Next Article in Journal
Advancing Research on Overlooked Invertebrates in Biological Control: A Case Study of Local Hoverflies and Wolf Spiders
Previous Article in Journal
Aluminum Sulfate and Straw Enhance Carbon Sequestration in Saline–Alkali Soils
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Agronomy
Volume 15
Issue 5
10.3390/agronomy15051202
agronomy-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Mitigating Gas Emissions from the Dairy Slurry Management Chain: An Enhanced Solid–Liquid Separation Technology with Tannic Acid

by
Zhiling Gao
1,2 and
Shanshan Wang
3,*
1
College of Resources and Environmental Sciences, Hebei Agricultural University, Baoding 071000, China
2
Key Laboratory for Farmland Eco-Environment of Hebei Province, Baoding 071000, China
3
School of Management, Shandong Technology and Business University, Yantai 264003, China
*
Author to whom correspondence should be addressed.
Agronomy 2025, 15(5), 1202; https://doi.org/10.3390/agronomy15051202
Submission received: 14 April 2025 / Revised: 13 May 2025 / Accepted: 15 May 2025 / Published: 15 May 2025
(This article belongs to the Section Agricultural Biosystem and Biological Engineering)
Browse Figures
Versions Notes

Abstract

:
Identifying novel flocculants to improve the separation efficiency of dairy slurries is important to facilitate slurry recycling with a low carbon footprint. Two microcosm experiments were conducted to differentiate ammonia (NH3), nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) emissions from liquid and solid fractions obtained using conventional (mechanical separator) and enhanced (flocculant + mechanical separator) solid–liquid separation (SLS) methods during the storage and soil application phases. Tannic acid (TA) was investigated as a potential flocculant in order to explore its effectiveness in reducing greenhouse gas (GHG) emissions during the storage and soil phases. Compared to the conventional SLS method, the employment of the enhanced SLS method reduced GHG emissions during the storage and soil application phases by 53.64% and 31.63%, respectively, thereby leading to an integrative mitigation of GHG emissions across the storage and soil application chain; however, it strongly increased NH3 emissions by 70.96% during the soil application phase, demonstrating a higher risk of gaseous N loss. Meanwhile, large trade-offs in N2O, CH4, and NH3 emissions between the solid and liquid fractions during the storage phase were observed, and the reduced CH4 and NH3 emissions during the storage phase were also partly offset by increased emissions during the soil application phase. In conclusion, enhanced separation technology using tannic acid as a flocculant can reduce GHG emissions from the management chain, with synergistic mitigation of CH4 and N2O, but the risk of increased NH3 emissions requires further attention. This study may be helpful in mitigating GHG emissions and recycling plant-derived tannic acid in the circular agriculture context.

1. Introduction

Large amounts of slurry are produced in dairy and pig farms. Efficiently reusing this liquid manure as a substitute for synthetic fertilizers is considered a smart strategy to reduce synthetic fertilizer consumption [1,2] and mitigate environmental risks, including global warming [3], water body eutrophication, and soil acidification caused by nitrogen deposition [4,5].
Among the various slurry management practices, solid–liquid separation (SLS) can effectively remove nutrients and chemical oxygen demand (COD) from the liquid fraction (LF) [6], reduce manure storage requirements, and facilitate long-distance transport and broader field application of the solid fraction (SF) from concentrated animal feeding operations (CAFOs) [7]. To further enhance separation efficiency, various flocculants have been studied [6,8,9,10,11]. For example, combining low- and high-charge density cationic polymers may improve slurry flocculation and pathogen removal [12].
Research has shown that significant amounts of greenhouse gases (GHGs) are emitted during the storage and field application of slurry [13,14,15,16,17]. Therefore, reducing GHG emissions throughout the entire slurry management process, from on-farm storage to field application, is crucial for achieving sustainable livestock production. Previous studies have indicated that SLS not only removes degradable organic matter and reduces CH4 emissions during storage [18,19,20], but it also modifies gas emissions in subsequent field applications [21,22,23]. This occurs because SLS produces an LF with concentrated NH4+-N that penetrates soil more easily [24,25,26], potentially increasing N2O emissions due to greater soil–LF contact [27]. However, some studies have reported decreased N2O and CO2 emissions following the application of separated LF [28,29,30,31]. These findings highlight the need for optimized SLS systems.
While aiming for broader slurry distribution and lower GHG emissions across the management chain, conventional flocculants such as Fe3+ and Al3+, which are used to enhance the efficiency of SLS, face scrutiny due to their potential public health risks and environmental burden [32]. Additionally, some cationic polymers show limitations in removing dissolved organic carbon (DOC) effectively [12]. Consequently, developing environmentally friendly flocculants from natural resources to improve mechanical SLS systems has become increasingly important [33].
Bio-based flocculants, including tannic acid (TA, sourced from gallnuts, chestnuts, black wattle, or golden acacia) [34], chitosan [9], sodium alginate [35], and microbial flocculants [36], can replace conventional options due to their cost-effective, large-scale production and low energy requirements. Recently, TA has gained particular attention for its ability to remove fine particles from wastewater by bridging them into larger precipitable aggregates [37]. Furthermore, TA can inhibit the microbial mineralization of manure while enhancing soil nitrogen retention, demonstrating significant (albeit short-term) effects on carbon, nitrogen, and phosphorus transformation [38,39,40].
However, the effectiveness of TA as a bio-flocculant for enhancing SLS efficiency in dairy slurry management has not been well investigated [15]. This study measured NH3 and greenhouse gas (GHG) emissions from both the solid fraction (SF) and liquid fraction (LF) during storage and soil application phases to (1) assess how flocculant-aided SLS affects gas emissions across different stages of slurry management, and (2) examine potential pollution swapping between long- and short-lived gases, such as N2O and CH4 [41,42]. The findings provide valuable insights into promoting sustainable livestock production in China.

2. Materials and Methods

The raw dairy slurry used in this study was collected from a dairy farm in Baoding, China. Initial analysis showed that the slurry contained 102.24 g kg−1 organic matter, 3.13 g kg−1 total nitrogen (TN), and 1.02 g kg−1 NH4+-N. The slurry was separated using two methods: (1) conventional solid–liquid separation using a commercial screw press separator (ZY-FLJ, Zhenyuan Machinery, Jining, China), and (2) enhanced SLS, where the slurry was first treated with tannic acid (TA) flocculant (C76H52O46, CAS 1401-55-4, Analytical Reagent, with a purity of 99.7%. Yuan Ye Bio-technology Co., LTD, Shanghai, China) before mechanical separation. Both methods yielded solid and liquid fractions for incubation experiments.
Soil samples were collected from the surface layer (0–20 cm depth) at Hebei Agricultural University’s Experimental Farm in June 2022. The soil had the following characteristics: a bulk density of 1.35 g cm−3, pH 7.9, 11.21 g kg−1 organic matter, and 0.89 g kg−1 TN. The initial mineral nitrogen levels were 3.86 mg kg−1 NH4+-N and 10.63 mg kg−1 NO3−-N.

2.1. Gas Emissions During the Storage Phase

For this phase, four treatments were considered: the liquid fraction of conventional SLS (LF) and enhanced SLS (LF + TA), and the solid fraction of conventional SLS (SF) and enhanced SLS (SF + TA). To increase separation efficiency, a TA solution (5%, w/w) was prepared and added to raw slurry at a rate of 3 mL L−1 raw slurry. The slurry–TA mixture underwent mechanical stirring for 1 h to facilitate floc formation before separation using the same screw press equipment, yielding the LF + TA and SF + TA fractions. All obtained fractions (LF, LF + TA, SF, SF + TA) were stored in laboratory incubation chambers maintained at 24 ± 1 °C with 60% relative air humidity. Each cylindrical PVC incubation chamber (16 cm inner diameter × 30 cm height) was designed (Figure 1A).
As shown in Figure 1, the emissions of NH3, CO2, N2O, and CH4 from the LF and SF were measured using a multichannel photoacoustic gas monitor (Innova 1412i, Lumasense, Denmark) during storage with flow-through chamber methodology (the flow rate was approximately 15 times the headspace per minute) [43]. Two-hour measurements occurred daily between 13 July and 11 August 2022, with three replicates per treatment. Concurrently, samples were taken for time-course analysis of TN and ammonium.

