Results and Discussion

         To compare the digestabilities of cellulase on wastepaper, office paper, newsprint, cardboard, and paper towel were treated with cellulases from A. niger, T. viride, and T. reesei. The DNS assay showed that a significant amount of reducing sugars were produced in these reactions (Figure 1), indicating that the cellulases did degrade the wastepapers examined into reducing sugars. This was also confirmed by the weight loss of the wastepaper used in the reaction. Among them, the paper towel reactions always released the highest amount of reducing sugars, and the cellulase from T. reesei showed the highest wastepaper degradation activity (Figure 1). 

        Celluclast® 1.5L, a commercial cellulase from T. reesei, was then used with or without cellobiase (Novozyme® 188) for the project. Cellobiase alone did not release any glucose from paper towel, but increased the conversion of cellulose from paper towel into glucose by 30% when used together with Celluclast® 1.5L (Figure 2A). 

        Three temperatures (25ºC, 37ºC, and 50ºC) were then tested for their effects on reducing sugar production. Reactions at 37ºC were more than two times faster for reducing sugar production than those at 25ºC while the differences between the reactions at 37ºC and 50ºC were minimal. The production of reducing sugar continued until most of the paper towels were digested. The first 12-hour incubation yielded about 50% conversion from cellulose to reducing sugars. Then the production of reducing sugar slowed down. At 48 hours, almost 100% of the cellulose in paper towel had been degraded (Figure 2B). 

        TLC was employed to further analyze the products of the reactions (Figure 3). Both filter paper and paper towel produced large amounts of glucose. The addition of Novozyme® 188 removed the cellobiose in the reactions and visibly increased glucose levels, indicating that the cellobiase converted cellobiose into glucose. 

        Paper towels from different sources were further examined for the conversion to glucose by Celluclast® 1.5L and Novozyme® 188. They all showed degradation by the enzymes comparable to filter paper (which is almost 100% cellulose), while office paper, newsprint, and cardboard were less digestible (Figure 4). Again, the end products after digestion by Celluclast® 1.5L and Novozyme® 188 were mainly glucose (Figure 5).

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