Addition of powdery sulfur to pig slurry to reduce NH3 and GHG emissions after mechanical separation

Effects of mechanical separation on GHG and ammonia emissions from cattle slurry under winter conditions

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.

Emissions of methane (CH4), carbon dioxide (CO2), nitrous oxide (N2O) and ammonia (NH3) during the storage of rough pig slurry and the fractions (solid and liquid) obtained by mechanical separation were investigated in a laboratory-scale study. Manures were stored for a period of 30 days in open vessels (1500 cm3 capacity) within a climate-controlled room which was kept at 25 ± 0.2°C. Gaseous emissions were determined with the dynamic chamber method by infrared photoacoustic detection. The main GHG emission from the liquid manures was CH4. CH4 losses from both liquid and solid fractions together were 3% higher than from the rough slurry. CO2 losses from both liquid and solid fractions together increased by 10% compared with rough pig slurry. Appreciable N2O fluxes were only measured from the solid fraction. Combining the losses during the storage of both liquid and solid fraction, they resulted in reduced NH3 emissions compared with the storage of the rough pig slurry. Evidence from the present study suggests that mechanical separation of pig slurry has the potential to increase up to 25% the emission of CO2-equivalents to the atmosphere during the storage of the separated fractions if compared with the rough slurry.

Effect of mechanical separation on emissions during storage of two anaerobically codigested animal slurries

A field trial was conducted to assess the emission of ammonia from rough cattle slurry and solid and liquid fractions (generated from its mechanical separation) applied to alfalfa pasture. Three materials (rough slurry, liquid fraction and solid fraction) were applied on alfalfa over two seasons (summer and autumn), with two application rates (40 and 70 kg N/ha) and with two air velocities (0–0.6 m/s) at the soil surface. Ammonia losses were measured either by a set of wind tunnels (adjusting the air velocity at 0.6 m/s) or by a funnel system, allowing measurements to be recorded at an air speed close to 0 m/s. Each trial lasted 5 days with daily sampling of the gaseous emissions. Trial results showed that the rough slurry substrate had the highest level of ammonia emissions, followed by the liquid and solid fractions. Up to 35% of the applied total Kjeldahl nitrogen was lost as ammonia from the rough slurry in 5 days in summer conditions and with an air velocity of 0.6 m/s. No effect due to the application rate was observed, however, a significant effect of the temperature and air velocity on ammonia emissions was measured. Ammonia emissions after the spreading of the rough slurry were up to 26% higher when compared with those generated after application of the two fractions (solid + liquid).

<abstract> Storage of dairy manure slurry allows flexibility in the timing of land application of manure to reduce environmental impacts related to water quality. However, manure storage can increase greenhouse gas (GHG) and ammonia (NH₃) emissions and cause operational issues due to the buildup of slurry solids. To combat these negative consequences, stored manure was treated with manure additives, i.e., More than Manure (MTM), Pro-Act Biotech (Pro-Act), and biochar, to quantify their effects on manure solids, nitrogen losses, and GHG emissions in two separate trails. Gaseous emissions were studied over a 48-day manure storage period with treatments of MTM, Pro-Act, aeration and Pro-Act, aeration alone, and biochar. Manure characteristics were further examined in a 28-day manure storage study with treatments of MTM at the supplier-recommended rate, MTM at 25x the recommended rate, aeration and Pro-Act at the supplier-recommended rate, aeration and Pro-Act at 10x the recommended rate, aeration alone, and two additional Pro-Act treatments without aeration, one at the recommended rate and one at 10x that rate. Biochar was the only manure treatment to impact manure characteristics, with significantly more ammoniacal nitrogen (TAN) on day 14 than the control (p < 0.012) in the manure composition study. Biochar did not reduce NH₃ emissions from the control, likely due to the 10 cm natural crust on the control. MTM increased CO₂ emissions, with significantly higher emissions on days 7 and 14 during the gaseous emissions study. Overall, no treatments were able to reduce manure solids or nitrogen emissions for these manure storage conditions.

