Efficiency Of Adsorption Removal Of Typical Heavy Metals By Polysaccharides And Humic Acid Extracted From Sludge EPS

With the rapid development of modern technology and the exploitation of various industries,the concentration of heavy metal in domestic sewage and industrial wastewater is increasing rapidly.The high concentration of metal ions is one of the most significant factors to inhibit the microbial activity of sludge in sewage treatment system and to reduce the efficiency of processing.Extacellular Polymeric Substances?EPS?is a kind of organic substance which is formed by bacteria under certain conditions for self-protection and mutual adhesion,and also provides carbon and energy for bacteria during hunger stage.It is the important channel for heavy metals entering the sludge cells.It also has a inseparable relationship with the dehydration and sedimentation of sludge floc.The main components of sludge EPS include polysaccharides,proteins,humic acid At present,there are many researches on the extraction method of EPS and its properties for the adsorption of heavy metals.However,studies about the adsorption of heavy metals by each component in EPS are pretty poor.Based on the rsearching status,in this experiment,aerobic activated sludge and anaerobic flocculent sludge were selected to adsorp 3 kinds of typical heavy metal ions by the extraction of polysaccharides and humic acids from two kinds of sludge,and the efficiency and mechanism of adsorption were studied.First,the extracted polysaccharides and humic acid were analyzed by elemental and structural methods.The type of sludge has no significant effect on the structure of polysaccharides and humic acid.The extracted polysaccharides mainly contain carboxyl groups,carbonyl groups and ester functional groups.The surface of humic acid is mainly composed of lipids,carboxylic acids and phenols,which also contains a small amount of fulic acid.Then,the effects of temperature and metal initial ion concentration on the adsorption reaction were investigated.In the range of 10³0? and the concentration of metal ions were 10¹00mg/L,the adsorption capacity increased with the increase of temperature and ion concentration.The effect of different sludge type was weak to the adsorption.Hunic acid performed better on Zn²⁺ and Cd²⁺adsorption,while the adsorption of polysaccharide on Cu²⁺ is more effective than that of humic acid.The study of the adsorption mechanism by FTIR and Zeta potentials showed that the association hydroxyl groups,carboxylic acids on the polysaccharide surface and C-O-C are involved in the adsorption of the heavy metals,the hydroxyl groups,aliphatic carbon chain,carboxylic acid and phenolic groups in the humic acid provide adsorption sites for metal ions.Polysaccharides and humic acids have strong negative charge,and ion exchange is the main mechanism of the two adsorption reaction with heavy metals.At last,the adsorption thermodynamics was used.The adsorption effect of Zn²⁺ on Langmuir adsorption isotherm was better.The Freundlich isothermal adsorption equation is more suitable for adsorption with Cu²⁺ and Cd2.The binding affinity of polysaccharides and heavy metal ions was:Cu²⁺> Zn²⁺>Cd²⁺,The maximum adsorption capacity under the optimum conditions was 5291.0mg / g,4181.4mg / g,3324.5mg / g,respectively;The tight degree of acid adsorption was:Zn²⁺?4610.4mg/g?> Cu²⁺?4140.8mg/g?> Cd²⁺?3414.1mg/g?.The adsorption reaction of EPS and heavy metals is mainly divided into three stages: rapid adsorption,slow adsorption and adsorption equilibrium.Using adsorption kinetics to fit the data of the absorption volumes changing with time.The results showed that the quasi-second order kinetic equation was more suitable for describing the adsorption reaction,and proved that the speed control process of this reaction was chemical adsorption rather than mass transfer.This experiment provides a theoretical basis for revealing the mechanism of heavy metal adsorption by sludge,and also plays an important role in the application of activated sludge in wastewater treatment system.