Value of Manure Library By Season

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Authors/Sponsors

The project team assembling this product includes Amy Schmidt, Leslie Johnson, and Rick Koelsch, University of Nebraska-Lincoln; Erin Cortus and Melissa Wilson, University of Minnesota; and Dan Andersen, Iowa State University. These resources represent our recommendations for discussing the Value of Manure.

This product was assembled with financial assistance from the North Central Region Sustainable Agricultural Research and Education program. NCR-SARE is one of four regional offices that run the USDA Sustainable Agriculture Research and Education (SARE) program, a nationwide grants and education program to advance sustainable innovation to American agriculture.

Value of Manure Library for Educators and Advisors

Purpose

Manure is a resource that comes with many benefits and challenges.  This library is designed to provide educators and advisors with access to recommended resources that will assist you in your discussion of manure’s benefits and challenges.  Educators, please feel free to share and re-purpose educational products in this library with local audiences. Advisors, the library’s resources shall provide you with decision tools and educational products for enriching your discussions with clientele and rural community residents.

How to find materials

For those seeking specific resources, materials are organized visually by topic area and type of media. For those that would rather search materials more linearly, there is a grid version available.

In all views, there is a search button in the top right corner that looks like a magnifying glass and an expansion button that looks like two outward pointing arrows to view in full screen.

By Topic Area

Preview of manure value library database sorted by topic.
    • Manure as a fertilizer
    • Manure economics
    • Soil quality/health effects
    • Water quality effects
    • Use in organic systems
    • Neighbors
    • Regulatory concerns
    • Logistics

By Media Type:

Preview of manure value library database sorted by purpose.
    • Social media
    • Short news articles and web pages
    • Educational publications
    • Decision support tools
    • Recommended research articles

 

Instructions for Re-purposing Educational Content

Our team encourages and welcomes educators and advisors re-purposing of many of the social media and web page/news article resources found in this library.  Would these resources be helpful to you for Tweeting to your followers? Assembling talking points for a local radio presentation or discussion with a county board?  Or adding an article to local print media or your blog?

Example of social media graphic to be re-purposed.
    • Twitter Posts:  A broad range of Twitter posts, graphics with an educational message and short text introduction, are included for use with your social media connections.  Please re-purpose these for your local use. We ask that you maintain the “N Extension” and “WSA” logos in your re-purposed post.  You may replace the “Manure Happens. Take Credit” caption and the “Learn more at: http:// ________”  with an appropriate recognition of your organization and/or a web page that you would like to promote.
    • Web Page/News Articles:  Many of these library products can be repurposed for a variety of local uses.  News articles and web pages may be revised to add local information with the new authors name included if the original authors continue to be listed.
    • Any Educational Products:  Any of the Library resources may be used as talking points for a local radio broadcast or community group presentations. Please recognize the original authors and resource title in your presentation.

 

Is something missing from our library?

We welcome your suggestions of resources that you have found beneficial in your educational or advisory role.  Please email any of the project team members with your suggestions or submit them via our google form for our consideration.

Authors/Sponsors

The project team assembling this product includes Amy Schmidt, Leslie Johnson, and Rick Koelsch, University of Nebraska-Lincoln; Erin Cortus and Melissa Wilson, University of Minnesota; and Dan Andersen, Iowa State University.  These resources represent our recommendations for discussing the Value of Manure.

This product was assembled with financial assistance from the North Central Region Sustainable Agricultural Research and Education program.  NCR-SARE is one of four regional offices that run the USDA Sustainable Agriculture Research and Education (SARE) program, a nationwide grants and education program to advance sustainable innovation to American agriculture.

Value of Manure Library By Media Type

Media types include social media, news articles, web pages, educational publications, decision support tools, and recommended research articles.

Authors/Sponsors

The project team assembling this product includes Amy Schmidt, Leslie Johnson, and Rick Koelsch, University of Nebraska-Lincoln; Erin Cortus and Melissa Wilson, University of Minnesota; and Dan Andersen, Iowa State University. These resources represent our recommendations for discussing the Value of Manure.

This product was assembled with financial assistance from the North Central Region Sustainable Agricultural Research and Education program. NCR-SARE is one of four regional offices that run the USDA Sustainable Agriculture Research and Education (SARE) program, a nationwide grants and education program to advance sustainable innovation to American agriculture.

Value of Manure Library By Topic Area

Topics include agronomics, economics and yield, soil health/quality, water quality, organic systems, neighbors, regulations and logistics.

Authors/Sponsors

The project team assembling this product includes Amy Schmidt, Leslie Johnson, and Rick Koelsch, University of Nebraska-Lincoln; Erin Cortus and Melissa Wilson, University of Minnesota; and Dan Andersen, Iowa State University. These resources represent our recommendations for discussing the Value of Manure.

