The improvement of flocculation performance of organic polymer flocculants via regulation of their branched structure and block structure in removal of soluble dyes from wastewater

The efficient treatment of dyeing wastewater, a typical industrial wastewater, has aroused widespread attention. Flocculation was a vital pretreatment in dyeing wastewater treatment as it removed colloidal particles, reduced organic loading and improved the treatment efficiency of subsequent processes. However, the soluble dyes were rarely removed by traditional flocculation. In this study, the removal efficiencies of soluble dyes by flocculation were enhanced via synthesizing organic polymer flocculants with branched structure and block structure (PADS). The block length on PADS was regulated by the molecular weight of the template. PADS owned the high molecular weight, rich functional groups and outstanding flocculation performance. The largest removal rates of soluble Congo red, chrome black T and toluidine blue, 90.16 %, 88.41 % and 80.19 %, were achieved. The flocculation mechanisms for dyeing wastewater treatment were emphasized via Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) calculations and molecular dynamics simulations. Charge neutralization and the interaction between PADS and dyes mainly contributed to dye removal. The block structure of PADS strengthened these two processes. The branched structure of PADS facilitated bridging and promoted the formation of large and compact flocs, improving solid-liquid separation of dyes. PADS were potential candidates for improving dye removal in the pretreatment of dyeing wastewater.