| Popis: |
Sweden's environmental objectives include that Sweden's use of renewable energy in 2020 must achieve at least 50% of the total energy consumption. In order to achieve these objectives an option is to utilize renewable energy sources, such as biogas. Biogas is produced by anaerobic digestion of organic material, and can be upgraded to receive energy-rich methane gas. In the city of Karlstad food waste is collected; however there is currently no biogas plant within a suitable range. As a result the collected food waste is transported to another city. Proposals have been made for the construction of a local biogas plant, but to make the plant profitable would require higher levels of food waste than current levels. The purpose of this project is to investigate whether the methane yield at co-digestion of food waste and biological sludge from pulp and paper mills is higher compared to digestion of food waste on its own. Would the addition of biosludge result in the desired amount of produced methane gas, and profitability to make the plant viable? Digestion experiments took place in Karlstad University laboratory in a semi-continuous, wet process under thermophilic conditions with a retention time of 20 days. Co-digestion with the mixing ratio of biosludge:food waste 1:2 generated 371 to 467 mL of methane gas/g VS, and this was the mixing ratio at co-digestion which generated the highest methane yield. The city of Karlstad will not, with the mixing ratio investigated, achieve the desired methane production by co-digestion of food waste and biological sludge from pulp and paper mills. To dilute the existing amounts of food waste by a third biosludge would however be an option when larger amount of substrate is needed, by reason of the results showing that the same amount of methane can be produced but with a smaller amount of food waste. |
