Tag: anaerobic digestion

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Digested Solids – Forms, Markets and Trends


Are Digested Solids a Viable Product?

Anaerobic digesters for U.S. livestock operations are becoming more complex. A study of livestock-based digesters in 2003 found they were built largely to meet on-farm needs for power or gas. Digester residuals were mostly land applied as nutrients for crop production. A few used fibrous solids as animal bedding (King, 2003). In recent years, more livestock-based digester projects have been built by third-party developer/managers. Projects increasingly employ a systems approach, where individual product streams are managed in concert for greatest profit by the project manager. This approach holds the promise that digestate residuals, especially fiber solids, will no longer be neglected, but instead play a larger role in offsetting weak performance in energy revenues.

What did we do?

Looking closely at dairy-based digesters, the solids recovered after separation from the digester eflluent have unique characteristics. Most notably, these solids tend to be fibrous with high cellulose, hemicellulose, and lignin content. Digestion also reduces pathogenic contaminants, volatile solids, odor, and viable weed seeds (MacConnell, 2010). These qualities can be influenced by the makeup of an animal’s feed and the use of co-digestion feedstocks, such as municipal or industrial wastes or other agricultural manures or byproducts

Table 1 shows the characteristics of dairy AD solids compared to raw manure and raw separated solids (MacConnell, 2010).

Table 1. Fiber Characteristics

Table 1.

As is. In bulk. Sold to a wholesale buyer—this is the easiest way to sell digested dairy fiber. Through a combination of literature search and expert interviews, this presentation looks at the methods project managers might use to add more value to their digested fiber.

What have we learned?

Composting. Perhaps the most basic way to add value to digested dairy fiber is simply to apply basic compost processing methods—aerating the material under controlled conditions for sufficient time to reduce odor and stabilize the organic matter. While already low in pathogens, hot composting practices can give additional assurance of pathogen reduction. In co-digestion situations, screening the material to remove contaminants and assure consistency and uniformity is desired. Even wholesale buyers will pay more for material that is already composted (King 2003)

Processing to compete – replacing peat. Because of its physical similarity, researchers have explored using digested dairy fiber as a direct replacement for peat moss in nursery and horticulture mixes. WSU was an early source of research and growth trials on such uses. Their research showed that with minimal post-digestion treatment, amended digested dairy fiber performed as well or better than peat in soilless mixes. (MacConnell, 2007, and Kruger, 2008) In 2007, Organix, a Washington company, announced the first shipments of RePeat, using their patent-pending FibreRite production system. Since then several new varieties of these peat replacements have hit the market nationwide, under such brands as Magic Dirt, EnerGro, and MooFiber.

Organic certification. Organic gardening and food production is growing rapidly in Washington state and around the nation. Getting an organic certification for organic matter and nutrients that have been digested and composted will add significant value to the final product (King, 2003).

Branding and marketing for retail. Moving away from bulk and wholesale are the next steps in moving material up the value chain. However, putting product in bags and selling into retail markets requires significant investments in packaging, branding, marketing and sales. This is like adding an additional business onto the back end of a digester project and demands its own feasibility analysis.

Vermicomposting. Using earthworms, especially redworms, to further process fiber solids and excrete earthworm castings, produces another specialty soil product. Vermicomposts and earthworm castings are well-known and appreciated in some growers in some markets. They are often used as a small additive in specialty soil mixes to allow the use of “earthworm castings” on the list of ingredients. Two commercial examples of vermicompost production lie on opposite coasts—Sonoma Valley Worm Farm in California and Worm Power in New York. Sonoma Valley Worm Farm direct markets high-quality vermicompost to a variety of growers throughout their region, with special emphasis on vineyards. Worm Power topped 2 million pounds of production in 2012 and signed an agreement with Rochester, NY-based Harris Seeds to market its vermicompost products regionally.

Specialty products produced from the separated fiber materials are another area of interest. Perhaps the best known of such products are the biodegradable planting nursery pots sold as Cow Pots by the Fruend Dairy Farm in Connecticut.

Biochar. This is another specialty product from a fledgling industry that fits in niche markets. It could be used to process digested fiber. It has received a strong research focus in the Pacific Northwest. The value of biochar in landscape or agricultural uses is still being studied, though at present it appears to have less to do with agronomic benefit, than on measured benefits for carbon sequestration and the value given to these benefits through carbon credits or other mechanisms (Galinato, 2011). On the other hand, replacing biochar for conventional forms of activated carbon for filtering stormwater or wastewaters shows some promising results and is getting a lot of attention.

Future Plans      

We will continue to evaluate methods to add value and publish the full results in a Anaerobic Digestion technology brief on this topic.

Authors        

Jim Jensen, Sr. Bioenergy & Alt Fuel Specialist, Washington State University Energy Program jensenj@energy.wsu.edu

Craig Frear, Chad Kruger, and Georgine Yorgey, Center for Sustaining Agriculture and Natural Resources, Washington State University

Additional information  

References:

Galinato, S., Yoder, J., Granatstein, D., 2011. The economic value of biochar in crop production. Energy Policy.

King, 2003. Study to Evaluate the Price and Markets for Residual Solids from a Dairy Cow Manure Anaerobic Digester—Final Report, King County Solid Waste, Seattle, WA.

