding 0.3mmol·L^-1 Fe²⁺,the degradation kinetic constant of0.1mmo·l L^-1 BPA is 0.163min^-1,and the degradation kinetic constant of 50mg·L^-1 X3B is0.209min^-1.Finally,the electro-fenton effect of B2 cathode in actual water was evaluated.