Investigation of sludge conditioning performance and mechanism by examining the effect of charge density on cationic polyacrylamide microstructure

Abstract

The relation between the microstructure and sludge conditioning performance and mechanism of cationic polyacrylamide (CPAM) (low charge density (CD) CPAM C1, medium CD CPAM C4, and high CD CPAM C7) was extensively studied and recognized in this study. Igarashi and Pyun models based on reactivity ratio characterized the microstructure of the polymers. Results indicated that the blockness percent and mean sequence length of acrylamide (AM) unit decreased, whereas those of cationic unit increased with CD. Effect of dosage on sludge conditioning performance and mechanism was studied by measuring turbidity, filter cake moisture content (FCMC), specific resistance of filtration (SRF), floc size distribution, and zeta potential. The longest AM unit sequence length and separated cationic unit of C1 were concluded to be responsible for bridging. Moreover, the conditioning disadvantages of AM were as follows: narrow flocculation window, high optimum dosage, and maximum FCMC. On the contrary, the highest cationic blockness percent of C7 favored efficient charge neutralization, which contributed to the generation of the lowest optimum dosage. However, the SRF was significantly high, which posed as a difficulty for future treatments. The medium cationic blockness percent and mean AM unit sequence length of C4 led to the combination of charge neutralization and bridging effect with a wide flocculation window and the lowest FCMC and SRF.