Frequent discharge leads to reduced methane gas

Currently, Danish agriculture accounts for 25 per cent of Denmark's total greenhouse gas emissions. Apart from CO2, the most important greenhouse gases from livestock production are methane and nitrous oxide.

Around 2.5 per cent of Denmark's total greenhouse gas emissions derive from methane emissions from housing units. Approximately 77 per cent of this methane is formed in the manure and the other 23 per cent via fermentation in the large intestine of the pig. But how can methane emissions be reduced when we only consider the methane that originates in the manure?

More frequent handling of manure – one part of the solution
Bacteria in the manure convert carbon into methane. These bacteria thrive at temperatures between 20 and 40°C. Methane formation is high from bacteria in this temperature range, and the longer the manure maintains these temperatures, the more carbon is converted into methane.

In traditional manure handling, manure is discharged every 4-5 weeks. This means that the manure stays in the housing unit for many days at temperatures of 18-20°C, providing strong growth conditions for the methane-producing bacteria. Frequent manure removal does away with precisely this long growth period.

New regulation
The regulation that changes manure handling was considered on 23 February 2023. The new regulatory requirements are expected to take effect on 1 May 2023. The requirements are likely to mean that:

• Discharge must be carried out at least every 7 days from all finisher units - with discharges to be recorded in a logbook.
• New units receiving environmental approval after 1 January 2023 must discharge at least every 7 days, and for larger units, requirements for automated discharge with a logging system can be expected. This also applies to gestation, farrowing and weaner units.
• Rules are expected for periods in which discharge can be exempted because of relatively small manure production. This applies especially in farrowing and weaner units.
• Audits of the discharge frequency will be performed under municipal auspices.

This practice appears to reduce methane in housing units by up to 45 per cent. But 45 per cent is not the final reduction. The manure that is discharged into the manure store has a relatively higher emission of methane in the manure tank than usual. Therefore, it is estimated that the resulting overall reduction of methane in the housing unit and manure tank will be approximately 16 per cent when the manure is discharged every 7 days.

"Discharging manure every 7 days is a step forward, but I believe that we can do even better, and this is why trials and tests of methods to reduce methane emissions in manure tanks are being carried out. The aim is, of course, to reduce the methane formation in manure storage through new technical means in order to ultimately achieve higher overall methane emission reductions than the current 16 per cent from the combination of housing units and manure storage," says Bent Ib Hansen, Senior Consultant, Danish Agriculture & Food Council.

Where possible, Danish pig producers have their manure collected by nearby biogas plants.