Tag: ghg emissions

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Impact of Swine Sludge Inclusion Rate on the Composting Process and Compost Quality

Purpose

The purpose of this study was to develop and analyze potential recipes for composting swine lagoon sludge. Composting is a simple treatment; it is widely adopted on farms, generates a stable value-added stackable product, and conserves organic matter and nutrients. All these benefits along with an affordable cost and lower environmental emissions make it a potential candidate for the management of lagoon sludge, a byproduct of swine operations in southeast US.

Sludge accumulation in lagoons can result in increased odor from lagoons, impact animal productivity, increase risk of environmental and social consequences and lead to operation non-compliance. Developing affordable sludge management alternatives is important because current practices (land application post dredging and dewatering using organic polymers and geo-bags) are not widely adoptable, cost-prohibitive and non-sustainable (Owusu-Twum and Sharara, 2020, Soil facts) and current farm nutrient management plans do not consider management of sludge nutrients.

What Did We Do?

We developed two recipes by mixing different sludge amounts with locally available low-cost amendments: poultry litter, Bermuda hay, yard debris and lagoon liquid. We composted these recipes in triplicates using 13-cubic feet in-vessel composters and recorded changes in temperatures, weight loss, volume, moisture, and organic matter. We also recorded greenhouse gases emitted from the piles at regular intervals. Forced, intermittent aeration was maintained during composting for replicates to ensure adequate oxygen supply and avoid prematurely drying mixtures. Finally, we analyzed the final compost to determine its suitability as a soil amendment.

We used the observations from the experiments to evaluate if proposed recipes resulted in successful compost and determine whether sludge inclusion significantly impacts composting process and product quality. We also analyzed which factors influence weight and organic matter losses in the piles and if the proposed recipes have comparable cumulative GHG and NH3 emissions to previous observations.

What Have We Learned?

We learned that sludge can be composted at both 10% and 20% inclusion rates using the above ingredients, as the process met time and temperatures for pathogen reduction (15A NCAC, 13B.1406) and the final product were stable (TMECC, US Composting council). For 100 lbs. of an initial wet mixture (60.8 to 61.4% moisture) both recipes experienced a total weight loss of 33.8-35.2 lbs. with 24.5 to 25.4 lbs. being lost as moisture and 8.8 to 9.7 lbs. lost as organic matter during the active phase of composting (31 days). Post-screening the recipes resulted in 42.3 to 48.6 lbs. of the stable final product (45 to 47% moisture) that can be directly land applied.

We learned that the composting process generated similar GHG, and ammonia emissions as reported in the previous studies however, most of the methane (CH4) and nitrous oxide (N2O) were generated in the later stages of composting, which can be potentially reduced by proper management of the composting process. Another observation was larger losses in ammonia in the earlier stages of composting which on reduction; using certain additives, changes in recipe or management practices, can result in optimal utilization of nitrogen, increase product value, and reduce environmental impacts.

Future Plans

We plan to further analyze the impact of the composting process on total nutrients and water-extractable fractions, this will provide information on land use rate and potential losses in runoffs. This information is critical for swine lagoon sludge-derived products due to the high concentration of P, Zn, and Cu in sludge as losses can lead to eutrophication in surface and marine waters and potential toxicity in soils.

Future work proposed also involves techno-economic evaluation of this process to determine the cost of treatment, and fair price of the final product. We also plan to conduct a cradle to gate life cycle assessment of the process to determine global warming potential, eutrophication, acidification, and particulate matter generation for farm and large-scale systems. These efforts will help guide further research to improve the technology and provide knowledge to stakeholders and producers on alternative sludge management options.

Figure 1. Swine lagoon sludge composting process and products.

 

References

Authors

Piyush Patil, Ph.D. Candidate, Bio&Ag. Engineering, North Carolina State University

Corresponding author

Mahmoud Sharara, Asst. Professor and Extension Specialist, Bio&Ag. Eng. North Carolina State University

Corresponding author email address

msharar@ncsu.edu

Additional authors

Stephanie Kulesza, Assistant Professor, Crop & Soil Sciences, North Carolina State University

Sanjay Shah, Professor and Extension specialist, Bio&Ag. Eng. North Carolina State University

John Classen, Associate Professor, Bio&Ag. Eng. North Carolina State University

Additional Information

Publication is in progress currently so best resource is the corresponding author.

Acknowledgements

We would like to acknowledge the support from Joseph Stuckey and Chris Hopkins (Poultry, livestock, and animal waste management facility, NCSU).