This product was assembled with financial assistance from the North Central Region Sustainable Agricultural Research and Education program. NCR-SARE is one of four regional offices that run the USDA Sustainable Agriculture Research and Education (SARE) program, a nationwide grants and education program to advance sustainable innovation to American agriculture.

Value of Manure Library Grid View

Authors/Sponsors

The project team assembling this product includes Amy Schmidt, Leslie Johnson, and Rick Koelsch, University of Nebraska-Lincoln; Erin Cortus and Melissa Wilson, University of Minnesota; and Dan Andersen, Iowa State University. These resources represent our recommendations for discussing the Value of Manure.

This product was assembled with financial assistance from the North Central Region Sustainable Agricultural Research and Education program. NCR-SARE is one of four regional offices that run the USDA Sustainable Agriculture Research and Education (SARE) program, a nationwide grants and education program to advance sustainable innovation to American agriculture.

Performance and Payback of a Solid-Liquid Separation Finishing Barn

A 1200-hd solid-liquid separation finishing barn was built in Missouri for improved manure management and air quality. The facility has a wide V-shaped gutter below slatted flooring (Figure 1), which continuously drains away liquids.  A scraper is used to collect the solids, which are then managed separately. Field sampling and research were conducted to evaluate the performance of the solid-liquid separation finishing barn in improving manure nutrient management, potential nutrient/water recycling based on filtration, and barn construction and operating costs.

What did we do?

The barn (built in 2010) was closely monitored for manure production and nutrient content, and operating costs. Laboratory-scale pretreatments and filtrations were conducted to evaluate the practicality of nutrient/water recycling from the separated liquid manure.

What we have learned?

The daily liquid manure production averaged 885 gallons and daily solid manure production averaged 299 gallons (about ¼ of the total manure volume). The separation system removed 61.7%, 41.7%, 74.8%, and 46.2% of the total manure nitrogen, ammonium, phosphorous, and potassium, respectively, with the collected solids. The filtration results indicate that the microfiltration and reverse osmosis were time and energy intensive, which was probably constrained by the relatively small-scale unit (inefficient compared with larger units), small filter surface area, and high concentration of dissolved nutrients.

The construction cost of the solid-liquid separation barn with solid manure storage was $323,000 ($269/pig-space, in 2010), 17% higher compared to the traditional deep-pit barn ($175 to $230/pig-space). It is likely that the solid-liquid separation barn will become less expensive when more barns of similar design are built, and the conveyor system can be improved and simplified for less maintenance and lower costs. Additional electricity cost was $331 per year for daily operation of the scraper and conveyor systems, and pumping the separated liquid manure fraction. The additional maintenance cost of the scraper system averaged $1,673/year. A net gain of $3,975/year was observed when considering the value of the separated manures, cost of land application, and annual maintenance cost.

A payback period of 15.1 years on the additional investment was estimated, when compared with the popular deep-pit operation. However, the payback period can be reduced by many factors, including improved conveyor system and growing popularity of the barn design in an area. When the distance to transport the slurry manure was increased from 5 miles to 7.5 and 10 miles, the payback periods became 12.7 and 11.3 years, respectively. The solid-liquid separation barn was shown to have better air quality when compared with deep-pit barns based on monthly measurements of ammonia and hydrogen sulfide concentrations.

Impacts/Implications of the Research.  

This study monitored the manure production of a commercial finishing barn utilizing a solid-liquid separation system. Overall, we can conclude that the final results obtained from monitoring the total manure production rate, air quality exiting the barn fans, and the pig growth rates made sense relative to other comparative sources. The overall results indicate that the barn design can attain some valuable benefits from separating the solid and liquid streams.  About a quarter of the manure volume was collected and managed as nutrient-dense solid manure (defined as ‘stackable’). The solid manure held 80% of the total solids and nearly 75% of the phosphorous.

Take Home Message

There are alternative barn designs and manure management systems (relative to lagoon and deep-pit operations) that should be considered when planning for a new operation or expansion. Considerations should include the need to better manage manure nutrients and improve air quality for human and animal occupants.

Future plans

Further consideration of the manure management, including work load and major- and micro-nutrients need to be furthered analyzed. Future research may look into application of a larger-scale crossflow system to see if nutrient removal and flow rates can be improved significantly. Future research may focus on improving manure filtrate flow, and determining the cost of installation and upkeep for a filtration unit that can operate at the level of a farm operation. Extrapolating the costs off of bench-scale model does not seem remotely indicative of the true cost, due to improved efficiency and power of larger unit.

Authors

Lim, Teng (Associate Professor and Extension Agricultural Engineer, Agricultural Systems Management, University of Missouri, limt@missouri.edu)

Brown, Joshua (University of Missouri); Zulovich, Joseph (University of Missouri); and Massey, Ray (University of Missouri).

