3.2 Flocculation and decolorization

3.2 Flocculation and decolorization performance of PET-DDF on the simulated printing and dyeing wastewater3.2.1 Influence of the flocculant dosage on flocculation and decolorization performanceSome researchers treated the high concentration printing and dyeing wastewater by adopting the long-chain linear polymeric materials to increase the adsorption sites and to enhance the net trapping and adsorption bridging ability of flocculants. However, the excessive dosage easily produce curling agglomerates, which will result in the weakened and limited flocculation ability [22,28-29]. The PET-DDF material prepared in this work, with the rigid and not prone to agglomeration and curling, can still expose many adsorption sites through increasing the dosing amount to a certain degree, resulting in the excellent decolorization efficiency for high dye concentrations.The influence of flocculant dosage on the decolorization performance is shown in Fig. 4(a) and Fig. 5. With the increase of PET-DDF dosage, the percentage removal of anionic dyes increases until the maximum decolorization rate is reached and gradually stabilized for a period and then decreases. In the range of 150 mg·L-1-300 mg·L-1 PET-DDF dosage, the high decolorization rate can be maintained. The high decolorization rate of >80% can be obtained for printing and dyeing wastewater with the initial concentration within 20-100 mol·L-1, which broadens the scope of engineering applications. The maximum decolorization rates of CR, RBY K-6G and AO 9 are respectively 91.47%, 83.55% and 96.79%. The turbidities of supernatant are respectively 3.54, 4.97 and 3.42 NTU. The chromaticities are respectively 8, 16 and 8 times.