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Evolution of the acid/base amount for (a) coldly stored (4.7 ± 1.1 • C) and (b) warmly stored (23.6 ± 2.1 • C) fattening pig slurry shown over 12 weeks to visualize the dynamics of the VFA (pH range 5.5 to 3.0), HCO 3 − (pH range 7.0 to 5.5) and CO 3 2− (pH range 9.5 to 11.5) buffer systems, vertical bars represent standard errors (n = 3).
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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, a...
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... amount of acid from 5.5 to 3.0 (VFA buffer) increased considerably from week 0 to 2, while the amount of acid between 7.0 and 5.5 (HCO 3 − buffer) remained constant during this period. Additionally, Figure 8b shows in detail the dynamics and interaction of these buffers with the CO 3 2− buffer. Thus, it could be seen that during the first week the amount of base from 9.5 to 11.5 (CO 3 2− buffer) remained constant as well. ...
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... amount of acid from 5.5 to 3.0 (VFA buffer) increased considerably from week 0 to 2, while the amount of acid between 7.0 and 5.5 (HCO3 − buffer) remained constant during this period. Additionally, Figure 8b shows in detail the dynamics and interaction of these buffers with the CO3 2− buffer. Thus, it could be seen that during the first week the amount of base from 9.5 to 11.5 (CO3 2− buffer) remained constant as well. ...
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... the following four weeks, a close interaction between the VFA buffer and the carbonate buffer became clear, as the VFA buffer capacity rapidly decreased and the carbonate buffer rose to a peak value for HCO3 − and CO3 2− concentrations. Figure 8. Evolution of the acid/base amount for (a) coldly stored (4.7 ± 1.1 °C) and (b) warmly stored (23.6 ± 2.1 °C) fattening pig slurry shown over 12 weeks to visualize the dynamics of the VFA (pH range 5.5 to 3.0), HCO3 − (pH range 7.0 to 5.5) and CO3 2− (pH range 9.5 to 11.5) buffer systems, vertical bars represent standard errors (n = 3). ...
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... the VFA and the carbonate buffer slowly but steadily decreased (Figure 7, 'warm', 'fattening pig'). Besides that, the two carbonate buffers showed only minor differences in their curve progressions and so did they in their buffer capacities dynamics during the entire storage period (Figure 8b). The initial pH value of the warmly stored fattening pig slurry developed contrarily to the VFA buffer. ...
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... the coldly stored fattening pig and the dairy cow slurry showed a clear delay in the development of the buffers. In addition, the VFA buffer in the coldly stored fattening pig slurry did not show any fluctuations but instead a linear degradation (Figure 7, 'cold', 'fattening pig' and Figure 8a). Furthermore, analogies between VFA buffer degradation and carbonate buffer formation were also observed in coldly stored fattening pig slurry, as the carbonate puffer increased in a similar ratio to what the VFA buffer decreased. ...
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... the same time, however, there was a much stronger increase in the VFA Hereafter, the VFA and the carbonate buffer slowly but steadily decreased (Figure 7, 'warm', 'fattening pig'). Besides that, the two carbonate buffers showed only minor differences in their curve progressions and so did they in their buffer capacities dynamics during the entire storage period (Figure 8b). The initial pH value of the warmly stored fattening pig slurry developed contrarily to the VFA buffer. ...
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... the coldly stored fattening pig and the dairy cow slurry showed a clear delay in the development of the buffers. In addition, the VFA buffer in the coldly stored fattening pig slurry did not show any fluctuations but instead a linear degradation (Figure 7, 'cold', 'fattening pig' and Figure 8a). Furthermore, analogies between VFA buffer degradation and carbonate buffer formation were also observed in coldly stored fattening pig slurry, as the carbonate puffer increased in a similar ratio to what the VFA buffer decreased. ...
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... faster and more intensive volatilization losses of CO 2 occur at higher temperatures [58]. These losses of CO 2 reduced the carbonate buffer capacity [43], which could explain the decrease in carbonate buffer capacity from week 0 to 2 and 6 to 12 in warmly stored slurry (Figure 8b). However, in the coldly stored slurry, the carbonate buffer increased continuously until week 12, indicating that this loss can be neglected at cold storage conditions (Figure 8a). ...
