Dynamics of Different Buffer Systems in Slurries Based on Time and Temperature of Storage and Their Visualization by a New Mathematical Tool

Abstract

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.

One-Time Acidification of Slurry: What Is the Most Effective Acid and Treatment Strategy?

“…The buffer effect of the deionized water was not considered because of its low ion content. The conversion processes and principles of action can also be detected in diluted slurry, as shown in previous studies [38]. The pH value and temperature of the slurry were both measured with the pH sensor 'InLab Expert Pro' (Mettler Toledo, OH, USA).…”

“…The temperature during storage influences the progress of biodegradation processes, and thus also the pH value increase. The authors of [15] and [38] observed a faster pH increase during warm storage than during cold storage. This effect could not be considered in our investigation due to capacity constraints, therefore the storage was only carried out at laboratory temperature (approximately 22 • C).…”

“…The amount of acid required to reach the target pH value is strongly dependent on the different buffer capacities of the slurries. These can be described as a dynamic system because they are able to interact with each other [38,39]. The buffer capacities and their interaction are generally influenced, for example, by the ingredients of the slurry as well as by the temperature and time of storage [38].…”

“…Apart from that, the pH value of all treatments in our investigation increased again during the storage period of 48 days. The pH increase in acidified and non-acidified slurry may be attributed to the mineralization of organic nitrogen and the degradation of organic acids which caused an increased bicarbonate concentration [26,[36][37][38]45,46]. However, acidification affects the buffer capacity of the slurry leading, for example, to a reduction in the carbonate buffer of the acidified slurry due to the release of gaseous carbon dioxide [10].…”

“…Due to the buffer capacity in the slurry, the pH value may return to its initial pH value after acidification [28]. Possible reasons for an increase in pH value can be the degradation of volatile fatty acids (VFA), mineralization of organic nitrogen, or dissolution of carbonates [36][37][38]. Studies on acidification have shown that, depending on the type of slurry, around three to six weeks after slurry is acidified to a pH of 5.5 the pH increase is stable [13,26,27].…”