Microwave assisted preparation and characterization of a chitosan based flocculant for the application and evaluation of sludge flocculation and dewatering

Abstract

In this study, a new type of graft modified flocculant (CS-g-PAD) was copolymerized of AM, DAC and chitosan (CS) by microwave assisted initiation and used for sludge conditioning and dewatering. The effect of reaction conditions on microwave assisted copolymerization was investigated and their optimal values were obtained by orthogonal experiments. The structure and chemical properties of CS-g-PAD were characterized and the results indicated that microwave assisted polymerization can cause the generated side polymer chain of PAD to react with the -NH₂ active group in CS. Thus, the graft copolymerization occurred at amino group connected with C₂ site. Compared with CCPAM, PAD and CS, the synthesized CS-g-PAD exhibits superior sludge dewatering performance (FCMC: 72.1%, SRF: 4.5 × 10¹² m/kg, d₅₀: 679.556 μm, D_f: 1.72, floc sedimentation rate: 5.72 cm/min) in a wide pH range (pH = 3.5-9.5). Because CS-g-PAD contains a large amount of cationic DAC and positively charged CS as well as many functional groups on CS, it increases the charge neutralization, electrical patching and adsorption capability. Additionally, the grafting PAD on CS has a good extension in solution to increase its adsorption bridging effect. The new grafted CS-g-PAD is promising and has great practical application value in sludge dewatering and condition.

Keywords: Chitosan; Flocculation; Grafting and copolymerization; Microwave assisted initiation; Sludge dewatering and conditioning.