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... losses of CO 2 reduced the carbonate buffer capacity [43], which could explain the decrease in carbonate buffer capacity from week 0 to 2 and 6 to 12 in warmly stored slurry (Figure 8b). However, in the coldly stored slurry, the carbonate buffer increased continuously until week 12, indicating that this loss can be neglected at cold storage conditions (Figure 8a). Furthermore, we were able to show that the CO 2 produced by the microbial decomposition of VFAs does not immediately emit, but rather functions as HCO 3 − and CO 3 2− buffer in the acidic or alkaline milieu. ...
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... we were able to show that the CO 2 produced by the microbial decomposition of VFAs does not immediately emit, but rather functions as HCO 3 − and CO 3 2− buffer in the acidic or alkaline milieu. This was particularly shown by the fact that the rapid degradation of VFA in the warmly stored fattening pig slurry caused a rapid increase in both carbonate buffer concentrations (Figure 8b). Coldly stored slurry showed a similar pattern, in which continuous VFA degradation caused a continuous increase in the carbonate buffer ( Figure 8a). ...
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... was particularly shown by the fact that the rapid degradation of VFA in the warmly stored fattening pig slurry caused a rapid increase in both carbonate buffer concentrations (Figure 8b). Coldly stored slurry showed a similar pattern, in which continuous VFA degradation caused a continuous increase in the carbonate buffer ( Figure 8a). Regardless of the storage temperature, both carbonate buffer curves showed minor differences, which confirms that the CO 2 produced by VFA degradation can act as HCO 3 − and CO 3 2− buffer. ...
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... amount of acid from 5.5 to 3.0 (VFA buffer) increased considerably from week 0 to 2, while the amount of acid between 7.0 and 5.5 (HCO 3 − buffer) remained constant during this period. Additionally, Figure 8b shows in detail the dynamics and interaction of these buffers with the CO 3 2− buffer. Thus, it could be seen that during the first week the amount of base from 9.5 to 11.5 (CO 3 2− buffer) remained constant as well. ...
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... amount of acid from 5.5 to 3.0 (VFA buffer) increased considerably from week 0 to 2, while the amount of acid between 7.0 and 5.5 (HCO3 − buffer) remained constant during this period. Additionally, Figure 8b shows in detail the dynamics and interaction of these buffers with the CO3 2− buffer. Thus, it could be seen that during the first week the amount of base from 9.5 to 11.5 (CO3 2− buffer) remained constant as well. ...
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... the following four weeks, a close interaction between the VFA buffer and the carbonate buffer became clear, as the VFA buffer capacity rapidly decreased and the carbonate buffer rose to a peak value for HCO3 − and CO3 2− concentrations. Figure 8. Evolution of the acid/base amount for (a) coldly stored (4.7 ± 1.1 °C) and (b) warmly stored (23.6 ± 2.1 °C) fattening pig slurry shown over 12 weeks to visualize the dynamics of the VFA (pH range 5.5 to 3.0), HCO3 − (pH range 7.0 to 5.5) and CO3 2− (pH range 9.5 to 11.5) buffer systems, vertical bars represent standard errors (n = 3). ...
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... the VFA and the carbonate buffer slowly but steadily decreased (Figure 7, 'warm', 'fattening pig'). Besides that, the two carbonate buffers showed only minor differences in their curve progressions and so did they in their buffer capacities dynamics during the entire storage period (Figure 8b). The initial pH value of the warmly stored fattening pig slurry developed contrarily to the VFA buffer. ...
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... the coldly stored fattening pig and the dairy cow slurry showed a clear delay in the development of the buffers. In addition, the VFA buffer in the coldly stored fattening pig slurry did not show any fluctuations but instead a linear degradation (Figure 7, 'cold', 'fattening pig' and Figure 8a). Furthermore, analogies between VFA buffer degradation and carbonate buffer formation were also observed in coldly stored fattening pig slurry, as the carbonate puffer increased in a similar ratio to what the VFA buffer decreased. ...
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... the same time, however, there was a much stronger increase in the VFA Hereafter, the VFA and the carbonate buffer slowly but steadily decreased (Figure 7, 'warm', 'fattening pig'). Besides that, the two carbonate buffers showed only minor differences in their curve progressions and so did they in their buffer capacities dynamics during the entire storage period (Figure 8b). The initial pH value of the warmly stored fattening pig slurry developed contrarily to the VFA buffer. ...