Funding sources

Bioenergy Research Initiative (BRI) – Contract No #17-072-4015, North Carolina Department of Agriculture & Consumer Services

National Institute of Food and Agriculture (NIFA) – Critical Agricultural Research and Extension (CARE) – Award No. 2019-68008-29894, U.S. Department of Agriculture

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2022. Title of presentation. Waste to Worth. Oregon, OH. April 18-22, 2022. URL of this page. Accessed on: today’s date.

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The Role of Manure for Dairy Carbon Neutrality Targets: An Environmental Assessment of Organic Farms

Purpose

Different dairy associations and cooperatives have been establishing aggressive environmental goals, including reaching carbon neutrality. Carbon sequestration has been largely absent from environmental dairy studies as it is challenging to estimate. The daily feed intake of dairy cows under organic management is composed mainly of pasture and forages, which have a significantly more developed root system than many other grain cropping systems usually included in conventionally managed feed rations. Moreover, manure is also an important source of carbon, that could be sequestered in the long-term depending on the farm’s management practices. This paper quantifies GHG emissions from organic dairy farms in the U.S., including the benefits of carbon sequestration from above and below ground residues.

What Did We Do?

The U.S. was divided into eight regions based on U.S. climate categories and management practices of the organic dairy farms that participated in the study. This paper presents the results for the Midwest-Great Lakes, New England, California, and the Northwest, where representative organic farms and management practices for each region are modeled with life cycle assessment (LCA) techniques to estimate GHG emissions (kg CO2-eq). The model keeps track of key constituents in milk, meat, and manure based on the defined feed ration and animal characteristics. All inputs and outputs at the farm level during feed production, herd management, milking, and manure management are included in the analysis. Results are expressed per 1 kg of fat and protein corrected milk (FPCM), adjusted to 4% fat and 3.3% protein.

A novel approach has been developed to estimate carbon sequestration from carbon staying in the field that considers environmental factors such as temperature and farm management practices that affect the carbon content of manure reaching the soil and posterior sequestration. Three major steps are used to estimate C sequestration from the pasture and crops portion of dairy feed in the modeled organic systems: i) estimate the C added to the soil from biomass in above ground residues, below ground residues, and manure; ii) estimate the change in C above and below ground as a result of crop and grassland management practices, iii) determine the amount of C from the first steps that will be sequestered long-term.

What Have We Learned?

Average GHG emissions for the modeled farms and regions range from 0.76 – 1.08 kg CO2-eq/kg FPCM after accounting for C sequestration. Enteric methane (CH4) represents more than half of total GHGs and is closely related to the efficiency of conversion of feed to milk by the cow. Carbon sequestration benefits reduce overall emissions by 7 – 20% in the modeled farms and regions. Farms in the Midwest and New England rely heavily on pasture during the grazing season and on grass forages produced on-farm during the non-grazing season, meaning that most of the C is sequestered through residue that stays in the soil system (42 – 49% from below ground residue vs. 35 – 42% from manure). The addition of carbon in manure is also significant, contributing more carbon to the soil than below ground residue in some farms, especially in those relying on imported feeds (43 – 47% from manure in California and the Northwest).

Future Plans

GHG emissions, ammonia emissions, resource depletion (energy, land, and water) and eutrophication potential of organic dairy farms will be estimated for the remaining regions in the U.S. The effect of alternative management practices, key to organic practices, will also be modeled to identify mitigation strategies. Finally, different LCA modeling decisions, such as allocation and use of enteric CH4 predictive equations, will be evaluated to determine their effect on final results.

Authors

Horacio Andres Aguirre-Villegas, Associate Scientist, Department of Biological Systems Engineering, University of Wisconsin-Madison

Corresponding author email address

Aguirreville@wisc.edu

Additional authors

Rebecca A. Larson, Associate Professor. Department of Biological Systems Engineering, University of Wisconsin-Madison

Nicole Rakobitsch, CROPP, Organic Valley.

Michel A. Wattiaux, Professor, Animal and Dairy Sciences, University of Wisconsin-Madison

Erin, Silva, Associate Professor, Plant Pathology, University of Wisconsin-Madison

Acknowledgements

This work was funded by the Cooperative Regions of Organic Producers Pools (CROPP) Cooperative – Organic Valley

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2022. Title of presentation. Waste to Worth. Oregon, OH. April 18-22, 2022. URL of this page. Accessed on: today’s date.

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Characterization of Nutrients and GHG Emissions from Separated Dairy Manure

This study has the objectives of characterizing dairy manure pre and post solid-liquid separation (SLS), estimating and comparing processing efficiencies between different technologies, and relating emissions to manure characteristics by using modeling tools.

What did we do?