2.2. Gas Emissions During Soil Application Phase

2.2.1. Experimental Design

In this phase, five treatments were conducted: (1) CK without any liquid/solid fraction, (2) LF with the liquid fraction of the conventional SLS, (3) SF with the solid fraction of the conventional SLS, (4) LF + TA with the liquid fraction of enhanced SLS, and (5) SF + TA with the solid fraction of the enhanced SLS. All applied fractions underwent five weeks of storage prior to use.
All treatments were conducted in triplicate using identical incubation chambers (plant-free) as shown in Figure 1B. The soil for incubation was air-dried and mixed by passing it through a 2 mm sieve. An amount of 5.5 kg of soil was packed into each incubation column, creating a 10 cm headspace above the soil and achieving a target bulk density of 1.25 g/cm3 (matching field conditions). Before the application of LF and SF, two continuous wetting–drying cycles were performed to stabilize the soil structure and minimize carryover microbes/nutrients effects. The physicochemical properties of all applied fractions are detailed in Table 1.

2.2.2. Gas Sampling and Measurement

All soil incubations were conducted under controlled laboratory conditions (24 ± 1 °C, 60% relative humidity). For NH3 measurement, a flow-through chamber system was employed (Figure 1) by closing port III and activating the air pump. Ambient air entered through port I, transported volatilized NH3 through port II into an acid trap (200 mL of 0.05 mol L−1 dilute H2SO4), and finally exited to the atmosphere. One-hour NH3 collections occurred daily from 15 to 24 August 2022, simultaneously capturing both the treatment emissions and background levels. The NH4+ concentrations in the trap solutions were quantified using a SmartChem200 discrete analyzer (KPM Analytics, Rome, Italy).
For greenhouse gas monitoring, a static chamber method was implemented from 15 to 31 August 2022 (16 days). Closing ports II and III, port I was used for air sampling for N2O, CO2, and CH4 measurements. The system remained sealed for 30 min intervals, with 20 mL air samples collected at T0 and T30 minutes. This limited sampling approach prevented significant pressure changes in the small headspace (16 cm diameter × 10 cm height), which could alter emission rates and introduce measurement errors. Collected samples were analyzed within 24 h using an Agilent 6820 GC system (Agilent Technologies, Santa Clara, CA, USA) [43].

2.2.3. Measurement of Soil Properties

Soil samples were collected every two days to determine the contents of soil nutrients, such as NO3−-N, NH4+-N, and DOC. After extraction with a KCl solution (2 mol L–1), the soils NH4+-N and NO3−-N were determined using a chemical analyzer (SmartChem® 200, KPM Analytics, Guidonia, Italy). Additionally, the DOC of soil samples was determined by measuring the absorbance at 495 nm on a spectrophotometer (752N, INESA Analytical Instrument Co., Ltd., Shanghai, China) [44].

2.3. Calculation of Gas Emissions

The emission rates of gases measured with the flow-through chamber method were calculated using Equation (1) [43]:
Q = ( C o u t − C i n ) × V / A × T 0 / ( T 0 + T )
where Q is the emission rate of different gases (mg m−2 h−1) and Cin and Cout are the inlet and outlet concentrations (mg m−3). V is the air flow rate (m3 h−1); A is the cross-sectional area of the incubation facility (m2); T0 is the absolute air temperature (K) under the standard state; and T is the actual air temperature (°C).
The gas emission rates during the soil application phase measured with the static chamber method were calculated using Equation (2) [43]:
Q = d C t / d t × H × T 0 / ( T 0 + T )
where Q is the gas emission rate (mg m−2 h−1), and dCt/dt is the linear slope of the gas concentration in the chamber changing over time (mg m−3 h−1). H is the height of the headspace of the incubation column (m); T0 is the absolute air temperature (K) under the standard state; and T is the actual air temperature (°C).
The NH3 emission rate during the soil application phase measured with the acid trap method was calculated using Equation (3) [43]:
Q = C × ( M / t ) / A
where Q is the NH3-N emission rate (mg m−2 h−1); C is the concentration of NH3-N absorbed by sulfuric acid (mg L−1); M is the volume of the acid solution (L); t is the sampling period (h); and A is the cross-sectional area of the incubation facility (m2).
The total gas emissions were calculated using Equation (4) [43]:
Q T = ∑ i = 1 n − 1 ( Q i + Q i + 1 / 2 × ( t i + 1 − t i ) )
where QT is the total emissions of different gases during measurement (mg m−2); n is the total number of measurement events; i is the serial number of one sampling event; Qi is the gas emission rate at the ith measurement (mg m−2 h−1); and t is the sampling duration (h).
This study evaluated the integrative impact of SLS on the gas emissions from the SF and LF in terms of the total equivalent emissions, and it was calculated using Equation (5) [43]:
                E = M 1 × L 1 + M 2 × L 2
where E represents the gas emission before solid–liquid separation (mg kg−1); M1 is the gas emissions of the LF (mg kg−1); L1 is the mass separation efficiency of LF (%); M2 is the gas emissions of the SF (mg kg−1); and L2 is the mass separation efficiency of SF (%).
In addition, the GHG of N2O, NH3, and CH4, in terms of CO2-e over the 100 year horizon, were calculated using Equation (6) [40]:
E G H G = N 2 O × 265 + C H 4 × 28 + N N H 3 × 44 / 28 × 1 % × 265
where EGHG indicates the sum of CO2-e in CH4 and N2O (including that derived from the deposition of volatilized NH3) (mg m−2).

2.4. Statistical Analysis

SPSS24.0 was used for statistical analysis, and the significance of differences among the treatments was evaluated at α = 0.05.

3. Results

3.1. Nutrient Dynamics During the Storage and Soil Application Phases

3.1.1. Manure NH4+-N and TN During Storage

During the storage phase, the NH4+-N contents of the liquid and solid fractions from conventional and enhanced SLS were relatively stable (Figure 2A). The NH4+-N content of the liquid fraction was much higher than that of the solid fraction for both separation methods. The NH4+-N of the solid fractions between the conventional and enhanced separation methods differed significantly, whereas they were similar in the liquid fractions (Figure 2A). As shown in Figure 2B, the TN of all fractions for the conventional and enhanced separation methods appeared to be stable, and the separation methods had little impact on the TN of the solid fractions. However, the higher TN of the LF and lower TN of the SF, compared with the respective values of the enhanced separation methods, demonstrated a higher TN separation efficiency.

3.1.2. Dynamics of Soil NO3−-N, NH4+-N, and DOC

Figure 3A shows the dynamics of the soil NH4+-N contents under the different treatments during incubation. At the initial stage, the soil NH4+-N contents of the SF and LF treatments were higher than those of the other treatments but declined quickly and eventually approached those of the other treatments. However, the soil NH4+-N of the SF+TA treatment exhibited different behaviors, showing a peak on day 5, although it eventually approached that of the other treatments. For soil nitrate, except for the relatively stable NO3– in the CK, it increased in all treatments during incubation. The LF treatment had the highest NO3– at the end of the incubation. Soil DOC peaked on day 5 in the SF + TA and LF + TA treatments and gradually declined in the SF and LF treatments. Therefore, the use of TA in the SLS had an apparent impact on the dynamics of soil NH4+ and DOC.

3.2. Gaseous Nitrogen Emissions

3.2.1. NH3 Emission

(1)
Storage phase
The NH3 emission characteristics during solid and liquid manure storage are shown in Figure 4A. During storage, the NH3 emission rates of the LF treatment continued to be higher than those of the other treatments, reaching the highest level of 103.43 mg m−2 day−1 on day 10, followed by the LF + TA treatment; nonetheless, low NH3 emissions from the SF + TA and SF treatments were observed, although the NH3 emission rates of the SF + TA treatment during the early stage were greater than those of the SF treatment.
Figure 4B shows the cumulative NH3 emissions for each treatment during storage. The cumulative NH3 emissions of the LF were the highest (1483.39 mg·m−2), significantly higher than those of the SF treatment. Compared with LF, the LF + TA treatment significantly reduced the cumulative NH3 emissions by 45.49%. In contrast, the cumulative NH3 emissions of the SF + TA treatment were 135.83 mg·m−2, significantly higher than those of the SF treatment. In summary, the NH3 emissions of the liquid fraction were significantly higher than those of the solid fractions during storage, and enhanced SLS significantly reduced the NH3 emissions of the liquid fraction but significantly increased the NH3 emissions of the solid fraction.
(2)
Soil application phase
The NH3 emission rates during the soil application phase are shown in Figure 5A. The LF + TA treatment had the highest NH3 emission rates, and the peak value reached 27.32 mg·m−2·h−1. The NH3 emission rates of all treatments decreased in the following order: LF + TA > LF > SF + TA > SF > CK. The emission rates of CK were the lowest.
Figure 5B shows the cumulative NH3 emissions for all treatments. The cumulative NH3 emissions of the LF + TA during the measurement period reached 1499.64 mg·m−2, significantly higher than those of other treatments. Of the solid and liquid fractions, greater NH3 emissions were observed from the liquid fraction (LF, LF + TA) than those from the solid fraction (SF, SF + TA), with those of the former being approximately 44.38 higher than those of the latter. Considering the NH3 among the two SLS, the enhanced SLS showed higher NH3 emissions from the LF compared with the LF + TA, but had little impact on the NH3 emissions of the solid fractions.

