Acidification of slurry with sulphuric acid is a widespread practice on Danish livestock farms and can reduce ammonia evaporation and methane emissions. The method works by transferring the slurry into a process tank into which sulphuric acid is added. Most of the acidified slurry is pumped back into the unit when the slurry has been acidified down to pH 5.5 and remains stable at this level, thus achieving a slurry level of 20-25 cm in the slurry pits. The excess is transferred to a storage tank. This process is carried out daily.
Acidification of manure in pig units is approved for 64% ammonia reduction in units with a fully drained floor. In tests, 11-13 kg sulphuric acid per tonne of slurry was used.
Higher yield potential
The reduction of ammonia will contribute to a high ammonium content in the slurry when applied, and at the same time, ammonia evaporation will also be reduced due to the low pH. The increased utilisation of the nitrogen in the slurry can lead to a higher yield potential and reduce the need for artificial fertiliser.
By acidifying the unit, the content of sulphur in the slurry increases, which means that there is no need for additional sulphur input to the field when 11-13 kg sulphuric acid per tonne has been added. The application of acidified slurry will result in a surplus of sulphur under normal slurry application rates, which also offers the potential for sulphate leaching.
Studies at Aarhus University in Denmark also show that unit-acidified slurry stored in slurry tanks for over 83 days had a reduced methane emission of over 90 per cent compared to the stored control slurry. Based on this, slurry acidification in the housing unit is expected to have a high impact on methane emissions from the slurry in housing units and storage. Aarhus University estimates 70% less methane emissions from slurry in both housing units and storage when slurry is acidified in the units.
In 2022, the percentage of slurry that was acidified was estimated to equate to 2.5% of pig slurry. At the same time, the adoption of the method is expected to become more widespread by 2030, reaching an estimated share of 3.5%.
The method is part of SEGES’ report on carbon mitigation measures, which describes the most effect initiatives to enable agriculture to meet the 2030 carbon reduction target. The report from SEGES Innovation shows that by deploying 26 measures, Danish agriculture can reduce greenhouse gas emissions by 14.1 million tonnes CO2-e in 2030 compared to the base year 1990.
Read more about climate mitigation measures in pig production here:
Climate mitigation measures in Danish pig production - Slurry cooling