| During the chemical coagulation process for treating dyeing and printing wastewater, coagulation efficiency is mainly dependent on the coagulant used. At present, cationic organic polymer has received wide attention. Because its advantages for treating dyeing and printing wastewater:high color removal, wide application, low chemical cost and low sludge, etc. Among them, cationic quaternary ammonium polymer is one floccuant that has great development foreground, and so systematic study on its coagulation is necessary. Synthesizing a number of references and literature, epichlorohydrin-dimethylamine ploymer (EPI-DMA) was prepared by the polycondensation of epichlorohydrin and dimethylamine with amines as the modifying agent. The flocculation efficiency of EPI-DMA for various dyes was investigated, and the flocculation performance and mechanism of EPI-DMA with different characteristics were clearly studied in the treatment of different pollutants. Through on-line monitoring the flocculation dynamic process of EPI-DMA, floc growth process, breakage resistance capability of floc and the regrowth ability of broken floc were studied. In order to improve the decolorization efficiency, a series of composite flocculants polyaluminum chloride-epichlorohydrin-dimethylamine ploymer (PAC-EPI-DMA) with different intrinsic viscosity (?), organic mass fraction (P) of EPI-DMA and basicity (B) of PAC, were prepared. The effect of?, P and B on the flocculation efficiency, flocculation mechanism, floc growth process, breakage resistance capability of floe, and the regrowth ability of broken floc were investigated. The improved flocculation efficiency of the composite flocculant was revealed, based on the combination organic with inorganic component, which provides theoretical guidance for the development and application of composite flocculant.The main conclusions are as follows:1. Infrared spectral analysis technology was used to investigate the molecular structure of epichlorohydrin monomer and EPI-DMA. The results confirmed the formation of quaternary ammonium. Based on the IR analysis of flocculants, dyes and flocs, the results showed that quaternary ammonium R4N+ of EPI-DMA reacted with sulfonic group-SO3- of dye molecule. TEM was used to study the flocculant morphology. The results showed that the appearance of the composite flocculant PAC-EPI-DMA was denser branch network structure, indicating the interaction between PAC and EPI-DMA. The zeta potential of EPI-DMA and PAC-EPI-DMA was determined using a Zetasizer3000HSA analyzer. The results showed that EPI-DMA with an intermediate?had the highest surface charge. The zeta potential of PAC-EPI-DMA was higher than that of EPI-DMA, and increased with the increse of P value.2. The effect of pH and inorganic salt on the flocculation efficiency of EPI-DMA and PAC-EPI-DMA was studied for the removal of various dyes. The experimental results showed that high flocculation efficiency of EPI-DMA could be achieved within a wide pH range, but was influenced by the inorganic salt in treated water. PAC-EPI-DMA also could obtain high flocculation efficiency within a wide pH range, especially under alkaline condition. However, the negative effect of ionic strength on the decolorization of PAC-EPI-DMA was exacerbated due to the exsit of the inorganic content.3. The flocculation efficiency of EPI-DMA with different?and cationicity (?) was stuied in the treatment of various simulation dyeing wastewater, and the variation of zeta potential was also investigated using a JS94F micro-electrophoresis analyzer, which explained the flocculation mechanism. In the treatment of water-soluble dye, EPI-DMA interacted first with dye molecules by electrostatic, hydrophobic as well as hydrogen bonding, after then, adsorption bridging or charge neutralization of EPI-DMA played a role for the decolorization. The adsorption bridging and charge neutralization of EPI-DMA was dependent on its?and?, respectively. In the treatment of reactive dye, higher?and?of EPI-DMA was more effictive based on its stronger adsorption bridging and charge neutralization ability, and adsorption bridge was dominant in the prophase of flocculation process. In the treatment of direct dye, higher?and?of EPI-DMA was more effictive based on its stronger adsorption bridging ability. In the treatment of acid dye, low?and?of EPI-DMA could obtain high color removal based on its adsorption bridging ability. In the treatment of disperse dye, higher?and?of EPI-DMA was more effictive based on its stronger adsorption bridging ability.4. The effect of?, P and B on the flocculation pefromance of PAC-EPI-DMA was investigated for the removal of reactive dye by jar test. The results showed that the decolorization of PAC-EPI-DMA was obviously superior to that of EPI-DMA. The?and P value were the key factors affecting the flocculation pefromance of PAC-EPI-DMA. PAC-EPI-DMA (?=2400 mPa·s) exhibited the highest decolorization. For water-soluble dye, PAC-EPI-DMA interacted first with dye molecules by electrostatic interaction and hydrogen bonding, after then, adsorption bridging and charge neutralization ability played an important role in removing dye. Adsorption bridging ability of PAC-EPI-DMA was stronger with the increase of P.5. PDA2000 laser scatter analyzer was used to on-line monitor the floc growth process of EPI-DMA and PAC-EPI-DMA, and floc aggregation parameters were calculated and analyzed. In the treatment of reactive, disperse, acid dyes, larger average floc size, faster floc growth velocity and sedimentation velocity, and smaller floc variance were achieved by higher?of EPI-DMA. In the treatment of direct dye, low?of EPI-DMA produced larger flocs with faster growth and sedimentation velocity, and smaller floc variance. The floc growth and sedimentation velocity, and average floc size of PAC-EPI-DMA were much larger than those of EPI-DMA. The effct of P and B on the floc growth velocity and average floc size was much more significant than that of?. Faster floc growth and sedimentation velocity, and larger average floc size were achieved by PAC-EPI-DMA (?=3200 mPa·s, P=10%, B= 1.5).6. PDA2000 laser scatter analyzer was used to investigate the breakage resistance capability of floc and the regrowth ability of broken floc of EPI-DMA and PAC-EPI-DMA. In the treatment of reactive and direct dyes, higher?of EPI-DMA could improve floc strength and regrowth ability. In the treatment of disperse dye, stronger floc strength and regrowth ability was achieved by EPI-DMA (?= 3200 mPa·s). In the treatment of acid dye, although high?of EPI-DMA improved the floc strength, foc regrowth ability was decreased slightly. For PAC-EPI-DMA, higher?and B could increase floc strength and regrowth ability in a certain extent.The above research investigeted the flocculation behavior and dynamics process of EPI-DMA and PAC-EPI-DMA in the treatment of dyes, indicating that both of them are highly efficient floccualnt for the treatment of dyeing wastewater, and the composite flocculant was more efficient. This research provides theoretical basis for the practical application. |
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