3.2.2. N2O Emission

(1)
Storage phase
Figure 6A shows the characteristics of N2O emissions during the storage of solid and liquid fractions of the two SLS. The N2O emissions of the LF and LF + TA were much lower (0–3.19 mg·m−2·day−1) than those from the solid fraction storage (1.89–215.22 mg·m−2·day−1). Regarding the N2O from solid fraction storage, much lower N2O emission rates for the SF + TA treatment were observed throughout the monitoring period compared with those of the SF. The cumulative N2O emissions of the SF were 2797.15 mg·m−2, significantly higher than those of the LF. The cumulative N2O emissions of the SF + TA treatment were 86.37% lower than those of the SF treatment. Similar emissions were observed for the LF and LF + TA treatments. Overall, the N2O emissions of the solid fraction during storage were much higher than those of the liquid fractions for both SLS. Therefore, enhanced SLS with the use of TA can effectively reduce the N2O emissions of the solid fractions while having little impact on the N2O emissions of the liquid fractions.
(2)
Soil application phase
The N2O emission rates of different treatments during the soil application phase are shown in Figure 7A. During days 1–2, the N2O emission rates of the LF and LF + TA treatments increased rapidly and reached peak values of 14.00 and 8.50 mg m−2 h−1, respectively; the emission rates of the SF treatment also peaked on day 2, with a value of 5.37 mg·m−2·h−1. The peak value of the LF treatment was significantly higher than that of the other treatments, and the peak values of all treatments decreased in the order of LF > LF + TA > SF > SF + TA > CK. The N2O emission rates of all treatments approached zero after day 6.
As shown in Figure 7B, compared with CK, the application of the liquid and solid fractions drastically increased N2O emissions. The cumulative N2O emissions of the LF (560.04 mg m−2) and LF + TA (437.02 mg·m−2) treatments were 99.88% and 69.30% higher than the emissions of the SF (280.19 mg m−2) and SF + TA (258.13 mg m−2) treatments, respectively. Compared with the LF treatment, the N2O emissions of the LF + TA treatment were 21.97% lower, whereas the total N2O emissions of the SF + TA treatment were slightly lower than those of the SF treatment.

3.2.3. Total Gaseous Nitrogen Losses During Soil Application

Table 2 shows the NH3-N and N2O-N loss coefficients of the nitrogen input for each treatment after fertilization. The NH3-N loss coefficient of the LF treatment was 3.63%, which was 1.8% higher than that of the SF treatment. The NH3-N loss coefficient of the LF + TA treatment was 4.15% higher than that of the LF treatment, whereas the NH3-N loss coefficient of the SF + TA treatment was similar to that of the SF treatment.
The N2O-N loss coefficient of the SF was 1.16% (Table 2) for the conventional SLS and 1.86% lower than the N2O-N loss coefficient of the LF treatment. Similar results were found for the enhanced SLS, where the coefficient of the SF + TA was 1.19% lower than that of the SF + TA. When comparing conventional and enhanced SLS, the N2O-N loss coefficient of the LF + TA treatment was 0.82% lower than that of the LF treatment. Considering the total (NH3 + N2O)-N loss, NH3-N emissions contributed more to the total N loss in both SLSs (Table 2). Additionally, the N losses from the enhanced SLS were 3.33 percentage points higher than those from the conventional SLS, mainly because of the higher NH3-N loss. However, similar N loss coefficients for the solid fraction storage were found for the conventional and enhanced SLS.

3.3. CH4 Emissions

3.3.1. Storage Phase

During the storage phase, the CH4 emission rates (0.0176–30.59 g m−2 day−1) of the liquid fractions were much greater than those of the solid fractions (0–0.85 g m−2 day−1) (Figure 8A). Meanwhile, the CH4 emission rates in the LF + TA treatment were lower than those in the LF treatment. On the other hand, the SF + TA treatment had higher CH4 emission rates than the SF treatment. In Figure 8B, the cumulative CH4 emissions of the LF treatment were 396.96 g m−2, significantly higher than those of the SF treatment under the conventional SLS. Compared with the LF treatment, the CH4 emissions from the LF + TA treatment were approximately 50.15% lower, indicating a significant reduction in CH4 emissions. In addition, the cumulative CH4 emissions of the SF and SF + TA treatments were 0.19 and 13.19 g m−2, respectively, much lower than those of the liquid fractions. It was also found that the enhanced SLS with TA significantly reduced the CH4 emissions of the liquid fraction but had no significant impact on the solid fractions.

3.3.2. Soil Application Phase

During the soil application phase, significant CH4 emissions occurred only in the LF and LF + TA treatments during the early incubation stage (days 1–3) (Figure 9A). The peak CH4 emissions of the LF + TA and LF treatments were 2.34 and 1.02 mg m−2 h−1, respectively, on the first day. There was no significant difference in the peak CH4 emission rates between the LF + TA and LF treatments, which were 0.53 and 0.46 mg m−2 h−1, respectively. Afterward, very low CH4 emission rates or even uptake by the soil were observed in all treatments (Figure 9A).
Figure 9B shows that, during soil application, the CH4 emissions of 41.60 mg m−2 in the LF were significantly higher than those of 0.79 mg·m−2 in the SF. The cumulative CH4 emission rate of the LF + TA treatment was 87.78 mg·m−2, which was higher than that of LF treatment (41.60 mg m−2); and that of the SF + TA treatment was significantly higher than that of the SF treatment. However, no significant differences were observed between SF and CK. In conclusion, CH4 emissions from the liquid manure were higher than those from the solid fraction. Enhanced SLS increased the emission of CH4 in the soil compared with the conventional SLS.

3.4. CO2 Emissions

The CO2 emission characteristics during solid and liquid manure storage are shown in Figure 10A. During the monitoring period, the CO2 emission rates of the SF were higher than those of the other treatments. Accordingly, the cumulative CO2 emissions from the SF treatment were the highest, at 1389.62 g m−2, significantly higher than those of the LF. However, the CO2 emissions of LF + TA and SF + TA were similar, indicating a weak effect of the enhanced SLS on CO2 emissions during the storage phase (Figure 10B).
During the soil application phase, the soil CO2 emission rates increased with the application of solid and liquid fractions (Figure 11A), and the SF + TA treatment appeared to have the highest emission rates. Figure 11B shows that the cumulative CO2 emissions of the SF + TA treatment amounted to 104.58 g m−2, which was 24.14% higher than that of the SF treatment. In addition, similar emissions in the LF and LF + TA treatments were observed, indicating a weak impact on the CO2 emissions from liquid fractions.

3.5. Integrative CO2-e Emissions of the Conventional and Enhanced SLS

3.5.1. CO2-e Emissions of Different Treatments During Storage

As shown in Table 3, during the storage phase, CH4 from the liquid fractions was the dominant contributor to the total CO2-e emissions, of which the LF + TA and LF treatments accounted for 99.71% and 99.90% of the total emissions of CO2-e, respectively. For the solid fraction, N2O emissions were the major contributor to the total emissions of CO2-e in the SF, but CH4 emissions were the major contributor to the CO2-e in the SF + TA treatment. The NH3 emissions of the different treatments contributed the least to the total CO2-e emissions.

3.5.2. CO2-e Emissions of Different Treatments During Soil Application

As shown in Table 4, during the soil application phase, the N2O emissions were the dominant contributor to CO2-e emissions in all treatments, followed by CH4 and NH3. The CO2-e values of the different treatments decreased in the following order: LF > LF + TA > SF > SF + TA > CK. The CO2-e emissions of the LF treatment were 153.22 g·m−2, significantly higher than those of the SF treatment. The LF + TA treatment resulted in significantly lower CO2-e emissions compared with the LF treatment, with a decrease of 18.73%. In summary, the CO2-e of the soil treated with LF was significantly higher than that of the soil treated with SF. The enhanced SLS was conducive to reducing the CO2-e emissions of the soil receiving LF but had no significant effect on the CO2-e emissions of the soil fertilized with solid fractions.

