Sustainable food

Bacteria reduce pig farm methane emissions

A Danish pig farm achieves significant methane emission reductions using a biofilter. This is shown by the results of the first full-scale test. Now the biofilter will be tested on more farms.

In the winter of 2022, DTU established a biofilter at a pig farm in Gilleleje. The filter breaks down the methane from the manure. Photo: DTU

Monday 02 December 2024

Lotte krull

In the spring of 2024, Denmark housed almost 11.5 million pigs. Although many are exported, some are also consumed in Denmark. Pork is such a popular part of our daily diet that one in three participants in a 2021 Epinion survey with 6,228 respondents stated that they had eaten pork the night before.

But our meatballs or roast porks leave a climate footprint because of the pig manure, which during storage in slurry tanks produces methane – an extremely potent greenhouse gas. This has created an opportunity to test biofilters in pig production, as the technology has previously shown promising results in reducing methane emissions from landfills.

In 2020, a group of researchers from DTU Sustain therefore started designing and constructing a biofilter which they in 2022 installed at a pig Danish producer in Gilleleje, north of Copenhagen.

Bacteria break down methane

A biofilter is established by excavating an area at a depth of about half a metre, which is filled with stones that act as gas distribution layers. An 80-cm thick layer of compost is placed on top of the stones. The compost holds a naturally occurring group of bacteria that feed on methane, which means that the bacteria break down the unwanted greenhouse gas in their encounter with the methane. The filter works completely without the addition of chemicals, and the solution can therefore be applied in both organic and conventional production.

At the Gilleleje test farm, a 400 m2 filter was created and placed close to the farm’s 4,400 m3 covered slurry tank. The entire biofilter plant was also fitted with measuring equipment so the researchers could monitor and document the fate of the methane and plant efficiency.

The biofilter system works by pumping slurry gas from the top of the slurry tank, after which it is led through pipes under the compost layer outside. From here, the methane-filled gas leaks out and up through the compost. Along the way, the methane is broken down by the methane-eating bacteria.

It was the first full-scale test of a biofilter’s ability to reduce methane emissions from a pig herd, and the results were excellent, says Charlotte Scheutz, Professor at DTU, who headed the project.

“The filter was able to break down 92 per cent of the methane that was passed through it in the first year. Our hopes were that it would break down 80 per cent, so the biofilter’s efficiency far exceeded our expectations,” says Charlotte Scheutz.

Facts

About the project

The BioMet project has demonstrated that biofilters can be a cost-effective technological solution for reducing methane emissions from slurry tanks.
In addition to DTU, partners included Cowi, Seges Innovation, the University of Copenhagen, and PFH Miljø & Anlæg.
The project was supported by the Danish Agricultural Agency's GUDP programme and ran from 2020 to 2023.
The work is now continuing in the BioMet 2.0 project, where biofilters will be established at two new pig farms to collect further documentation.

Cheaper than CO2 tax

During the test period, 75 per cent of the slurry gas was collected from the tank. The remaining 25 per cent have escaped autonomously through the cover of the slurry tank, which means that the total plant efficiency is a 69 per cent methane reduction.

As part of the project, the costs incurred were reviewed by calculating ‘shadow prices’. Shadow prices for a climate initiative indicate the cost of reducing by one tonne of CO2 equivalents (CO2-e). CO2 equivalents are a conversion of greenhouse gases to the same ‘currency’ so that they can be compared. This is necessary because there are differences in how much the greenhouse gases from different products contribute to global warming.

The calculations have shown that the shadow price for the test plant is DKK 74 per tonne of reduced CO2-e. In comparison, the CO2 tax that a majority in the Danish parliament passed this summer will be DKK 300 per tonne of CO2-e emitted from animal production. Until 2035, the amount will increase to DKK 750. However, the actual cost will be lower because a deduction will be introduced at the same time.

“This shows that even though there are costs involved in establishing and operating a biofilter at a pig farm, it’s cheaper than being charged the agreed CO2 tax,” explains Charlotte Scheutz.

More tests at pig farms

Biofilters as a methane-reducing solution for covered slurry tanks look so promising that the research group has now been granted additional funding for technology maturation.

“The new grant enables us to continue to monitor the biofilter in Gilleleje and later this year establish two more biofilter plants at other pig producers,” says Charlotte Scheutz.

In 2022, there were a total of 2,399 Danish pig farms. The extent of methane emissions from the farms is not known. The research group from DTU Sustain will remedy this, as they will measure emissions in a new project that includes 18 pig farms.Based on the measurements, it will eventually be possible to estimate how much methane the Danish pig production emits.

Topic

Sustainable food

26 % of the world's total CO2 emissions come from food production. Livestock in particular account for a large share.
To reduce the climate impact of food production, we need a green transition. This can be achieved through the use of technology, digitalization and the development of new foods.

Contact

Charlotte Scheutz Professor, Head of Section Waste, Climate & Monitoring Phone: +45 45251607 Mobile: +45 26285828 chas@dtu.dk