One-third of all the animal slurries and manures produced in Denmark are currently put through an anaerobic digestion (AD) plant to produce biogas.

The plan is to double this figure over the next five years, at which time biogas will replace all the fossil-fuel-based natural gas, sourced from either the North Sea or Russia.

Recent years have seen a large number of AD operations developed in Denmark, all of which are located close to the country’s natural gas pipeline.

As a consequence, the biogas produced by the various AD operations can be easily pumped into the pipeline that was developed 40 years ago.

Anaerobic digestion

Torkild Birkemose, a department manager with Denmark’s SEGES Innovation organisation, updated members of the Irish Farm Buildings Association on the potential to further develop AD in Denmark, during a learning trip this week.

From a farming perspective, he cited a number of benefits linked to the adoption of the technology at farm level.

These include the development of green energy, the recycling of organic wastes and a reduction in the environmental impact of farm wastes.   

Birkemose also highlighted the potential for farmers to use digestate that, potentially, has a higher fertiliser value than the original slurry and manures used in the AD process.

Significantly, the digestate is also free of pathogens and weed seeds.

Centralised AD operations in Denmark are currently sourcing slurries and animal manures from a number of farming businesses.

Anaerobic digestion plant in Denmark
Part of the AD operation at Frijsenborg in Denmark

In addition to these products, a range of other feed stocks are used to produce biogas. These include waste from the food processing sector and straw.

Birkemose commented: “Large tonnages of straw are produced in Denmark. One third of this output is destined for animal bedding, and a similar proportion is included in cattle diets.

“This leaves the final one-third, which is normally chopped and incorporated back into the soil. It is this latter fraction which could be used as an AD feed stock.”

Birkemose confirmed that straw would have to have pre-treated in some way before it could be used in an AD operation.

“Farmers in Denmark are being paid for the slurries and manures they supply to AD operations. This is especially so, where deep litter is concerned,” he added.

“AD operators secure environmental certificates for the green biogas they produce.

“These have real value, a proportion of which can be passed down the line to those farmers supplying the manures and other AD feed stocks.”