(573e) Anaerobic Digestion of Different Type of Wastepaper and Cardboard: Effect of Enzymatic Pretreatment

Anaerobic digestion (AD) is a biological waste management technology able to treatment and valorise different organic material. The main product of the process is biogas that can be used for energy generation. Boosted by new regulations, the raise in the market share of renewable energy has created the need for identifying alternative feedstock for the AD process and aiming to replace more traditional materials such as energy crops. The list with the potential feedstock for AD systems includes the by-products from the paper industry, however, the biomethanation of these materials is usually low. The AD process can be divided into four different stages including hydrolysis, acidogenesis, acetogenesis and finally methanogenesis. For many substrates, the rate-limiting step of AD is the first one, hydrolysis. This step seems to be the major controller of the whole process. During hydrolysis, complex macromolecules are breaking down into their monomers by extracellular enzymes which are excreted by the hydrolytic microorganisms.

In the present study, six different types of wastepaper products, including toilet paper, office paper, cardboard, glossy magazine, newspaper, and kitchen towel were chosen to be examined for their biomethane potential with and without a prior enzymatic pretreatment stage. Obviously, paper is mainly cellulose and due to that, the enzymatic pretreatment was conducted with the application of a commercially available product of cellulase (A868 Novozymes, Denmark). Subsequently, the biomethanation of the feedstock was examined in a biomethane potential test (BMP) experiment. Based on the results of this experiment, the application of enzymes offers the potential to improve the biodegradability of the examined paper products. The highest improvement in gas yield was found when the enzymes treated the glossy magazine paper (47%) while the lowest enhancement was reported for newspapers (6%). It is also worth mentioning that the enzymatic pretreatment not only seemed to increase the cumulative methane production but it can also effect the rate of the overall process. According to the results of this experiment, for most of the examined substrates, the enzymatic pretreatment seemed to minimize the lag phase and to increase the gas production during the first days of the experiment. This is an interesting outcome as it shows that the enzymatic pretreatment can be used not only to enhance the final gas yield but also to decrease the required digestion time, which would be significantly important, especially for difficult to digest substrates that usually require very long retention times in order to be efficiently digested.