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All over the world there is a strong interest and also potential for biogas production fromorganic residues as well as from different crops. However, to be commercially competitive withother types of fuels, efficiency improvements of the biogas production process are needed. In this paper the results of the project BioGasOpt, Performance optimization of the Växtkraft biogas production plant and surrounding system, are summarized. The project is performed in cooperation between Mälardalen University, the biogas plant Svensk Växtkraft AB, the membrane filtration company Mercatus Engineering AB and the farm Nibble Lantbruk AB.

In the Växtkraft biogas plant organic wastes from households and restaurants are mixed and digested with crops from graze land. Four areas of importance for the performance of the plant are addressed in the BioGasOpt project: treatment of the feed material to enhance the fermentation rate, transport performance of gas and nutrients in the reactor, limitation of the ballast of organics in the water stream recirculated in the process, and use of the biogas plant residues at farms.

The results indicate a potential to increase the biogas yield from the process with up to 40 % with pre-treatment of the feed and including membrane filtration in the process. The possibilities to improve the mixing in the digester also show a significant potential for even higher biogas yields. Modelling of the biogas process for better process control is also identified as a possible way to further improve the biogas yield. However, model development taking into account what input data is possible to get at a biogas plant in operation is needed.

Further, the results from the project show that the residues from biogas production can be used as fertilizers but that the emission of N2O from the fertilised soil is dependent on the soil type and spreading technology.