Additional information

Please visit https://www.pork.org/research/sustainability-evaluation-solid-liquid-manure-separation-operation/ for the final report, and ASABE Paper No. 1801273 (St. Joseph, Mich.: ASABE. DOI: https://doi.org/10.13031/aim.201701558) for more information.

Acknowledgements

Funding for this research project was provided by the National Pork Checkoff and University of Missouri Extension.

Figure 1. The V-shape pit with automated manure scraper and trough at center (Left), and gravity draining of liquid manure from the trough to the sump pit (Right).
Figure 1. The V-shape pit with automated manure scraper and trough at center (Left), and gravity draining of liquid manure from the trough to the sump pit (Right).
Figure 2. The storage shed for solid manure to the north of the modified scraper barn (Left), and stored solid manure (Right).
Figure 2. The storage shed for solid manure to the north of the modified scraper barn (Left), and stored solid manure (Right).

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.

Cataloging and Evaluating Dairy Manure Treatment Technologies


Proceedings Home | W2W Home w2w17 logo

Purpose

To provide a forum for the introduction and evaluation of technologies that can treat dairy manure to the dairy farming community and the vendors that provide these technologies.

What Did We Do?

Newtrient has developed an on-line catalog of technologies that includes information on over 150 technologies and the companies that produce them as well as the Newtrient 9-Point scoring system and specific comments on each technology by the Newtrient Technology Advancement Team.

What Have We Learned?

Our interaction with both dairy farmers and technology vendors has taught us that there is a need for accurate information on the technologies that exist, where they are used, where are they effective and how they can help the modern dairy farm address serious issues in an economical and environmentally sustainable way.

Future Plans

Future plans include expansion of the catalog to include the impact of the technology types on key environmental areas and expansion to make the application of the technologies on-farm easier to conceptualize.

Corresponding author name, title, affiliation  

Mark Stoermann & Newtrient Technology Advancement Team

Corresponding author email address  

info@newtrient.com

Other Authors 

Garth Boyd, Context

Craig Frear, Regenis

Curt Gooch, Cornell University

Danna Kirk, Michigan State University

Mark Stoermann, Newtrient

Additional Information

http://www.newtrient.com/

Acknowledgements

All of the vendors and technology providers that have worked with us to make this effort a success need to be recognized for their sincere effort to help this to be a useful and informational resource.

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.

Estimating the Economic Value of the Greenhouse Gas Reductions Associated with Dairy Manure Anaerobic Digestion Systems Located in New York State

Proceedings Home W2W Home w2w17 logo

Purpose

There is a worldwide concern in controlling the anthropogenic emissions of greenhouse gas (GHG) emissions. GHGs pertinent to this paper, include carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) and are measured in CO2 equivalents (CO2 eq.). On a 100-year basis, CH4 is 34 times as potent as CO2, while N2O is 298 times as potent as CO2 (IPCC, 2013); CO2 eq. is referred to as the global warming potential (GWP) of these gases. The carbon from feed used on a dairy farm originally comes from CO2 recently removed from the atmosphere during photosynthesis and so has a neutral impact on climate change. However, carbon that is converted to CH4 and N2O is a significant concern since their GWPs are much higher. Dairy farms create GHG emissions when they use fossil fuel-based sources to provide energy for the farm, when importing fertilizer to grow crops and to harvest milk. However, emissions from the animals in the form of enteric CH4 and GHGs from manure management ! are much more significant due to the GWP. While every farm is different, estimates from Thoma et al. (2012) show that of the 34.9 Tg of CO2 eq. in the US dairy supply chain, 19% comes from feed production and 53% comes from milk production. Of the milk production, CO2 eq., 49% is from enteric emissions while 44% is from manure management, predominately from CH4 emissions from manure storages.

New York State, the third largest dairy state in the nation (NASS, 2015), has established ambitious overall renewable energy goals including incorporating 50% renewable energy in the electricity used in the State by 2030 (Energy to Lead, 2015) and reducing GHG emissions 40% by 2040 based on 1990 year baseline values (Executive Order, 2009). The New York State Public Service Commission (PSC) is charged with the responsibility of developing a system that encourages utilities to help meet these goals. This includes reforming the energy vision, a new clean energy standard that is being developed to value electric products from distributed energy sources that includes an economic value for the environmental attributes (E).

An attempt at quantifying the environmental benefits of AD (E) might be expressed as follows:

Etotal=∑▒〖Eghg+Eair quality+Ewater quality+Esoil quality+E…〗

As the State’s renewable energy goals are realized, there needs to be a way for the process to include special provisions for those renewable energy sources that have extra societal benefits, including economic and environmental, and that support the rural character of upstate NY. The dairy industry is New York’s leading agricultural sector, accounting for more than one-half of the state’s total agricultural receipts. The increased milk supply has been very important in helping to meet the tremendous growth in the production of yogurt in NYS. However, the margin between the cost of producing milk and the price received for milk sales, is shrinking. Investing in farm facilities like ADSs will need to be analyzed carefully to ensure a return on investment that merits their implementation. An economic value for the environmental attributes of electricity produced from an ADS would aid in the analysis, showing a more positive overall benefit.