Acidification of raw and co-digested pig slurries with alum before mechanical separation reduces gaseous emission during storage of solid and liquid fractions

In many places on earth, livestock and feed production are decoupled, as feed is grown in one region and fed to livestock in another. This disrupts nutrient cycles by depleting resources in feed producing regions and accumulating resources in livestock areas, which leads to environmental degradation. One solution is to recouple livestock and feed production at a more local level, which enhances nutrient circularity. Recoupling livestock and feed production creates a natural ceiling for livestock numbers based on the feed producing capacity of a region. In this study we assess the consequences of recoupling livestock and feed production (i.e., by avoiding the import and export of animal feed) on ammonia and greenhouse gas (GHG) emissions, with and without feed-food competition. To this end, we used FOODSOM, an agro-ecological food system optimisation model representing the Dutch food system in this study. The Netherlands is one example of a region with high livestock densities and resource accumulation. We found that recoupling decreased livestock numbers (beef cattle: −100 %; dairy cattle: −29 %; broiler chickens: −57 %; laying hens: −67 %; pigs: −62 %; sheep −100 %) and animal-sourced food exports (−59 %) while still meeting the current human diet in the Netherlands. Consequently, ammonia emissions and GHG emissions decreased, and the nitrogen use efficiency increased from 31 % to 38 % at the food systems level. Recoupling alone was almost sufficient to meet national emission targets. Fully meeting these targets required further small changes in livestock numbers. Avoiding feed-food competition decreased livestock productivity and GHG emissions but did not improve nitrogen use efficiency. Total meat production could not meet domestic consumption levels while avoiding feed-food competition, and resulted in additional beef cattle. We show that recoupling livestock and feed production is a promising next step to enhance circularity while decreasing agricultures environmental impact.

Biochar amendment to cattle slurry reduces NH3 emissions during storage without risk of higher NH3 emissions after soil application of the solid fraction

There is continuing debate and public health concern regarding the previously confirmed association between high livestock density and human health. The primary aim of the current study is to assess the prevalence of respiratory and other health problems in a livestock dense area in the Netherlands, based on recent longitudinal health data and a large sample. Analyses are expanded with the investigation of different subgroups of patients with respiratory health problems and the inclusion of various chronic and acute health outcomes, as well as prescribed medication. Prevalence of health symptoms and chronic conditions was assessed for the period 2014–2016, based on electronic health records registered in 26 general practices located in areas with intensive livestock farming in the Netherlands (“livestock dense area”, n = 117,459 unique residents in total). These were compared with corresponding health data from general practices (n = 22) in different rural regions with a low density of livestock farms or other major environmental exposures (“control area”, n = 85,796 unique residents in total). Multilevel regression models showed a significantly higher prevalence of pneumonia in the total sample in the livestock dense area, which was also observed among susceptible subgroups of children, the elderly, and patients with chronic obstructive pulmonary disease (COPD). Lower respiratory tract infections, respiratory symptoms, vertigo, and depression were also more common in the livestock dense area compared to the control area. In general, there were no significant differences in chronic conditions such as asthma, COPD, or lung cancer. Prescription rates for broad-spectrum antibiotics were more common among patients with pneumonia in the livestock dense area. Acute respiratory infections and symptoms, but not chronic conditions, were considerably more common in areas with a high livestock density. Identification of causal pathogens on the basis of serological analyses could further elucidate the underlying mechanisms behind the observed health effects.

Separation of slurries can facilitate the nutrient management on farms through nutrient partitioning between the liquid and the solid fraction. The distribution of nutrients in the slurry fractions depends largely on the type of separator used. The current study assessed the separation efficiency of a two-step separation treatment of pig slurry including in-series a screw press and a centrifuge followed by acidification (to pH 5.9) of the final liquid effluent. The system concentrated 73.8% of the slurry's Phosphorus (P) content, 52.6% of Total solids (TS) and 14.4% of total Nitrogen to the solid fraction. The apparent N recovery from ryegrass fertilized with the raw slurry and non-acidified liquid fractions was not decreased by the separation treatment. The acidified liquid fraction showed 28% and 9% higher apparent N recovery compared to the raw slurry and the non-acidified liquid effluent from the centrifuge respectively. The biochemical methane production potential (Bo) of the acidified liquid fraction was reduced by 50% and 25%, compared to the non-acidified counterpart and the raw slurry, respectively. The results highlight the potential of a double separation system coupled with acidification of the liquid fraction, to extract P into a solid fraction which can be transported outside the farm, and to increase N utilization from the liquid fraction when this is used as organic fertiliser on or nearby the farm. The study further highlights the potential to reduce CH4 emissions from slurry storage after mechanical separation and acidification of the liquid slurry fraction.

