Evaluating digestate processing methods at Linköping biogas plant : A resource efficient perspective

Production of biogas is one of several alternatives to meet sustainable energy solutions and waste management. However, managing the by-product (digestate) can be problematic with its high handling costs. Digestate from wet co-digestion biogas plants contains large volumes of water, causing high transportation costs and low concentration of the valuable nutrients. An alternative to try and reduce the associated costs is by processing the digestate. Processing the digestate for volume reduction allow for more economic and resource efficient ways of handling the product. This master thesis was performed on an initiative from Tekniska verken AB and address digestate handling from Linköping biogas plant, a large co-digestion biogas plant in Sweden. The project aimed to find a feasible, more resource efficient management of their digestate by looking at digestate processing alternatives.The approach systematically evaluated a large number of processing techniques by both literature and communication with TvAB or experts. A selection of techniques were further evaluated were studies in laboratory and a market analysis on digestate provided complementary information, aiding the economical evaluation. Results suggest that processing by centrifuge is a viable, economic option when digestate management is costly and a liquid fraction can be recirculated in the process. It has the potential to significantly reducing digestate management costs. Other processing alternatives may be beneficial if transportation distance can be greatly reduced and/or synergies can be found, but the findings in this project suggest that only treatment with centrifuge is of interest. The results are subject to a number of conditions (such as size of the plant) and assumptions (such as recirculation of a liquid fraction) and therefore need individual adaption to be applicable at any specific plant. Conclusive remarks are that although site specific conditions affect the choice of processing, a project such as this may help reducing the necessary time spent on evaluation. Both research process and results may provide valuable findings for similar evaluations in any industry