Dairy farms are also under increasing pressure to improve conditions environmentally. The New York State Department of Environmental Conservation (NYSDEC) proposed revisions for the CAFO state permit, regulating the water quality impact of farms with more than 300 cows, will require manure storages to be built to limit spreading on at-risk fields during the winter and early spring seasons. These are farm sizes where manure-based ADSs have been built in the past and where many more could be implemented, given a reasonable rate of return. Manure storages are an important best management practice (BMP) to reduce the potential for water pollution by allowing farms to avoid manure spreading during inappropriate times. Unfortunately, if the manure system does not have a way to capture the GHGs produced, they are released into the atmosphere. Manure-based ADSs installed on farms would be a win-win-win to capture and reduce GHGs and to produce renewable energy from the captured! CH4, fur thermore helping to meet the NYS renewable energy and GHG reduction goals. ADSs installed on farms would stimulate the rural economy and also provide the farm and rural community with all the additional benefits contained in Appendix A.

This paper presents an analysis of the GHG reduction potential for a NYS dairy manure management system that includes AD, post-digestion solid-liquid separation (SLS) and long-term manure storage of SLS liquid effluent. This system is representative of almost all of the 27 ADSs currently operating on-farm in NYS today.

METHODS

The mass of GHG emission reductions (i.e., the mass of carbon dioxide equivalents [MT CO2 eq.]) associated with AD (in this analysis, AD followed by SLS with liquid effluent stored long-term) located in New York State (NYS), was quantified and is discussed in this paper. The following protocols were used: IPCC (2006), AgSTAR (2011), and EPA (Federal Register, 2009) combined with reasonable input values that are representative of a farm’s baseline condition (long-term manure storage with no pre-treatment by ADS). The reductions quantified include: 1) the replacement of fossil fuel-based electrical energy by using AD produced biogas to operate an on-site engine-generator set, and 2) GHG emissions from CAFO required (for water quality purposes) long-term manure storages. The difference between the baseline condition and the conditions post-implementation of an ADS yields the farm’s net GHG emission associated with manure storage. To quantify the economic value! of the G HG emission reductions, the EPA social cost of carbon (SC-CO2) was used (EPA, 2016).

What did we do? *

PROCEDURE

The baseline condition is represented in Figure 1. Typical liquid/slurry long-term manure storages have manure that consists of urine plus feces, solid bedding and milking center washwater, added continuously as is produced on the farm. A natural crust may form as lighter organic material floats to the surface. The storages are constructed as a designed earthen storage with 2:1 side slopes or fabricated from concrete or steel. The fabricated structures have straight sides so less surface area is exposed. A few storages have a SLS prior to storage, while very few have a manure storage cover. Without a cover, they are exposed to rainfall from both annual precipitation and from extreme storms. To determine the baseline condition, storage with no SLS and with a natural crust was considered.

Figure 1. Baseline emissions from dairy farm with no renewable energy system (per cow, per year)

Figure 1. Baseline Emissions from Dairy Farm with No Renewable Energy System (Per cow per year)

Establish Long-Term Manure Storage Baseline Emissions

Part I – Estimating typical CH4 emissions from a long-term manure storage

An independent panel of experts agreed (USDA, 2014) that GHG emission reductions are best estimated using the Intergovernmental Panel on Climate Change (IPPC) Tier 2 method. For long-term manure storages, the daily methane emissions can be calculated by using Equation 1.

Equation 1. ECH4 = VS x Bo x 0.67 x (MCF/100)

where:

ECH4 = Mass of CH4 emissions (kg CH4/cow-day)

VS = Mass of volatile solids in manure going to storage (kg/cow-day)

Bo = Maximum volume of CH4 producing capacity for manure (m3 CH4/kg VS)

= 0.24 m3 CH4/kg VS (for dairy cow manure)

0.67 = Conversion factor for m3 CH4 to kg CH4

MCF = CH4 conversion factor for the manure management system

Yearly CH4 emissions (kg CH4/cow-yr.) can be estimated by summing the daily emissions (or multiplying an average representative daily emission by 365 days). The MCF is largely dependent on the temperature and the type of manure management system. The MCF will change throughout the year as the manure storage temperature changes. Using a summer ambient temperature representative of Upstate New York, of 18°C (64°F) and a winter ambient temperature of < 10°C (< 50°F), a farm can limit the amount stored and the time in storage during the warmer months to reduce the average yearly MCF. Different manure systems also have a different MCF based on the oxygen levels, interception of CH4 gases, and moisture content.