Gaseous emissions from the storage of untreated slurries and the fractions obtained after mechanical separation

Pig slurry separation is a slurry treatment technique that can reduce excess loads of P, Cu and Zn to the arable land. This study investigated the effects of different commercial and laboratory separation treatments for pig slurry on P, Cu and Zn distribution into solid and liquid fractions. Solid and liquid separation fractions were collected from two commercial separators installed on the farm. Five different separation treatments were performed (polymer flocculation and drainage; coagulation with iron sulphate addition and polymer flocculation and drainage; ozonation and centrifugation; centrifugation only; and natural sedimentation) on sow and suckling piglet raw slurry. Particle size fractionation was performed on raw slurry and all separation fractions by sequential wet sieving and P, Cu and Zn concentrations were then measured in the particle size classes. Dry matter and total P, Cu and Zn were separated with higher efficiency when chemical pretreatments with flocculants and coagulants were introduced before mechanical separation at both commercial and laboratory scale. When solid fractions are utilized as crop fertilizer (primarily as P fertilizer), the loads of Cu and Zn to the soils are not markedly different than the loads applied with raw slurry. When liquid fractions are used as crop fertilizer (primarily as N fertilizer), the loads of Cu and Zn are markedly lower than those supplied with raw slurry. The loads of Cu and Zn introduced to the soil were lowest on application of the liquid fraction produced by optimized separation treatments that included flocculation and coagulation.

The use of housed wintering systems (e.g., barns) associated with dairy cattle farming is increasing in southern New Zealand. Typically, these wintering systems use straw or a woodmix as bedding material. Ammonia (NH) and greenhouse gas (GHG) emissions (nitrous oxide [NO] and methane [CH]) associated with storage of slurry + bedding material from wintering systems is poorly understood. A field incubation study was conducted to determine such emissions from stored slurry where bedding material (straw and sawdust) was added at two rates and stored for 7 mo. During the first 4 mo of storage, compared with untreated slurry, the addition of sawdust significantly reduced NH and CH emissions from 29 to 3% of the initial slurry nitrogen (N) content and from 0.5 to <0.01% of the initial slurry carbon (C) content. However, sawdust enhanced NO emissions to 0.7% of the initial slurry-N content, compared with <0.01% for untreated slurry. Straw generally had an intermediate effect. Extending the storage period to 7 mo increased emissions from all treatments. Ammonia emissions were inversely related to the slurry C:N ratio and total solid (TS) content, and CH emissions were inversely related to slurry TS content. Mitigation of GHG emissions from stored slurry can be achieved by reducing the storage period as much as possible after winter slurry collection, providing ground conditions allow access for land spreading and nutrient inputs match pasture requirements. Although adding bedding material can reduce GHG emissions during storage, increased manure volumes for carting and spreading need to be considered.

Storage of cattle slurry leads to emissions of methane (CH(4)), nitrous oxide (N(2)O), ammonia (NH(3)), and carbon dioxide (CO(2)). On dairy farms, winter is the most critical period in terms of slurry storage due to cattle housing and slurry field application prohibition. Slurry treatment by separation results in reduced slurry dry matter content and has considerable potential to reduce gaseous emissions. Therefore, the efficiency of slurry separation in reducing gaseous emissions during winter storage was investigated in a laboratory study. Four slurry fractions were obtained: a solid and a liquid fraction by screw press separation (SPS) and a supernatant and a sediment fraction by chemically enhanced settling of the liquid fraction. Untreated slurry and the separated fractions were stored in plastic barrels for 48 d under winter conditions, and gaseous emissions were measured. Screw press separation resulted in an increase of CO(2) (650%) and N(2)O (1240%) emissions due to high releases observed from the solid fraction, but this increase was tempered by using the combined separation process (CSP). The CSP resulted in a reduction of CH(4) emissions ( approximately 50%), even though high emissions of CH(4) (46% of soluble C) were observed from the solid fraction during the first 6 d of storage. Screw press separation increased NH(3) emissions by 35%, but this was reduced to 15% using the CSP. During winter storage greenhouse gas emissions from all treatments were mainly in the form of CH(4) and were reduced by 30 and 40% using SPS and CSP, respectively.