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... the coldly stored fattening pig and the dairy cow slurry showed a clear delay in the development of the buffers. In addition, the VFA buffer in the coldly stored fattening pig slurry did not show any fluctuations but instead a linear degradation (Figure 7, 'cold', 'fattening pig' and Figure 8a). Furthermore, analogies between VFA buffer degradation and carbonate buffer formation were also observed in coldly stored fattening pig slurry, as the carbonate puffer increased in a similar ratio to what the VFA buffer decreased. ...
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... faster and more intensive volatilization losses of CO 2 occur at higher temperatures [58]. These losses of CO 2 reduced the carbonate buffer capacity [43], which could explain the decrease in carbonate buffer capacity from week 0 to 2 and 6 to 12 in warmly stored slurry (Figure 8b). However, in the coldly stored slurry, the carbonate buffer increased continuously until week 12, indicating that this loss can be neglected at cold storage conditions (Figure 8a). ...
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... losses of CO 2 reduced the carbonate buffer capacity [43], which could explain the decrease in carbonate buffer capacity from week 0 to 2 and 6 to 12 in warmly stored slurry (Figure 8b). However, in the coldly stored slurry, the carbonate buffer increased continuously until week 12, indicating that this loss can be neglected at cold storage conditions (Figure 8a). Furthermore, we were able to show that the CO 2 produced by the microbial decomposition of VFAs does not immediately emit, but rather functions as HCO 3 − and CO 3 2− buffer in the acidic or alkaline milieu. ...
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... we were able to show that the CO 2 produced by the microbial decomposition of VFAs does not immediately emit, but rather functions as HCO 3 − and CO 3 2− buffer in the acidic or alkaline milieu. This was particularly shown by the fact that the rapid degradation of VFA in the warmly stored fattening pig slurry caused a rapid increase in both carbonate buffer concentrations (Figure 8b). Coldly stored slurry showed a similar pattern, in which continuous VFA degradation caused a continuous increase in the carbonate buffer ( Figure 8a). ...
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... was particularly shown by the fact that the rapid degradation of VFA in the warmly stored fattening pig slurry caused a rapid increase in both carbonate buffer concentrations (Figure 8b). Coldly stored slurry showed a similar pattern, in which continuous VFA degradation caused a continuous increase in the carbonate buffer ( Figure 8a). Regardless of the storage temperature, both carbonate buffer curves showed minor differences, which confirms that the CO 2 produced by VFA degradation can act as HCO 3 − and CO 3 2− buffer. ...
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... amount of acid from 5.5 to 3.0 (VFA buffer) increased considerably from week 0 to 2, while the amount of acid between 7.0 and 5.5 (HCO 3 − buffer) remained constant during this period. Additionally, Figure 8b shows in detail the dynamics and interaction of these buffers with the CO 3 2− buffer. Thus, it could be seen that during the first week the amount of base from 9.5 to 11.5 (CO 3 2− buffer) remained constant as well. ...
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... amount of acid from 5.5 to 3.0 (VFA buffer) increased considerably from week 0 to 2, while the amount of acid between 7.0 and 5.5 (HCO3 − buffer) remained constant during this period. Additionally, Figure 8b shows in detail the dynamics and interaction of these buffers with the CO3 2− buffer. Thus, it could be seen that during the first week the amount of base from 9.5 to 11.5 (CO3 2− buffer) remained constant as well. ...
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... the following four weeks, a close interaction between the VFA buffer and the carbonate buffer became clear, as the VFA buffer capacity rapidly decreased and the carbonate buffer rose to a peak value for HCO3 − and CO3 2− concentrations. Figure 8. Evolution of the acid/base amount for (a) coldly stored (4.7 ± 1.1 °C) and (b) warmly stored (23.6 ± 2.1 °C) fattening pig slurry shown over 12 weeks to visualize the dynamics of the VFA (pH range 5.5 to 3.0), HCO3 − (pH range 7.0 to 5.5) and CO3 2− (pH range 9.5 to 11.5) buffer systems, vertical bars represent standard errors (n = 3). ...
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... the VFA and the carbonate buffer slowly but steadily decreased (Figure 7, 'warm', 'fattening pig'). Besides that, the two carbonate buffers showed only minor differences in their curve progressions and so did they in their buffer capacities dynamics during the entire storage period (Figure 8b). The initial pH value of the warmly stored fattening pig slurry developed contrarily to the VFA buffer. ...