Manure samples from nine dairy farms in southern and eastern Wisconsin were collected every two weeks. All nine farms separated manure into liquid and solid streams and seven farms used anaerobic digesters (ADs) prior to solids separation (Table 1). For all farms, manure was sampled pre-processing (untreated manure) and after any individual processing step in order to isolate the performance of each treatment unit at each farm (Figure 1). All manure samples were analyzed for total solids (TS), volatile solids (VS), total nitrogen (TN), ammonia (NH3), total phosphorus (TP), total potassium (TK) and chemical oxygen demand (COD). Separation efficiency was estimated by solving a system of two equations of separation mass balance (Equations 1 and 2) based on the concentrations of each constituent.

equations

       Where:

        • X (kg) is the constituent under evaluation (e.g. TS, NH3, etc.)
        • [  ] indicates percent concentration in the solid (solid, out), liquid (liquid, out) fractions after separation, and total before separation (total, in)
        • Manure (kg) is the manure mass in the solid (solid, out), liquid (liquid, out) fractions after separation, and total before separation (total, in)

What have we learned?

Both screw press and centrifuge technologies achieve higher separation efficiencies for TS and VS than for TN, NH3, TP, and TK, meaning that more TS and VS stay with the solids fraction. Moreover, NH3 stays almost entirely in the liquid fraction. Results indicate that centrifugation might achieve higher TP separation efficiencies than screw pressing. Greenhouse gas (GHG) emissions, were affected by the management practices used to handle the liquid and solid fractions. Methane emissions from liquid storage are reduced as a percentage of the VS stays with the solids fraction. However, nitrous oxide emissions from the separated solids might increase if separated solids are stored and not quickly land applied or transported outside of the farm for posterior use.     

Future Plans

Analysis for anaerobic digestion efficiency and pathogen inactivation will be incorporated in this study to conduct a complete assessment of manure characteristics after AD and SLS and their impact on different environmental indicators.

 

Table 1.  Summary of each farm’s manure management process.
Farm ID

AD

SLS

Feedstock
1

Mixed plug flow

Screw press

Dairy manure
2

No

ABRU

Dairy manure
3 Complete Mix

Screw press with blower

Dairy manure
4

Mixed plug flow

Screw press

Dairy manure
5

Mixed plug flow

Screw press

Paunch manure, food waste
6

Mixed plug flow

Screw press

Dairy manure
7

Mixed plug flow

Screw press

Dairy manure
8

Complete Mix

Centrifuge

Dairy manure, ethanol byproduct, FOG
9

No

ABRU

Dairy manure
AD: anaerobic digestion, SLS: solid-liquid separation, ABRU: aerobic bedding recovery unit , FOG: fat, oil, and grease

 

Scheme of the manure processing technologies and sampling locations.
Figure 1. Scheme of the manure processing technologies and sampling locations.

Authors

Aguirre-Villegas Horacio Andres. Assistant Scientist. Department of Biological Systems Engineering, University of Wisconsin-Madison. aguirreville@wisc.edu

Sharara Mahmoud. Assistant Professor. Department of Biological and Agricultural Engineering. NC State University

Larson Rebecca. Associate Professor. Department of Biological Systems Engineering, University of Wisconsin-Madison

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2019. Title of presentation. Waste to Worth. Minneapolis, MN. April 22-26, 2019. URL of this page. Accessed on: today’s date.

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Estimating GHG Emissions from Manure Management Practices in Dairy Systems

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Purpose

This study had the objective of quantifying greenhouse gas (GHG) emissions from different manure management practices and dairy farm sizes. A comparison of the main practices among farm sizes was also conducted to highlight practices that are able to minimize GHG emissions.

What did we do?

First, a survey was sent to Wisconsin dairy farms to collect information on manure management, machinery power, and time of operation. Manure management practices includeTable 1. Summary of the effects of various livestock antibiotics on decomposition under aerobic, anaerobic, and denitrifying conditionsd collection, transportation, storage, land application, and processing (anaerobic digestion (AD), solid-liquid separation (SLS), and sand separation (SS)). Second, modelling tools were used to estimate GHG emissions based on farm size and practice. Four farm sizes have been evaluated: small (1-99 animal units, 1 AU = 1,000 pounds of animal), medium (100-199 AU), large (200-999 AU) and permitted facilities (≥ 1,000 AU).

Three representative farms were modeled for GHG emissions based on survey results: a small farm (75 AU) handling 1.8 ton solid manure/day, a large farm (425 AU) handling 21.7 ton liquid manure/day, and a permitted facility (2,000 AU) handling 140 ton liquid manure/day and with manure processing. In addition, a base case scenario with the most representative practices for each farm size, and a low and a high GHG emitting scenario were modeled to analyze potential mitigation strategies (Table 1).

