Simple Summary: Efficient slurry management is a key strategy to reduce the release of environmentally harmful gases produced by farm animals. Slurry treatments such as acidification and alkalization have proven to be promising solutions to reduce these emissions. In this context, it is crucial to understand how buffer capacities behave and may influence each other during storage under the influence of different temperatures. To realize this, we have developed and successfully verified a new mathematical tool. It allows an exact calculation and detailed visualization of the most important buffer systems found in the analyzed slurries. This knowledge can be used to optimize slurry treatments, as it allows faster, more precise and efficient timing of pH adjustment, thus, reducing the use of resources.Abstract: 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 HCO 3 − and the CO 3 2− buffer. Furthermore, a drop in the pH value caused by enhanced microbial production of VFAs can be mitigated by the presence of the NH 3 buffer. In conclusion, we demonstrated that the buffers cannot be considered individually but must be interpreted as a complex and interacting system.

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.

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