Enhanced municipal sludge dewaterability using an amphiphilic microblocked cationic polyacrylamide synthesized through ultrasonic-initiation: Copolymerization and flocculation mechanisms

Abstract

Flocculation is an important pretreatment technique for sludge dewatering, the performance of employed flocculants is the key factor determine the flocculation efficiency. Herein, an amphiphilic cationic polyacrylamide (CPAM) with microblock structure was synthesized through template copolymerization initiated by ultrasonic. The chemical components and cationic microblock structure of copolymers were confirmed through comparative characterization by Fourier Transform Infrared (FTIR) and Nuclear Magnetic Resonance (1H NMR) spectrum. The copolymerization mechanism was investigated through kinetics study and association coefficient (KM) determination. The results indicated that the reaction followed free radical copolymerization and terminated mainly through bimolecular termination. The pre-adsorption between acryloyloxyethyltrimethylammonium chloride (DAC) and sodium polyacrylate (NaPAA) before reaction confirmed the template polymerization met the type I (ZIP) mechanism. Cationic microblocks and hydrophobic association together contributed to the optimal dewaterability (FCMC=67.2 %, SRF=3.84×1012 m·kg−1) using TP(AM-DAC-LA). Hydrophobic association enhanced bridging and sweeping effect to promote the floc size growth. Cationic microblocks produced compacter flocs with stronger mechanical strength through enhanced charge neutralization and patching effects, which acted as skeletons to make filter cakes less compressible and more permeable in mechanical dewatering. This work developed a highly effective flocculant for sludge dewatering, the synthesis and working mechanism of which were also given.