Research On Treatment Of Silk Degumming Wastewater With Modified Chitosan

Sericin, a kind of natural protein resources, is mostly discarded with the discharge of thesilk degumming wastewater. And so far, its recovery technologies still need more investigation.Chitosan flocculant which is high molecular polymer, has many common physicochemicalproperties and application areas with sericin. Therefore, it shows great significance to carry outthe hydrophilic modification on chitosan and use the products to treat the silk degummingwastewater. It not only solves the waste problem, but also recycles the available resource.2-hydroxypropyltrimethyl ammonium chloride chitosan (HACC) was prepared with goodwater solubility by the reaction between2,3-epoxypropyl trimethyl ammonium chloride (ETA)and chitosan. According to the jar test experiments, products with98%degree of substitution(DS) were obtained by controlling the reaction temperature at70oC, molar ratio of ETA tochitosan at3:1, reaction time for8hours and pH at8. It was confirmed by FTIR and NMR thatnucleophilic substitution reaction indeed happened on the-NH2of the chitosan. And HACCshowed better solubility and stronger positive property than chitosan.The evaluation of HACC for the coagulation of sericin in silk degumming waste solutionwas carried out using jar-test flocculation experiments. And the best treatment effects wereobtained on the conditions of DS at98%, HACC dosage of1g/L, pH at8, stirring speed at400rpm, settling time for3hours and temperature at30℃. In this case, removals of turbidity,protein and COD could achieve99%,86%and41%respectively. Compared with otherflocculants (aluminum salt, ferric salt and chitosan), HACC was proved to be efficient forflocculation and friendly to environment.To assess the practicability, HACC was utilized to treat the silk degumming wastewaterfrom Silk Road Co. Ltd. After flocculation, most indexes of the effluent could satisfy thethree-level drainage standard except COD, which had to decrease in the latter process. Inaddition, HACC-sericin flocs were used as finishing agent to modify properties of cotton fabric,and the results showed that hygroscopicity and antibacterial property of the fabric were greatlyimproved, meanwhile, crease resistance of the cotton was better than the original one. The flocculation kinetics and mechanism were deeper investigated. Influence of velocitygradient (G) and time on growth rate of the flocs was studied in the thesis. And the optimalprocess, according to response surface methodology, was shown as follows: G0=3281.53s-1,T0=59.03s, G1=200s-1and T1=15.18min. In this case, the growth rate of the flocs could achievethe maximum at71.87μm/min and it was helpful to form big-size flocs and settle them down sothat the treatment effects on wastewater could be ideal. Meanwhile, dynamic conditions for otherflocculation experiments were advised to control G0=3000~3400s-1, T0=48~64s, G1=0~400s-1and T1=13~17min. As to flocculation mechanism, we could conclude from the research thatflocculation mainly depended on charge neutralization and adsorption bridging mechanismplayed a subsidiary role.