Livestock farming, and in particular slurry management, is a major contributor to ammonia (NH₃) and methane (CH₄) emissions in Europe. Furthermore, reduced NH₃ and CH₄ emissions are also relevant in licensing procedures and the management of livestock buildings. Therefore, the aim is to keep emissions from the barn as low as possible. Acidification of slurry in the barn can reduce these environmental and climate-relevant emissions by a pH value of 5.5. In this study, an acidification technology was retrofitted in an existing fattening pig barn equipped with a partially slatted floor. The slurry in a compartment with 32 animals was acidified. An identical compartment was used for reference investigations (case-control approach). Several times a week slurry was pumped for acidification in a process tank outside the barn compartment in a central corridor, where sulphuric acid (H₂SO₄) was added. Then the slurry was pumped back into the barn. In contrast to other systems, where acidified slurry was stored mainly in external storage tanks, in this study the slurry was completely stored in the slurry channels under the slatted floor, during the entire fattening period. The emission mass flow of NH₃ and CH₄ was measured continuously over three fattening periods, with one period in spring and two periods in summer. On average 17.1 kg H₂SO₄ (96%) (m³ slurry)^-1 were used for acidification during the three fattening periods. NH₃ and CH₄ emissions were reduced by 39 and 67%, respectively. The hydrogen sulphide (H₂S) concentration in the barn air of the acidification compartment was harmlessly low (0.02 ppm). Thus, despite the storage of the acidified slurry in the barn, the system leads to a lower concentration of detrimental gases, which is beneficial for the animals' as well as for the workers' health. The study shows that it is possible to retrofit acidification technology into existing pig barns. Further investigations shall identify possible measures to reduce the amount of H₂SO₄ used and thus minimise the sulphur input into the slurry.

Acidification of slurry is a common practice to reduce ammonia and methane emissions. Sulfuric acid is usually used for this process. However, this has been criticized due to the high sulfur input into soils. Therefore, the objective of this study is to show the effectiveness of a one-time acidification with alternative acids also in combination with other treatment strategies. The amount of acid as well as the change of pH value during storage were investigated. For most variants, a strong pH increase occurred within the first ten days after acidification. Mineral acids (sulfuric or hydrochloric acid) resulted in a lower pH increase compared to organic acids (lactic, acetic, and citric acid). Under anaerobic storage conditions, the pH remained significantly lower. The addition of glucose before acidification resulted in lower pH values during the first week, but in the long term, the conversion of glucose to carbonate led to higher pH values. A previous separation process was able to reduce the amount of acid. Although the pH increase was not that strong in the first days after acidification, it was much faster and stronger afterwards due to the lower buffer capacity in the separated slurry. A long-term pH reduction was achieved by acidification to pH 3.0, but this was associated with an increased amount of acid. On the basis of the results, a combination of organic acids with anaerobic storage can be recommended as an alternative to sulfuric acid.

Slurry treatments such as acidification and alkalization have proven to be promising solutions to reduce gaseous emission produced by farm animals. The optimization of these technologies requires detailed knowledge of how and to what extent the buffer capacities in slurries will change during storage under the influence of different temperatures, as this may save resources needed to adjust a targeted pH value. Fresh slurries from dairy cows, fattening pigs and sows were collected and stored for 12 weeks under either cold (4.7 ± 1.1 °C) or warm (23.6 ± 2.1 °C) conditions to perform titrations in acidic and alkaline milieu at regular intervals. Based on these results, we successfully verified a new mathematical tool that we have developed to be able to calculate and visualize the most important buffer systems found in the analyzed slurries. Our experimental results showed a strong correlation between the degradation of the volatile fatty acid (VFA) buffer and the emergence of the carbonate buffers, i.e., the HCO₃⁻ and the CO₃²⁻ buffer. Furthermore, a drop in the pH value caused by enhanced microbial production of VFAs can be mitigated by the presence of the NH₃ buffer. In conclusion, we demonstrated that the buffers cannot be considered individually but must be interpreted as a complex and interacting system.