What have we learned?

Nitrous oxide (N2O) after manure land-application is the major contributor to GHG emissions in small farms (Figure 1). Most small farms land-apply manure daily or have short termFigure storage. Emissions can be reduced by using a barn cleaner instead of a skid steer as it is more efficient in terms of energy consumption. The high emitting scenario in small farms indicates that adding long term storage would increase GHG emissions mostly in the form of methane (CH4) from storage.

Storage is the major contributor to GHG emissions for large farms, where most emissions occur in the form of CH4. Storage CH4 emissions can be reduced by minimizing the storage retention time or by using a cover. Despite that manure storage has implications on air quality, its role is crucial for water quality purposes and therefore, removing the storage structure from the dairy farm is not a feasible option.

Manure processing is an interesting GHG mitigation strategy as shown in the permitted facility scenarios (Figure 1). AD and SLS achieve significant GHG emission reductions, where negative emissions indicate that AD displaces more GHG emissions from the production of grid electricity than the emissions coming from all manure handling processes. Injecting manure instead of surface applying it has proven to reduce ammonia emissions, but it resulted in an increase in N2O emissions in our model.

Future Plans

There is opportunity for future work analyzing data collected in the survey. These data include nutrient use, crop yields, bedding use and replacement, and milk yield and characteristics, which can be analyzed in the context of farm size and management practices.

Corresponding author, title, and affiliation

Aguirre-Villegas, Horacio Andres. Assistant Scientist. Department of Biological Systems Engineering, University of Wisconsin-Madison.

Corresponding author email

aguirreville@wisc.edu

Other authors

Rebecca Larson. Assistant Professor. Department of Biological Systems Engineering, University of Wisconsin-Madison

Additional information

References

Aguirre-Villegas, Horacio A., and Rebecca A. Larson. 2017. “Evaluating Greenhouse Gas Emissions from Dairy Manure Management Practices Using Survey Data and Lifecycle Tools.” Journal of Cleaner Production 143: 169–79. doi:10.1016/j.jclepro.2016.12.133.

Acknowledgements

 

This material is based upon work that is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 2013-68002-20525. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2017. Title of presentation. Waste to Worth: Spreading Science and Solutions. Cary, NC. April 18-21, 2017. URL of this page. Accessed on: today’s date.

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Calculating Carbon Footprints for the UGA Dairy And Swine Farms Using Selected Models


Why Examine Carbon Footprints of Farms?

World Agriculture is currently faced with the challenge of feeding a rapidly increasing global population, predicted to peak at 9.2 billion by 2075, while meeting an obligation to reduce greenhouse gas (GHG) emissions. The emission of GHG can cause many serious problems, such as global temperature rise, sea level rise and ocean acidification.

Satellite map of university of georgia dairy farmAgriculture releases significant amounts of CO2, CH4 and N2O to the atmosphere. It is estimated that the agriculture sector contributes around 10-12% (~ 5-6 Gt CO2-equivelents yr-1 in 2005) of total global anthropogenic GHG emissions, which is about 50 and 60% of methane and nitrous oxide emissions, respectively. UGA made a commitment to reduce the GHG emissions. These emissions are currently calculated using a model called campus-carbon-calculator. However this model is limited in agricultural applications because it does not account for many management changes that might reduce GHG emissions. The purpos e of our project was to select or develop a model for estimating the GHG emissions from UGA farms. It was necessary for this model to account for crop production, dairy production and swine production and desirable for the model to have limited data requirements, be easy to use and allow for a variety of management options to reduce GHG emissions.

What did we do?

We selected four models (Cool Farm Tool (Version 2.0), COMET-FARM Tool, Farm Smart (Version 1.5) and Pig Production Environmental Footprint Calculator (Version 3.X)) and also used the current-used model Clean Air-Cool Planet Campus Carbon Calculator (Version 6.9) to calculate GHG emissions on the UGA swine farm and dairy farm. We gathered inputs needed in both farms based on models with the help of farm managers, experts and references. Some inputs needed to be calculated and summarized and this was done using best available information. We entered information about swine farm into selected models and compared results on GHG emissions.

satellite map of University of Georgia swine farmWhat have we learned?