The two variables that can be controlled by the farm management are the VS loading per cow and the methane conversion factor (MCF). The VS loading rate can be reduced by any pre-manure storage treatment process that reduces the storage organic loading rate; fine tuning the diet to reduce VS in the manure and SLS are examples of two methods used to control the VS.

Typically in NYS, manure is stored both in the summer and winter in a liquid/slurry system with no natural crust. Using average typical winter and summer manure storage temperatures, average MCF values can be used in Equation 1 to estimate average methane emissions for these 6-month storage periods. The MCF values are shown in Table 1.

Table 1. Typical Long-Term Manure Storage Methane Conversion Factors for Storage Periods in NYS1

Storage Period

Winter

Summer

Average Manure Storage Temperature (°C)

<10

18

MCF

17

35

1These numbers are based on liquid/slurry storage without a natural crust cover.  (Source:  IPCC, 2006)

Using these MCF values shown in Table 1 and a per-cow VS excretion rate of 7.7 kg/cow-day (representative of high producing NY dairy cows – ASABE, 2006), manure storages could be estimated to produce 38 kg CH4/cow (for the winter storage period) and 79 kg CH4/cow (for the summer storage period) or an average of 4 metric tons (MT) of CO2 eq. per cow per year since 1 kg of CH4 = 34 kg CO2 eq.

Part II – Estimating typical N2O emissions from a long-term manure storage

There could be N2O emissions from a raw manure storage facility. The CO2 equivalent from N2O emissions can be estimated by using Equation 2.

Equation 2. CO2eq = 298 CO2/N2O GWP x EF3 x N x44 N2O/28 N2O-N

where:

CO2eq = Equivalent global warming potential expressed as carbon dioxide

298 CO2/N2O = GWP factor for N2O

EF3 = Emission Factor for N2O-N emissions from manure management

N = Mass of N excreted per cow per day = 0.45 kg/cow-day (ASAE, 2005)

Using an EF3 value of 0.005 (USEPA, 2009) for long-term storage of slurry manure with a crust and multiplying it by 0.45 kg of N/cow-day and by 365 days per year yields an additional 0.38 MT of CO2 eq. per cow per year from N2O emissions from a long-term manure storage facility.

Summary of long-term storage GHG emissions

Combining both the CO2 eq. per cow per year from CH4 emissions and the CO2 eq. per cow per year from N2O emissions from a manure storage facility provides a baseline emission of 4.38 MT of CO2 eq. per cow per year from the manure storage systems that the NYS CAFO permit requires. These emissions can be mitigated by implementing a renewable energy system including an ADS with SLS of the digestate before storage.

Establish GHG Emissions and Emission Reductions for an ADS

If a manure-based ADS was installed on a farm, it could reduce the GHG emissions from manure management as well as replace fossil fuel use or energy for both the farm and other users. By capturing the CH4 produced, and combusting it for energy or simply flaring the excess, CH4 releases are converted back to the neutral CO2 originally consumed by the animals in the form of feed products. The ADS could help to meet NYS renewable energy and GHG reduction goals, however, farms with an ADS would need to manage the system to minimize leaks. With no incentives to control leaks, the CH4 produced potentially could add to overall farm GHG emissions.

Part I – Estimating typical CH4 emissions and emission reductions

There are a number of factors that need to be taken into consideration when estimating the GHG reductions that an ADS will provide. Leaks in the ADS can be very detrimental as more methane is produced in an ADS than is emitted naturally from a manure storage facility in the baseline condition. In addition, there are uncombusted CH4 losses from flares and even some from the engine as well. Although every farm system is different, typical values can be determined from the literature, on-farm measurements, and experience.

ADSs designed and built to supply only the quantity of electricity consumed on-farm and to reduce odors may not be as effective as systems designed specifically to reduce GHG emissions. The conservative values in Table 2 could be used to describe these types of systems. ADSs built specifically to reduce GHG emissions in addition to maximizing the renewable energy produced would achieve significantly better GHG reductions. The optimum numbers are achievable, while the obtainable values are based on ADSs that consider GHG emissions and are built to optimize CH4 production.

Table 2. ADS variables that can be controlled by the system equipment, operation, and management

Conservative

Optimum

Obtainable

Reference

Leaks from system (% CH4)

10

0

1

AgSTAR (2011) and on-farm
Flare Efficiency (%)

90

99

95

AgSTAR (2011) and on-farm
Engine capacity factor (decimal)

0.85

0.97

0.95

On-farm measurements
Engine efficiency (%)

38

42

38

On-farm measurements
ADS Parasitic load

(kWh/cow-yr)

0.30

0.07

0.18

On-farm measurements
Biodegradability post-digestion (%)

70

50

60

On-farm measurements
VS left after SLS (%)

60

20

50

On-farm measurements

The additional societal benefit of this technology can be calculated using EPA’s SC-CO2 of $47.82 as the 2017-2019 average SC CO2 value per metric ton of C02 eq. (at a 3% discount rate) for the methane and nitrous oxide emissions (EPA, 2016).

