Preparation of amine-modified lignin adsorbent for highly efficient and selective removal of sodium dodecyl benzene sulfonate from greywater

Greywater reuse is a promising solution to alleviate water scarcity, but surfactants in greywater can harm the environment. This study presents a novel lignin-based adsorbent, synthesized by modifying lignin with polyethyleneimine (PEI), to effectively eliminate anionic surfactants from greywater. Batch experiments showed a remarkable removal efficiency exceeding 90 % for sodium dodecyl benzene sulfonate (SDBS) within one hour at a starting concentration of 100 mg/L and an adsorbent loading of 1 g/L. The source of lignin did not significantly impact SDBS removal. Adsorbents based on organosolv lignin and lignosulfonate exhibited similar maximum adsorption capacities for SDBS (626.53 mg/g vs 629.78 mg/g), much higher than that of alkali lignin-based counterparts (520.74 mg/g). Moreover, PEI-lignin demonstrated remarkable reusability over six adsorption–desorption cycles. Notably, treatment of synthetic and real greywater indicated minimal interference from coexisting substances (NO3−, SO42−, PO43−, etc.), achieving SDBS removal rates exceeding 90 %. The primary adsorption mechanisms involved hydrogen bonding and hydrophobic interactions, supplemented by the electrostatic interactions and π-π stacking. This study presents a low-cost lignin-based material with exceptional efficiency, regeneration performance, and practical application potential for surfactant removal, while also providing a viable approach for reutilizing discarded lignin.