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... the coldly stored fattening pig and the dairy cow slurry showed a clear delay in the development of the buffers. In addition, the VFA buffer in the coldly stored fattening pig slurry did not show any fluctuations but instead a linear degradation (Figure 7, 'cold', 'fattening pig' and Figure 8a). Furthermore, analogies between VFA buffer degradation and carbonate buffer formation were also observed in coldly stored fattening pig slurry, as the carbonate puffer increased in a similar ratio to what the VFA buffer decreased. ...
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... the same time, however, there was a much stronger increase in the VFA Hereafter, the VFA and the carbonate buffer slowly but steadily decreased (Figure 7, 'warm', 'fattening pig'). Besides that, the two carbonate buffers showed only minor differences in their curve progressions and so did they in their buffer capacities dynamics during the entire storage period (Figure 8b). The initial pH value of the warmly stored fattening pig slurry developed contrarily to the VFA buffer. ...
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... the coldly stored fattening pig and the dairy cow slurry showed a clear delay in the development of the buffers. In addition, the VFA buffer in the coldly stored fattening pig slurry did not show any fluctuations but instead a linear degradation (Figure 7, 'cold', 'fattening pig' and Figure 8a). Furthermore, analogies between VFA buffer degradation and carbonate buffer formation were also observed in coldly stored fattening pig slurry, as the carbonate puffer increased in a similar ratio to what the VFA buffer decreased. ...
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... faster and more intensive volatilization losses of CO 2 occur at higher temperatures [58]. These losses of CO 2 reduced the carbonate buffer capacity [43], which could explain the decrease in carbonate buffer capacity from week 0 to 2 and 6 to 12 in warmly stored slurry (Figure 8b). However, in the coldly stored slurry, the carbonate buffer increased continuously until week 12, indicating that this loss can be neglected at cold storage conditions (Figure 8a). ...
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... losses of CO 2 reduced the carbonate buffer capacity [43], which could explain the decrease in carbonate buffer capacity from week 0 to 2 and 6 to 12 in warmly stored slurry (Figure 8b). However, in the coldly stored slurry, the carbonate buffer increased continuously until week 12, indicating that this loss can be neglected at cold storage conditions (Figure 8a). Furthermore, we were able to show that the CO 2 produced by the microbial decomposition of VFAs does not immediately emit, but rather functions as HCO 3 − and CO 3 2− buffer in the acidic or alkaline milieu. ...
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... we were able to show that the CO 2 produced by the microbial decomposition of VFAs does not immediately emit, but rather functions as HCO 3 − and CO 3 2− buffer in the acidic or alkaline milieu. This was particularly shown by the fact that the rapid degradation of VFA in the warmly stored fattening pig slurry caused a rapid increase in both carbonate buffer concentrations (Figure 8b). Coldly stored slurry showed a similar pattern, in which continuous VFA degradation caused a continuous increase in the carbonate buffer ( Figure 8a). ...
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... was particularly shown by the fact that the rapid degradation of VFA in the warmly stored fattening pig slurry caused a rapid increase in both carbonate buffer concentrations (Figure 8b). Coldly stored slurry showed a similar pattern, in which continuous VFA degradation caused a continuous increase in the carbonate buffer ( Figure 8a). Regardless of the storage temperature, both carbonate buffer curves showed minor differences, which confirms that the CO 2 produced by VFA degradation can act as HCO 3 − and CO 3 2− buffer. ...
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Filtered tailings present many advantages over slurry tailings (e.g., stronger mechanical properties, lower risks of dam failure and easier reclamation) and are more and more considered as an alternative mine waste management approach for surface disposal. However, low degrees of saturation also expose filtered tailings to oxidation and to the risk...
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... Titration curves were generated for the substrates PSld and CSld ( Figure A1) by adding a defined volume of sulfuric acid to the substrates in several steps and measuring the pH value after each step. The respective current buffer capacity (CBC) in mmol kg −1 slurry/pH was calculated from these titration curves according to the method described by Overmeyer et al. [36], which represents the reciprocal slope of the titration curve ( Figure A2). ...
... For example, the PShd used for this experiment has a buffer system in the pH 7 to pH 6 range (see Figure A2). The buffer that is effective in this pH range is the hydrogen carbonate (H2CO3/HCO3 − ) buffer [36], which is the most important buffer in liquid organic fertilizers [57]. This buffer ensures that the pH value of the substrate changes little to not at all when an acid from the corresponding buffer range is added. ...