Part II – Estimating typical N2O emissions and emission reductions for an ADS

An EF3 value of 0 (IPCC, 2006) for an uncovered liquid manure storage describes the typical emission factor from an ADS with SLS since post-digestion there would be no free oxygen, and after solids removal, there would not be a crust forming.

The resulting calculations from the conservative, optimum and obtainable ADS values are shown in Table 3. The fossil fuels avoided are based on the kilo-Watt hours (kWh) produced minus the parasitic load. The uncombusted CH4 from the engine is based on a rich burn engine. The CO2 equivalents from the system leaks and the digestate storage are the major emissions in the conservative scenario, the uncombusted emissions from the flare and the digestate storage are minor emissions from the optimum scenario, while storage contributes the most to the continuing emissions from the obtainable scenario.

Table 3. GHG Emissions from electric production converted with a $47.82 SC-CO2 into a value of E for conservative, optimum and obtainable ADS with solid separation of the digestate before storage.

Units Conservative Optimum Obtainable
Fossil Fuels Avoided
MT CO2 eq/cow-yr

0.70

1.16

0.99

Engine uncommuted CH4 MT CO2 eq/cow-yr

2.5 x 10-3

3.2 x 10-3

3.1 x 10-3

Flare uncommuted CH4 MT CO2 eq/cow-yr

0.19

0.00

0.03

System Leaks CH4 MT CO2 eq/cow-yr

1.41

0.00

0.14

Storage emissions CH4 MT CO2 eq/cow-yr

2.98

0.50

1.9

ƩCO2eq emitted – FF avoided MT CO2 eq/cow-yr

3.81

0.65

1.06

Baseline MT CO2 eq/cow-yr

4.38

4.38

4.38

Reduction in CO2eq MT CO2 eq/cow-yr

0.57

5.03

3.32

SC-CO2 Benefit $/cow-yr

$27

$240

$149

Gross Electricity produced kWh/cow-yr

1,590

2,229

1,955

Value of E $/kWh

0.017

0.11

0.081

Summary of long-term storage GHG emissions

The obtainable value of E $0.081/kWh, for an ADS with SLS of the digestate could be used to better determine the value of renewable energy in meeting NYS’s goals of reducing GHG emissions, increasing renewable energy, and supporting the dairy industry and the upstate NY economy.

More specific values for each individual ADS could be determined as a more granulated value (i.e., a value based on a more detailed/thorough analysis) through the implementation of NYS’s renewable energy vision. By using a value of E that reflects the actual environmental benefit of an ADS, this would incentivize dairy farms with an ADS to improve their CH4 production to produce more electrical energy. This would also increase the interest of more dairy farms in controlling GHG emissions and producing renewable energy by investing in ADS on their farms.

What have we learned?

ADSs can be used to reduce the manure management generated GHG emissions from dairy farms. With careful management, 3.32 MT of CO2 eq. per cow-year can be credited to the ADS. Using EPA’s SC-CO2 average price during 2017-2019 of $47.82, this could amount to a GHG benefit of over $140/cow-year. At this time, the benefit to society is unrewarded and high costs for ADSs both to construct and to operate, discourage farms from installing them. Working towards New York State’s renewable energy goals, as well as the reduction in GHG emission goals by compensating farms for the societal value of $0.081 per kWh of electricity produced from a well-run ADS would better incentivize farms to both install and operate ADSs to the advantage of the State.

Future Plans

DISCUSSION

ADSs can provide additional GHG reductions by utilizing organic wastes that currently go to landfills or aerobic waste treatment facilities. Some landfills may be able to capture a portion of the CH4 that the organic waste produces as renewable energy, but typically the leaks from a landfill gas recovery system are greater than those of farm-based ADS. NYS has some interest in diverting organic waste from landfills to reduce: the fill rate, the potential GHG emissions, and O&M costs in landfills. The value of the diverted organic waste can be best recovered by society if the energy is recovered through manure-based AD since the nutrients would also be recovered by mixing the food waste with manure, digesting it and recycling the nutrients in the effluent to the land for growing crops.

Nutrients to grow crops that are currently utilized in the form of commercial fertilizer, could be offset by the nutrients contained in a post-digested liquid, which would also reduce the energy and accompanying fossil fuel emissions now emitted when manufacturing commercial nutrients.

Aerobic treatment of organic wastes requires additional energy that adds to the fossil fuel-based carbon dioxide emissions and typically does not recover nutrients. While anaerobic digestion creates renewable energy and preserves nutrients.

Typical ADSs produce a large portion of energy from CH4 as waste heat from the engine(s). Operating a Combined Heat and Power (CHP) system in conjunction with an enterprise that would utilize the heat produced, would enable the system to harvest even more renewable energy.