3.5.3. Integrative CO2-e Emissions of the Conventional and Enhanced SLS and Trade-Offs

As shown in Table 5, during the storage phase, the CH4 emissions dominated the CO2-e emissions, accounting for 98.98% and 98.81% of the total CO2-e emissions, respectively, while the CO2-e emissions of N2O and NH3 were relatively low. Meanwhile, considering the total CO2-e emissions, the total CO2-e emissions of the enhanced SLS were 23.43 g·kg−1, which were 53.64% lower than those of the conventional SLS. During the soil phase, the N2O emissions contributed the most to CO2-e emissions during soil application, accounting for 94.59% and 97.32% of the total CO2-e emissions, respectively (Table 5). The total CO2-e emissions of the enhanced SLS were 707.45 g·kg−1, approximately 31.63% lower than those of the conventional SLS.
To evaluate the integrative impact of the conventional and enhanced SLS on the total CO2-e emissions along the storage–soil chain, the CO2-e of N2O, CH4, and indirect N2O from the NH3 emissions during the storage and soil application phases were calculated on a per-kilogram-of-raw slurry basis. The CO2-e emissions during storage and soil application were dominated by N2O emissions during the soil application for both SLS. The enhanced SLS with TA significantly reduced CO2-e emissions by 32.7% compared with the conventional SLS (Table 5).
However, large trade-offs in different gases during two management phases were identified (Figure 12). During the storage phase, the reduced CH4 and NH3 emissions from the liquid fraction were offset partly by the respective increased emissions from the solid fraction (Figure 12A). Meanwhile, trade-offs in the CH4 and N2O emissions were observed during the soil application phase (Figure 12B). Additionally, trade-offs in the CH4 and NH3 emissions between the storage and soil application phases occurred (Figure 12C). This demonstrates that special attention should be paid to control the increased gas emissions from the aforementioned sources.

4. Discussion

4.1. Impact on NH3 Emissions

This study found significantly higher NH3 emissions from the LF treatment than from the SF treatment during storage, which is consistent with several previous studies [18,45]. This difference may be attributed to the absence of a thick surface crust forming during storage [18]. The enhanced SLS significantly reduced NH3 emissions during LF storage, suggesting that TA could serve as an effective flocculant for mitigating NH3 volatilization in stored LF.
Previous studies have shown that LF application results in lower NH3 volatilization compared to raw slurry application [46,47]. The higher NH3 emissions from raw slurry may stem from poor conditions for slurry infiltration [48]. Additionally, during the soil application, the higher NH3 emissions from LF + TA versus LF alone could be due to the greater NH4+-N input in LF + TA (Table 1). Therefore, while improving liquid manure separation efficiency via TA flocculation may reduce storage-phase NH3 emissions, it could also increase NH3 loss risks during soil application. Further research on this trade-off is warranted.

4.2. Impact on N2O Emissions

This study found that N2O emissions during LF storage were lower than those from SF storage, likely due to the anoxic/anaerobic conditions suppressing N2O production in LF [18,49]. The results show that N2O emissions during liquid manure storage depend on nitrogen availability, oxygen levels, pH, and redox status [21]. In contrast, the higher N2O emissions from SF storage may result from enhanced nitrification in solid manure [50]. Compared to the SF treatment, the SF + TA treatment significantly reduced N2O emissions during storage, suggesting that TA may inhibit N2O production.
During soil application, N2O emissions were significantly higher in the LF treatment than in the SF treatment, consistent with the findings of Dinuccio et al. [49]. This difference may be explained by the high concentration of water-soluble carbon and NH3-N in the liquid fraction, which altered fungal α-diversity after soil application [51], increased the abundance of ammonia-oxidizing bacteria (AOB) and nirS genes, and reduced the abundance of nosZ genes during denitrification [52,53,54,55]. Compared to LF alone, LF + TA significantly reduced N2O emissions, likely because tannin–organic nitrogen complexes slow organic N mineralization. This decreased the soil NH4+-N and NO3−-N availability [56], ultimately reducing N2O emissions [57].
Both the LF + TA and SF + TA treatments lowered the soil NH4+-N and NO3−-N levels compared to the LF and SF treatments, possibly because residual TA in the LF inhibited microbial mineralization and nitrification/denitrification by suppressing soil enzyme activity, thus reducing NH4+-N and NO3−-N accumulation. The increase in soil dissolved organic carbon (DOC) may be attributed to tannins acting as a microbial carbon source [58,59,60,61].

4.3. Impact on CH4 Emissions

This study observed higher CH4 emissions during the storage phase of both LF and SF compared to the soil application phase, which is consistent with findings of Holly et al. [18]. Notably, SF exhibited significantly lower CH4 emissions than LF during both phases, primarily due to its more aerobic environment, which suppresses the anaerobic conditions required for methanogenesis [62]. Additionally, the reduced CH4 emissions from SF may result from the retention of readily degradable carbon in the liquid fraction, limiting substrate availability for CH4 production [19,63].
During storage, the LF + TA treatment significantly reduced CH4 emissions relative to LF alone. However, during soil application, this trend reversed, likely because TA formed complexes with organic carbon during storage, slowing its decomposition in the liquid fraction. Conversely, the elevated CH4 emissions from the LF + TA and SF + TA treatments may reflect TA’s role as a microbial carbon source [60,61,64], potentially serving as a substrate for methanogens [61]. During the soil application phase, CH4 emissions peaked within the first two days, likely due to the release of dissolved CH4 from the manure [65,66].

4.4. Impact on CO2 Emissions

The CO2 emission rate serves as an indirect indicator of organic matter decomposition and microbial activity [67]. This study showed that CO2 emissions from the SF treatment exceeded those from the LF treatment during storage, which is consistent with previous studies, linking this difference to the solid fraction’s higher carbon content and adequate oxygen availability [18].
During soil application, the lower CO2 emissions from the LF-treated soil compared to the SF-treated soil likely resulted from the reduced organic matter content in the liquid manure following solid–liquid separation [18]. Both the SF + TA and LF + TA treatments exhibited rapid increases in CO2 emissions, aligning with findings of Kraal et al. [68]. This effect is probably attributable to TA serving as a microbial carbon source [60,61].

4.5. Implication

This study demonstrated that TA as a flocculant can effectively improve separation efficiency while reducing greenhouse gas (GHG) emissions across the dairy slurry management chain, achieving co-reduction in both long-lived N2O and short-lived CH4. These findings support the promising use of plant-derived biological flocculants [60,61] and could advance circular agriculture by utilizing residues and byproducts from fruit crops, food waste, and the brewing industry [69,70].
However, enhanced solid–liquid separation (SLS) presents some limitations. First, increased nitrogen loss, primarily through NH3 emissions during storage and field application, significantly reduces the nutrient value of both LF and SF fractions. This necessitates targeted strategies to control nitrogen loss. Second, emission trade-offs between different fractions and management sectors require complementary practices to address hotspot emissions [71].
Current mitigation options include covers [72] and acidification [73,74] for the storage phase, and urease inhibitors (e.g., NBPT or limus compounds) for field application [75,76]. For circular agriculture systems, we recommend integrating enhanced SLS for GHG reduction with targeted NH3 mitigation practices during storage and field application. However, field validation is needed to assess actual impacts on crop yields and overall mitigation effectiveness.

5. Conclusions

This study demonstrated that enhanced SLS with the use of tannic acid has promising potential to reduce the GHG emissions of the separated fractions by 32.66% across the storage and soil application chain, with synergistic mitigation of CH4 and N2O. However, the resulting trade-offs of N2O/CH4 between the SF and LF treatments, as well as the storage and field application phases, may halt the mitigation potential of enhanced SLS. Meanwhile, the increased NH3 emissions by 28.58% due to enhanced SLS could also be a barrier limiting the spread of this technology. Therefore, further attention is required to minimize the trade-offs of gas emissions between the fraction and the management sectors to mitigate GHG emissions during the recycling of plant-derived tannic acid in the circular agriculture context.

6. Patents

Hebei Agricultural University. Soil column uniform filling device: 202321245577. X [P]. 2024-03-26.

Author Contributions

Z.G.: conceptualization, methodology, writing—review and editing, supervision, and funding acquisition. S.W.: conceptualization, methodology, investigation, writing—original draft preparation. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Natural Science Foundation of China (NSFC: Grant No. 42375170).

