Effects of Two Manure Additives on Methane Emissions from Dairy Manure

Methane emission reduction by adding sulfate to liquid dairy manure

Dairy farmers are interested in reducing the carbon footprint of milk. Reducing methane (CH4) emissions is a key part of this goal, and manure is a significant CH4 source. Technologies like anaerobic digesters for biogas production are effective; however, adoption rates are slowed by upfront costs and infrastructure needs. Achieving near-term emission reductions needs low-cost alternatives that can be quickly and widely adopted. Previous studies have shown that "acidification" of manure by adding sulfuric acid (H2SO4) suppressed CH4 emissions; however, widespread adoption may be hindered by the challenge of handling acid on farms. This laboratory study was performed for 157 days at 24°C, and compared the efficacy of a sulfate-based non-acidic fertilizer (CaSO4), and two rates of acidification, one at pH > 7 and one at pH < 7, for a sulfate-based acid (H2SO4) and a sulfate-free acid (H3PO4). Methane suppression by CaSO4 at multiple rates was also analyzed. Two mechanisms of suppression were observed: acidification had a demonstrable early effect, lowering cumulative CH4 emission within 40 days by up to 65% for H2SO4 and 54% for H3PO4, while sulfate-containing compounds showed increasing suppression after 50 days. Final cumulative CH4 suppression was up to 63% for CaSO4 and 91% for H2SO4, while H3PO4 was least effective. These results suggest H2SO4 is highly effective due to the combination of acidity and sulfate. Adding sulfate alone (CaSO4) was more effective than adding acid alone (H3PO4). Hence, sulfate-based additives-like gypsum-may hold promise as an alternative near-term solution for dairy farms to make large CH4 reductions.

Rumen microbial degradation of bromoform from red seaweed (Asparagopsis taxiformis) and the impact on rumen fermentation and methanogenic archaea

BACKGROUND

The red macroalgae Asparagopsis is an effective methanogenesis inhibitor due to the presence of halogenated methane (CH4) analogues, primarily bromoform (CHBr3). This study aimed to investigate the degradation process of CHBr3 from A. taxiformis in the rumen and whether this process is diet-dependent. An in vitro batch culture system was used according to a 2 × 2 factorial design, assessing two A. taxiformis inclusion rates [0 (CTL) and 2% DM diet (AT)] and two diets [high-concentrate (HC) and high-forage diet (HF)]. Incubations lasted for 72 h and samples of headspace and fermentation liquid were taken at 0, 0.5, 1, 3, 6, 8, 12, 16, 24, 48 and 72 h to assess the pattern of degradation of CHBr3 into dibromomethane (CH2Br2) and fermentation parameters. Additionally, an in vitro experiment with pure cultures of seven methanogens strains (Methanobrevibacter smithii, Methanobrevibacter ruminantium, Methanosphaera stadtmanae, Methanosarcina barkeri, Methanobrevibacter millerae, Methanothermobacter wolfei and Methanobacterium mobile) was conducted to test the effects of increasing concentrations of CHBr3 (0.4, 2, 10 and 50 µmol/L).

RESULTS

The addition of AT significantly decreased CH4 production (P = 0.002) and the acetate:propionate ratio (P = 0.003) during a 72-h incubation. The concentrations of CHBr3 showed a rapid decrease with nearly 90% degraded within the first 3 h of incubation. On the contrary, CH2Br2 concentration quickly increased during the first 6 h and then gradually decreased towards the end of the incubation. Neither CHBr3 degradation nor CH2Br2 synthesis were affected by the type of diet used as substrate, suggesting that the fermentation rate is not a driving factor involved in CHBr3 degradation. The in vitro culture of methanogens showed a dose-response effect of CHBr3 by inhibiting the growth of M. smithii, M. ruminantium, M. stadtmanae, M. barkeri, M. millerae, M. wolfei, and M. mobile.

CONCLUSIONS

The present work demonstrated that CHBr3 from A. taxiformis is quickly degraded to CH2Br2 in the rumen and that the fermentation rate promoted by different diets is not a driving factor involved in CHBr3 degradation.

Automatic temperature rise in the manure storage tank increases methane emissions: Worth to cool down!

