Efficient Extraction Of Extracellular Polymers From Activated Sludge And Their Adsorption On Cu²⁺ And Pb²⁺

Activated sludge extracellular polymer（EPS）is a promising future biosorbent with the advantages of being environmentally friendly,non-toxic,renewable,degradable,and easily available in source,etc.The presence of a large number of adsorption sites on many functional groups in EPS has high research value and application prospects in heavy metal wastewater treatment,etc.At present,there are many methods for EPS extraction from activated sludge,and there is no unified and efficient extraction method.There is an urgent need to establish an efficient EPS extraction method.The activated sludge EPS extraction experiment by sodium oxalate was found to have a high extraction amount.On this basis,the compositional properties were analyzed to investigate the process and mechanism of EPS adsorption of heavy metal ions,and to provide a theoretical basis for the subsequent application of EPS to actual heavy metal wastewater treatment.The results of the study are as follows.（1）The activated sludge EPS extraction experiments led to the following conclusions:comparison of EPS extraction amount by single method: sodium oxalate method > Na OH method > heating method > ultrasound method,and the degree of damage to cells: heating method > Na OH > sodium oxalate method > ultrasound method.The response surface optimization experiment was designed by Design expert 11.0 data analysis software,and the regression equation model was established to obtain the predicted optimal conditions:sodium oxalate concentration of 0.1 mol/L,sonication time of 5 min,and sodium oxalate extraction time of 46.342 min.The difference between the actual EPS extraction amount and the actual EPS extraction amount under this optimal condition by three parallel tests was not significant,which confirmed the The good correlation between the predicted and experimental values was confirmed.（2）The analysis of EPS composition by FTIR,EMM,SEM,zeta potential and XPS showed the following conclusions: FTIR showed the presence of various organic functional groups in EPS,most of which are found in polysaccharides and proteins,in addition to trace amounts of lipids in EPS;EMM showed the presence of tryptophan-like substances in EPS,which are aromatic proteins.SEM showed that the EPS sample had an irregular surface lamellae and some small raised structures with certain void ratio;Zeta potential showed that EPS gradually decreased with increasing p H and was generally electronegative;BET test yielded a specific surface area of 6.1814 m2/g and an average pore size of 8.2159 nm;XPS showed that C elements in EPS were mainly in the form of Four groups are combined into C-C,mainly from the hydroxyl group in the side chain of amino acid,C-N/C-S,mainly from the peptide bond and sulfur group in the protein,and O-C=O from the carboxyl or ester group.（3）EPS adsorption experiments on Cu2+ and Pb2+ led to the following conclusions:the optimal conditions for EPS on Cu2+ and Pb2+ are: when the p H is 6,the dosing ratio m（M2+）: m（EPS）= 1 : 2,the time is 120 min,and the temperature is 45°C.The desorption experiments showed that the desorption rates of Cu2+ and Pb2+ for 60 min at p H 1 reached90.5% and 92.6%,respectively.The theoretical equilibrium adsorption amounts of Cu2+ and Pb2+ under this model were 588 mg/g and 608 mg/g,respectively;the adsorption process of EPS on Cu2+ was in accordance with the proposed secondary kinetic model,and the adsorption process of EPS on Pb2+ was in accordance with the proposed primary kinetic model.model;FTIR and SEM-EDX analyses of EPS before and after adsorption of Cu2+and Pb2+ showed that: the adsorption sites were mainly hydroxyl,methyl,methylene and amide groups;Na,Mg,Ga and K peaks were substantially weakened,indicating the existence of ion exchange,in which oxygen-containing functional groups were involved in the adsorption reaction.Figure [37] Table [18] Reference [89]...