GHG emissions for the swine farm calculated using four different models are shown in Table 1. Estimates for GHG emissions in 2013 varied from 328228.06 kg CO2-equivalent (Pig Production Environmental Footprint Calculator (Version 3.X)) to 575000 kg CO2-equivalent using Clean Air-Cool Planet Campus Carbon Calculator (Version 6.9). While the Clean Air-Cool Planet Campus Carbon Calculator (Version 6.9) was the simplest one to use with only two inputs needed, it provided the highest estimates. Conversely, the Pig Production Environmental Footprint Calculator (Version 3.X) was the most complex and difficult to use but was the only tool that could adequately account for the anaerobic digester at this farm.

Table 1. Greenhouse gas emissions in swine farms 2013 using different models

We will finish calculating GHG emissions on the dairy farm and compare models based on carbon footprints and time and effort required. We will investigate a variety of proposed management changes on both farms to determine the resulting impacts on carbon footprints.

Authors

Lin Ma, master student in Department of Crop and Soil Science, University of Georgia malin12@uga.edu

Mark Risse, professor in Department of Crop and Soil Science, University of Georgia

Additional Information

Cool Farm Tool (Version 2.0) https://app.coolfarmtool.org/account/login/?next=/

COMET-FARM Tool http://cometfarm.nrel.colostate.edu/

Farm Smart (Version 1.5) http://sites.usdairy.com/farmsmart/Pages/Home.aspx

Acknowledgements

Thanks to Drs. Lane Ely and Robert Dove and the employees and managers at the UGA Swine and Dairy Centers for supplying information and time to us for this effort.

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2015. Title of presentation. Waste to Worth: Spreading Science and Solutions. Seattle, WA. March 31-April 3, 2015. URL of this page. Accessed on: today’s date.

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Sources of Agricultural Greenhouse Gases

The conversation about climate change largely revolves around greenhouse gases. Agriculture is both a source and sink for greenhouse gases (GHG). A source is a net contribution to the atmosphere, while a sink is a net withdrawal of greenhouse gases.  In the United States, agriculture is a relatively small contributor, with approximately 8% of the total greenhouse gas emissions, as seen in Figure 1.

Most agricultural emissions originate from soil management, enteric fermentation (microbial action in the digestive system), energy use, and manure management (Figure 2).  The primary greenhouse gases related to agriculture are (in descending order of magnitude) methane, nitrous oxide, and carbon dioxide.

Fact sheet: Contribution of Greenhouse Gases: Animal Agriculture in Perspective (look below the preview box and title for a download link)

U.S. GHG Inventory Figure 1: U.S. greenhouse gas inventory with electricity distributed to economic sectors (EPA, 2013) 

Ag Sources of GHGs

Figure 2: U.S. agricultural greenhouse gas sources (Adapted from Archibeque, S. et al., 2012)

Animal Agriculture’s Contribution to Greenhouse Gas Emissions

Within animal production, the largest emissions are from beef followed by dairy, and largely dominated by the methane produced in during cattle digestion (Figure 3).

Greenhouse gas emissions from livestock in 2008

Figure 3: Greenhouse gas emissions from livestock in 2008 (USDA, 2011)

Excess nitrogen in agriculture systems can be converted to nitrous oxide through the nitrification-denitrification process. Nitrous oxide is a very potent greenhouse gas, with 310 times greater global warming potential than carbon dioxide.  Nitrous oxide can be produced in soils following fertilizer application. This includes both commercial, inorganic fertilizer as well as organic fertilizers like manure or compost.

As crops grow, photosynthesis removes carbon dioxide from the atmosphere and stores it in the plants and soil life. Soil and plant respiration adds carbon dioxide back to the atmosphere when microbes or plants breakdown molecules to produce energy.  Respiration is an essential part of growth and maintenance for most life on earth. This repeats with each growth, harvest, and decay cycle, therefore, feedstuffs and foods are generally considered to be carbon “neutral.”

Some carbon dioxide is stored in soils for long periods of time.  The processes that result in carbon accumulation are called carbon sinks or carbon sequestration.  Crop production and grazing management practices influence the soil’s ability to be a net source or sink for greenhouse gases.  Managing soils in ways that increase organic matter levels can increase the accumulation (sink) of soil carbon for many years.

Enteric Fermentation

The next largest portion of livestock greenhouse gas emissions is from methane produced during enteric fermentation in ruminants – a natural part of ruminant digestion where microbes in the first chamber of the stomach, the rumen, breaks down feed and produces methane as a by-product. The methane is released  primarily through belching.

As with plants, animals respire carbon dioxide, but also store some in their bodies, so they too are considered a neutral source of atmospheric carbon dioxide.

Manure Management

A similar microbial process to enteric fermentation leads to methane production from stored manure.  Anytime the manure sits for more than a couple days in an anaerobic (without oxygen) environment, methane will likely be produced.  Methane can be generated in the animal housing, manure storage, and during manure application. Additionally, small amounts of methane is produced from manure deposited on grazing lands.

