Valorization of an untapped resource: Energy and greenhouse gas emissions benefits of converting manure to biogas through anaerobic digestion

Livestock farming generates animal manure as a by-product. In comparison to in some countries, manure is hardly used for energy production in Switzerland. A growing awareness of renewable energy needs, resource depletion, and climate challenges make the huge untapped potential of livestock manure very attractive, particularly regarding biogas technology. Here, we assessed the energy and greenhouse gas (GHG) emissions benefits of using manure for biogas, considering its spatial distribution in Switzerland. First, laboratory measurements were conducted to compare the composition of fresh manure with values from literature. Then, detailed assessments of manure availability for biogas production were performed. Finally, the mitigation potential regarding GHG emissions was estimated for three scenarios. The new lab-scale values confirmed early storage as an important phase that is still not considered in practice. Under current farming practice, Swiss manure could produce 430 million m(3) biogas or 15 PJ gross biogas yearly, mostly from cattle. However, only 6% of this manure is currently being used for anaerobic digestion. The manure is widely spread across the country in relatively small farms. Considering the spatial distribution of manure and Swiss agricultural structures, there is considerable potential for small-scale individual installations, with a peak of approximately 250 GJ gross biogas yearly, as well as for joint-farm installations. If the currently exploitable amount of manure were used for energy, the emission of 159 kt of CO2 equivalent could be prevented compared to emissions under current management practices. Thus, manure digestion could be promoted for its wide environmental and energetic benefits.