Self-adaptive starch-based flocculant enabling irreversible stimulus-mediated phase separation: Achieving ultralow residual and simultaneous demulsification/decolorization for textile wastewater reclamation.

Treating complex wastewater containing coexisting oily emulsions and dyes via flocculation technology encounters extremely intractable challenges, such as poor simultaneous removal efficiency and high residual flocculant level, which severely impede the closed-loop reuse of reclaimed water. Herein, we fabricated a novel multifunctional starch-based flocculant (ST-GPMDES-BDAT) to address key challenges in treating oil-dye composite wastewater. ST-GPMDES-BDAT exhibits multi-stimuli-responsive phase transition behavior. The extent of reversibility of ST-GPMDES-BDAT (reversible, semi-reversible and irreversible) was regulated by varying the environmental stimulus. As a result, irreversible stimulus-mediated phase separation of resulting polymer enables ultralow residual levels of the flocculant in the filtrate. This residual level significantly outperforms conventional commercial flocculants, thereby overcoming the key bottleneck of flocculant interference in closed-loop water reuse. Leveraging the synergistic effects of charge neutralization and hydrophobic bridging, ST-GPMDES-BDAT achieves highly efficient simultaneous removal of emulsified oil and anionic dyes (exceeding 99%). It also demonstrates exceptional versatility across various oil-dye composite systems, indicating broad applicability for treating diverse complex wastewaters. Furthermore, closed-loop reusability tests further confirm that the treated wastewater can be stably used for fabric dyeing over three consecutive cycles. Notably, no significant decline in dyeing performance is observed, which validates the practical feasibility of ST-GPMDES-BDAT for sustainable wastewater treatment.