Nitrous oxide is also produced from manure storage surfaces, during land application, and from manure in bedded packs & lots. Related: Archived webinar on GHG Emissions Research in Animal Ag

Other sources

There are many smaller sources of greenhouse gases on farms. Combustion engines exhaust carbon dioxide from fossil fuel (previously stored carbon) powered vehicles and equipment.  Manufacturing of farm inputs, including fuel, electricity, machinery, fertilizer, pesticides, seeds, plastics, and building materials, also results in emissions.

To learn more about how farm emissions are determined and see species specific examples, see the Carbon Footprint resources.

To learn about how to reduce on-farm emissions through mitigation technology and management options, see the Reducing Emissions resources.

Carbon Footprint

Definition: carbon footprint is the total greenhouse gas emissions for a given person, place, event or product.

Carbon footprints are created using a process called life cycle assessment. Life cycle assessment or LCA is a method of resource accounting where quantitative measures of inputs, outputs and impacts of a product are determined.

Life cycle assessment is commonly used to:

  • find process or production improvements
  • compare different systems or products
  • find the ‘hot spots’ in a product’s life cycle where the most environmental impacts are made
  • help businesses or consumers make informed sourcing decisions

diagram

Key Assumptions

boundaries of the system: each higher tier provides a more complete picture of the product’s impacts, however requires more time and resources to complete.

  1. Gate to Gate (LCA Tier I) – inventories the direct emissions for a single product of process
  2. Cradle to Gate (Tier II) – inputs are taken back to the initial extraction as natural resources up to a certain point in the product’s life such as its sale from the farm, i.e. farm gate.  This will include both direct  and indirect emissions from the product.
  3. Cradle To Grave (Tier III) – the product is followed through the consumer to its eventual recycling or disposal.

Sources of variation

Different researchers may get different results when performing a LCA on the same product. This can happen for many reasons:

  • System boundary definition
  • Inclusion/exclusion of secondary/ indirect sources
  • Inclusion/exclusion of biogenic carbon (stored in organisms)
  • Inclusion/exclusion of carbon dioxide from fuel combustion
  • Functional relationships used
  • Global warming potential indexes
  • Inclusion/exclusion of carbon sequestration

Related: Six archived webinars on the sources of animal ag ghg’s (some are general and some are species-specific)

Educator Materials

If you would like to use the video, slides, or factsheet for educational programs, please visit the curriculum page for download links for this and other climate change topics.

Recommended Reading – How Many Greenhouse Gases Does Agriculture Emit?

U.S. Agriculture Emissions

International Agriculture Emissions

Carbon Footprints and Life Cycle Analysis

Greenhouse Gas Regulations for Animal Agriculture

Visit Climate Change Regulation, Policy, and Market Opportunities

Acknowledgements

Author: Crystal A. Powers – University of Nebraska-Lincoln cpowers2@unl.edu

This material was developed through support from the USDA National Institute for Food and Agriculture (NIFA) under award #2011-67003-30206.

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From Waste to Energy: Life Cycle Assessment of Anaerobic Digestion Systems

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Abstract

In recent years, processing agricultural by-products to produce energy has become increasingly attractive due to several reasons: centralized availability of low cost by-products, avoiding the fuel vs. food debate, reduction of some associated environmental impacts, and added value that has the potential to generate additional income for producers. Anaerobic digestion systems are one waste-to-energy technology that has been proven to achieve these objectives.  However, investigation on the impacts of anaerobic digestion has focused on defined segments, leaving little known about the impacts that take place across the lifecycle. Current systems within the U.S. are dairy centric with dairy manure as the most widely used substrate and electricity production as the almost sole source for biogas end use.  Recently, there is more interest in exploring alternative feedstocks, co-digestion pathways, digestate processing, and biogas end uses.  Different operational and design practices raise additional questions about the wide reaching impacts of these decisions in terms of economics, environment, and operational aspects, which cannot be answered with the current state of knowledge.

Why Study the Life Cycle of Anaerobic Digestion?

Waste management is a critical component for the economic and environmental sustainability of the agricultural sector. Common disposal methods include land application, which consumes large amounts of land resources, fossil energy, and produces significant atmospheric GHG emissions. Proof of this is that agriculture accounts for approximately 50% of the methane (CH4) and 60% of the nitrous oxide (N2O) global anthropogenic emissions, being livestock manure one of the major sources of these emissions (Smith et al., 2007). In the last decades, the development of anaerobic digestion (AD) systems has contributed to achieve both climate change mitigation and energy independence by utilizing agricultural wastes, such as livestock manure, to produce biogas. In addition, it has been claimed that these systems contribute to nutrient management strategies by adding flexibility to the final use and disposal of the remaining digestate. Despite these advantages, the implementation of AD systems has been slow, due to the high investment and maintenance costs. In addition, little is still known about the lifecycle impacts and fate and form of nutrients of specific AD systems, which would be useful to validate their advantages and identify strategic and feasible areas for improvement.

