Synthesis And Application Of The Lignin-based Decolorizing Flocculant

Lignin is a byproduct of wood hydrolyzing and paper making industry. However, as aresult of not full utilization, it becomes the main polluting resource, not only leading to severepollution but also resource waste. Lignin is a natural macromolecular compound. And itsconfiguration space, molecular weight and functional group of flocculation performance canbe modified by oxidizing, sulfomethylating, esterifying and acylating, which result a betterflocculant of high efficient and stable performance of flocculation.The lignin-based flocculant（LDH） was synthesized with lignin, dicyandiamide andformaldehyde as main raw material. The orthogonal test were designed to find out the optimalconditions, which including the dosage of lignin, dicyandiamide, formaldehyde andammonium chloride as well as the reaction time and temperature. The physical and chemicalparameters of LDH were determined and its structure was characterized using FTIR and TGA.Application of LDH in the decolorizing of several dye model wastewater and the dewateringof activated sludge were investigated.The experimental results show that: The optimal synthesis conditions of LDH are lignin20g, dicyandiamide40g, formaldehyde60mL, ammonium chloride20g, reaction temperature80℃and reaction time2h. Some parameters of LDH are as follows: the shear viscosity is0.531Pa·s, the intrinsic viscosity number is5.583mL·g-1. LDH is a cationic organicmacromolecular flocculant and its electric density is4.663mmol·g-1. Through FTIR and TGAcharacterization, LDH is a copolymer composed with lignin, dicyandiamide, formaldehydeand ammonium chloride. The coagulation results show that high removal efficiency could beobtained when the solution pH is adjusted to2and250mg·L^-1of LDH is used. The dosage ofLDH can be reduced to150mg·L^-1when combined with300mg·L^-1of PAFC, thedecolorization efficiency of Acid Scarlet, Methyl Orange, Reactive Red and ReactiveBrilliant Blue solution are84.1%,91.3%,88.7%and94.3%, and CODCrremoval efficiencyare75.5%,77.0%,73.2%and77.6%, respectively. The use of LDH as flocculant provides aneffective advanced treatment method for the dye-stuff wastewater. Applying LDH to theactivated sludge show that the average sedimentation speed increased from original3.53to 4.33mL·min-1, which is1.23times as the original sedimentation speed. LDH can obviouslyspeed up the sedimentation rate and decrease moisture content of the sludge.