Abstract
Cationic polyacrylamides have been employed widely to improve sludge dewatering performance, but the cationic units are randomly distributed in the molecular chain, which restricts the further enhancement of dewaterability. Common template technology to prepare block copolymers requiring a huge number of templates reduces the polymer purity and molecular weight. Here, we adopted the surface-active monomer benzyl dimethyl 2-(methacryloyloxy)ethyl ammonium chloride (BDMDAC) to synthesize cationic microblocky polyacrylamide initiated by ultrasound. The reactivity ratio of monomers suggested that novel cationic monomer BDMDAC had higher homopolymerization ability, and was thus more prone to forming a microblock structure. The statistical analysis of sequence-length distribution indicated that the number and length of cationic segments increased in the PAB molecules. In addition, the characteristic results of Fourier transform infrared (FTIR), proton nuclear magnetic resonance (1H NMR), and thermogravimetric analysis (TGA) provided evidence for the synthesis of copolymer with cationic microblocks. Finally, the results of dewatering tests demonstrated that sludge dewaterability was greatly improved by adding the synthesized novel flocculants, and the sludge-specific resistance to filtration, filter cake moisture content and residual turbidity all reached a minimum (68.7%, 5.4 × 1012 m·kg−1, and 2.6 NTU, respectively) at 40 mg·L−1. The PAB flocs were large, compact, difficult to break, and easy to regrow. Furthermore, PAB was more effective in the removal of protein from soluble extracellular polymeric substances (SEPSs). In summary, this study provides a novel solution to synthesize cationic microblock polyacrylamide for improving sludge dewatering.
Highlights
Nowadays, an ever-increasing amount of wastewater is treated using the biologically-activated sludge process, which results in a dramatic increase of waste sludge amount [1]
We introduced a new functional monomer to synthesize chemical conditioning flocculants with cationic microblock structures
The reactivity ratios of AM and cationic monomers calculated according to three methods are shown in Table 3 and the results were close to those of the previous study
Summary
An ever-increasing amount of wastewater is treated using the biologically-activated sludge process, which results in a dramatic increase of waste sludge amount [1]. The management of Materials 2017, 10, 282; doi:10.3390/ma10030282 www.mdpi.com/journal/materials. Materials 2017, 10, 282 the waste sludge is confronted with a crucial challenge due to high water content [2]. Sludge dewatering is regarded as an effective method before handling and disposal. Sludge is a complex colloidal system in which the dispersed particles at sizes around 10−9 m are always negatively charged due to the ionization of anionic functional groups [3]. The colloidal size and electrostatic repulsion interactions make the solid–liquid separation very difficult under natural conditions. Chemical conditioning is often necessary prior to dewatering to aggregate small particles into bigger flocs
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