... Acidification of the liquid organic fertilizer shifts the balance between NH4 + and NH3 towards NH4 + so that less ammonia is emitted. This equilibrium is also a buffer system and is mainly effective in the pH range of 10.0 to 8.0 [36,58]. Acidification below pH 8.0 to pH 7.5 should, therefore, significantly reduce ammonia emissions. ...
Acidification of slurry is a promising approach for reducing ammonia emissions during the application procedure. Since only a few studies have been conducted focusing on ammonia emissions during the application of liquid organic fertilizers on the soil surface, a suitable incubation system was developed to evaluate the effects of acidification under controlled conditions. This incubation system was used to measure the ammonia emissions of various liquid organic fertilizers. The substrates were acidified with sulfuric and citric acid to different pH values to determine both the influence of the pH value of the substrates and of the type of acid on the ammonia emissions. The emissions decreased with declining pH value, and the reduction in emissions compared to the initial pH of the substrate was over 86% for pH 6.5 and over 98% for pH 6.0 and below. At the same pH value, the ammonia emissions did not differ between substrates acidified with citric acid and sulfuric acid, although more than twice as much 50% citric acid was required compared to 96% sulfuric acid to achieve the same pH value. Overall, our results demonstrate that the incubation system used is suitable for measuring ammonia emissions from surface-applied liquid organic fertilizers. The system allows for the differentiation of emission levels at various pH levels and is therefore suitable for testing the effectiveness of additives for reducing ammonia emissions from liquid organic fertilizers.
... Total alkalinity (ALK) is the parameter that best describes the buffer capacity (Husted et al., 1991), and it is significantly different among slurries (p < 0.001) and higher in the digestates than in the other slurries (p < 0.001). In the digestates, the acidifying component constituted by VFA has been partly removed with the anaerobic digestion process, and the CO 2 derived from the degradation of VFA is not immediately emitted; therefore, CO 2 can act as a buffer in the form of carbonates (HCO 3 − and CO 3 2− ) (Overmeyer et al., 2020). Although the ALK of dairy cattle and pig slurries does not differ significantly, it is slightly lower in dairy cattle slurry, probably because the lower TAN content, which also differed significantly between dairy cattle and pig slurries. ...
... In contrast, the pH2w of dairy cattle slurry showed significant negative correlations with TOC, TS and VS (r > − 0.797), while it was more correlated with TKN, P, ALK and VFAs than pH1w (r > − 0.683). The initial pH of the dairy cattle slurry, on the other hand, did not show significant correlations with the added acid, confirming what was reported by Husted et al. (1991) and Overmeyer et al. (2020) and with pH1w and pH2w. ...
... Slurry sanitization, a crucial aspect related to the safety of biobased fertilizers, can also be attained through pH modification (Rodrigues et al., 2021). Alkalinization followed by stripping technologies also allows recovery of ammonia and the production of ammonium-based fertilizers (Overmeyer et al., 2020). There are, however, problems to overcome, including replacing inorganic with organic acid/alkali compounds to allow treated slurry to be used in organic agriculture (see European Regulation 2019/1009) and effective integration of this technique with others in an overall manure management strategy (Hjorth et al., 2010;Varma et al., 2021). ...
This chapter discusses optimizing slurry management in agricultural practices. It begins by first highlighting current decision tools for optimizing manure management, then goes on to review modifying animal slurry pH to enhance its value as a biobased fertilizer through methods such as bio acidification and alkalinization. A section on improving manure management systems to minimize trade-offs is also provided, followed by an overview of combining manure management with anaerobic digestion. The chapter also reviews pre- and post-treatment for anaerobic digestion as well as the optimization of anaerobic digestion operations to optimize digestate quality.
... In the context of waste water treatment, for example, Larsen et al. 2021 highlighted that the alkaline stabilization of urea with urine pH values of about 10 using wood ash can be considered a valid alternative to acidic stabilization [38]. Moreover, in the context of slurry storage and utilization, the process of alkalization is also reported as a method to reduce emissions [39,40]. In contrast to the observed behavior in our simulation, the main line of argumentation in the literature is, however, that shifting the equilibrium towards NH 3 by increasing the pH value results in high ammonia concentrations, which can be captured to produce ammonium-based mineral fertilizers. ...