Kruger, Chad, et.al., 2008. High-quality fiber and fertilizer as co-products from anaerobic digestion. Journal of Soil and Water Conservation.

MacConnell, C.B., Collins, H.P., 2007. Utilization of re-processed anaerobically digested fiber from dairy manure as a container media substrate. Proceedings of the International Symposium on Growing Media, Nottingham, UK.

MacConnell, C., Frear, C., Liao W., 2010. Pretreatment of AD-treated fibrous solids for value-added container media market, Center for Sustaining Agriculture and Natural Resources, Pullman, WA.

Acknowledgements      

This research was supported by funding from USDA National Institute of Food and Agriculture, Contract #2012-6800219814; Biomass Research Funds from the Washington State University Agricultural Research Center; and the Washington State Department of Ecology, Waste 2 Resources Program.

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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The Dairy Manure Biorefinery


Why Consider Additional Technologies with Anaerobic Digestion?

Some dairy farms have experimented with “add-on” technologies to enhance the value of the products generated from anaerobic digesters to improve economics and address other environmental and management concerns. This effort has intensified in recent years, as prices paid for electricity continue to fall. This trend is making it more difficult to justify the installation of new digesters or maintain active anaerobic digestion (AD) projects based on electricity sales alone. 

What did we do?

Based on ten years of research and extension within the field of dairy digesters, we are proposing that the concept of a dairy manure biorefinery can be useful to focus ongoing research and commercialization efforts (Figure 1). A biorefinery integrates a core biomass conversion process (in this case, AD, converting manure and in many cases other organic substrates) with additional downstream technologies. These combined technologies generate multiple value-added products including fuels, electricity, chemicals, and other products (NREL, 2009). Most add-on technologies relevant to dairy facilities have been modified from technologies used in the wastewater treatment and oil and gas industries. 

What have we learned?

Ongoing research and commercialization efforts by our team and others aim to:

  • Adapt technologies to fit the economic and other constraints of dairy digesters.
  • Increase efficiency and reduce costs by maximizing the complimentary nature of technologies (e.g. waste heat from one process is used in another process).

Specific add-on technologies that are continuing to evolve within the biorefinery context include:

Biogas Upgrading to remove impurities from biogas (primarily carbon dioxide, hydrogen sulfide, and water vapor).

Output: Purified biogas that can be used as a transportation fuel (e.g. liquefied natural gas) or injected directly into natural gas piplelines.

Additional social and economic benefits: Renewable fuel can reduce demand for fossil fuels, and can often receive economic credits (e.g. renewable identification numbers, low carbon fuel standard)

Fiber Upgrading to process the fiber that is removed from AD effluent.

Output: Upgraded fiber can be sold as a higher-value soil amendment in the horticultural industry

Additional social and economic benefits: Fiber can replace use of non-renewable resource (peat moss) by horticultural industry

Nutrient Recovery to strip nitrogen (N) and phosphorus (P) from anaerobic digester effluent.

Outputs: Soil amendment products that can be sold offsite where nutrients are needed

Additional social and economic benefits: Reductions in N and P applied to nearby fields, and reduced effluent hauling distances/costs for land application due to lower nutrient concentration in effluent

Water Recovery to generate “recycled” water using advanced technologies

Output: Water that can be used for animal drinking, or as dilution water for the AD facility

Additional social and economic benefits: Reduces consumption of fresh water, a limited resource, and reduces costs for land-application of AD effluent

Overall Potential Impact. Improving economics and addressing other critical issues for dairy producers (e.g. nutrient issues) has the potential to advance farm-based AD adoption significantly beyond its current 244 farms. It has been estimated that a mature bio-refinery industry based on AD on large U.S. dairy farms could create an estimated bio-economy of nearly $3 billion that complements the production of milk and dairy products (ICUSD, 2013).

Figure 1. Stepwise depiction of the process

Figure 2. Total likely value added by most likely scenario

Authors

Georgine Yorgey (presenting author)a, Craig Frearb, Nick Kennedya, Chad Krugera, Jingwei Mab, and Tara Zimmermana

a Center for Sustaining Agriculture and Natural Resources, Washington State University

b Department of Biological Systems Engineering, Washington State University

Future Plans

An extension document describing this concept and the add-on technologies in additional detail is being prepared. This document is part of a series of extension documents on Dairy AD Systems, being prepared by the authors and other colleagues at Washington State University. In addition, ongoing work and collaborations by our team are seeking to investigate, evaluate, and improve individual technologies and the linkages amongst them.

Additional Information

ICUSD, 2013. National market value for anaerobic digestion products. Report to Innovation Center for US Dairy, August 2013.

Acknowledgements

This research was supported by USDA National Institute of Food and Agriculture, contract #2012-6800219814; and Biomass Research Funds from the Washington State University Agricultural Research Center.

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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Economical Anaerobic Digestion of CAFO Animal Waste


Purpose

The application of manure on croplands is increasingly under regulatory scrutiny, especially from impaired watersheds. The challenge facing many small farms is to find cost-effective and innovative solutions for manure reuse whilst responding to environmental, regulatory and public concerns. One option is to install an anaerobic digester (AD) in which microorganisms break down biodegradable material in the absence of oxygen. However, not all farmers are financially able to install an AD but do need the AD’s benefits to keep their livestock operation sustainable. This paper discusses a novel, cost effective and patented manure treatment system which can reduce the volume of manure for field application (see Figure 1).Earthmentor N2RTS Schematic

What did we do?

The EarthMentor® Natural Nutrient Reclamation and Treatment System (EMS), uses a combination of innovative sand separation technology (if necessary) and anaerobic treatment to concentrate manure nutrients into solid phases and treat approximately 70% of manure liquids into a product which can be applied to active cropland as low-nutrient liquid using irrigation methods. The primary economic advantage of using an EMS to treat livestock manure prior to land application is lower total manure disposal costs. The total manure handling costs are reduced because up to 75 % of the original manure volume can be handled as low-nutrient value irrigation quality liquid in bulk instead of hauling it by tanker for land application. This fact alone reduces total manure handling costs by over 50 %. Other tangible benefits of using an EMS include low odor, minimized environmental risks, and greater flexibility in proper land application of the treated manure. It can be installed at farms with as few as 250 cows. Depending on farm size, operators can realize a return on investment in as little as three years. Compared to a traditional AD installed to generate biogas the EMS is simple to operate, requires less energy, requires no chemicals or substrates to treat the waste, and reduces manure disposal costs.

The EMS involves six major steps: 1) collection of raw manure and transport to the processing center, 2) sand bedding is separated from the manure stream, 3) coarse manure components are removed from the liquid manure stream, 4) additional settling of the fine manure solids and sand particles occurs in a settling basin to a concentration of 8 to 10 percent solids, 5) AD treatment of the liquid manure and dissolved solids occurs in anaerobic treatment lagoon (ATL), and 6) The ATL effluent is stored in a Storage Pond for eventual discharge to active growing crops; additional natural treatment of the liquid manure occurs while in the Storage Pond.

All settling basins and ATL lagoon must meet state guidelines, such as Natural Resource Conservation Service technical guidelines or state requirements for waste storage facilities.

The ALT of the EMS system has a smaller footprint compared to traditional ALTs (primarily use in the south and western United States) because the majority of the nutrient-rich semi-solids are removed from the manure before discharge to the ATL. Due to this major operational change the EMS is economical to install and operate even in the northern climates of the United States where many of the top producing dairy states are located. While many facilities separate solids before land application, the EMS is different because is adds the AD step which converts the manure into a low-nutrient liquid capable of irrigation-style land disposal.  The method of solid separation can be as simple as a sloped screen followed by additional gravity separation as described in Step 4 above. The EMS ATL must be sized to account for reduced biodegradation during the colder weather. The EMS has successfully operated at multiple swine facilities and several Midwestern dairy farms.

If there is sufficient land near the farmstead, the EMS can be installed at existing dairies with minimum difficulty since the treatment system works equally well with multiple bedding materials and varying manure collection methods. Another benefit of the EMS is that is allows application on fields that may be high in phosphorus since much of the phosphorus will be stored in the accumulating ATL sludge. For dairies bedding with sand, a patented sand removal system can be provided that relies on a decanting method of sand separation. Once the sand is removed, it can be reused in the barn. 

What have we learned?

Typical Cost Savings for Manure Application Using EMS
Component
Disposal Method
Conventional Manure Handling
EarthMentor® Treatment System Handling
Liquid Manure

 

 Land Application 100% $0.02/gallon 0% $0
Separated Solids Land Application 0% $0 10% $0.016/gallon
($4/ton equiv.)
Heavy Slurry Land Application 0% $0 20% $0.02/gallon
Treated Wastewater Center Pivot over Crop 0% $0 70% $0.002/gallon
Combined Cost   100% $0.02/gallon 100% $0.007/gallon
(weighted average of all components)

Using financial data from 2010 for a 2,000-cow Michigan dairy, it was estimated that the cost to handle manure using an EMS is reduced from $0.02/gallon to $0.007/gallon. The cost saving using the EMS is based on the assumption that the average dairy cow produces nearly 25 gallons/day of manure, including wastewater but excludes bedding since farms used different types and volumes of bedding for their dry and lactating cows. Based on the financial analysis, installation of an EMS benefits the farm’s economic sustainability while providing other benefits including reduced environment risk associated with manure land application.

Far beyond the obvious cost savings associated with the EMS installation, a livestock producer will realize many other benefits. A partial list is provided below:

  • This practical and manageable manure treatment system requires little or no additional farm labor commitments yet greatly reduces overhead expenditures to keep the farm sustainable and competitive,
  • All manure is treated prior to land application (environmentally sound),
  • The more consistent high solids slurry can be precisely applied to fields with the greatest need as opposed to the highly variable manure nutrient concentrations recovered from a traditional manure pond,
  • Minimizes the environmental risks (ecologically viable) and farm nuisance potential,
  • The window of opportunity for manure application is extended to over 200 days instead of being limited to spring and fall applications for typical liquid manure,
  • Can provide a safe unlimited recycled bedding source for cattle, if so desired, by the dairy owner,
  • Permits farmer to follow BMPs for soil conservation,
  • Permits farmer to follow timing, rate, source, and place for fertilizer/crop nutrient applications,
  • Benefits the non-farm neighbors and community through reduced nuisance odors, and
  • Continues using the farm’s manure as a soil amendment for crop production, the most efficient use known.

Future Plans

The immediate future plans for EMS is to target small livestock producers, especially those within impaired watersheds.  Since many ADs need a substrate material imported from outside the farm to be economically sustainable, the EMS is ideal for those farms that want to be good neighbors with reduced farm air emissions, need greater convenience in manure management, and desire to maximize the real cash value of their manure.

As the EMS adapts well to any bedding material, by investing time and dedicating property for the ATL any size operation can begin to treat their manure prior to land application and reduce their overall cost for manure management.

In addition to small farms we envision four possible adaptations of EMS; these examples are provided to show the transferability of this technology to farms desiring various outcomes from an EMS:

  1. Installation of an Energy-Generating AD – if a farm wishes to generate energy using a traditional AD, it would be installed prior to the EMS system whereby the AD digestate discharges into the settling ponds. Since the residence time of a traditional AD is measured in days, there is a great deal of additional treatment that can occur so that the cost savings for land application can still be realized.
  2. Use manure solids for other uses besides land application – if the livestock producer decides to bed their cattle on manure solids or to compost the manure solids for sale off-farm to landscapers or bag and sell direction from the farm then the solids from the SS can be further treated with a screw press or roller then composting by various means.
  3. Greenhouse gas capture and sale of carbon credits – a geosynthetic liner cover can be added to the ATL and all captured gases burned through a flare. However, it should be noted that by removing a significant amount of high organic solids during the initial fiber solids separation step, much less organic material is subject to organic degradation into methane gas.
  4. Greenhouse gas capture and burning of the gases – to generate electricity or heat water (typically for on-farm use or export to an adjoining business, such as a greenhouse).

One future issue to resolve includes educating state governments on the benefits of installing an EMS, especially for those farms that may be under a Consent Order or other regulatory actions or those farms that may need to implement a manure treatment system to mitigate odors from the livestock operation.  The duration to install an EMS and get it operational is much shorter than the lead time to design and install a traditional AD so the EMS can help when farms need to implement changes quickly.  A second issue to overcome is to properly educate producers on the benefits of EMS and differences between traditional ADs.  Swine, beef, and dairy producers who already have a farm irrigation system will have a lower capital investment to begin achieving the reduced manure management costs referenced above.

Author

Matthew J. Germane, P.E., President at Germane Environmental Consulting, LLC MGermane@GECEnvironmental.net

Additional information

https://www.gecenvironmental.com, Envirolytic Technologies, LLC

Acknowledgements

Acknowledgements to Envirolytic Technologies, LLC, Greenville, OH manufacturer of the Earthmentor® N2RTS system and RAM Technologies, LLC, manufacturer of the sand separation equipment used in the EMS for their assistance in providing the laboratory data used in this paper.

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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Technologies for Anaerobic Digestion of Flushed Swine Manure

Hog farmers face a unique challenge to implement digestion — namely the low volumetric methane yield of wet swine manure.  The most common digester used on hog farms using flushing systems is the covered lagoon.  This presentation explores the technical feasibility of high rate reactors for low solids swine manure.  Systems compared are Contact Stabilization Reactors, Upflow Anaerobic Sludge Blanket Reactors (UASB), Fixed Filmed Reactors, and Anaerobic Sequencing Batch Reactors (ASBR).  Contact Stabilization and UASB technology have been available since the 1970s, but are mostly found in industrial settings. Their main drawback for swine manure treatment is the required operator skill level.  UASB digesters also have difficulty handling the uneven solids flow from flushed or pull-plug barns.  Fixed film reactors have been successfully used in agriculture, but require solids separation before digestion.  The separator creates two waste streams and removes organic matter that could potentially be available for digestion.  ASBR technology was developed in the 1990s.  An ASBR digester was successfully operated at the Oklahoma Swine Research and Education Center in the 2000s.  Hydraulic retention time for this farm scale ASBR ranged between 5 and 20 days.  Maximum methane yield was 0.55 m3 CH4 kg-1 VS day-1.  Organic matter reduction efficiency was 50 to 75 % measured as Chemical Oxygen Demand (COD).  Current work on solids settling and retention will allow ASBR digesters to reach their full potential in swine production systems. Related: Treatment Technologies for Livestock Manure

Why Consider Anaerobic Digestion on Pig Farms?

Anaerobic digestion can reduce the carbon footprint of swine production, while substantially lowering the fossil fuel energy required to feed and raise hogs. However, economic analyses show that anaerobic digestion on swine farms using complete mix digesters to produce electrical energy have a net negative present value unless carbon credits in the price range of $10 to $12 per metric ton of CO2eq are given for methane emissions reduced (Cowley, 2015). The two factors negatively affecting the economic viability of complete mix digesters are high capital cost and relatively low biogas output of reactors. Capital cost of digesters is directly related to the hydraulic retention time (HRT) of reactors. Farm-scale complete-mix digesters treating swine manure have retention times ranging from 18 to 30 days (Fisher, et al., 1979; Schulte, et al., 1985; Zhang, et al., 1990). Methane yields of these digesters was between 0.22 to 0.25 m3 CH4 kg-1 V S, and reactor volumetric efficiencies ranged between 0.35 to 0.40 m3 CH4 m-3 reactor day-1.

What did we do?

High rate digesters are reactors that separate solids retention time (SRT) from HRT. High rate reactors shorten HRT, which results in smaller, less costly digesters. High rate digesters also have higher methane yields than complete mix reactors. Several high rate systems have successfully treated swine manure at the laboratory and pilot scale. Systems tested include fixed film, suspended particle attached growth (SPAG), and upflow anaerobic sludge blanket (UASB) reactors treating the liquid portion of swine manure after solid-liquid separation; and contact stabilization, anaerobic sequencing batch (ASBR), and anaerobic baffled (ABR) reactors treating whole, diluted swine manure. ASBR systems have used both single reactor and multiple reactors in series. Despite the success of laboratory studies, few farm-scale high rate reactors exist on the farm scale.you

What have we learned?

A 400 m3, single vessel ASBR was operated for two years on a 128 sow farrow-to-finish hog farm at the Oklahoma State University Swine Research and Extension Center. (Hamilton and Steele, 2014) . Methane yield was 0.55 m3 CH4 kg-1 VS, and COD removal efficiency was 73% when operated at a 20 day HRT with operating temperature ranging between 22 and 32oC. Methane yield was 0.38 m3 CH4 kg-1 VS and COD removal efficiency was 57% when operated at a 5 day HRT with operating temperature between 22 and 24oC. The digester, as built, was 4 times larger than it needed to be. Using microbial kinetic modeling, the volumetric efficiency of a 100 m3 digester operating at 5 day HRT was estimated to be 0.73 m3 CH4 m3 reactor day-1.

Future Plans

Further work with ASBR digesters is underway. We are working to improve the mixing, settling, and solids trapping efficiency of the ASBR. ASBR reactors are also highly adaptable to receive high energy low solids digestion co-products. Pilot testing has shown volumetric efficiency of swine manure ASBR can be increased 4 to 6 fold with augmentation with waste glycerol from biodiesel production.

Author

Douglas W. Hamilton, Associate Professor at Oklahoma State University

dhamilt@okstate.edu

Additional information

Cowley, C. 2015. Economic Feasibility of Anaerobic Digesters with Swine Operations. Unpublished Thesis. Stillwater, OK: Oklahoma State University.

Fisher, J.R., N.F. Meador, D.M. Sievers, C.D. Fulhage, and E.L. Iannotti. 1979. Design and operation of a farm anaerobic digester for swine manure. Trans ASABE 22(5):1129.

Hamilton, D.W. and M.T. Steele. 2014. Operation and performance of a farm-scale anaerobic sequencing batch reactor treating dilute swine manure. Trans ASABE. 57(5):1473.

Schulte, D.D., Kottwitz, T.J. Siebenmorgen. 1985. Design and operation of a flexible cover, precast concrete anaerobic digester for swine manure. Pp 509-515, in Agricultural Waste Utilization and Management, Proceedings of the 5th International Symposium on Agricultural Wastes. St Joseph, MI: ASABE.

Zhang, R.H., J.R. North, and D.L. Day. 1990. Operation of a field-scale anaerobic digester on a swine farm. Applied Engineering in Agriculture. 6(6):771.

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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Lifecycle greenhouse gas (GHG) analysis of an Anaerobic Co-digestion Facility Processing Dairy Manure and Industrial Food Waste in NY State

While the theoretical benefits of anaerobic digestion have been documented, few studies have utilized data from commercial-scale digesters to quantify impacts.  Previous studies have analyzed a range of empirical studies to constuct emission factors for a generic European AD plant processing source separated municipal solid waste.  However, most U.S. studies have applied reporting protocols and have been based upon theoretical assumptions.  Furthermore, GHG analyses of U.S. co-digestion facilities are limited to one scenario in protocol based analysis of community digester options. 

Purpose          

We are not aware of any peer-reviewed studies of US anaerobic co-digestion. Several case studies have presented calculations of impacts using GHG reporting protocols, however significant portions of the lifecycle have been neglected such as the feedstock reference case emissions, digestate storage emissions and fertilizer displacement impacts. Furthermore, they have often been modeled using general theoretical assumptions such as number of cows rather than empirical data on feedstock volume and characteristics and digester operation.

What did we do? 

A lifecycle GHG analysis was performed based upon data reported on a farm-based anaerobic co-digestion system in New York State, resulting in an 71% reduction in GHG impact relative to conventional treatment of manure and food waste.

The objective of this study was to provide a comprehensive analysis of GHG emissions based upon a NYS digester that co-digests manure and industrial-sourced food waste. Empirical data on feedstock (t-km transport, avoided disposal, TS, VS, TKN), digester operation (m3CH4, KWh, exhaust emissions) and effluent properties (TS,VS,TKN) were combined with regional parameters (i.e., climate, soil type and management practices) to represent a state-of-the-art, anaerobic co-digestion facility in NYS. This data was combined with information collected through interviews in order to model a reference case, representing the business-as-usual food waste disposal and manure management practices en lieu of the anaerobic co-digestion system.

What have we learned? 

Displacement of grid electricity provided the largest benefit followed by avoidance of food waste landfill emissions and reduced impacts associated with storage of digestate vs. undigested manure. Nominal land application N2O emissions were offset by inorganic fertilizer displacement and carbon sequestration in both cases. The higher volume of digestate increased net land application emissions as did increased transportation distance to the fields and lower carbon sequestration. Digestate is a by-product of the co-digestion process and its treatment must be considered in an LCA. Modeling of land application impacts are highly uncertain and can be significant.

The largest source of direct emissions was CH4 emissions. N2O emissions were larger in the land application phase than during storage. Direct fossil fuel emissions had a minor impact. Emissions were offset by displacement of grid electricity and fossil based fertilizers along with carbon sequestration.

Future Plans    

More empirical research is needed to measure emissions and to provide emission factors that incorporate key variables and characteristics affecting emissions. A whole system, dynamic approach is necessary to incorporate complex interdependencies between stages of farm and manure management.

Authors

Jennifer L. Pronto, Research Assistant, Cornell University jlp67@cornell.edu

Ebner, Jackie      jhe5003@rit.edu              Rochester Institute of Technology

Rodrigo A. Labatut, Matthew J. Rankin, Curt A. Gooch, Anahita A. Williamson, Thomas A. Trabold

Additional information               

www.manuremanagement.cornell.edu

Figure 1: Contributional analysis of GHG impacts for the reference and anaerobic co-digestion cases.

Figure 1: Contributional analysis of GHG impacts for the reference and anaerobic co-digestion cases.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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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Effect of Temperature on Methane Production from Field-Scale Anaerobic Digesters Treating Dairy Manure

Why Study Temperature and Anaerobic Digestions?

Anaerobic digestion is a process that results in the production of biogas that can be used a renewable source of electricity on-farm or sold to the distribution grid. Temperature is a critical parameter for anaerobic digestion since it influences both system heat requirements and methane production. Although anaerobic digestion can take place under psychrophilic (15-25°C), mesophilic (35-40°C), and thermophilic (50-60°C) conditions, temperatures of 35-37°C are typically recommended for methane production from animal manure. However, digesters require significant amount of heat energy to maintain temperatures at these levels. There is limited information about methane production from dairy digesters at temperatures less than 35°C and results in the literature are presented from laboratory-scale rather than field-scale systems.

The objective of this study was to evaluate the effect of two relatively low digestion temperatures (22 and 28°C) on methane production using replicate continuously-fed, field-scale dairy manure digesters at two organic loading rates. The results were compared with those from identical digesters operated at 35°C.

field scale anaerobic digesters

Field scale (FS) anaerobic digesters

What did we do?

Anaerobic digestion experiments were carried out using six modified Taiwanese-model field-scale (FS) on-site digesters (Fig. 1) at the USDA Beltsville Agricultural Research Center (BARC). Each FS digester has a total capacity of 3 m3 and was operated at a liquid capacity of 67% (2 m3 working volume) with 33% headspace for biogas collection. The FS digesters are plug-flow reactors and operated without mixing. First, duplicate field-scale (FS) anaerobic digesters were maintained at one of three set temperatures (22 ± 2, 28 ± 2 and 35 ± 2°C) and fed with solids-separated manure for 80 days (period 1). The digesters were subsequently operated under the same temperature regime (22 ± 2, 28 ± 2 and 35 ± 2°C) but were fed at a higher organic loading rate (OLR) using solids-separated manure amended with manure solids for 56 days (period 2). The hydraulic retention time (HRT) was 17 days for all digesters throughout the study. Digesters were fed once daily five days a week with 160 L d-1 of separated manure for period 1, and 148 L d-1 of separated manure amended with 16 kg d-1 (wet weight) manure solids (roughly 12 L in volume) for the period 2.

What have we learned?

Our results suggest that anaerobic digesters treating dairy manure at lower temperatures can be nearly as effective as digesters operated at 35°C, even with a relatively short 17-day retention time. Methane production from digesters operated at 28°C was about 90% of that from digesters operated at 35°C but the differences were not statistically significant. Digesters operated at 22°C produced about 70% as much methane as digesters operated at 35°C without affecting digester stability. Small farm digester systems that may not have access to waste heat from electrical generation, could efficiently operate at these lower temperatures to produce methane and reduce greenhouse gas emissions and odors. Larger digester systems could also choose to operate at these lower temperatures if reducing digester heating would allow for more valuable uses of their heat energy such as drying solids or treating liquids to remove nutrients.

Future Plans 

We are currently investigating the fate and effect of antibiotics and feed additives during the anaerobic digestion of manure.

Authors     

Osman Arikan, Assoc. Prof., Istanbul Technical Univ., Dept. of Environmental Eng., Istanbul, Turkey. Visiting Scientist, USDA-ARS, BARC, Beltsville, MD, Visiting Assoc. Prof., University of Maryland, Dept. of Environmental Science&Tech., College Park, MD. arikan@itu.edu.tr

Walter Mulbry, Research Microbiologist, USDA-ARS, Beltsville Agricultural Research Center, Beltsville, MD. Stephanie Lansing, Assistant Professor, University of Maryland, Department of Environmental Science and Technology, College Park, MD.

Additional information

Data is to be published.

Acknowledgements

The authors gratefully acknowledge Jose Colina and Lorianny Rivera for assistance in operating the digesters and Anna Kulow for analyzing biogas and effluent samples.

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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Anaerobic Digestion: Co-Digestion and Operational Issues

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Abstract

A study was conducted to assess the performance of various mixing regimes on methanogen biomass content in anaerobic digesters.  Methane production in anaerobic digesters is directly related to the methanogens within the system.  Current systems involve mixing to increase biogas production and system efficiency, however little is known about the underlying mechanisms of this relationship.  In this study three pilot scale anaerobic digestion systems with three different mixing regimes were run with replication to examine the impacts to methanogen biomass content and biogas production.  The results will provide insight for operational recommendations as well as the basic microbial processes with digestion systems which are critical for optimization.

Authors

Rebecca Larson, University of Wisconsin-Madison            ralarson2@wisc.edu

Purpose

To evaluate various feedstocks and operational parameters for anaerobic digesters, including impacts to biogas production, quality, and operational issues.

What Did We Do?

Evaluated numerous co-feedstocks with manure in laboratory and large scale systems to identify biogas production impacts and potential operational issues associated with each.

What Have We Learned?

Analysis of ffedstocks is critical for determination of digester fundtioning.  Constituents can significantly impact the quantity and quantity of biogas produced.

Future Plans

To evaluate scale up to determine if small scale biomethane potential analyses can be used to determine full scale biogas production.

Authors

Rebecca Larson, Assistant Professor, University of Wisconsin – Madison

Corresponding author email address   ralarson2@wisc.edu

Asli Ozkaynak, Post-Doctoral Researcher, University of Wisconsin – Madison

Additional Information

Data is to be published

Acknowledgements

 

Funded by the USDA

 

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. 2013. Title of presentation. Waste to Worth: Spreading Science and Solutions. Denver, CO. April 1-5, 2013. URL of this page. Accessed on: today’s date.

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On-Site Analytical Laboratories to Monitor Process Stability Of Anaerobic Digestion Systems

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Abstract

The anaerobic digestion of complex materials is a highly dynamic, multi-step process, where physicochemical and biochemical reactions take place in sequential and parallel ways.  The stability of the process depends on a delicate balance between the formation and consumption of products. When the concentration of a particular substance reaches the homeostatic equilibrium of certain organism or group of organisms, such balanced is disrupted, and the process becomes upset. If measures to correct the source of the problem are not taken, substrate stabilization and biogas production will progressively decrease, and eventually stop. Recovery of a digester can take several weeks to months, during which, energy generation and waste treatment are not possible, resulting in increased operational costs for the facility. To detect process perturbations and prevent major digester upsets, periodic monitoring is essential.

In this study, analytical laboratories were installed on selected on-farm anaerobic digestion systems in New York State, to periodically monitor key process parameters and to evaluate performance and stability of the operations.  Preliminary results showed that analytical labs were critical to detect process upsets efficiently, particularly in co-digestion systems, where loading rates and influent characteristics are usually variable. The laboratory is rather optional in manure-only operations, where the influent consists of a steady and predictable waste.

Authors

Rodrigo Labatut, Cornell University ral32@cornell.edu   

Curt Gooch, Cornell University

 

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Converting Onion Waste into Energy as a Co-digestant with Dairy Waste

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Lab scale anaerobic digesters constructed from PVC pipe used to evaluate co-digestion of manure with onion waste

Ninety liter (90 L) anaerobic digesters (anaerobic filters) were constructed from PVC pipe.  The digesters were filled with lava rock.  A thermocouple is placed in the center of each digester to be used in controlling temperature.  Each digester is controlled by a datalogger by reading temperature and turning on or off pumps to circulate water around digester maintaining temperature at 35 oC.  Biogas is collected in a tipping bucket and recorded on datalogger.

Abstract

Consumers demand high quality fruits and vegetables. As a result, packing sheds around the country cull or remove bad fruits and vegetables prior to packing then in boxes for shipment to stores. The culling process produces millions of pounds of waste fruits and vegetables annually. This culled fruit or vegetable then has to be disposed of in some form or fashion. Therefore, a project was designed to investigate the feasibility of using culled onions in conjunction with dairy waste to produce methane gas. The experiment used 90 liter downflow anaerobic filters to process a 50/50 mix of onion juice and dairy waste. Results from this study indicate the co-digestion of culled onions and dairy waste provides a good way to dispose of the waste onions while at the same time producing a renewable energy that can potentially be used in the packing shed where the onions are separated. The 50/50 blend of onion waste and dairy waste has consistently returned an average of 15 liters of biogas (70-75% methane) per 3 liters of mixed waste entering the digesters with a cleaning efficiency over 85%.

Why Look at Food Waste for Co-Digestion with Manure?

Culled onions or any fruit and vegetable has to be disposed.  Some of these are fed to animals, but some are thrown on fields and potentially tilled into the soil.  However, if they are piled and allowed to decay in place the liquid produced during the decaying process can have a high chemical oxygen demand (COD).  If this liquid is allowed to run into waterbodies they could be polluted or if allowed to infiltrate could be transferred to a waterbody through underground movement.  Therefore, this project investigated the characteristic of liquid produced from decaying onions as well as the feasibility of using waste onions along with dairy waste to produce methane gas in anaerobic digesters.  If feasible, the culled onions (or other fruits and vegetables) could be used as a source of energy verses a disposal issue.

What Did We Do?

The experiment had two parts.  The first part placed whole onions in a steel tank on a 2 foot bed of sand where the onions could naturally decay.  The liquid along with any rainwater was collected in portions and tested for its pH and Chemical Oxygen Demand.  Additionally, waste onions were juiced and mixed with dairy wastewater in a 50/50 mixture and used as feedstock for an anerobic filter digester.  Temperature was controlled in the mesophilic range and biogas was measured.

What Have We Learned?

As expected, the decaying onions release a liquid that over time increases the COD profile of the liquid draining from the decaying pile.  It is expected that if onions were continually piled on the same spot, the COD and pH of the liquid would equalized at a COD value measured to be approximately 80 g/L and the pH would drop to approximately 3.5 (these numbers based on some previous studies and bench scale observations).  The data also suggest that, and as would be expected, onions decay faster in the summer months as opposed to winter months in Georgia.  It was also found that a 50/50 mix of onion waste and dairy wastewater fed to a pilot scale mesophilic anaerobic filter fed at 3 liters per day and a retention time of 7 days will produce approximately 15 liters of biogas daily with a methane composition of 70-75%.  The treatment level of the influent was also found to average greater than 85%.

The Chemical Oxygen Demand (COD) of liquid collected from the bottom of a tank full of decaying onions increases over time. Likewise, the pH of the liquid decreases. If these onions are disposed of in a wet area or area adjacent to a waterbody, the stre

The Chemical Oxygen Demand (COD) of liquid collected from the bottom of a tank full of decaying onions increases over time.  Likewise, the pH of the liquid decreases.  If these onions are disposed of in a wet area or area adjacent to a waterbody, the stream would be affected by the high COD and low pH liquid.
Biogas production from the mixed 50/50 onion/dairy waste fed at a rate of 3 liters per day. The methane composition of the biogas ranged from 70-75%. Treatment efficiencies of the waste, based on COD reduction, averaged greater than 85% (over 20 g L-1 i

Biogas production from the mixed 50/50 onion/dairy waste fed at a rate of 3 liters per day.  The methane composition of the biogas ranged from 70-75%.  Treatment efficiencies of the waste, based on COD reduction, averaged greater than 85% (over 20 g L-1 influent to less than 2 gL-1 in effluent).

Future Plans

Future plans will be continue the investigation of using waste onions (and other fruit and vegetables) as a feedstock for anaerobic digesters.  This feedstock, which is very available in onion growing regions seasonally, liquid from the onions can be stored over time (as observed in other research project) to provide a year round feedstock for the production of methane gas.  As we now know that the decaying onions release a liquid that has a high COD, using the onions for production of energy may reduce potential problems with water pollution as well as provide growers with additional income streams.  Plans will be to continue this work and look at optimizing the feed rate and mix ratios.

Authors

Gary Hawkins, University of Georgia, ghawkins@uga.edu

Additional Information

A few articles have been written about the project, research papers will be written in the near future.

Acknowledgements

The Vidalia Onion Research Committee and the USDA-AFRI Speciality Crops Initative

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. 2013. Title of presentation. Waste to Worth: Spreading Science and Solutions. Denver, CO. April 1-5, 2013. URL of this page. Accessed on: today’s date.

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Coupling Dairy Manure Anaerobic Digesters with Commercial Greenhouses – An assessment of Technical and Economic Feasibility

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Abstract

Despite all of the positive environmental benefits of anaerobic digestion, the economics are not sufficient for widespread adoption by US farmers when selling surplus power to the grid.  Often farms are only paid the wholesale price (2 to 3 cents/kWh) for electricity, making it difficult to justify generating it in the first place.  In addition, typically in the Northeast, approximately 40% of the energy from a digester goes unused (excess heat).  Therefore, promising value-added technology/business partnerships need to be evaluated and demonstrated, such as partnering anaerobic digestion with commercial greenhouses. 

Greenhouses are an ideal end user of the waste heat and surplus electricity produced by a digester.  In the Northeast and other similar climates, heat and electricity represent a major expense for greenhouse growers.  Greenhouses can make use of excess heat to provide the necessary growing conditions for year-round production and excess electricity can be used to run supplemental lighting to keep production constant year-round.

To facilitate the adoption of digester/greenhouse unions, we are developing a comprehensive computer model of both the energy output of farm-based digesters, the energy requirements of the associated farm, and the energy required by greenhouses, in terms of timing and magnitude.  We will use existing and project-developed data collected from five Northeast digesters and three greenhouse operations to aid in developing and validating the model.  The model will be complex enough to handle varying biomass inputs and required outputs, and the economics of operation.  We will use the model to run several real-world “what ifs” and use the outputs for making recommendations to existing anaerobic digesters considering coupling with greenhouses. System economics are also going to be included.

Authors

Curt Gooch, Cornell PRO-DAIRY cag26@cornell.edu

Tim Shelford, Cornell PRO-DAIRY

 

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. 2013. Title of presentation. Waste to Worth: Spreading Science and Solutions. Denver, CO. April 1-5, 2013. URL of this page. Accessed on: today’s date.

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