Data Availability Statement

Data will be made available upon request.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
NH3Ammonia
N2ONitrous oxide
CO2Carbon dioxide
CH4Methane
SLSSolid–liquid separation method
GHGGreenhouse gas

References

  1. Zhang, T.; Hou, Y.; Meng, T.; Ma, Y.; Tan, M.; Zhang, F.; Oenema, O. Replacing synthetic fertilizer by manure requires adjusted technology and incentives: A farm survey across China. Resour. Conserv. Recycl. 2021, 168, 105301. [Google Scholar] [CrossRef]
  2. Dróżdż, D.; Wystalska, K.; Malińska, K.; Grosser, A.; Grobelak, A.; Kacprzak, M. Management of poultry manure in Poland—Current state and future perspectives. J. Environ. Manag. 2020, 264, 110327. [Google Scholar] [CrossRef] [PubMed]
  3. Xu, P.; Houlton, B.Z.; Zheng, Y.; Zhou, F.; Ma, L.; Li, B.; Liu, X.; Li, G.; Lu, H.; Quan, F.; et al. Policy-enabled stabilization of nitrous oxide emissions from livestock production in China over 1978–2017. Nat. Food 2022, 3, 356–366. [Google Scholar] [CrossRef]
  4. Fyfe, J.; Hagare, D.; Sivakumar, M. Dairy shed effluent treatment and recycling: Effluent characteristics and performance. J. Environ. Manag. 2016, 180, 133–146. [Google Scholar] [CrossRef]
  5. Mehta, C.M.; Khunjar, W.O.; Nguyen, V.; Tait, S.; Batstone, D.J. Technologies to recover nutrients from waste streams: A critical review. Crit. Rev. Environ. Sci. Technol. 2014, 45, 385–427. [Google Scholar] [CrossRef]
  6. Meetiyagoda, T.A.O.K.; Takahashi, T.; Fujino, T. Response surface optimization of chemical coagulation for solid–liquid separation of dairy manure slurry through Box–Behnken design with desirability function. Heliyon 2023, 9, 17632. [Google Scholar] [CrossRef]
  7. Christensen, M.L.; Christensen, K.V.; Sommer, S.G. Solid–liquid separation of animal slurry. Anim. Manure Recycl. Treat. Manag. 2013, 9, 105–130. [Google Scholar] [CrossRef]
  8. Amon, B.; Amon, T.; Boxberger, J.; Alt, C. Emissions of NH3, N2O and CH4 from dairy cows housed in a farmyard manure tying stall (housing, manure storage, manure spreading). Nutr. Cycl. Agroecosyst. 2001, 60, 103–113. [Google Scholar] [CrossRef]
  9. Garcia, M.C.; Szogi, A.A.; Vanotti, M.B.; Chastain, J.P.; Millner, P.D. Enhanced solid–liquid separation of dairy manure with natural flocculants. Bioresour. Technol. 2009, 100, 5417–5423. [Google Scholar] [CrossRef]
  10. Lakavathu, S.; Reddy, V.K.; Singh, N.; Kamble, P.; Jadhav, J.; Choudhury, A.R.; Palani, S.G. Feasibility study of faecal sludge treatment by Geotube and jute tube–based technologies. Environ. Sci. Pollut. Res. 2023, 30, 124382–124400. [Google Scholar] [CrossRef]
  11. Vanotti, M.; Rashash, D.; Hunt, P. Solid–liquid separation of flushed swine manure with PAM: Effect of wastewater strength. Trans. ASAE 2002, 45, 1959–1969. [Google Scholar] [CrossRef]
  12. Liu, Z.; Carroll, Z.S.; Long, S.C.; Gunasekaran, S.; Runge, T. Use of cationic polymers to reduce pathogen levels during dairy manure separation. J. Environ. Manag. 2016, 166, 260–266. [Google Scholar] [CrossRef] [PubMed]
  13. Owen, J.J.; Silver, W.L. Greenhouse gas emissions from dairy manure management: A review of field-based studies. Glob. Change Biol. 2014, 21, 550–565. [Google Scholar] [CrossRef] [PubMed]
  14. Yusuf, R.O.; Noor, Z.Z.; Abba, A.H.; Hassan, M.A.A.; Din, M.F.M. Methane emission by sectors: A comprehensive review of emission sources and mitigation methods. Renew. Sustain. Energy Rev. 2012, 16, 5059–5070. [Google Scholar] [CrossRef]
  15. Ambrose, H.W.; Dalby, F.R.; Feilberg, A.; Kofoed, M.V. Additives and methods for the mitigation of methane emission from stored liquid manure. Biosyst. Eng. 2023, 229, 209–245. [Google Scholar] [CrossRef]
  16. Viaene, J.; Peiren, N.; Vandamme, D.; Lataf, A.; Cuypers, A.; Jozefczak, M.; Vandecasteele, B. Biochar amendment to cattle slurry reduces NH3 emissions during storage without risk of higher NH3 emissions after soil application of the solid fraction. Waste Manag. 2023, 167, 39–45. [Google Scholar] [CrossRef]
  17. Zervas, G.; Tsiplakou, E. An assessment of GHG emissions from small ruminants in comparison with GHG emissions from large ruminants and monogastric livestock. Atmos. Environ. 2012, 49, 13–23. [Google Scholar] [CrossRef]
  18. Holly, M.A.; Larson, R.A.; Powell, J.M.; Ruark, M.D.; Aguirre-Villegas, H. Greenhouse gas and ammonia emissions from digested and separated dairy manure during storage and after land application. Agric. Ecosyst. Environ. 2017, 239, 410–419. [Google Scholar] [CrossRef]
  19. Amon, B.; Kryvoruchko, V.; Amon, T.; Zechmeister-Boltenstern, S. Methane, nitrous oxide and ammonia emissions during storage and after application of dairy cattle slurry and influence of slurry treatment. Agric. Ecosyst. Environ. 2006, 112, 153–162. [Google Scholar] [CrossRef]
  20. Aguirre-Villegas, H.A.; Larson, R.A.; Sharara, M.A. Anaerobic digestion, solid-liquid separation, and drying of dairy manure: Measuring constituents and modeling emission. Sci. Total Environ. 2019, 696, 134059. [Google Scholar] [CrossRef]
  21. Chadwick, D.; Sommer, S.; Thorman, R.; Fangueiro, D.; Cardenas, L.; Amon, B.; Misselbrook, T. Manure management: Implications for greenhouse gas emissions. Anim. Feed Sci. Technol. 2011, 166, 514–531. [Google Scholar] [CrossRef]
  22. Chisholm, C.M.W.; Cameron, K.C.; Di, H.J.; Green, T.C. The effect of polyferric sulphate treated farm dairy effluent and clarified water on leaching losses, greenhouse gas emissions and pasture growth. J. Agric. Res. 2020, 64, 271–285. [Google Scholar] [CrossRef]
  23. Wang, X.M.; Di, H.J.; Cameron, K.C.; Li, B. Effect of treated farm dairy effluent on E. coli, phosphorus and nitrogen leaching and greenhouse gas emissions: A field lysimeter study. J. Soils Sediments 2019, 19, 2303–2312. [Google Scholar] [CrossRef]
  24. Baral, K.R.; Jégo, G.; Amon, B.; Bol, R.; Chantigny, M.H.; Olesen, J.E.; Petersen, S.O. Greenhouse gas emissions during storage of manure and digestates: Key role of methane for prediction and mitigation. Agric. Syst. 2018, 166, 26–35. [Google Scholar] [CrossRef]
  25. Hjorth, M.; Christensen, K.V.; Christensen, M.L.; Sommer, S.G. Solid–Liquid Separation of Animal Slurry in Theory and Practice. Sustain. Agric. 2011, 2, 953–986. [Google Scholar] [CrossRef]
  26. Møller, H.B.; Lund, I.; Sommer, S.G. Solid–liquid separation of livestock slurry: Efficiency and cost. Bioresour. Technol. 2000, 74, 223–229. [Google Scholar] [CrossRef]
  27. Meng, X.; Ma, C.; Petersen, S.O. Sensitive control of N2O emissions and microbial community dynamics by organic fertilizer and soil interactions. Biol. Fertil. Soils 2022, 58, 771–788. [Google Scholar] [CrossRef]
  28. Möller, K.; Stinner, W. Effects of different manuring systems with and without biogas digestion on soil mineral nitrogen content and on gaseous nitrogen losses (ammonia, nitrous oxides). Eur. J. Agron. 2009, 30, 1–16. [Google Scholar] [CrossRef]
  29. Petersen, S.O. Nitrous Oxide Emissions from Manure and Inorganic Fertilizers Applied to Spring Barley. J. Environ. Qual. 1999, 28, 1610–1618. [Google Scholar] [CrossRef]
  30. Thomsen, I.K.; Pedersen, A.R.; Nyord, T.; Petersen, S.O. Effects of slurry pre-treatment and application technique on short-term N2O emissions as determined by a new non-linear approach. Agric. Ecosyst. Environ. 2010, 136, 227–235. [Google Scholar] [CrossRef]
