Efficiency And Mechanism Of Heavy Metals Adsorption By Ploysaccharide-based Microbial Flocculant

Recent years,the issue of water pollut ion caused by heavy metal is increasing seriously which is threatening human's health and environment.Because of the existence of limitations in conventional treatment approaches,polysaccharide-based microbial flocculants are used to treat heavy metal in industrial wastewater with high efficiency and non-second pollut ion in this thesis.This study could provide theoretical basis for directional transformation of polysaccharide-based microbial flocculants and increasing its universality.The competitive adsorption of two-metal systems could guide the actual treatment of the heavy metal wastewater.The concentration of polysaccharide-based microbial flocculants was an important factor.The most suitable of concentration were 200 mg/L,700 mg/L and 800 mg/L for remove Pb²⁺,C d²⁺,N i²⁺.Low pH would cause the opposite impact for remove heavy metal ion.The optimal removal effic iency of heavy metal by polysaccharide-based microbial flocculants was obtained under pH 6.The adsorption reached equilibrium at 15 min,20 min and 20 min,and then slight ly dropped.When the initiate concentration of heavy metal ion were 30 mg/L,20 mg/L and 15 mg/L respectively,it could gain the optimal removal efficiency.The optimal removal effic iency of Pb²⁺,Cd²⁺,Ni²⁺ by polysaccharide-based microbial flocculants were 99.13%,94.44% and 84.55% under the optimum adsorption conditions,respectively.Thermodynamics analysis results showed Langmuir,Freundlich and Dubinin-Radushkevich adsorption isotherm model could describe the adsorption process.Correspondingly,8 < E < 16 k J/mol it represented ion exchange.K inetics analys is showed that pseudo-second order kinetics model could describe the adsorption process.40 < Ea < 800 kJ/mol it confirmed that the nature of the adsorption process was chemisorption.The characterization of SEM?FTIR?3D-EEM?Zeta potential was used to analyze the adsorption mechanism.The results of SEM showed that polysaccharide-based microbial flocculants were porous structures.The results of EDAX indicated ion-exchange mechanism played an important role in the biosorption process.The results of FTIR indicated that C-O-C and C-O of polysaccharide,–O H groups were the main action site during the adsorption process.The results of 3D-EEM indicated that tryptophan and tyrosine of polysaccharide-based microbial flocculants played an important role in the adsorption process.Based on the thermal analys is,the kinetic analys is and the mechanis m analysis,it was concluded that the adsorption of heavy metals Pb²⁺,Cd²⁺ and Ni²⁺ by polysaccharide-based microbial flocculants was mainly based on the chemical adsorption.The competitive Langmuir adsorption isotherm model could describe the adsorption process of two-metal systems.C oexisting heavy metal ions would cause the opposite impact for remove target heavy metal ion.The adsorption order was Pb²⁺ > Cd²⁺ > Ni²⁺ by polysaccharide-based microbial flocculants.