Preparation,Characterization And Flocculation Of Novel Polysaccharide Flocculants Modified Based On High Molecular Weight Dextran

Novel flocculants based on natural polysaccharides have broad application prospects in the fields of water treatment,food and medicine,etc.,and have attracted extensive attention in recent years.Dextran is a microbial polysaccharide with good water solubility,biocompatibility and biodegradability.In this study,on the basis of enzymatic preparation of high molecular weight dextran,the flocculating active groups were introduced into the dextran molecular chain through crosslinking and esterification,so as to develop safe and environmentally friendly polymer flocculants based on dextran.The specific research results are as follows:(1)Firstly,a cationic dextran crosslinked derivative flocculant was prepared by usingε-polylysine(PL)to modify dextran by crosslinking method.The preparation conditions were optimized by response surface methodology to improve the product yield.The optimal preparation conditions are: the reaction p H is 8.8,the dosage of PL is 2.2 g/g dextran,and the dosage of crosslinker is 0.9 m L/g dextran.The corresponding yield is119.7 ± 1.9%.The flocculation activity of the product was tested by using kaolin suspension,and the flocculation conditions were optimized by response surface methodology to improve the flocculation efficiency.The optimal flocculation conditions are: the flocculation p H is 6.3,the flocculation temperature is 36 °C,and the dosage of flocculant is 86 mg/L.The corresponding flocculation efficiency reaches 96.0 ± 1.5%.The flocculation mechanism includes charge neutralization and adsorption bridging.(2)Secondly,a cationic dextran esterified derivative flocculant was prepared by esterification using PL.The results of flocculation activity test show that when the p H is6,the temperature is 30 °C,and the dosage of flocculant is 40 mg/L,the flocculation efficiency is the highest,and the stable value of 99.8% is reached after settling for 120 s.The flocculation mechanism is mainly charge neutralization and adsorption bridging.The product was used in the flocculation study of the Escherichia coli culture medium.The results show that the flocculation is difficult under alkaline conditions,but the flocculation effect is obvious under neutral and acidic conditions,and the maximum flocculation efficiency is more than 99%.(3)Then the application of the cationic dextran esterified derivative flocculant in the clarification of sugarcane juice was investigated.The dosage of reagents used in the preparation process was optimized.The results show that when the dosage of carboxyl activator is one-tenth of PL and the dosage of PL is one half of dextran,the resulting product has the strongest clarifying ability to sugarcane juice.The clarification efficiency reaches 91.4% at the dosage of 118mg/L.The clarification mechanism includes charge neutralization and adsorption bridging.The results of biodegradation experiments show that the product can be biodegraded by enzymatic hydrolysis.(4)Finally,an anionic dextran-based flocculant was prepared by esterification of dextran with citric acid.The flocculation activity of the product was tested with hematite suspension.The results show that when the p H is 6,the temperature is 40 °C,and the dosage of flocculant is 24 mg/L,the flocculation efficiency is the highest,reaching a stable value of 88.5% after settling for 150 s.In conclusion,this study provides reference and experience for the development and application of new polysaccharid-based flocculants,and lays a foundation for future research.