  31. Ellison, R.J.; Horwath, W.R. Reducing greenhouse gas emissions and stabilizing nutrients from dairy manure using chemical coagulation. J. Environ. Qual. 2021, 50, 375–383. [Google Scholar] [CrossRef] [PubMed]
  32. Zhang, Z.; Wang, J.; Liu, D.; Li, J.; Wang, X.; Song, B.; Yue, B.; Zhao, K.; Song, Y. Hydrolysis of polyaluminum chloride prior to coagulation: Effects on coagulation behavior and implications for improving coagulation performance. J. Environ. Sci. 2017, 57, 162–169. [Google Scholar] [CrossRef]
  33. Aljuboori, A.H.R.; Idris, A.; Abdullah, N.; Mohamad, R. Production and characterization of a bioflocculant produced by Aspergillus flavus. Bioresour. Technol. 2013, 127, 489–493. [Google Scholar] [CrossRef] [PubMed]
  34. Singh, R.; Kumar, S.; Garg, M. Domestic wastewater treatment using tanfloc: A tannin based coagulant. In Geostatistical and Geospatial Approaches for the Characterization of Natural Resources in the Environment: Challenges, Processes and Strategies; Springer: Berlin/Heidelberg, Germany, 2016; pp. 349–354. [Google Scholar] [CrossRef]
  35. Sievers, D.; Jenner, M.; Hanna, M. Treatment of dilute manure wastewaters by chemical coagulation. Trans. ASAE 1994, 37, 597–601. [Google Scholar] [CrossRef]
  36. Salehizadeh, H.; Shojaosadati, S. Extracellular biopolymeric flocculants: Recent trends and biotechnological importance. Biotechnol. Adv. 2001, 19, 371–385. [Google Scholar] [CrossRef]
  37. Sánchez-Martín, J.; González-Velasco, M.; Beltrán-Heredia, J. Surface water treatment with tannin-based coagulants from Quebracho (Schinopsis balansae). Chem. Eng. J. 2010, 165, 851–858. [Google Scholar] [CrossRef]
  38. Nierop, K.G.; Preston, C.M.; Verstraten, J.M. Linking the B ring hydroxylation pattern of condensed tannins to C, N and P mineralization. A case study using four tannins. Soil Biol. Biochem. 2006, 38, 2794–2802. [Google Scholar] [CrossRef]
  39. Nierop, K.G.J.; Verstraten, J.M.; Tietema, A.; Westerveld, J.W.; Wartenbergh, P.E. Short- and Long-term Tannin Induced Carbon, Nitrogen and Phosphorus Dynamics in Corsican Pine Litter. Biogeochemistry 2006, 79, 275–296. [Google Scholar] [CrossRef]
  40. IPCC. Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change; Edenhofer, O., Pichs-Madruga, R., Sokona, Y., Farahani, E., Kadner, S., Seyboth, K., Adler, A., Baum, I., Brunner, S., Eickemeier, P., et al., Eds.; Cambridge University Press: Cambridge, UK; New York, NY, USA, 2014. [Google Scholar]
  41. Ridoutt, B.; Lehnert, S.A.; Denman, S.; Charmley, E.; Kinley, R.; Dominik, S. Potential GHG emission benefits of Asparagopsis taxiformis feed supplement in Australian beef cattle feedlots. J. Clean. Prod. 2022, 337, 130499. [Google Scholar] [CrossRef]
  42. Cain, M.; Lynch, J.; Allen, M.R.; Fuglestvedt, J.S.; Frame, D.J.; Macey, A.H. Improved calculation of warming-equivalent emissions for short-lived climate pollutants. NPJ Clim. Atmos. Sci. 2019, 2, 29. [Google Scholar] [CrossRef]
  43. Wang, S.; Wang, W.; Cui, Y.; Bai, Y.; Liu, C.; Liao, W.; Gao, Z. Impacts of liquid fractions from two solid–liquid separation technologies on the soil porosity, ammonia, and greenhouse gas emissions. Agronomy 2024, 14, 186. [Google Scholar] [CrossRef]
  44. Bartlett, R.J.; Ross, D.S. Colorimetric determination of oxidizable carbon in acid soil solutions. Soil Sci. Soc. Am. J. 1988, 52, 1191–1192. [Google Scholar] [CrossRef]
  45. Dinuccio, E.; Berg, W.; Balsari, P. Gaseous emissions from the storage of untreated slurries and the fractions obtained after mechanical separation. Atmos. Environ. 2008, 42, 2448–2459. [Google Scholar] [CrossRef]
  46. Owusu-Twum, M.Y.; Polastre, A.; Subedi, R.; Santos, A.S.; Ferreira, L.M.M.; Coutinho, J.; Trindade, H. Gaseous emissions and modification of slurry composition during storage and after field application: Effect of slurry additives and mechanical separation. J. Environ. Manag. 2017, 200, 416–422. [Google Scholar] [CrossRef]
  47. Pedersen, J.; Nyord, T.; Feilberg, A.; Labouriau, R.; Hunt, D.; Bittman, S. Effect of reduced exposed surface area and enhanced infiltration on ammonia emission from untreated and separated cattle slurry. Biosyst. Eng. 2021, 211, 141–151. [Google Scholar] [CrossRef]
  48. Bhandral, R.; Bittman, S.; Kowalenko, G.; Buckley, K.; Chantigny, M.; Hunt, D.; Bounaix, F.; Friesen, A. Enhancing soil infiltration reduces gaseous emissions and improves N uptake from applied dairy slurry. J. Environ. Qual. 2009, 38, 1372–1382. [Google Scholar] [CrossRef]
  49. Dinuccio, E.; Berg, W.; Balsari, P. Effects of mechanical separation on GHG and ammonia emissions from cattle slurry under winter conditions. Anim. Feed. Sci. Technol. 2011, 166, 532–538. [Google Scholar] [CrossRef]
  50. Sun, B.; Bai, Z.; Li, Y.; Li, R.; Song, M.; Xu, S.; Zhang, H.; Zhuang, X. Emission mitigation of CH4 and N2O during semi-permeable membrane covered hyperthermophilic aerobic composting of livestock manure. J. Clean. Prod. 2022, 379, 134850. [Google Scholar] [CrossRef]
  51. Wen, Y.C.; Li, H.Y.; Lin, Z.A.; Zhao, B.Q.; Sun, Z.B.; Yuan, L.; Xu, J.K.; Li, Y.Q. Long-term fertilization alters soil properties and fungal community composition in fluvo-aquic soil of the North China Plain. Sci. Rep. 2020, 10, 7198. [Google Scholar] [CrossRef]
  52. Blagodatskaya, E.; Zheng, X.; Blagodatsky, S.; Wiegl, R.; Dannenmann, M.; Butterbach-Bahl, K. Oxygen and substrate availability interactively control the temperature sensitivity of CO2 and N2O emission from soil. Biol. Fertil. Soils 2014, 50, 775–783. [Google Scholar] [CrossRef]
  53. Charles, A.; Rochette, P.; Whalen, J.K.; Angers, D.A.; Chantigny, M.H.; Bertrand, N. Global nitrous oxide emission factors from agricultural soils after addition of organic amendments: A meta-analysis. Agric. Ecosyst. Environ. 2017, 236, 88–98. [Google Scholar] [CrossRef]
  54. Domeignoz-Horta, L.A.; Philippot, L.; Peyrard, C.; Bru, D.; Breuil, M.; Bizouard, F.; Justes, E.; Mary, B.; Léonard, J.; Spor, A. Peaks of in situ N2O emissions are influenced by N2O-producing and reducing microbial communities across arable soils. Glob. Change Biol. 2018, 24, 360–370. [Google Scholar] [CrossRef] [PubMed]
  55. Xu, X.; Liu, Y.; Singh, B.P.; Yang, Q.; Zhang, Q.; Wang, H.; Xia, Z.; Di, H.; Singh, B.K.; Xu, J.; et al. NosZ clade II rather than clade I determine in situ N2O emissions with different fertilizer types under simulated climate change and its legacy. Soil Biol. Biochem. 2020, 150, 107974. [Google Scholar] [CrossRef]
  56. Hättenschwiler, S.; Vitousek, P.M. The role of polyphenols in terrestrial ecosystem nutrient cycling. Trends Ecol. Evol. 2000, 15, 238–243. [Google Scholar] [CrossRef]
  57. Sahiner, N.; Sagbas, S.; Sahiner, M.; Silan, C.; Aktas, N.; Turk, M. Biocompatible and biodegradable poly(Tannic Acid) hydrogel with antimicrobial and antioxidant properties. Int. J. Biol. Macromol. 2016, 82, 150–159. [Google Scholar] [CrossRef]
  58. Adamczyk, S.; Kiikkilä, O.; Kitunen, V.; Smolander, A. Potential response of soil processes to diterpenes, triterpenes and tannins: Nitrification, growth of microorganisms and precipitation of proteins. Appl. Soil Ecol. 2013, 67, 47–52. [Google Scholar] [CrossRef]
  59. Villalba, J.J.; A Beauchemin, K.; Gregorini, P.; MacAdam, J.W. Pasture chemoscapes and their ecological services. Transl. Anim. Sci. 2019, 3, 829–841. [Google Scholar] [CrossRef]