ADSs could improve GHG mitigation efforts if the effluent storage was covered and if the gas collected was included in the biogas utilization system, eliminating any emissions from the effluent storage while producing even more renewable energy.

Farm Disadvantages

Managing a complex and expensive ADS requires dedication and a sophisticated management effort that clearly competes for time with other tasks on the farm. There is the potential to emit excess CH4 if: 1) leaks are not properly controlled, 2) the engine generator, boiler and/or flare are not efficient or 3) if the effluent storage continues to produce uncontained CH4. These can all be compounded if off-site organics are imported to the farm. The existing NYS net metering program makes the current price paid for exported electricity, very low. This reduces the motivation to produce and capture the maximum amount of CH4 from the ADS.

Planning and installing an on-farm ADS takes time to consider the benefits and costs so that a business decision can be reached. Capital costs of ADSs vary, but can range from $4,000 to $5,500 per kW of generation capacity. Operating costs have been estimated at $0.02 to $0.03 per kWh. Much of the capital investment is considered lost capital by lenders. The existing manure management system should be examined to determine any disadvantages from extra solids, contaminants, or dilution. If the successful operation of the ADS depends on tipping fees from imported organics, the reliability and quality of these sources needs to be determined. If electricity is to be sold, the utility should be consulted to determine how/if the distribution lines to the farm can handle what is expected to be generated.

Corresponding author, title, and affiliation

Peter Wright, Agricultural Engineer, Cornell University

Corresponding author email

cag26@cornell.edu

Other authors

Curt Gooch, Dairy Environmental Systems and Sustainability Engineer, Cornell University

Additional information

www.manuremanagement.cornell.edu

Early Stage Economic Modeling of Gas-permeable Membrane Technology Applied to Swine Manure after Anaerobic Digestion

 

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Purpose

The objective of this study was to conduct cost versus design analysis for a gas-permeable membrane system using data from a small pilot scale experiment and projection of cost versus design to farm scale.

What did we do?

This reported work includes two major steps. First, the design of a small pilot scale batch gas-permeable membrane system was scaled to process effluent volumes from a commercial pig farm. The scaling design maintained critical process operating parameters of the experimental membrane system and introduced assumed features to characterize effluent flows from a working pig farm with an anaerobic digester. The scaled up design was characterized in a spreadsheet model. The second step was economic analysis of the scaled-up model of the membrane system. The objective of the economic analysis was to create information to guide subsequent experiments towards commercial development of the technology. The economic analysis was performed by introducing market prices for components, inputs, and products and then calculating effects on costs and on performance of changes in design parameters.

What have we learned?

First, baseline costs and revenues were calculated for the scaled up experimental design. The commercial scale design of a modular gas-permeable membrane system was modeled to treat 6 days accumulation of digester effluent at 16,300 gallons per day resulting in a batch capacity of 97,800 gallons. The modeled large scale system is 19,485 times the capacity of the 5.02 gallon experimental pilot system. The installation cost of the commercial scale system was estimated to be $903,333 for a system treating 97,800 gallon batches over a 6 day period.

At $1/linear ft. and 7.9 ft./gallon of batch capacity, membrane material makes up 86% of the estimated installation cost. Other installation costs include PVC pipes, pumps, aerators, tanks, and other parts and equipment used to assemble the system, as well as water to dilute the concentrated acid prior to initiating circulation. The annual operating cost of the system includes concentrated sulfuric acid consumed in the process. Using limited experimental data on this point, we assume a rate of 0.009 gallons (0.133 pounds) of acid per gallon of digester effluent treated. At a price of $1.11 per gallon ($0.073/lb) of acid, acid cost per gallon of effluent treated is $0.010. Other operating costs include electric power, labor, and repairs and maintenance of the membrane and other parts of the system estimated at 2% of investment cost for non-moving parts and 6% of investment for moving parts. Potential annual revenue from the system includes the value of ammonium sulfate produced. Over the 6 day treatment period, if 85% of the TAN-N in the digester effluent is removed by the process, and if 100% of the TAN-N removed is recovered as ammonium sulfate, and given the TAN-N concentration in digester effluent was 0.012 pounds per gallon (1401 mg/l), then 0.01 pounds of TAN-N are captured per gallon of effluent treated. At an ammonium sulfate fertilizer price of $588/ton or $0.294/pound and ammonium sulfate production of 0.047 pounds (0.01 pounds TAN-N equivalent), potential revenue is $0.014 per gallon of effluent treated. No price is attached here for the elimination of internal and external costs associated with potential release to the environment of 0.01 pounds TAN-N per gallon of digester effluent or 59,073 pounds TAN-N per year from the system modeled here.

Several findings and questions, reported here, are relevant to next steps in experimental evaluation and commercial development of this technology.

1. Membrane price and/or performance can be improved to substantially reduce installation cost. Membrane material makes up 86% of the current estimated installation cost. Each 10% reduction in the product of membrane price and length of membrane tube required per gallon capacity reduces estimated installation cost per gallon capacity by 8.6%.

