Fabrication of salt-tolerant chitosan-based polyelectrolyte flocculant through enhancing H-bond hydration effect for treating and recycling of highly saline dyeing wastewater

Abstract

The textile industry is required to execute water conservation and contamination management techniques owing to increasingly serious water scarcity and pollution. Herein, a novel salt-tolerant chitosan-based flocculant (CT-CTA-BGE3) with high charge density was synthesized through chitosan (CT) etherification with 2,3-epoxypropyl trimethylammonium chloride (CTA) and butyl glycidyl ether (BGE). The H-bond hydration effect between BGE segments and water molecules weakens the salt-induced polyelectrolyte effect, allowing CT-CTA-BGE3 to chains keep an extended conformation in high-salty aqueous solution and thus endowing excellent salt-tolerant properties. Meanwhile, the incorporation of CTA segments offers a high positive charge on the flocculant surface. Thus, the beneficial effect of satisfying color removal was obtained by CT-CTA-BGE3 in a highly saline system because it would render the more exposed active sites with strong positive charges along stretched polymer chains. The outstanding flocculability of CT-CTA-BGE3 (3054 mg/g) for the reactive brilliant red 2 (a widely commercial grade dye) could be obtained within 5 min (pH = 6). As expected, because the CT-CTA-BGE3 impurities can be reduced in reclaimed water via the pH-mediated hydrophilicity-hydrophobicity switch of polymer, the obtained clarified saline wastewater after flocculation can be recycled in a new dyeing bath without sacrificing fabric quality (ΔE*less than1), and over 88 % of NaCl can be regenerated for each cycle. This work develops an alternative strategy for the fabrication of salt-tolerant flocculants through enhancing H-bond hydration, revealing the promising application prospects in treating and recycling highly saline textile wastewater.