Ammonia emission rates from naturally ventilated livestock housing systems can be estimated in multiple ways. By coupling different modeling approaches towards a semi-mechanistic barn-scale ammonia emission model, we investigated the influence of urine puddle pH dynamics on the (sub)daily and seasonal pattern of ammonia emissions. We compared the simulated ammonia emission patterns using about ten months of on-farm measurements obtained from a naturally ventilated dairy cattle building with a scraped solid floor in Northern Germany. The dataset included gas concentration measurements as well as wind data (ranging from 0 m s−1 to about 8.6 m s−1) and air temperature data (ranging from about −4 ∘C to about 32 ∘C), the average number of housed cows (about 380) and information on the average cow mass (about 700 kg). In addition, the average dry matter intake, total gross energy intake and nitrogen intake were used to model the ammonia emission potential. In the emission modeling, we considered two potential types of pH dynamics in the urine puddles: a saturating scenario and a peaking scenario. For both of them, 21 different combinations of initial pH and maximum pH were considered within a range of 6.5 to 11. We showed that the non-linear interaction of the puddle pH and temperature caused specific emission patterns, where the degree of influence of the two parameters changed over the course of the emission process. Low initial pH values together with high asymptotic pH values were associated with the largest emissions. Considering the same asymptotic pH value, the higher the initial pH value, the lower the observed emissions; especially when assuming peak pH dynamics, the emission values were significantly lower. In natural pH settings (i.e., low to intermediate initial pH and intermediate asymptotic pH), the winter emissions were considerably lower than the summer emissions (i.e., the winter emission was about half of the summer emission, as observed in the on-farm studies). In contrast, artificial pH settings with high pH values led to markedly lower emissions in the summer (i.e., the summer emission was about the same as winter emission), reducing the total annual emission value. Our sensitivity study indicated that the urine puddle alkalizing dynamics play a key role in the overall emission model accuracy in order to capture seasonal and diurnal variability of the ammonia emission of naturally ventilated dairy cattle barns in mechanistic modeling approaches. Thus, future studies should investigate the range of pH dynamics that naturally occur in urine puddles in cattle barns depending on the flooring material, the entry of litter or feed leftovers, the cleaning and cooling system (e.g., in terms of use of water) and so on in order to further refine the emission model.
... Low pH decreases NH 3 emission by triggering the higher portion of NH 4 + and the low portion of free NH 3 in the balance of NH 4 + /NH 3 buffer system. By contrary, pH higher than 10 was adjusted to achieve NH 3 stripping during wastewater treatment process (Sui et al., 2015;Overmeyer et al., 2020). For CH 4 mitigation, some studies found the CH 4 mitigation efficiency could be as high as 80%-90% when pH is below 6 (Shin et al., 2019;Vechi et al., 2022;Ó lafsdóttir et al., 2023). ...
Animal slurry storage is a significant source of greenhouse gas (GHG) and ammonia (NH3) emissions. pH is a basic but key factor that could pose great influence on gas emissions, but the simultaneous evaluation of its influence on GHG and NH3 emissions and the understanding of its underlying mechanism are not enough. In this work, pH was adjusted between 5.5 and 10.0 by a step of 0.5 unit by adding lactic acid and sodium hydroxide (NaOH) properly and frequently to the stored slurry during a 43-day storage period. The cumulative NH3 emissions were linearly correlated with the slurry pH, with R2 being 0.982. Maintaining the slurry pH at 5.5-6.0 could reduce NH3 emissions by 69.4%-85.1% compared with the non-treated group (CK). The pH ranges for maximum methane (CH4) and nitrous oxide (N2O) emissions were 7.5-8.5 and 6.5-8.5, respectively, and the slurry under pH 7.5-8.5 showed the highest GHG emissions. Acidification to pH 5.5 helped reduce the CH4, N2O, and total GHG emissions by 98.0%, 29.3%, and 81.7%, respectively; while alkalinization to pH 10.0 helped achieve the mitigation effects of 74.1%, 24.9%, and 30.6%, respectively. The Pearson's correlation factor between CH4 and the gene copy of mcrA under different pH values was 0.744 (p < 0.05). Meanwhile, the correlation factors between N2O and the gene copies of amoA, narG, and nirS were 0.644 (p < 0.05), 0.719 (p < 0.05), and 0.576 (p = 0.081), respectively. The gene copies of mcrA, amoA, narG, and nirS were maintained at the lowest level under pH 5.5. These results recommended keeping slurry pH lower than 5.5 with lactic acid can help control GHG and NH3 emissions simultaneously and effectively.
