Utilisation of wheat- and maize straw in biogas plants

In Austria, only 50 % of the 2 million tons of wheat-straw produced per year are commercially exploited. This raw material attracts more and more attention in the last few years as one of the possible energy sources for the future. By new decomposition procedures straw can also become a potential substrate for biogas production. For this purpose, the Upper Austrian University of Applied Sciences in Wels owns a steam explosion pilot plant, which allows pre-treatment of various substrates. Initial experiments with pre-treated wheat- and maize straw show a significant increase in yield of biogas. Experiments according to VDI 4630 with untreated wheat- and maize straw showed that these substrates are not appropriate for usage in biogas plants if compared to maize silage. However, if the straw is pre-treated by means of steam explosion the yield of biogas can be increased further by at least 25 %. The pre-treatment with steam explosion causes a significant increase in biogas yield. Admittedly, these results – as well as those mentioned in the present literature – come from batch experiments according to VDI 4630. That’s why further investigation with continuously working facilities have to be done. In doing so, special attention has to be paid to the carbon/nitrogen ratio, which is too high in straw. If a continuous co-fermentation using substrates with a higher nitrogen content will be carried out, one could expect a further increase in biogas yield.