Biogas production from maize and dairy cattle manure - Influence of biomass composition on the methane yield

There is an increasing world wide demand for energy crops and animal manures for biogas production. To meet these demands, this research project aimed at optimising anaerobic digestion of maize and dairy cattle manures. Methane production was measured for 60 days in 11 eudiometer batch digesters at 38 degrees C. Manure received from dairy cows with medium milk yield that were fed a well balanced diet produced the highest specific methane yield of 166.3 Nl CH4 kg VS- 1. Thirteen early to late ripening maize varieties were grown on several locations in Austria. Late ripening varieties produced more biomass than medium or early ripening varieties. On fertile locations in Austria more than 30 Mg VS ha(-1) can be produced. The methane yield declined as the crop approaches full ripeness. With late ripening maize varieties, yields ranged between 312 and 365 Nl CH4 kg VS-1 (milk ripeness) and 268-286 NI CH4 kg VS-1 (full ripeness). Silaging increased the methane yield by about 25% compared to green, non-conserved maize. Maize (Zea mays L.) is optimally harvested, when the product from specific methane yield and VS yield per hectare reaches a maximum. With early to medium ripening varieties (FAO 240-390), the optimum harvesting time is at the "end of wax ripeness". Late ripening varieties (FAO ca. 600) may be harvested later, towards "full ripeness". Maximum methane yield per hectare from late ripening maize varieties ranged between 7 100 and 9000 Nm(3) CH4 ha(-1). Early and medium ripening varieties yielded 5300-8500 Nm(3) CH(4)ha(-1) when grown in favourable regions. The highest methane yield per hectare was achieved from digestion of whole maize crops. Digestion of corns only or of corn cob mix resulted in a reduction in methane yield per hectare of 70 and 43%, respectively. From the digestion experiments a multiple linear regression equation, the Methane Energy Value Model, was derived that estimates methane production from the composition of maize. It is a helpful tool to optimise biogas production from energy crops. The Methane Energy Value Model requires further validation and refinement. (c) 2006 Elsevier B.V. All rights reserved.