  60. Dalby, F.R.; Hansen, M.J.; Feilberg, A.; Kümmel, S.; Nikolausz, M. Effect of tannic acid combined with fluoride and lignosulfonic acid on anaerobic digestion in the agricultural waste management chain. Bioresour. Technol. 2020, 307, 123171. [Google Scholar] [CrossRef]
  61. Dalby, F.R.; Svane, S.; Sigurdarson, J.J.; Sørensen, M.K.; Hansen, M.J.; Karring, H.; Feilberg, A. Synergistic tannic acid-fluoride inhibition of ammonia emissions and simultaneous reduction of methane and odor emissions from livestock waste. Environ. Sci. Technol. 2020, 54, 7639–7650. [Google Scholar] [CrossRef]
  62. Ravindran, B.; Awasthi, M.K.; Karmegam, N.; Chang, S.W.; Chaudhary, D.K.; Selvam, A.; Nguyen, D.D.; Milon, A.R.; Munuswamy-Ramanujam, G. Co-composting of food waste and swine manure augmenting biochar and salts: Nutrient dynamics, gaseous emissions and microbial activity. Bioresour. Technol. 2021, 344, 126300. [Google Scholar] [CrossRef]
  63. Fangueiro, D.; Senbayran, M.; Trindade, H.; Chadwick, D. Cattle slurry treatment by screw press separation and chemically enhanced settling: Effect on greenhouse gas emissions after land spreading and grass yield. Bioresour. Technol. 2008, 99, 7132–7142. [Google Scholar] [CrossRef] [PubMed]
  64. Kraus, T.E.; Zasoski, R.J.; Dahlgren, R.A.; Horwath, W.R.; Preston, C.M. Carbon and nitrogen dynamics in a forest soil amended with purified tannins from different plant species. Soil Biol. Biochem. 2004, 36, 309–321. [Google Scholar] [CrossRef]
  65. Chadwick, D.; Pain, B.; Brookman, S. Nitrous oxide and methane emissions following application of animal manures to grassland. J. Environ. Qual. 2000, 29, 277–287. [Google Scholar] [CrossRef]
  66. Clemens, J.; Trimborn, M.; Weiland, P.; Amon, B. Mitigation of greenhouse gas emissions by anaerobic digestion of cattle slurry. Agric. Ecosyst. Environ. 2006, 112, 171–177. [Google Scholar] [CrossRef]
  67. Jeong, S.T.; Cho, S.R.; Lee, J.G.; Kim, P.J.; Kim, G.W. Composting and compost application: Trade-off between greenhouse gas emission and soil carbon sequestration in whole rice cropping system. J. Clean. Prod. 2019, 212, 1132–1142. [Google Scholar] [CrossRef]
  68. Kraal, P.; Nierop, K.G.; Kaal, J.; Tietema, A. Carbon respiration and nitrogen dynamics in Corsican pine litter amended with aluminium and tannins. Soil Biol. Biochem. 2009, 41, 2318–2327. [Google Scholar] [CrossRef]
  69. Hameed, Y.T.; Idris, A.; Hussain, S.A.; Abdullah, N.; Man, H.C. Effect of pre-treatment with a tannin-based coagulant and flocculant on a biofilm bacterial community and the nitrification process in a municipal wastewater biofilm treatment unit. J. Environ. Chem. Eng. 2020, 8, 103679. [Google Scholar] [CrossRef]
  70. Tonhato Junior, A.; Hasan, S.D.M.; Sebastien, N.Y. Optimization of coagulation/flocculation treatment of brewery wastewater employing organic flocculant based of vegetable tannin. Water Air Soil Pollut. 2019, 230, 202. [Google Scholar] [CrossRef]
  71. Meng, X.; Sørensen, P.; Møller, H.B.; Petersen, S.O. Greenhouse gas balances and yield-scaled emissions for storage and field application of organic fertilizers derived from cattle manure. Agric. Ecosyst. Environ. 2023, 345, 108327. [Google Scholar] [CrossRef]
  72. Fang, C.; Yin, H.; Han, L.; Ma, S.; He, X.; Huang, G. Effects of semi-permeable membrane covering coupled with intermittent aeration on gas emissions during aerobic composting from the solid fraction of dairy manure at industrial scale. Waste Manag. 2021, 131, 1–9. [Google Scholar] [CrossRef]
  73. Im, S.; Mostafa, A.; Shin, S.-R.; Kim, D.-H. Combination of H2SO4-acidification and temperature-decrease for eco-friendly storage of pig slurry. J. Hazard. Mater. 2020, 399, 123063. [Google Scholar] [CrossRef] [PubMed]
  74. Wang, K.; Huang, D.; Ying, H.; Luo, H. Effects of acidification during storage on emissions of methane, ammonia, and hydrogen sulfide from digested pig slurry. Biosyst. Eng. 2014, 122, 23–30. [Google Scholar] [CrossRef]
  75. Cantarella, H.; Otto, R.; Soares, J.R.; de Brito Silva, A.G. Agronomic efficiency of NBPT as a urease inhibitor: A review. J. Adv. Res. 2018, 13, 19–27. [Google Scholar] [CrossRef] [PubMed]
  76. Li, Q.; Yang, A.; Wang, Z.; Roelcke, M.; Chen, X.; Zhang, F.; Pasda, G.; Zerulla, W.; Wissemeier, A.H.; Liu, X. Effect of a new urease inhibitor on ammonia volatilization and nitrogen utilization in wheat in north and northwest China. Field Crop. Res. 2015, 175, 96–105. [Google Scholar] [CrossRef]
Agronomy 15 01202 g001
Figure 1. Illustration of the setup for gas measurements during the storage phase (A) and soil application phase (B).
Figure 1. Illustration of the setup for gas measurements during the storage phase (A) and soil application phase (B).
Agronomy 15 01202 g001
Agronomy 15 01202 g002
Figure 2. Dynamics of NH4+-N and TN of the liquid and solid fractions during the storage phase. (A) NH4+-N. (B) TN.
Figure 2. Dynamics of NH4+-N and TN of the liquid and solid fractions during the storage phase. (A) NH4+-N. (B) TN.
Agronomy 15 01202 g002
Agronomy 15 01202 g003
Figure 3. Changes in NH4+-N, NO3−-N, and DOC in soil under different treatments. (A) NH4+-N content in soil; (B) NO3−-N content in soil; (C) DOC content in soil.
Figure 3. Changes in NH4+-N, NO3−-N, and DOC in soil under different treatments. (A) NH4+-N content in soil; (B) NO3−-N content in soil; (C) DOC content in soil.
Agronomy 15 01202 g003
Agronomy 15 01202 g004
Figure 4. Ammonia emissions from the storage phase of the solid and liquid fractions. (A) The NH3 emission rate during storage; (B) cumulative NH3 emissions during storage. The small letters in the bars indicate significant differences among the treatments, α = 0.05.
Figure 4. Ammonia emissions from the storage phase of the solid and liquid fractions. (A) The NH3 emission rate during storage; (B) cumulative NH3 emissions during storage. The small letters in the bars indicate significant differences among the treatments, α = 0.05.
Agronomy 15 01202 g004
Agronomy 15 01202 g005
Figure 5. Ammonia emissions from the soil application phase of the solid and liquid fractions. (A) The NH3 emission rate during application; (B) cumulative NH3 emissions during application. The small letters in the bars indicate significant differences among the treatments, α = 0.05.
Figure 5. Ammonia emissions from the soil application phase of the solid and liquid fractions. (A) The NH3 emission rate during application; (B) cumulative NH3 emissions during application. The small letters in the bars indicate significant differences among the treatments, α = 0.05.
Agronomy 15 01202 g005
Agronomy 15 01202 g006
Figure 6. Nitrous oxide emissions from the storage phase of the solid and liquid fractions. (A) The N2O emission rate during storage; (B) cumulative N2O emissions during storage. The small letters in the bars indicate significant differences among the treatments, α = 0.05.
Figure 6. Nitrous oxide emissions from the storage phase of the solid and liquid fractions. (A) The N2O emission rate during storage; (B) cumulative N2O emissions during storage. The small letters in the bars indicate significant differences among the treatments, α = 0.05.
Agronomy 15 01202 g006
Agronomy 15 01202 g007
Figure 7. Nitrous oxide emissions from the soil application phase of the solid and liquid fractions. (A) The N2O emission rate during application; (B) cumulative N2O emissions during application. The small letters in the bars indicate significant differences among the treatments, α = 0.05.
