Synthesis and characterization of a cationic dextran-based flocculant and its application in bacterial sedimentation

As a promising material in the field of wastewater treatment, polysaccharide-modified flocculants have received increasing attention due to their environmental friendliness. In this study, an efficient and environmentally friendly flocculant was synthesized using a graft copolymerization reaction of dextran and [2-(methacryloyloxy) ethyl] trimethylammonium chloride (METAC). The reaction conditions were optimized at 3 mol/mol METAC/dextran, 60 g/L dextran concentration, 3 h reaction time, 60 ℃ and pH 7. The results of elemental analysis, Fourier transform infrared (FTIR) spectroscopy, NMR hydrogen spectroscopy ( 1 H NMR), X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA) and viscosity measurement confirmed that the graft copolymerization reaction was successful. When flocculating a kaolin suspension used as synthetic wastewater, the flocculant showed effective flocculation performance at a low dosage. The results indicate that this cationic polysaccharide flocculant removed 98.2% of the kaolin solid suspended particles. Investigation of the flocculation mechanism showed that the flocculation process consisted of charge neutralization, charge patching and adsorption bridging mechanisms. When flocculating an E. coli culture medium, this flocculant showed high efficiency under acidic, neutral and alkaline conditions. In addition, this flocculant can be easily biodegraded by the enzymatic method. As a biomaterial, this cationic dextran derivative can contribute to future treatment of industrial wastewater and harvesting of microbial cells. • A cationic flocculant based on dextran was developed. • Dextran prepared in our laboratory can achieve high molecular weight (thousands of kDa). • The dextran-based flocculant showed high flocculation performance on kaolin suspension and E. coli culture medium. • Biodegradation of the dextran-based flocculant by enzymatic method was investigated.