Modification Of Chitosan And Its Application In Dye Wastewater Treatment

Printing and dyeing wastewater is a kind of industry wastewater to be hardly treated with the characteristics of high chroma and changeful colour.The industrialized way is a combinative method with flocculation and biology.So flocculantion plays an important part in dealing with . Chitosan had good flocculating effect to many kinds of dyes because of its special molecular structure. This paper studied the synthesis of modified chitosan and its application in printing and dyeing wastewater.The main contents and conclusions are described as follows:The first work of this paper studied the factors which affected flocculating effect of chitosan,such as molecular weight,degree of deacetylation(DD). The experiment results indicated that the flocculating effect of chitosan with molecular weight 8.0×105 is better than chitosan with molecular weight 4.0×105. Degree of deacetylation(DD) has little affection to flocculating effect.Then different kinds of new modified chitosan absorbent were synthesized with chitosan(CS),acrylamide(AM),dimethyl diallyl ammonium chloride(DMDAAC),2,3-epoxy propyl-trimethyl ammonium chloride(EPTMAC) as raw materials.The products were confirmed by FTIR.The flocculating effect of modified chitosan to acid dyes was studied.The results indicated EPTMAC and chitosan with molecular weight 8.0×105 were the best raw materials.Different styles modified chitosan(HACC) were prepared using EPTMAC and chitosan with different DD and the products were confirmed by FTIR .It was studied that the factors affected flocculating effect of HACC,such as dosage of flocculant ,settlement time blending way and so on.The results showed the decolouration rate of acid dyes and reactive dyes treated with HACC obtained maximum value when the dosages of HACC were 10-20mg/L,20-40mg/L. The decolouration rate of disperse dyes was above 95% ,at the same time,the dosages of HACC were nearly 100mg/L .Blending way had important affection to flocculating effect ,so correct blending speed and blending time were necessary.Adsorption function to most kinds of dyes became steady when settlement time was 60 min.The flocculating effect can only be raised a little as blending time became longer.Flocculating effect to dyeing assistants and wasterwater from factory was studied.The results showed the decolouration rate of dyeing assistants were above 80%.Dealing with wasterwater from factory with HACC and PAC together ,it not only reduced the dosage of modified chitosan,but also added the decolouration rate to 90% and added the reduced rate of CODcr to 92%.