Adsorption Of Typical Heavy Metals On Municipal Sludge EPS And Its Influence Mechanism On Anaerobic Digestion Of Sludge

As Chinese municipal sewage treatment input continues to increase,Chi nese sewage treatment has made great progress.However,Ignoring sludge phenomenon is serious in the process of sewage treatment in China,resulting in a large amount of municipal sludge not being effectively treated.In the process of sewage treatment,a large amount of organic matter is transferred to the sludge.A lot of sludge is not only easy to cause secondary pollution,but also causes waste of resources.The anaerobic digestion technology of sludge is one of the most widely used methods for sludge resource and stabilization,and is easily affected by the heavy metals that are enriched in the sludge.Therefore,the heavy metal problem in sludge has received extensive attention.The sludge extracellular polymer is the main component of the organic matter i n the sludge,which is mainly composed of proteins,humic acids and polysaccharides,etc.The functional groups such as hydroxyl and carbonyl groups can bind and adsorb heavy metals through bond formation.Simultaneously,sludge EPS is used as Electronegativity groups can effectively bind heavy metals through neutralization and other methods.Therefore,it is of great significance to study the mechanism of sludge adsorption of heavy metals by EPS and the effect of typical heavy metals on the anaerobic digestion of sludge.In this study,EPS was extracted from anaerobic sludge and aerobic sludge.The adsorption efficiency of Cu²⁺,Cd²⁺,and Zn²⁺ on EPS was studied under different temperature and pH conditions.Three-dimensional fluorescence spectroscopy,Fourier transform infrared spectroscopy,and Zeta were applied.The change of the structure of EPS before and after the adsorption of heavy metals was analyzed.The mechanism of the adsorption of three heavy metals by the sludge EPS was explored in combination with the adsorption thermodynamics and adsorption kinetic model.The effect of typical heavy metals on the anaerobic digestion process was determined by the anaerobic digestion reactor.Different concentrations of Cu²⁺,Cd²⁺,and Zn²⁺ were added to investigate the effect of typical heavy metals attached to EPS on the anaerobic digestion process of the sludge.The adsorption capacity of anaerobic sludge for three metal ions was Cd²⁺（380mg/g）>Zn²⁺（353.28mg/g）>Cu²⁺（337.89mg/g）.Anaerobic EPS adsorbed Cu²⁺,Cd²⁺,and Zn²⁺ mainly through amine groups.The adsorption of amides,carbonyl groups,carboxyl groups,phenol groups and other functional groups into bonds and electric neutralization are the main reasons for the above adsorption.The thermodynamics indicate that in addition to the adsorption of Cd²⁺,the Freundlich model of the heterogeneous adsorption is satisfied;The adsorptive capacity of EPS for three metal ions was Cd²⁺（438.3 mg/g）>Zn²⁺（403.02 mg/g）>Cu²⁺（388.57 mg/g）.The adsorption of Cu²⁺,Cd²⁺,and Zn²⁺ by EPS from aerobic sludge mainly passed.The thermodynamic studies showed that adsorption of EPS from aerobic sludge to all three heavy metals conformed to the Freundlich model of heterogeneous adsorption;different concentrations were observed for the binding of functional groups such as amine groups,amide groups,hydroxyl groups,carbonyl groups,and phenol groups.The effect of Cu²⁺,Cd²⁺ and Zn²⁺ on the anaerobic digestion of sludge showed that under the experimental conditions,the low concentration of three metal ions promoted the anaerobic digestion of the sludge,while the high concentration of metal ions inhibited the anaerobic digestion;Sludge Extraction EPS Analysis in Reactor Now,the composition of the experimental group and the control group structure of EPS substantially uniform.This project provides a theoretical basis for the study of the enrichment of heavy metals in sludge and the influence on the anaerobic digestion process of sludge.