Development of characterization methods for lignocellulosic biogas substrates

University essay from Lunds universitet/Kemiteknik (CI)

Abstract: As the need of environmentally friendly alternatives to fossil fuels is growing bigger, so is the need for knowledge and research around possible new raw materials that could serve that pur-pose. One discussed product is biogas. Since biogas can be produced from not only food waste and wastewater residue, but from any substrate that contains fats, proteins and/or car-bohydrates, with the help of degrading microorganisms, there is a new interest for using ligno-cellulosic biomass such as straw as a raw material. The biggest issue with using lignocellulose is its low bioaccessibility to enzymes because of its crystalline structure, where cellulose poly-mers are stabilized by hemicellulose and lignin polymers. Furthermore, straw contains a lot of trapped air which causes it to float on the liquid surface in the fermenters, minimizing the con-tact surface area towards the degrading enzymes. Different mechanical pre-treatment methods for the straw aim to solve that problem. In order to facilitate the optimization of these pre-treatment methods, there is a need for a more time efficient characterization method than the biochemical methane potential tests that are usually run for 30-50 days, to determine the me-thane yield. This master thesis investigated whether enzymatic hydrolysis for 3 days of differ-ent straw samples would show the same tendency in how much cellulose and hemicellulose that were degraded to soluble sugars, as in how high the methane productivity of those sam-ples would be. Wheat, rye, barley and canola straw as well as granulated wheat straw (achieved by extrusion) were analysed. The results showed a correlation between the methane yield and the xylan/xylose digestibility indicating that an increase in density, particle size and total surface area also generated an increase in cumulative methane yield and digestibility of xylan to xylose. To investigate this characterization method further, extensive statistical analy-sis should be performed on more samples.

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