The main goal of this study is to quantify the lifecycle GHG emissions, ammonia emissions, net energy, and fate and form of nutrients of alternative dairy manure management systems including land-spread, solid-liquid separation, and anaerobic digestion. As cow manure is gaining an important role within the biofuel research in the pursuit for new and less controversial feedstocks, such as corn grain, the results of this study will provide useful information to researchers, dairy operators, and policy makers.

What Did We Do?

Lifecycle sustainability assessment (LCSA) methods were used to conduct this research, which is focused in Wisconsin. The state has nearly 1.3 million dairy cows that produce approximately 4.7 million dry tons of manure annually and is the leading state for implemented agricultural based AD systems. Manure from a 1,000 milking cow farm (and related maintenance heifers and dry cows) was taken as the base-case scenario. Four main processes were analyzed using the software GaBi 5 (PE, 2012) for the base case: manure production and collection, bedding sand-separation, storage, and land application. Three different manure treatment pathways were compared to the base-case scenario: including a solid-liquid mechanical separator, including a plug-flow anaerobic digester, and including both the separator and the digester. The functional unit was defined as one kilogram of excreted manure since the function of the system is to dispose the waste generated by the herd. A cradle-to-farm-gate approach was defined, but since manure is considered waste, animal husbandry and cultivation processes were not included in the analysis (Fig. 1). Embedded and cumulative energy and GHG emissions associated with the production of material and energy inputs (i.e. sand bedding, diesel, electricity, etc.) were included in the system boundaries; however, the production of capital goods (i.e. machinery and buildings) were excluded.

Figure 1. System boundaries of the base case scenario (land-spread manure) and the three manure treatment pathways: 1) solid-liquid separation, 2) anaerobic digestion, 3) anaerobic digestion and solid-liquid separation.

Global warming potential (GWP) was characterized for a 100-year time horizon and measured in kg of carbon dioxide equivalents (CO2-eq). Characterization factors used for gases other than CO2 were 298 kg CO2-eq for N2O, 25 kg CO2-eq for abiotic CH4 based on the CML 2001 method, and 24 kg CO2-eq for biotic CH4. CO2 emissions from biomass are considered to be different from fossil fuel CO2 emissions in this study; the former recycles existing carbon in the system, while the latter introduces new carbon into the atmosphere. In this context, it will be assumed that CO2 emissions from biomass sources were already captured by the plant and will not be characterized towards GWP[1]. This logic was applied when characterizing biogenic methane as one CO2 was already captured by the plant, therefore, reducing the characterization factor from 25 kg CO2-eq to 24 kg CO2-eq. Even though ammonia (NH3) does not contribute directly to global warming potential, it is considered to be an indirect contributor to this impact category (IPCC, 2006).

Data was collected from different sources to develop lifecycle inventory (LCI) as specific to Wisconsin as possible, in order to maximize the reliability, completeness, and representativeness of the model. The following points summarize some of the data sources and assumptions used to construct the LCI:

  • Related research (Reinemann et al., 2010): This model provided data about animal husbandry and crop production for dairy diet in Wisconsin.
  • Manure management survey: The survey, sent to dairy farms in Wisconsin, has the objective of providing information related to manure management practices and their associated energy consumption.
  • In house experiments: laboratory experiments, conducted at the University of Wisconsin-Madison, provided characterization data about manure flows before and after anaerobic digestion and solid-liquid separation and manure density in relation to total solids (Ozkaynak and Larson, 2012).
  • Material and energy databases: National Renewable Energy Laboratory U.S. LCI dataset (NREL, 2008), PE International Professional database (PE, 2012), and EcoInvent (EcoInvent Center, 2007), which are built into GaBi 5. The electricity matrix used in this LCA represents the mix of fuels that are part of the electric grid of Wisconsin.
  • Representative literature review.

Biotic emissions from manure have been cited to be very site specific (IPCC, 2006) and even though the Intergovernmental Panel on Climate Change (IPCC) provides regional emission factors, they are only for CH4 and N2O. Specific GHG emission factors were developed for Wisconsin based on the Integrated Farm System Model (IFSM) (Rotz et al., 2011), and by using key parameters that affect emissions (e.g. temperature, volatile solids, manure management practices) for each stage of the manure management lifecycle.