A significant amount of CH₄ is emitting from livestock manure (LM) storage tank, which is being counted according to the guidelines provided by the Intergovernmental Panel on Climate Change (IPCC). Among various parameters affecting CH₄ conversion factor (MCF) of LM, temperature is known as the most influential factor. As a degree of temperature, atmospheric temperature (T_a), not the manure temperature (T_m), is used for determining the MCF. Currently, the closed-type tank is more common than open-type tank, which would cause the substantial difference between T_a and T_m, probably due to the automatic temperature rise (ATR). Here, we repeatedly observed the ATR by storing pig slurry (PS) in a pilot-scale tank (30 m³, surface/volume ratio of 1.9), and its consequent impact on the increased CH₄ emissions by comparing with the results from a lab-scale tank (1 L, surface/volume ratio of 72.2) controlled at 30 °C. As storage began, the T_m increased gradually from 16 to 23 °C to above 30 °C even in winter (-5 °C < T_a < 15 °C). During 30 d of storage, the CH₄ emissions of 1.3-2.5 kg CH₄/ton PS (MCF 26-29%) was observed in the lab-scale tank, while the emissions was increased to 2.6-4.2 kg CH₄/ton PS (MCF 40-50%) in the pilot-scale tank (Two-Tail test, |t_t|<|t_c|). For the first time, a detailed heat energy balance considering the waste heat from organic degradation, the heat requirement for warm up, and the heat loss by convection, was conducted, proving that the waste heat generated during storage was enough to reach above 30 °C. Cooling-down of LM at 20 °C was found to be effective for reducing CH₄ emissions by 90%, which sufficiently offset the greenhouse gas emissions in power consumption for cooling. Our findings strongly suggest that more CH₄ is emitting from LM storage tank than expected, and therefore, the IPCC needs to develop guidelines more accurately in determining MCF.

Manure methane emissions over three years at a swine farm in western Canada

Swine manure is kept in outdoor storage facilities until it is applied to cropland. Anaerobic conditions facilitate microbial methane (CH₄ ) production at a rate that depends on temperature. Manure CH₄ emissions can be the largest contributor to the carbon footprint of pork production. Despite the importance of CH₄ , its actual emissions in cold temperate climates are highly uncertain. This study measured emissions from a single-cell earthen manure storage facility at a commercial swine farm near Brandon, Manitoba, Canada, for 3 yr. Complimentary laboratory measurements were done to assess CH₄ potential (B₀ ). The manure storage regularly received manure from the barn and was only emptied in October. In the summer, manure temperature was usually lower than the air temperature, with the manure temperature (averaged across depths) warming to between 15 and 18.5 °C for only 9 wk. Emissions of CH₄ were low, with the CH₄ conversion factor being between 3.0 and 11.0%, depending on the year (using the IPCC 2019 default B₀ ). Scaled by the number of swine reaching market weight (125 kg) each year, CH₄ emissions were between 250 and 902 g CH₄ animal^-1 . Laboratory measurements of CH₄ production potential scaled by VS were 335 ml CH₄ g^-1 VS at 37 °C, perhaps lower than the IPCC 2019 default value due to barley (Hordeum vulgare L.) in the ration and degradation in the under-barn pit prior to transfer outdoors. Taken together, the low manure temperatures, short warm season, and barley in the ration suggest that emissions from swine manure in cold climates like western Canada are considerably lower than previously estimated based on default factors.

Alternative Management Systems of Beef Cattle Manure for Reducing Nitrogen Loadings: A Case-Study Approach

Livestock manure is one of the main sources of agricultural nonpoint source pollution and poses a great threat to the environment and human health. Sustainable management of manure via recycling is an effective means to tackle the problem. Based on field interviews in China, multiple case studies were employed to investigate alternative manure management systems. Four conclusions arose. First, compost-based systems, product-based systems, substrate-based systems, and biogas-based systems were identified as four main types of manure management systems, with each possessing its success factors and risk factors. The adoption of a system was driven by various factors. Second, market-oriented operation was the dominant operation mechanism of all the manure management systems. Third, compared to direct application of manure to croplands, all the four manure management systems could reduce nitrogen loadings from livestock farms and lower their environmental effects. Among the systems, biogas-based systems could reduce nitrogen loadings to the greatest extent, followed by product-based systems and substrate-based systems, and then by compost-based systems. Lastly, integrated management of manure with mixed recycling systems is imperative for reducing its environmental effects, which can benefit from the increasing role of third-party entities in manure recycling. Policy implications were also discussed.