Evaluation of renewable pH-responsive starch-based flocculant on treating and recycling of highly saline textile effluents.

Herein, we report a novel renewable pH-responsive starch-based flocculant (CIAT-ST) via etherifying 2-chloro-4,6-isopropylamino-[1,3,5]-triazine (CIAT) onto the starch backbones for decontamination and reuse of highly saline effluents. The obtained CIAT-ST shows a unique pH-sensibility and reversibility in response to a subtle pH change due to a pH-controllable surface charge density of polymer chains. The level of residual CIAT-ST in the solution can be facilely monitored by using UV-vis detection. The dye flocculation performance of CIAT-ST was evaluated by using a batch experiment. The results exhibited that the dye removal was highly dependent on the solution pH (optimal pH was 2), the flocculation equilibrium can be achieved within 5 min, and the maximum flocculation capacity of CIAT-ST for K-2BP and KN-B5 were calculated to be 2452.6 ± 23.9 and 792.7 ± 14.1 mg/g, respectively. The multiple flocculation mechanisms, including charge neutralization, bridging and charge patching, may participate in the flocculation process. Adjustment in pH-mediated hydrophilicity-hydrophobicity switch of flocculant facilitates readily recovery and then sequentially reused three times while retaining satisfying flocculation efficiency. A significant contribution was also confirmed that the highly saline effluents after flocculation and sedimentation were reused in three successive dyeing processes without sacrificing fabric quality (ΔE* < 1) due to relatively low polymer residuals, and the efficiency of salt reuse for consecutive regeneration processes could be achieved above 85%. The present work could provide alternative thoughts for the reutilization of spent flocculant and clarified saline wastewater, which is also an efficient and sustainable strategy for textile wastewater management.

Advanced treatment and reuse of dye wastewater using thermo-irreversible on/off switch starch with disruption of dissolution/precipitation dynamic equilibrium.

The development of irreversible on/off switching materials is a potential strategy for unidirectional capture and encapsulation of pollutants, preventing the pollutant leakage problem resulting from the reversible dissolution of flocculants. Herein, a thermo-irreversible on/off switch starch (TISS) is prepared through modifying starch by etherification grafting glycidyl phenyl ether and 2,4-bis(dimethylamino)-6-chloro-[1,3,5]-triazine. It breaks the dissolution/precipitation dynamic equilibrium across heating-cooling cycles by thermal-induced irreversible coil-to-globule self-assembly of polymer chains, resulting in a 50-fold decrease in polymer solubility. Particularly, TISS shows a superior double-locking effect on pollutants and flocculants through its unique irreversible conformation memory capability, leading to a high-quality reuse water. 99.9 % of reactive brilliant red dye and 97.9 % of TISS remain fixed within sludge flocs even after prolonged immersion in cold water at 24 °C for 60 days. Furthermore, direct recycling and reuse of dye-bath energy can be realized through the isothermal flocculation and dyeing method, showing a 75 % decrease in energy consumption after three cycles compared to traditional dyeing techniques. This work presents a novel approach to constructing an irreversible pollutant delivery system using thermo-irreversible on/off switch starch, addressing the problems of high energy dissipation and water quality fluctuations during wastewater treatment.