Enhanced dewaterability of sewage sludge by grafted cationic lignin-based flocculants

Shiqin Wang; Hongbo Chen

doi:10.1016/j.scitotenv.2023.166958

Enhanced dewaterability of sewage sludge by grafted cationic lignin-based flocculants

Sci Total Environ. 2023 Dec 10:903:166958. doi: 10.1016/j.scitotenv.2023.166958. Epub 2023 Sep 9.

Authors

Shiqin Wang¹, Hongbo Chen²

Affiliations

¹ College of Environment and Resources, Xiangtan University, Xiangtan 411105, China.
² College of Environment and Resources, Xiangtan University, Xiangtan 411105, China. Electronic address: chenhongbo@hnu.edu.cn.

PMID: 37696410
DOI: 10.1016/j.scitotenv.2023.166958

Abstract

Lignin-based flocculants are widely used for wastewater purification, but their application in sludge dewatering has not yet been documented. In this study, a novel cationic lignin-based flocculant named LS-g-CPA was prepared by grafting cationic polyacrylamide (CPA) synthesized from methacryloyloxy ethyltrimethyl ammonium chloride (DMC) and acrylamide (AM) onto sodium lignosulfonate (LS), and its roles and underlying mechanisms in sludge conditioning were investigated. The results showed that LS-g-CPA effectively improved the dewaterability of sludge, reducing the filtration resistance and filter cake moisture content of sludge from 0.61 ± 0.05 × 10¹² m/kg to 0.14 ± 0.02 × 10¹² m/kg and 85.64 ± 0.25 % to 76.84 ± 0.41 %, respectively. The dewatering performance of LS-g-CPA was positively correlated with the DMC/AM ratio. The quaternary ammonium groups brought by DMC disrupted the reticular structure of extracellular polymeric substances, exposing hydrophobic residues and releasing bound water. Nevertheless, the key to LS-g-CPA for improving sludge dewatering lies more in the amphoteric flocculant properties that enhance sludge flocculation and the octopus-type structure that provides good drainage channels. This study reveals that lignin-based flocculants are effective in improving the dewaterability of sludge, which provides direct evidence for their application in sludge dewatering.

Keywords: Acrylamide; Grafted cationic lignin-based flocculants; Methacryloyloxyethyl trimethyl ammonium chloride; Quaternary ammonium groups; Sludge dewaterability.