A Danish pig farm has achieved significant methane emission reductions using a biofilter. Now researchers with the Technical University of Denmark will be testing the biofilter on more farms across the country.

In 2020, a group of researchers from DTU Sustain started designing and constructing a biofilter and in 2022 installed it at a Danish pig farm in Gilleleje, north of Copenhagen. A biofilter is created by excavating an area at a depth of about half a meter, which is filled with stones that act as gas distribution layers. An 80-cm thick layer of compost is then 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. According to the researchers, 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.

Related:Pecze named director of Topigs Norsvin Central Europe

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% of the methane that was passed through it in the first year. Our hopes were that it would break down 80%, so the biofilter’s efficiency far exceeded our expectations."

Cheaper than CO2 tax

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

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.

Related:Extended storage times ineffective for partial African swine fever inactivation

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,” says 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 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 measure emissions in a new project that includes 18 pig farms. Based on the measurements, the researchers say it will eventually be possible to estimate how much methane Danish pig production emits.

Related:PIC highlights benefits of PRRS-resistant pig ahead of World Economic Forum