Biogas potentials in manure and effect of pre-treatment

The overall objective of the project has been to provide a precise determination of the biogas potential and the ultimate methane yield of manure from a broad range of animal categories and how it is affected by pre-treatment. Furthermore it has been the aim to develop faster methods for determining the gas potential than traditional methods.
Different Feedstuff used for animals has shown to play a major role for the biogas potential. The feedstuff used for animals differs especially for dairy cattle. The tests illustrates that the type of roughage is important, maize and early grass roughage thus is better than grass from late harvest. Furthermore addition of rape seed which is used for reducing the enteric fermentation in cows has a positive influence on methane potential. Before manure is subjected to digestion it is stored for shorter or longer period inside the livestock buildings, which can result in losses of methane. During summertime with temperature around 20 C the loss can be around 1% per day. The national energy potential that can be produced from animal manure is calculated to approx. 22 PJ which is approx. 15% less than the previous assumptions that were made for a number of years back.
The effect of different pre-treatments technologies has been evaluated. The technologies that have been tested most thoroughly are extrudation and high temperature treatment. Upon extrusion of different biomass types, the relative methane yield increased ultimately from 9% to 28%. NIRS has been used for predicting biogas potentials. NIRS however were not able to predict the biogas potential very well, with a best R2 value of 0.43 for sow manure. Besides NIR different chemical parameters has been used to predict the biogas potential. The correlation was low and the chemical parameter giving the best correlation was lignin.