2. The longevity and maintenance requirements of the membrane in this system were not examined in the experiment. Installation cost recovery per gallon of effluent decreases at a declining rate with longevity. For example, Cost Recovery Factors (percentage of initial investment charged as an annual cost) at 6% annual interest rate vary with economic life of the investment as follows: 1 year life CRF = 106%, 5 year life CRF = 24%, 10 year life CRF = 14% . Repair costs are often estimated as 2% of initial investment in non-moving parts. In the case of the membrane, annual repair and maintenance costs may increase with increased longevity. Longevity and maintenance requirements of membranes are important factors in determining total cost per gallon treated.

3. Based on experimental performance data (TAN removal in Table 1) and projected installation cost for various design treatment periods ( HRT = 2, 3, 4, 5, or 6 days), installation cost per unit mass of TAN removal decreases and then increases with the length of treatment period. The minimum occurs at HRT = 4 days when 68% reduction of TAN-N in the effluent has been achieved.

Table 1. Comparison of installation cost and days of treatment capacity

4. Cost of acid relative to TAN removal from the effluent and relative to fertilizer value of ammonium sulfate produced per gallon of effluent treated are important to operating cost of the membrane system. These coefficients were beyond the scope of the experiment although some pertinent data were generated. Questions are raised about the fate of acid in circulation. What fraction of acid remains in circulation after a batch is completed? What fraction of acid reacts with other constituents of the effluent to create other products in the circulating acid solution? What fraction of acid escapes through the membrane into the effluent? Increased efficiency of TAN removal from the effluent per unit of acid consumed will reduce the cost per unit TAN removed. Increased efficiency of converting acid to ammonium sulfate will reduce the net cost of acid per gallon treated.

5. Several operating parameters that remain to be explored affect costs and revenues per unit of effluent treated. Among those are parameters that potentially affect TAN movement through the membrane such as: a) pH of the effluent and pH of the acid solution in circulation, b) velocity of liquids on both sides of the membrane, and c) surface area of the membrane per volume of liquids; effluent and acid solution, in the reactor. Similarly, the most profitable or cost effective method of raising pH of the digester effluent remains to be determined, as it was beyond the scope of the current study. Aeration was used in this experiment and in the cost modeling. Aeration may or may not be the optimum method of raising pH and the optimum is contingent on relative prices of alternatives as well as their effect on overall system performance. Optimization of design to maximize profit or minimize cost requires knowledge of these performance response functions and associated cost functions.

6. Management of ammonium sulfate is a question to be addressed in future development of this technology. Questions that arise include: a) how does ammonium sulfate concentration in the acid solution affect rates of TAN removal and additional ammonia sulfate production, b) how can ammonium sulfate be removed from, or further concentrated in, the acid solution, c) can the acid solution containing ammonium sulfate be used without further modification and in which processes, d) what are possible uses for the acid solution after removal of ammonium sulfate, e) what are the possible uses for the effluent after removal of some TAN, and f) what are the costs and revenues associated with each of the alternatives. Answers to these questions are important to designing the membrane system and associated logistics and markets for used acid solution and ammonium sulfate. The realized value of ammonium sulfate and the cost (and revenue) of used acid solution are derived from optimization of this p art of the system.

7. LCA work on various configurations and operating parameters of the membrane system remains to be done. Concurrent with measurement of performance response functions for various parts of the membrane system, LCA work will quantify associated use of resources and emissions to the environment. Revenues may arise where external benefits are created and markets for those benefits exist. Where revenues are not available, marginal costs per unit of emission reduction or resource extraction reduction can be calculated to enable optimization of design across both profit and external factors.

Future Plans

A series of subsequent experiments and analyses are suggested in the previous section. Suggested work is aimed at improving knowledge of performance response to marginal changes in operating parameters and improving knowledge of the performance of various membranes. Profit maximization, cost minimization, and design optimization across both financial and external criteria require knowledge of performance response functions over a substantial number of variables. The economic analysis presented here addresses the challenge of projecting commercial scale costs and returns with data from an early stage experimental small pilot; and illustrates use of such preliminary costs and returns projections to inform subsequent experimentation and development of the technology. We will continue to refine this economic approach and describe it in future publications.

Corresponding author, title, and affiliation

Kelly Zering, Professor, Agricultural and Resource Economics, North Carolina State University

Corresponding author email

kzering@ncsu.edu

Other authors

Yijia Zhao, Graduate Student at BAE, NCSU; Shannon Banner, Graduate Student at BAE, NCSU; Mark Rice, Extension Specialist at BAE, NCSU; John Classen, Associate Professor and Director of Graduate Programs at BAE, NCSU

Acknowledgements

This project was supported by NRCS CIG Award 69-3A75-12-183.