Waste from food production, shops, and households, together with slurry, becomes biogas and contributes to the green transformation of the gas grid. At the same time, climate and environmental benefits will be obtained for both the agricultural and energy sectors as well as for society in general.
Denmark is an international leader in large-scale biogas technology for the treatment of manure and other waste fractions from food production. Biogas plants reduce the climate impact of food production without compromising high hygiene standards in livestock production.
Biogas plants have positive effects on agriculture, the environment and on energy and climate when manure is digested in a biogas plant. This is an excellent example of a sector coupling, providing synergies in several sectors, including contributions to a green transformation of the energy sector.
"First, they laugh at the fact that in Denmark we have more pigs than inhabitants. But they are deeply impressed when they hear about how we can maintain high veterinary standards in livestock production, recycle and refine resource streams, and capture the climate and environmental benefits."
Anne Seth Madsen, Senior Project Manager in NIRAS.
The amount of manure production in Denmark that went through a biogas plant in 2021.
Manure is not the feedstock with the highest biogas yield, but it ensures process stability in the biogas plant, allowing the biogas plant to feed other feedstocks with a higher gas content and produce biogas stably 365 days a year. In 2021, about 25% of Denmark's total manure production was sent to a biogas plant.
The other feedstocks received by biogas plants are typically organic waste from food production, shops, restaurants, and households. These are waste types that are poorly utilised in, for example, incineration plants. Biogas plants therefore have an important societal function, as they can offer cost-effective waste treatment while ensuring that the nutrients in the waste are recycled in a hygienic way.
The many benefits of biogas
Biogas produced from livestock manure and organic waste can replace fossil natural gas. Waste from agriculture, industry and households is thus a raw material for renewable energy production. Biogas is climate neutral in that the raw materials from which the gas is produced are typically from one-year crops. This means, that CO2 from the biogas used is generally reabsorbed by the new crops. Thus, biogas reduces the climate impact when it replaces fossil natural gas, which is often imported to Denmark. The fact that Danish biogas production reached 25% of natural gas consumption in 2021 and that we are on track for a carbon-neutral gas grid by 2034 is something that has been noted internationally!
"The fact that Danish biogas production in 2021 could supply 25% of the country's national consumption of natural gas is something that has been noticed internationally!"
Anne Seth Madsen, Senior Project Manager in NIRAS.
Another positive effect is that the biogas process changes the nitrogen in the manure. This means that when the farmer gets the digestate back from the biogas plant, it is a more efficient fertiliser than raw manure, as the nitrogen can be more easily absorbed by the crops in the field. Furthermore, the nutrients from different sources are distributed in the digestate and can be analysed before spreading, allowing an optimal allocation of nutrients to the different crops. Both digestion of the feedstock and compliance with national requirements for spreading during the period of growth reduce nitrogen leaching to rivers, streams, and the sea from the fields to the benefit of the environment.
Also, common biogas plants allow for hygienic redistribution of both phosphorus and nitrogen from livestock producers to crop growers or organic farmers. Furthermore, nutrients from the waste fed into the biogas plant are recycled, which would otherwise be lost in an incineration plant or end up in a landfill. Degassed biomass reduces the need for fossil fertilisers in agriculture and therefore further contributes to reducing the climate impact of food production.
Figures on biogas in Denmark
- 25 per cent of the gas in the Danish gas grid comes from biogas - primarily from manure and other waste streams.
- 25 per cent of manure today goes through a biogas plant - by 2030, 60 per cent is expected to be degassed.
- Biogas consists of 60-65% methane CH4 and 35-40% biogenic carbon dioxide CO2.
- In Denmark, landfilling of organic waste has been banned since 1994, but this is not always the case abroad, so there are potentially large energy and nutrient gains to be made.
When the digestate is spread on the fields in spring, it smells less and for a shorter period of time than raw animal manure. For one thing, the odorous substances in the raw materials have been converted and, for another, the digestate penetrates the soil more quickly, as it is more watery than raw manure.
What Denmark can offer
But why is it in Denmark that the technology to treat manure and waste in co-digestion has been developed? This is due to a combination of several factors. The energy crisis of the 1970s initiated the first trials and resulted in the installation of a number of small-scale farm biogas plants. The government supported the development through a research and development programme, where gas production was investigated for different waste types and the veterinary aspects were studied, including regulation of heat treatment requirements, etc. In the 1980s, the adoption of the Danish Environment Act indirectly stimulated the construction of large biogas plants. At the same time, government subsidies were granted for the investment costs and gas production.
With the establishment of larger biogas plants, the energy production and use of biogas came into focus. This triggered the co-digestion of livestock manure with organic waste fractions resulting in a higher gas production per tonne of input. Co-digestion is a good idea, and it works, although it requires process knowledge and experience, as the biogas process can slow down or stop completely if the composition of the biomass, temperature, pH, etc. are not under control. Over the last 35 years, Denmark has gained extensive experience in how to operate biogas plants and achieve a stable process and optimal biogas production from the raw materials fed into the plant.
Want to learn from our experience with biogas?
Today, Denmark is an international leader in the installation and operation of biogas plants based on manure in combination with organic waste from various sources. Furthermore, the technology has proven benefits for both agriculture and society. Biogas plants are an important tool to ensure both efficient, hygienic food production and reduce the climate impact of agriculture, while producing local renewable energy and closing the nutrient cycle.
When foreign countries look at Denmark and how we link energy production, agriculture, climate change and environment with biogas, they are blown away. At NIRAS, for example, we have a partner in Canada - the large food producer Maple Leaf Foods - which is extremely interested in learning from Danish experiences with biogas.
First, they laugh at the fact that in Denmark we have more pigs than inhabitants. But they are deeply impressed when they hear about how we can maintain high veterinary standards in livestock production, recycle and refine resource streams, and capture the climate and environmental benefits described in this article. And all this while also increasing the share of renewable energy sources in Denmark's energy supply.
We need to do much more to take this knowledge beyond our borders! For the sake of the climate. For the sake of the environment. For the benefit of livestock production around the world. For the sake of the green energy transformation. Globally!
“Maple Leaf is very happy to work with NIRAS in our effort to reduce methane emissions from manure storage in our hog production. Building on the vast Danish experience with capturing methane from manure in biogas plants has huge potential for us. We can co-digest the manure with waste from our own processing facilities and utilize the biogas as a replacement of fossil fuel – or add it to the natural gas grid. The Danish experience within this field will help us mover closer to our vision – to be the most sustainable protein company on earth.”
Mauricio Alanis, Director of Sustainability Strategy & Partnerships, Maple Leaf Foods.