Case Story Denmark

Deep bedding – a codigestion substrate with significant potential

Danish experience with handling and feeding deep bedding to biogas plants

November 2020

Benefits of co-digesting deep bedding

In Denmark, about one-third of all dry matter in livestock manure is contained in deep bedding. Over the last decade, most Danish biogas plants added deep litter to their codigestion substrates. This not only increased the biogas production, but also brought about environmental and agro-economic benefits. Mono-digestion of animal slurries can yield 15-25 Nm3 biogas / t biomass, depending on quality. However biogas plants need 35-45 Nm3 biogas / t to allow a financialy sustainable facility. In a situation with shortage of biomass and high gate fees for industrial high yielding biomethane wastes, co-digestion of deep litter is an obvious solution. Deep litter also can often be obtained free of charge.

Deep bedding varies in composition and nutrient content (Table 1); this variation impacts how it can be used in biogas production. Raising the dry matter content of the feedstock in the reactor increases the biogas production significantly. Danish experience shows that increasing the dry matter content from 6.8 to 14 % can increase gas yield from about 20 to 36 m3 /t.

Economic, environmental, and agricultural benefits are also achieved through better fertiliser quality. Compared to untreated deep bedding, digested deep bedding is easier and cheaper to apply and incorporate in soil, and with a higher nitrogen utilistion efficiency (Table 2).