What Have We Learned?

Emissions are produced from consumed energy and from manure during each stage of the manure management lifecycle. In the base-case scenario, manure storage is the major contributor to GHG emissions. In this scenario, a crust tends to form on top of stored manure due to the higher total solids content when compared to digested manure and the liquid fraction of the separated manure. The formation of this crust affects overall GHG emissions (e.g. crust formation will increase N2O emissions but reduce CH4 emissions). The installation of a digester reduces CH4 emissions during storage due to the destruction of volatile solids that takes place during the digestion process. However, some of the organic nitrogen changes form to ammoniacal nitrogen, increasing ammonia and N2O emissions posterior to storage and land application. Energy consumption increases with both anaerobic digester and separation, but net energy is higher with anaerobic digestion due to the production of on-farm electricity. The nutrient balance is mostly affected by the solid-liquid separation process rather than the anaerobic digestion process.

Future Plans

A comprehensive and accurate evaluation of the lifecycle environmental impacts of AD systems requires assessing the multiple pathways that are possible for the production of biogas, which are defined based on local resources, technology, and final uses of the resulting products.  A second goal of this research is to quantify the net GHG and ammonia emissions, net energy gains, and fate of nutrients of multiple and potential biogas pathways that consider different: i) biomass feedstocks (e.g miscanthus and corn stover), ii) management practices and technology choices, and iii) uses of the produced biogas (e.g. compressed biogas for transportation and upgraded biogas for pipeline injection) and digestate (e.g. bedding). This comprehensive analysis is important to identify the most desirable pathways based on established priorities and to propose improvements to the currently available pathways.

Authors

Aguirre-Villegas Horacio Andres. Ph.D. candidate. Department of Biological Systems Engineering, University of Wisconsin-Madison.  aguirreville@wisc.edu

Larson Rebecca. Ph.D. Assistant Professor. Department of Biological Systems Engineering, University of Wisconsin-Madison.

Additional Information

    • Ozkaynak, A. and R.A. Larson.  2012.  Nutrient Fate and Pathogen Assessment of Solid Liquid Separators Following Digestion.  2012 ASABE International Meeting, Dallas, Texas, August 2012

References

De Klein C., R. S.A. Novoa, S. Ogle, K. A. Smith, P. Rochette, T. C. Wirth,  B. G. McConkey, A. Mosier, and K. Rypdal. 2006. Chapter 11: N2O emissions from managed soils, and CO2 emissions from lime and urea application. In Volume 4: Agriculture, Forestry and Other Land Use. IPCC 2006, 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Prepared by the National Greenhouse Gas Inventories Programme, Eggleston H.S., Buendia L., Miwa K., Ngara T. and Tanabe K. (eds). Published: IGES, Japan.

Ecoinvent Centre.2007. Ecoinvent Eata. v2.0. Ecoinvent Reports No.1-25. Swiss Centre for Life Cycle Inventories. Dübendorf.

National Renewable Energy Laboratory (NREL). 2008. U.S. Life-Cycle Inventory (LCI) Database.

Ozkaynak, A. and R.A. Larson.  2012.  Nutrient Fate and Pathogen Assessment of Solid Liquid Separators Following Digestion.  2012 ASABE International Meeting, Dallas, Texas, August 2012

PE International. 2012. Software-systems and databases for lifecycle engineering.

Reinemann D. J., T.H. Passos-Fonseca, H.A. Aguirre-Villegas, S. Kraatz, F. Milani, L.E. Armentano, V. Cabrera, M. Watteau, and J. Norman. 2011. Energy intensity and environmental impact of integrated dairy and bio-energy systems in Wisconsin, The Greencheese Model.

Rotz, C. A., M. S. Corson, D. S. Chianese, F. Montes, S.D. Hafner, R. Jarvis, and C. U. Coiner. 2011. The Integrated Farm System Model (IFSM). Reference Manual Version 3.4. Accessed on Nov, 2012. Available at: http://www.ars.usda.gov/Main/docs.htm?docid=8519

Smith, P., D. Martino, Z. Cai, D. Gwary, H. Janzen, P. Kumar, B. McCarl, S. Ogle, F. O’Mara, C. Rice, B. Scholes, O. Sirotenko. 2007: Agriculture. In Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [B. Metz, O.R. Davidson, P.R. Bosch, R. Dave, L.A. Meyer (eds)], Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Acknowledgements

This work was funded by the Wisconsin Institute for Sustainable Agriculture (WISA-Hatch)

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