Flocculation performance of papermaking sludge-based flocculants in different dye wastewater treatment: Comparison with commercial lignin and coagulants.

In this study, papermaking sludge-based flocculant (PSBF) and commercial lignin-based flocculant (LBF) have been synthesized by the same graft copolymerization procedures. The structures of alkaline lignin (AL), commercial lignin and the two flocculants were characterized by the modern analytical methods, also, the molecular weights and charge properties were analyzed. The effects of coagulant/flocculant dosages, pH conditions and coexistent dye auxiliaries on flocculation efficiencies were studied in the treatment of reactive turquoise blue (RTB) and disperse red (DR) dye wastewater. The flocculation experiments indicated that PSBF and LBF performed better in the removals of RTB and DR than commercial PAC and PAM. PSBF and LBF were insensitive to pH variation due to their strong charge neutralizing abilities and bridging effects even with the pH changing. In the existence of dye auxiliaries, PSBF and LBF could also exhibit superior decolorization efficiencies by slightly enlarging their dosages. Furthermore, PSBF and LBF had similar flocculation behaviors under all measured experimental conditions, suggesting that PSBF also had excellent flocculation performances even if it was prepared from papermaking sludge.