Preparation,Modification And Heavy Metal Removal Performance Of Sludge Biochar

Sewage treatment plants can produce a large amount of activated sludge every year,so it is urgent to rationalize and efficiently dispose of sludge.Because activated sludge is rich in various elements,it can be used to prepare various environmental protection materials.Among them,sludge biochar is expected to be used in heavy metal wastewater treatment due to its low preparation cost and excellent adsorption performance.Municipal dehydrated sludge from a sewage treatment plant was used as raw material in this study.Hydrothermal charcoal was prepared by hydrothermal method using dehydrated activated sludge as raw material.Moreover,pyrolysis was also used to prepare metal-supported pyrolysis carbon by using iron or magnesium.These two kinds of biochar were applied to the removal of heavy metals including Cu²⁺and Pb²⁺in water.Besides that,the effects of multiple influencing factors such as biochar dosage,ionic strength,and the initial concentration of heavy metal on the adsorption of heavy metals on biochar were investigated.Adsorption kinetics and isotherms were studied by using multiple models.Finally,the reusability and cost analysis of biochar were also explored.The main experimental results were shown as the followings:（1）The specific surface area of hydrothermal biochar produced at 180℃was the highest to reach 16.42 m²/g while that of the pyrolysis biochar was lower than 10 m²/g.The hydrothermal biochar exhibited acidic while pyrolysis biochar was weakly alkaline.The hydrothermal biochar showed coarse and agglomerated microscopic structure while pyrolysis biochar was sheet structure.The types of organic functional groups of sludge biochar made by hydrothermal and pyrolysis methods were different to some extent while those of biochar using the same method were generally identical.（2）Under the optimal operation conditions,the adsorption capacity of hydrothermal carbon,Mg-doped pyrolysis biochar,and Fe-doped pyrolysis biochar for Cu²⁺was 1.6 mg/g,15 mg/g and 127.6 mg/g while that for Pb²⁺was 3.7 mg/g,10.5 mg/g and 36.3 mg/g,respectively.Na Cl with concentration of 1 mol/L inhibited the adsorption of Cu²⁺and Pb²⁺while higher Na Cl concentration had more significant inhibition effect.A competative adsorption inhibition effect occurred when Cu²⁺and Pb²⁺coexisted in the solution to decrease the adsorption capacity of sludge biochar.（3）Pseudo-second order kinetic model could better fit the adsorption of Cu²⁺and Pb²⁺by hydrothermal carbon and pyrolytic carbon while Freundlich model could better describe the adsorption isotherm of heavy metal on sludge biochar.The enthalpy variableΔH and the free energy variableΔG of the thermodynamic function wee both less than 0,illustrating that adsorption of Cu²⁺and Pb²⁺on sludge biochar was an endothermic reaction spontaneously.（4）The adsorption capacity was still acceptable after the sludge biochar was reused 4 times,showing that the sludge biochar possessed some application prospect.Mg-doped pyrolysis biochar possessed good adsorption capacity for heavy metals and low cost to possibly have good performance in the application.The results obtained in this study provide research data support for sludge resource utilization and heavy metal wastewater treatment,and provide feasible research ideas for rational sludge disposal.