Study On The Immobilization Of Enzyme By Modified Chitosan Microspheres And Its Treatment Of Dissolved And Colloidal Substances In White Water

In this dissertation, the immobilization of pectinase, lipase and double-enzyme on modified chitosan microspheres were studied, and the high activity of immobilized enzyme was achieved. Then the preparation conditions and characteristics of the immobilized enzyme were also studied, and the effect of treatment on the dissolved and colloidal substances in white water with immobilized enzyme has also been studied. This research provides a highly efficient and green bio-route for white water treatment in paper mill.Four immobilization methods were tested firstly for the immobilization of pectinase on chitosan microspheres modified with glutaraldehyde and EDC. Results showed that the highest activity and protein content of immobilized pectinase were achieved by using the cross-linking method, in which pectinase was immobilized to the amino groups of chitosan by cross-linking with glutaraldehyde, followed by the immobilization of more pectinase molecules with its EDC-activated hydroxyl groups. With this method, the activity, protein content and specific activity of the pectinase reached 72.6U/g, 180.6μg/g and 402 U/mg, repectively. After immobilization, the thermal stability, pH stability and storage stability of pectinase were significantly improved. After operating repeatedly for 7 batches, the level of its activity remained high, maintaining above 60% of its original activity, indicating a makedly improved operational stability. In addition, the immobilization of lipase on chitosan microspheres modified with glutaraldehyde and EDC was studied. Among the four immobilization methods, the following method showed to be the best for achieving the highest activity and protein content: lipase was first immobilized through its EDC activated hydroxyl groups and then more lipase molecules was linked to the amino groups of chitosan by cross-linking with glutaraldehyde. Its activity reached 64.6U/g, protein content was 253.7μg/g, and specific activity could reach 254.6U/mg. Besides, evident improvements in the thermal stability, pH stability, storage stability and operational stability of lipase were also observed. After operating repeatedly for 5 batches, the level of its activity remained high, maintaining above 70% of its original activity. At last, immobilization of two kinds of enzymes on macroporous resin coated chitosan was explored and their synergy effects on controlling the anionic trash and resin deposits in white water were analyzed for the first time. The results showed that the highest activities of immobilized double-enzyme (pectinase-lipase) were achieved by immobilization of double-enzyme on the HP2MGL macroporous resin coated chitosan, being of 84.3U/g and 87.3U/g, respectively.The effect of treatment on the harmful components in white water with immobilized enzyme has also been studied, it was found that the anionic trash and resin deposits in white water could be removed effectly by immobilized enzyme. Firstly, the effect of catalytic decomposition of PGA by immobilized pectinase was very significant, after 20min reaction in the best conditions, the cationic demand of PGA reduced by 87%. In addition, the immobilized pectinase showed significant effect on controlling the anionic trash in white water and exhibited good reuse performance. The cationic demand of white water could be reduced 37% even after 5 times reuse of the immobilized pectinase. Secondly, the immobilized lipase was used for controlling the resin deposits in white water. Due to the good hydrolysis-catalytical perfomence of this immobilized biocatalyst, the removal rate of resin deposits reached 66.8%; the particle average size of resin deposits in white water decreased from 552μm to 276μm; and the turbidity of white water decreased from 101NTU to 80.8NTU. At last, it was also found that the effect of removal the anionic trash and resin deposits in white water by immobilized double-enzyme was very significant, with the removal rate of resin deposits being of 74.3%. And the particle average size of resin deposits in white water decreased from 552μm to 151μm; the turbidity of white water decreased from 101NTU to 75.1NTU; and the cationic demand decreased from 4.29meq/L to 1.81meq/L.