Biogas Production from Enzymatically Pretreated Agricultural and Forest Raw Materials

Biogas is a methane and carbon dioxide containing gas, produced by biomass degraded by microorganisms in anaerobic environment. Forest and agricultural residues contains higher proportions of cellulose and hemicellulose than substrates used in biogas production today, which makes them highly attractive for biogas production. However, the biogas yield of these materials is low due to the complex crystalline structure of the cell wall matrix. By separating the cell wall matrix and reduce the carbohydrate chain length by performing enzymatic pretreatments, such as partial enzymatic hydrolysis. The biogas yield is expected to be high since improvement in biogas production has been shown when commercial enzymes are used in the pretreatment of cellulose rich, complex, raw materials. The goal of this project is to evaluate the efficiency of enzymatic hydrolysis and compare the biogas yield of the following untreated and pretreated materials: wheat straw, spruce, pine and birch. In order to investigate the ability of enzymes to release sugars, enzymatic hydrolysis was performed. Since some of the materials to be investigated were pretreated as slurries, it was crucial to investigate how the slurry state of the material is affecting the overall hydrolysis of the material as well. Also, the materials were prehydrolyzed prior to the reactor experiments in order to study the effect on the biogas yield. In the reactor experiments, the ability of each pretreated materials to produce biogas was investigated. In addition, detoxifying agents was added to the reactor experiments in order to investigate if detoxification was necessary in order to improve the biogas production.The results showed that hydrolysis of pretreated wheat straw released the highest amount of sugars, whereas hydrolysis of pretreated birch improved the amount of released sugars most, compared to untreated birch. Pretreated birch produced the highest amount of methane during the reactor experiments, whereas pretreated pine improved the production of biogas, compared to untreated, the most. Detoxification only improves the methane potential when laccase is added to toughtreated spruce and pine. Prehydrolysis did not improve the biogas production except for birch, for which the methane potential was increased by 6-7%. Birch is the most efficient pretreated material to be hydrolyzed, compared to the untreated material, and the methane potential of pretreated birch is the highest value achieved by all the materials used. The efficiency might be explained by the favorable composition of hardwoods which makes it easier to degrade than spruce and pine. The large improvement of pine during the reactor experiments is probably time dependent since the enzymes might require a lot of time in order to efficiently hydrolyze pine.Validerat; 20141111 (global_studentproject_submitter