Preliminary Research On Flocculation Removal Law And Mechanism Of Direct Dye Wastewater

In this paper, The effect of different flocculant dosages on the flocculation decolorization efficiency of simulated direct dyeing wastewater with single component was studied by using beaker flocculation method, and the flocculation mechanism has been discussed.By using four kinds of inorganic coagulants (PAC、PFS、FS and AS), cationic homopolymers(PDM、PDAC and PDMC) and cationic copolymers[P(AM-DAC)], the jar tests were used to treat two kinds of direct dye simulated wastewater with single component. The influences of flocculant dosages on color removal rate, CODcr value of supernate and zeta potential of the suspended particles were also tested. The effects of the the kind of flocculant, the pH value of wastewater,the intrinsic viscosity and the cationicity of polyquaternium, the settling time and the dye structure on the color removal rate were analyzed. The flocculation removal mechanism was analyzed through zeta potential and quantity of electricity.The results showed that under each best coagulation condition, the maximum decolorization rate were respectively97%,94%,92%and89%in treating direct ruby dye wastewater. CODcr value of supernatant samples were respectively13.2,13.8,14.3mg/Land18.7mg/L. The maximum decolorization rate were respectively96%,94%,88%and82%in treating direct navy blue dye wastewater. CODcr value of supernatant samples were respectively13.2,13.8,14.3mg/L and18.7mg/L.Their optimum pH value range were respectively8-11,7-9,10-11,6-9.For homopolymer,decolorization rate increased first and then decreased with increase of the flocculant dosages. Zeta potential increased in the flocculant dosages. When the intrinsic viscosity of PDM, PDAC and PDMC were respectively0.57-2.98dL/g,0.84-6.88dL/g dL/g and1.50-6.16dL/g,the effect of the intrinsic viscosity on the maximum decolorization rate was not obvious. When the settling time was2hours, the maximum decolorization rate did not go over85%and CODcr value of supernatant samples were little changed. When the settling time was24hours, the maximum decolorization rate increased significantly and the maximum decolorization rate were all more than95%for homoplymer. CODcr value of supernatant samples was about14mg/L.Zeta potential analysis showed that zeta potential of the suspended particles was negative in the optimal dosage. Charge neutralization played a important role.Three kinds of homopolymers quantity of electricity indicated that approximate quantity of electricity accounted for respectively66%and86%of direct ruby dye and navy blue dye. When the cationicity of P(AM-DAC) was30%and50%,the maximum decolorization rate increased with the increase of intrinsic viscosity. However when the cationicity was70%, the maximum decolorization rate of P(AM-DAC) with medium intrinsic viscosity was worse. When the intrinsic viscosity was all about7.5dL/g,cationicity of P(AM-DAC) was higher, charge neutralization capacity was stronger and the best decolorization efficiencies was higher. Quantity of electricity showed that approximate quantity of electricity was provided by homoplymers and copolymers. Charge neutralization played a important role.Through the researches, The influence laws of flocculation dosage, the intrinsic viscosity, the cationicity,the structure of dye and the settling time on the color removal efficiency were gained,which have offered a feasible foundation for research of multicomponent wastewater.