... b i o s y s t e m s e n g i n e e r i n g 2 2 9 ( 2 0 2 3 ) 2 0 9 e2 4 5 to larger emissions (Dalby, Hafner, et al., 2021;Overmeyer et al., 2020). ...
... High concentrations of protonated volatile fatty acids (VFAs) have shown prominent inhibition effects on anaerobic digestion (Sun et al., 2020;Xiao et al., 2016;Zhang et al., 2018). Slurry acidification results in increased levels of protonated VFAs possibly leading to the inhibition of methanogens (Ottosen et al., 2009;Overmeyer et al., 2020). Protonated short-chain VFAs lead to the acidification of cytoplasm, thereby inhibiting cellular reactions (Baronofsky et al., 1984). ...
... total ammonia species (NH 4 þ /NH 3 ) (Overmeyer et al., 2020(Overmeyer et al., , 2021. The buffer capacity of the slurry may vary depending on the feed characteristics, species and feed digestibility by the animal, and storage conditions (Miller & Varel, 2003;Villamar et al., 2013). ...
The storage of liquid manure (slurry) is a major source of methane (CH 4) and thus contributes significantly to the climate impact of agriculture. The necessity to store slurry in barns and storage tanks at different seasons has led to increasing research in the mitiga-tion of CH 4 emissions from the manure management chain. In this review, a holistic view of CH 4 mitigation strategies targeting slurry pits and storage tanks classified based on the mechanism of interaction (physical, chemical, and biological) with slurry and their CH 4 mitigation efficiency is presented. Also, the combination of chemical additives with other methods is discussed. The key methods include slurry cover, solideliquid separation, acidification, antimicrobial agents, and aeration. Among various methods, acidification to pH 5.5 acts as a benchmark since it achieves a reduction in CH 4 emission in the range of 95 e99% and 65e99% from stored pig slurry and cattle slurry, respectively. Other chemical treatments such as antimicrobial agents and oxidants also reduce CH 4 in a wide range depending on efficiency and dosage. Further, the combination of acidification with physical and chemical treatments yields a cumulative or synergistic effect in reducing the CH 4 emission. This review identifies significant factors that influence the efficiency of the additives , which helps to mitigate CH 4 emissions from slurry storage. Based on mitigation efficiency, acidification is a good choice of technology to reduce CH 4 emissions from slurry storages. This technology would fit well with frequent removal of slurry from the barn to the outside storage in cold regions.
... This pattern can be explained by the increase in TAN concentrations post treatment, the volatilization of NH 3 and the subsequent decline in pH as a result. This explanation resembles closely the role of the buffer system in slurry as outlined by Husted et al. (1991) and Overmeyer et al. (2020). ...
... As a result, the pH increases after stirring from 6.75 to 7.31 and 7.55 for FP/CC300 and FP/ CC500, respectively, as well as from 6.84 to 6.98 and 7.11 for DC/CC300 and DC/CC500, respectively. The intensity of the rise may vary as the pH in slurry can be strongly influenced by many factors such as the type of slurry, temperature, buffer capacity, time of storage and organic matter content (Overmeyer et al., 2020). Liao et al. (1995) demonstrated that at a constant stripping rate, the temperature and pH of the slurry are significantly responsible for high NH 3 recovery rates. ...
... However, the addition of CaCN 2 appeared to inhibit the microbial degradation of VFA during storage, resulting in a pronounced VFAs accumulation (Table 1). In slurry, VFA are one of the predominant buffering systems responsible for a natural and self-induced decrease in pH and are therefore considered to be the cause of the lower pH measured in the samples containing high VFA concentrations (Georgacakis et al., 1982;Overmeyer et al., 2020;Sommer and Husted, 1995). Further, in our previous study Overmeyer et al. (2020) were able to visualize and record the formation of VFA in slurry, which showed a peak value after 1-2 weeks indicating that a pH drop in the recent study might have also occurred during that period. ...
... In slurry, VFA are one of the predominant buffering systems responsible for a natural and self-induced decrease in pH and are therefore considered to be the cause of the lower pH measured in the samples containing high VFA concentrations (Georgacakis et al., 1982;Overmeyer et al., 2020;Sommer and Husted, 1995). Further, in our previous study Overmeyer et al. (2020) were able to visualize and record the formation of VFA in slurry, which showed a peak value after 1-2 weeks indicating that a pH drop in the recent study might have also occurred during that period. Additional information about the mode of action is presented in 4.3.1. ...
