Evaluation of molecular weight, chain architectures and charge densities of various lignin-based flocculants for dye wastewater treatment.

In this work, four alkaline lignin (AL) based flocculants with distinct molecular weight, chain architectures and charge densities (denoted as AL-g-DMC, AL-g-DMC, AL-GTA and AL-GTA) were prepared from paper mill sludge, which were designed via graft copolymerization of dimethyl diallyl ammonium chloride (DMC) or etherification of 2, 3-epoxypropyl trimethyl ammonium chloride (GTA). The characteristics of the aforementioned flocculants were evaluated by a series of analysis technologies, which essentially confirmed the successful introduction of quaternary ammonium groups onto the AL. The flocculation performances of the four synthesized lignin-based polymers as the coagulant aids for PAC were investigated in disperse dye (DY) wastewater treatment, and the effects of dosages, initial pH, coexisting ions, humic acid (HA) or kaolin particles were also studied. The results indicated that branched copolymers with high molecular weight like AL-g-DMC and AL-g-DMC exerted excellent color removals and satisfactory floc properties in comparison with linear polymers with low molecular weight (AL-GTA and AL-GTA). Furthermore, AL-g-DMC and AL-g-DMC exhibited remarkable tolerance on pH alteration and coexisting ions owing to their strong bridging action.