A dual crosslinked biodegradable zwitterionic chitosan–lignosulfonate derived aerogel for microbial decontamination of wastewater

Abstract

In this work, a set of novel chitosan-derived zwitterionic aerogels was synthesized via graft polymerization of acrylamide (Am) and 2-(N-3-sulfopropyl-N′,N′-dimethylammonium)ethyl methacrylate (DMAPS). The resulting copolymer aerogel underwent chemical crosslinking via the covalent bonds formed with N′,N′-methylenebisacrylamide (MBA), and ionic crosslinking through the electrostatic interactions between the cationic chitosan-grafted poly(DMAPS) backbone and the anionic groups of lignosulfonic acid (LSA). The morphological examination of the different aerogels by scanning electron microscopy suggested the formation of a fibrous network with varying degrees of porosity, depending on the type and amount of crosslinkers used. FT-IR, SEM, EDAX, TGA, and XRD techniques were employed to confirm the aerogel synthesis. The antimicrobial potency of the as-prepared aerogels was evaluated primarily against E. coli. This strain was selected as a representative Gram-negative model organism due to its high prevalence in wastewater and its relevance to environmental contamination. Preliminary investigation of the tested aerogels demonstrated that both CSH1 and CSH2 aerogels were efficient in eradicating E. coli from nutrient broth media at 2000 ppm after 4 h. In addition to growth-inhibition studies, the interaction between the aerogels and E. coli cells was examined using transmission electron microscopy and zeta potential measurements. Furthermore, the effects of aerogel dosage and contact time on antibacterial performance were systematically assessed. The results indicated that contact time is a critical factor for aerogel potency against E. coli. A 4 h treatment outperformed both 2 and 24 h exposures. CSH2 was selected for further evaluation using a real wastewater sample collected from a local drain. In field trials, CSH2 reduced total coliforms, fecal coliforms, Salmonella, and Shigella counts to levels deemed safe by WHO guidelines, and improved wastewater physicochemical properties. Overall, the CSH2 polymer offers a viable approach for mitigating pathogen risks in wastewater for sustainable agricultural management.