Calcium cyanamide (CaCN2) has been used in agriculture for more than a century as a nitrogen fertilizer with nitrification inhibiting and pest-controlling characteristics. However, in this study, a completely new application area was investigated, as CaCN2 was used as a slurry additive to evaluate its effect on the emission of ammonia and greenhouse gases (GHG) consisting of methane, carbon dioxide, and nitrous oxide. Efficiently reducing these emissions is a key challenge facing the agriculture sector, as stored slurry is a major contributor to global GHG and ammonia emissions. Therefore, dairy cattle and fattening pig slurry was treated with either 300 mg kg-1 or 500 mg kg-1 cyanamide formulated in a low-nitrate CaCN2 product (Eminex®). The slurry was stripped with nitrogen gas to remove dissolved gases and then stored for 26 weeks, during which gas volume and concentration were measured. Suppression of methane production by CaCN2 began within 45 min after application and persisted until the storage end in all variants, except in the fattening pig slurry treated with 300 mg kg-1, in which the effect faded after 12 weeks, indicating that the effect is reversible. Furthermore, total GHG emissions decreased by 99% for dairy cattle treated with 300 and 500 mg kg-1 and by 81% and 99% for fattening pig, respectively. The underlying mechanism is related to CaCN2-induced inhibition of microbial degradation of volatile fatty acids (VFA) and its conversion to methane during methanogenesis. This increases the VFA concentration in the slurry, lowering its pH and thereby reducing ammonia emissions.
... The pH value in the process tank and the frequency of the acidification process were adjusted to the amount of slurry in the slurry channels during the fattening period. Slurry contains buffers that cause the pH to rise after acidification (Overmeyer et al., 2020, therefore a waiting period of 10 min was kept before the pH value was measured again. If the pH increased, acidification was repeated to the required pH value. ...
... Possibly this resulted in an increased amount of acid. Feeding-related causes leading to a higher buffer capacity in the slurry would also be conceivable (Overmeyer et al., 2020). In our study, an average of 7.1 kg H 2 SO 4 per fattening pig was used for the acidification of the slurry. ...
... However, more frequent acidification results in increased electrical energy consumption for the acidification technology. We recommend acidification at least three times a week, but this also depends on the farm-specific differences in the slurry buffer (Overmeyer et al., 2020;Sommer and Husted, 1995). ...
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.
... After mixing, 750 mL slurry were taken from each 20 L bucket and were filled into 1 L plastic vessels (17.5 cm × 13.5 cm × 6 cm height), which were stored on a shaded table in the barn during the measurement period. As in [36,37], the plastic vessels were stored under aerobic conditions. The stored slurry vessels were covered with lids perforated with 12 2 mm-diameter holes, similar to [36]. ...
... The slurry pH increase over the experiment was consistent with recent findings by [37] and is related to the decomposition of organic matter and organic acids in the slurry, and the release of CO 2 [37,56]. A slightly higher slurry pH was found for the two rock powders than for the control, which was expected due to the H + buffering capacity of the rock powders [30]. ...
... The slurry pH increase over the experiment was consistent with recent findings by [37] and is related to the decomposition of organic matter and organic acids in the slurry, and the release of CO 2 [37,56]. A slightly higher slurry pH was found for the two rock powders than for the control, which was expected due to the H + buffering capacity of the rock powders [30]. ...
For several decades, farmers have been mixing rock powders with livestock slurry to reduce its NH3 emissions and increase its nutrient content. However, mixing rock powders with slurry is controversial, and there is currently no scientific evidence for its effects on NH3 and greenhouse gas (GHG) emissions or on changes in its nutrient content due to element release from rock powders. The major aim of this study was therefore to analyse the effects of mixing two commercially established
rock powders with cattle slurry on NH3, CO2, N2O and CH4 emissions, and on nutrient release over a course of 46 days. We found that rock powders did not significantly affect CO2 emission rates. NH3 and N2O emission rates did not differ significantly up until the end of the trial, when the emission rates of the rock powder treatments significantly increased for NH3 and significantly decreased for N2O, respectively, which coincided with a reduction of the slurry crust. Cumulative NH3 emissions did not, however, differ significantly between treatments. Unexpected and significant increases in
CH4 emission rates occurred for the rock powder treatments. Rock powders increased the macroand micronutrient content of the slurry. The conflicting results are discussed and future research directions are proposed.
