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A new flocculant with cationic microblock structure was prepared by using template polymerization. Acrylamide (AM) and acryloyl­oxyethyl­tri­methyl­ammonium chloride (DAC) were used as monomers, and sodium polyacrylate was used as the template. The reactivity ratio, 1H NMR, 13C NMR, and thermogravimetric analysis were employed to characterize the structural properties of products. Results show that, with the addition of the template, the reactivity ratio of DAC increased, whereas that of AM decreased. Evident microblock structure was synthesized in copolymers when the molar ratio of template to DAC was 1.0. Activated sludge dewatering experiment results reveal that the cationic microblocky flocculant exhibited superior dewatering efficiency, and a low moisture content of 71% and a specific resistance of 1.99 × 1012 m·kg–1 were acquired at pH 7.0 and a 40 mg L–1 dosage. The enhanced charge neutralization and bridging effect of the cationic microblocky flocculant contributed to the formation of floc with a large size and compact structure.

The effects of the cationic surfactant (cationic cetyl trimethyl ammonium bromide, CTAB) on the improvement of the sludge dewaterability using the cationic flocculant (cationic polyacrylamide, CPAM) were analyzed. Residual turbidity of supernatant, dry solid (DS) content, extracellular polymeric substances (EPS), specific resistance to filtration (SRF), zeta potential, floc size, and settling rate were investigated, respectively. The result showed that the CTAB positively affected the sludge conditioning and dewatering. Compared to not using surfactant, the DS and the settling rate increased by 8%–21.2% and 9.2%–15.1%, respectively, at 40 mg·L−1 CPAM, 10×10−3 mg·L−1 CTAB, and pH 3. The residual turbidities of the supernatant and SRF were reduced by 14.6%–31.1% and 6.9%–7.8% compared with turbidities and SRF without surfactant. Furthermore, the release of sludge EPS, the increases in size of the sludge flocs, and the sludge settling rate were found to be the main reasons for the CTAB improvement of sludge dewatering performance.

Grafting copolymers of polyacrylamide (PAM) with Konjac gum (KGM) have been synthesized using ceric-ion-induced initiation technique. The copolymers were characterized using several instrumental techniques, including infrared (IR) spectroscopy, elementary analysis, scanning electron microscopy (SEM), size exclusion chromatography (SEC) analysis, and intrinsic viscosity to confirm the success of grafting. The flocculation performance of graft copolymers was characterized by two methods. One was to study the relationship between the flocculants doses in kaolin suspension and the supernatant transmittance, and the other is to examine the time dependence of sediment height of kaolin suspensions. It was found that the graft copolymer is better than KGM and pure PAM. Biodegradation behavior was testified by monitoring the decay of relative viscosities, and approved by KGM ether bonds breaking in IR spectra and the molecule weight reduction in SEC analysis. The results indicate that the grafted KGM copolymers have improved both, flocculation performance and better biodegradable properties than the unmodified parent KGM and pure PAM.

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