Figure 7. Nitrous oxide emissions from the soil application phase of the solid and liquid fractions. (A) The N2O emission rate during application; (B) cumulative N2O emissions during application. The small letters in the bars indicate significant differences among the treatments, α = 0.05.
Agronomy 15 01202 g007
Agronomy 15 01202 g008
Figure 8. Methane emissions from the storage phase of the solid and liquid fractions. (A) The CH4 emission rate during storage; (B) cumulative CH4 emissions during storage. The small letters in the bars indicate significant differences among the treatments.
Figure 8. Methane emissions from the storage phase of the solid and liquid fractions. (A) The CH4 emission rate during storage; (B) cumulative CH4 emissions during storage. The small letters in the bars indicate significant differences among the treatments.
Agronomy 15 01202 g008
Agronomy 15 01202 g009
Figure 9. Methane emissions from the soil application phase of the solid and liquid fractions. (A) The CH4 emission rate during application; (B) cumulative CH4 emissions during application. The small letters in the bars indicate significant differences among the treatments.
Figure 9. Methane emissions from the soil application phase of the solid and liquid fractions. (A) The CH4 emission rate during application; (B) cumulative CH4 emissions during application. The small letters in the bars indicate significant differences among the treatments.
Agronomy 15 01202 g009
Agronomy 15 01202 g010
Figure 10. Carbon dioxide emissions from the storage phase of the solid and liquid fractions. (A) The CO2 emission rate during storage; (B) cumulative CO2 emission during storage. The small letters in the bars indicate significant differences among the treatments, α = 0.05.
Figure 10. Carbon dioxide emissions from the storage phase of the solid and liquid fractions. (A) The CO2 emission rate during storage; (B) cumulative CO2 emission during storage. The small letters in the bars indicate significant differences among the treatments, α = 0.05.
Agronomy 15 01202 g010
Agronomy 15 01202 g011
Figure 11. Carbon dioxide emissions from the soil application phase of the solid and liquid fractions. (A) The CO2 emission rate during application; (B) cumulative CO2 emissions during application. The small letters in the bars indicate significant differences among the treatments, α = 0.05.
Figure 11. Carbon dioxide emissions from the soil application phase of the solid and liquid fractions. (A) The CO2 emission rate during application; (B) cumulative CO2 emissions during application. The small letters in the bars indicate significant differences among the treatments, α = 0.05.
Agronomy 15 01202 g011
Agronomy 15 01202 g012
Figure 12. The ratios of CH4, N2O, NH3, and GHG emissions from the sources related to enhanced SLS to the respective gas emissions related to conventional SLS. (A) Emissions of the solid and liquid fractions during the storage phase; (B) emissions of the solid and liquid fractions during the soil application phase; (C) gas emissions of the solid and liquid fractions of different SLSs.
Figure 12. The ratios of CH4, N2O, NH3, and GHG emissions from the sources related to enhanced SLS to the respective gas emissions related to conventional SLS. (A) Emissions of the solid and liquid fractions during the storage phase; (B) emissions of the solid and liquid fractions during the soil application phase; (C) gas emissions of the solid and liquid fractions of different SLSs.
Agronomy 15 01202 g012
Table 1. Inputs of nutrients per column during the incubation.
Table 1. Inputs of nutrients per column during the incubation.
TreatmentTN (mg)TAN (mg)Organic Matter (mg)
SF + TA264.942.7817.33
SF264.942.848.92
LF + TA264.9451.872.92
LF264.9422.861.52
SF, solid fraction; LF, liquid fraction; TA, tannic acid; TN, total nitrogen; TAN, total ammoniacal nitrogen.
Table 2. Proportions of NH3-N and N2O-N losses to the N inputs in different treatments.
Table 2. Proportions of NH3-N and N2O-N losses to the N inputs in different treatments.
TreatmentsNH3-N/%N2O-N/%(NH3 + N2O)-N/%
SF + TA1.60 ± 0.38 c1.01 ± 0.03 c2.61 ± 0.18 c
SF1.83 ± 0.40 c1.16 ± 0.10 c2.99 ± 0.35 c
LF + TA7.78 ± 0.21 a2.20 ± 0.01 b9.98 ± 0.21 a
LF3.63 ± 0.50 b3.02 ± 0.01 a6.65 ± 0.61 b
Different letters in the same column indicate significant differences among the different treatments (α = 0.05).
Table 3. Emissions of CO2-e from different treatments during storage (g m−2).
Table 3. Emissions of CO2-e from different treatments during storage (g m−2).
TreatmentsCH4N2ONH3Total
SF + TA331.23 ± 44.62 c101.09 ± 12.90 b0.60 ± 0.04 c432.88 ± 74.80 d
SF4.61 ± 0.95 d741.24 ± 29.65 a0.004 ± 0.003 d745.91 ± 28.82 c
LF + TA4947.20 ± 158.97 b11.40 ± 1.40 c2.77 ± 0.21 b4961.38 ± 158.3 b
LF9924.04 ± 338.05 a4.71 ± 0.50 c5.09 ± 0.29 a9933.89 ± 337.53 a
SF, solid fraction; LF, liquid fraction; TA, tannic acid. Different letters in the same column indicate significant differences among the different treatments (α = 0.05).
Table 4. Emissions of CO2-e from different treatments (g m−2).
Table 4. Emissions of CO2-e from different treatments (g m−2).
TreatmentsCH4N2ONH3Total
SF + TA0.52 ± 0.03 c64.60 ± 1.41 c2.38 ± 0.24 c71.31 ± 1.33 c
SF0.12 ± 0.008 c74.25 ± 3.97 c2.53 ± 0.40 c76.90 ± 4.2 c
LF + TA2.46 ± 0.17 a115.81 ± 0.49 b6.24 ± 0.13 a124.51 ± 0.5 b
LF1.16 ± 0.19 b148.41 ± 5.61 a3.65 ± 0.31 b153.22 ± 5.94 a
CK−0.03 ± 0.01 d28.23 ± 4.39 d1.38 ± 0.15 d29.59 ± 4.52 d
Different letters in the same column indicate significant differences among the different treatments (α = 0.05).
Table 5. Emissions of CO2-e from different treatments (g kg−1).
Table 5. Emissions of CO2-e from different treatments (g kg−1).
PhaseTreatmentCH4N2ONH3Total
StorageEnhanced SLS23.19 ± 1.00 b0.22 ± 0.02 a0.02 ± 0.004 a23.43 ± 1.06 b
Conventional SLS49.94 ± 0.71 a0.57 ± 0.04 a0.03 ± 0.008 a50.54 ± 0.74 a
ApplicationEnhanced SLS10.87 ± 0.63 a669.20 ± 5.80 b27.38 ± 0.89 a707.45 ± 5.48 b
Conventional SLS6.43 ± 0.20 b1007.06 ± 32.56 a21.28 ± 1.11 b1034.77 ± 33.17 a
Storage + ApplicationEnhanced SLS34.06 ± 0.90 b669.42 ± 5.73 b27.40 ± 0.89 a730.88 ± 4.42 b
Conventional SLS56.37 ± 1.45 a1007.63 ± 32.55 a21.31 ± 1.11 b1085.31 ± 32.74 a
Different letters for the same management phase in one column indicate significant differences among the different treatments (α = 0.05).
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Gao, Z.; Wang, S. Mitigating Gas Emissions from the Dairy Slurry Management Chain: An Enhanced Solid–Liquid Separation Technology with Tannic Acid. Agronomy 2025, 15, 1202. https://doi.org/10.3390/agronomy15051202

AMA Style

Gao Z, Wang S. Mitigating Gas Emissions from the Dairy Slurry Management Chain: An Enhanced Solid–Liquid Separation Technology with Tannic Acid. Agronomy. 2025; 15(5):1202. https://doi.org/10.3390/agronomy15051202

Chicago/Turabian Style

Gao, Zhiling, and Shanshan Wang. 2025. "Mitigating Gas Emissions from the Dairy Slurry Management Chain: An Enhanced Solid–Liquid Separation Technology with Tannic Acid" Agronomy 15, no. 5: 1202. https://doi.org/10.3390/agronomy15051202

APA Style

Gao, Z., & Wang, S. (2025). Mitigating Gas Emissions from the Dairy Slurry Management Chain: An Enhanced Solid–Liquid Separation Technology with Tannic Acid. Agronomy, 15(5), 1202. https://doi.org/10.3390/agronomy15051202

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop