Tag: anaerobic digestion

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Anaerobic Co-digestion of Agro-industrial Feedstocks to Supplement Biogas Produced from Livestock Manure

Purpose

Anaerobic digestion (AD) is commonly used in agriculture to break down livestock manure and produce a sustainable source of energy by producing biogas, which is predominantly methane. Digestion of livestock manure can be supplemented with additional agricultural or industrial organic waste, potentially adding sources of revenue to the farm or digestion facility through tipping fees and additional biogas production. However, quantifying the anticipated impact on digester performance and operation is challenging, particularly as some potential feedstocks have not been studied previously. Understanding how a feedstock might impact a digester’s performance is critical, as digester upsets can lead to loss of revenue or even digester failure.

What Did We Do?

We conducted a set of mono-digestion biomethane potential experiments of several feedstocks currently in use at an agricultural AD facility that accepts mixed industrial waste streams in addition to digesting beef manure. The mono-digestion studies used triplicate 1-L working volume batch digesters which ran for 30-38 days. We tested beef manure, off-spec starch from food manufacturing, slaughterhouse wastewater treatment sludge, waste activated sludge from a corn processing facility, soap stock from glycerin refining, filter press slurry from a food grade water treatment facility, and food waste dissolved air flotation sludge. We also included a treatment for the effluent from the digester’s ammonia recovery system and a mixture of all the feedstocks at the same time. A blank (inoculum only) and positive control (cellulose with inoculum) digester were included as controls. This set of studies is described here as Experiment 1 (E1).

We then conducted a set of co-digestion biomethane potential tests combining the manure pairwise with some of the industrial feedstocks, specifically starch, slaughterhouse waste, soap stock, and filter press slurry (Experiment 2 or E2). These combinations were made at two different ratios of the two feedstocks. The first set of treatments combined the manure and an additional substrate at a 1:1 ratio on a volatile solids basis. The second set of treatments combined the feedstocks proportional to the amounts commonly used in the AD facility providing the materials. A final treatment pairing starch and soap stock at a 3:1 ratio was also included. These co-digestion treatments were conducted in triplicate alongside a single mono-digestion treatment of each feedstock for comparison. Finally, we examined the potential synergistic or antagonistic impacts of these combinations on methane yield and production rate. This was done by comparing the measured methane production at each time point compared to the expected methane production if the feedstocks each contributed additively to the methane production.

What Have We Learned?

Figure 1 shows the cumulative specific biogas production on a volatile solids basis for the mono-digestion experiment (E1). Some feedstocks, such as soap stock and slaughterhouse waste, experienced a substantial lag phase at the beginning of the experiment, which may have been due to the high levels of lipids and proteins.

Figure 1: Average biogas production of all treatments during mono-digestion experiment (Experiment 1).

During the co-digestion experiment (E2), we observed both total yield and kinetic synergy in all treatments. Only two digesters (one of the replicates from the starch and manure proportional treatment and one from the starch and soap stock treatment) produced substantially less (<30%) methane than would be expected for an additive effect for more than one day. This effect can be seen in Figure 2, which shows the cumulative methane curves (corrected for inoculum contribution and averaged over the three replicates) of the mono-digestion digesters for manure and starch individually and the curves for both co-digestion treatments using both manure and starch. Figure 3 shows the same curves for the co-digestion of manure and slaughterhouse waste. These co-digestion treatments show that combining the feedstocks causes an increase in methane production at a faster rate. They also show that co-digestion alleviates the lag phase experienced by the slaughterhouse waste.

Figure 2: Cumulative specific methane production for manure (F1) and starch (F2). F1 + F2 Eq = 1:1 ratio of VS; F1 + F2 Pr = ratio of VS is proportional to what full-scale digester receives.
Figure 3: Cumulative specific methane production for manure (F1) and slaughterhouse waste (F3). F1 + F3 Eq = 1:1 ratio of VS; F1 + F3 Pr = ratio of VS is proportional to what full-scale digester receives.

Future Plans

We plan to continue exploring the impact of co-digestion on methane yield and production rate by using additional combinations of these feedstocks and exploring the impact of macromolecular composition (percentages of carbohydrates, proteins, and lipids) on synergistic effects. These results will help inform current or future agricultural AD operators regarding the use of co-digestion feedstocks for optimal energy production and best practices in selecting new feedstocks for co-digestion.

Authors

Jennifer Rackliffe, Graduate Research Fellow, Purdue University

Corresponding author email address

jracklif@purdue.edu

Additional authors

Dr. Ji-Qin Ni, Professor, Purdue University; Dr. Nathan Mosier, Professor, Purdue University

Additional Information:

https://www.sare.org/wp-content/uploads/2021-NCR-SARE-GNC-Funded.pdf

Acknowledgements:

This material is based upon work that is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under agreement number 2020-38640-31522 through the North Central Region SARE program under project number GNC21-334. USDA is an equal opportunity employer and service provider. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture. We also thank Purdue’s Institute for Climate, Environment and Sustainability for supporting the dissemination of this work. Finally, we acknowledge the assistance of Gabrielle Koel, Kyra Keenan, Amanda Pisarczyk, and Emily McGlothlin in conducting the laboratory work.

 

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

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Dairy Anaerobic Digestion Simulation Software

Purpose

Co-digestion of organic material with dairy manure represents an opportunity to provide both a revenue stream to anaerobic digester operations, through the collection of a tipping fee and/or increased biogas/electricity production, as well as a means for waste generators to dispose of their product in a beneficial way.

However, there are many factors for an operator to consider when deciding on whether to accept organic waste.  A major consideration is the volume of biogas that the material will generate when co-digested.  This can be used both to assign a value to the waste through increased biogas production and/or electricity sales, as well as to size equipment for producing, treating and potentially selling/using the biogas.   Estimating the biogas produced is a complicated process, encompassing many different factors of digester design, waste characteristics, and environmental factors.

To assist in this estimation, we have developed software that allows a user to predict the biogas production from mixed wastes and dairy manure based on changing herd sizes, as well as providing the ability to vary the timing and volume of addition of multiple organic wastes, throughout the course of a simulated year.  With this user-friendly tool, we hope to enable producers to better explore the opportunities that co-digestion offers.

What Did We Do?

The originally developed Cornell Anaerobic Digester Simulations software allowed the user to input a herd size and to select how much (if any) of seven wastes would be co-digested with the dairy manure.  This rudimentary method of simulation assumed that the same volume/mass would be applied to the digester in a steady-state constant fashion for the entire year that the simulations were run for.  However, that is unlikely to be the case in a real-world production environment.

In the new version of the software, we have incorporated the characteristics of over 200 wastes into a user selectable interface.  Once a waste type is selected, the user has the option to select when the waste is placed into the digester, whether that be on an everyday, weekly, monthly or custom basis with the option to select to which months of the year the additions occur.  When selecting a weekly or monthly basis, the user can select which day(s) of the week or month wastes are added, and in the custom basis, the user can select which days of the year additions occur.

Once the timing of addition is completed, the user can select how much of the waste is applied during each addition.  Whether that be a constant volume for each addition, or a custom volume for each addition.

The data for the specific wastes includes the dry matter and organic matter content as well as the biogas and methane yields.  Based on the type of waste we have also assigned a “digestibility” curve to the particular waste which when assuming a first order kinetic model of gas production, can provide the production of gas a function of time.  The production of biogas from all added wastes and the added manure is then summed for each day of the year to provide an estimate of the biogas production, on a daily basis, that can be summarized with a minimum/maximum/average on a monthly and annual basis.

What Have We Learned?

During the process of developing the software, we examined a few different techniques for estimating the timing of biogas production from co-digested wastes.  There are more complicated models available such as Anaerobic Digestion Model #1 (ADM1), however many more parameters must be known/estimated for each waste type, (not to mention requiring a much more complicated user interface).  We felt that using a simplified first order kinetic model provides a good way to add the necessary complexity to model biogas production over time without overly complicated calculations.  The simplification allowed us to include a more complicated and yet more real world means of modeling the addition of wastes to a digester that wouldn’t be possible with more complicated digestion/biogas production models.

Future Plans

Currently, the Cornell Dairy Anaerobic Digestion Simulation Software is capable of predicting the amount of heat necessary to maintain digester temperatures, as well as the parasitic electrical load.  Future additions will include modeling the energy usage (and effects on biogas) of treatment processes to produce Renewable Natural Gas (RNG) from biogas.

We would also like to include the ability to track nutrients through the process of digestion.  Nutrient additions from the co-digestion of wastes also represent an important consideration for farm as they may or may not have the land base/crop requirements to use all of the imported nutrients.  The cost of treatment of the effluent from the digester to remove nutrients, or the shipment of effluent off site may have to be added into the determination of how much of a “tipping fee” a farmer would need to charge for taking an organic waste for co-digestion.

We hope to make the program freely available to the public to use.  Currently, the software is written in MATLAB which ordinarily requires a license to operate, however it is possible to create an executable standalone program that can be shared and run without the need to purchase MATLAB.

Authors

Timothy Shelford, Extension Associate, School of Integrated Plant Science, Cornell University

Corresponding author email address

tjs47@cornell.edu

Additional authors

Curt Gooch, Senior Extension Associate Emeritus, Department of Biological and Environmental Engineering, Cornell University

Peter Wright, Agricultural Engineer, Department of Animal Science, Cornell University

Lauren Ray, Agricultural Energy Systems Engineer, Cornell University

 

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

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Characterization of General E. coli and Salmonella in Pre- and Post-Anaerobically Digested Diary Manure

Purpose

Anaerobic digestion (AD) speeds up natural degradation of manure during storage, reduces odor, and produces energy by capturing methane. After AD, wastewater can be utilized on farms as a crop fertilizer and irrigation, and solids can be used for animal bedding.

Manure can be environmentally problematic and a reservoir of infectious agents (Guan et al., 2003). Previous studies have shown that anaerobic digestion of dairy manure decreases concentrations of viable fecal bacteria known to cause zoonotic diseases, notably E. coli and Salmonella (Aitken et al., 2007; Frear et al., 2011; Pandey and Soupir, 2011; Manyi-Loh et al., 2014; Chiapetta et al., 2019)

This study’s objective was to characterize and compare genetic changes in pathogens pre- and post-AD as evaluated by metabolic changes (sugar fermentation) or antimicrobial resistance to antibiotics. Generic E. coli (GEC) and Salmonella were selected for evaluation in this study as both are known to cause food borne and zoonotic disease. While a limited number of specific bacteria have been studied, AD has shown efficacy in pathogen reduction for both GEC and Salmonella. Characterizing these bacteria in AD influent and effluent can more firmly establish the efficacy of AD for reducing potential risks to human and animal health posed by these pathogens. We hypothesized that GEC and Salmonella would meet the 75% threshold of genetic similarity (post-AD vs pre-AD), suggesting limited mutation and lowered risk of AD creating resistant strain.

What Did We Do

An anaerobic digester (AD) in Monroe, WA was utilized from December 2008 through March 2010 to assess its effects on the survival and adaptation of pathogens in dairy manure (Chiapetta et al., 2019). The AD was a plug-flow design with a capacity of approximately 6.1million liters that was operated at ~38°C for a 17-day retention time. Inputs to the AD were comprised of 70% dairy cow manure and 30% pre-consumer food wastes from the dairy farm where the AD was located and from local food processors, respectively. Salmonella and general E. coli (GEC) were isolated from samples collected before and after AD. GEC isolates were characterized by sugar fermentation profiles (adonitol, dulcitol, melibiose, raffinose, rhamnose, salicin, sorbose, sucrose and the indicator medias MAC and MUG) and genetically compared using repetitive extragenic palindromic chain reaction (REP-PCR) followed by Ward’s cluster analysis. Salmonella were separated into serogroups. The Kirby Bauer disk diffusion method was used to identify antibiotic resistance (AMR). Antibiotics used were: ampicillin, chloramphenicol, gentamycin, amikacin, kanamycin, sulfamethaxazole/triemthroprim, streptomycin, tetracycline, amoxicillin/clavulanic acid, nalidixic, sulfisoxazole, and ceftazidime.

What Have We Learned

Antibiotic resistant GEC isolates were isolated from 22.3% and 19.1% of pre- and post-AD samples, respectively, and were observed to be genetically similar after clustering for sugar fermentation. Analysis of genetic similarity using the Pearson’s chi square method (e.g. likelihood–ratio) revealed that AD status (pre- vs. post AD) antibiotic resistance was not statistically significantly associated with AD (Figure 1, Table). Any effect of AD on AMR was dependent on grouping based on % genetic similarity.

Genetic analysis (REPPCR for GEC) yielded similar results, following a Pearson’s Chi Square test of log likelihood it was determined that AD status (pre- vs. post AD) and AMR were not significantly associated (Figure 1). Any effect of AD on AMR was dependent on grouping (Table 1).

Salmonella predominant serogroups (Table 2) (B, C1, and E1) remained at 23%, 9%, and 2% AMR pre- and post-AD. Analyses showed a significant interaction between Salmonella serogroup vs. source (p=0.0004) and serogroup vs. AMR (p<0.0001). No interaction was observed between source (pre- or post-AD) and AMR for Salmonella, p=0.12. There was no uniform effect for Salmonella as a group based on AD.

In summary, GEC sampled pre- and post-AD showed no difference in sugar fermentation, nor significant genetic dissimilarity, nor antibiotic resistance. Salmonella serotypes were observed to be equally or inconsistently effected by AD. Overall, the evidence suggests that anaerobic digestion does not create antibiotic resistant GEC and Salmonella.

Figure 1. Dendrogram of the sugar fermentation cluster analysis of generic E. coli. G= group based on sugar fermentation similarity, and n= number of isolates within each group.

Running a Chi Square on that: AD status (pre- vs. post AD) antibiotic resistance was not statistically significantly associated with this set of fermentation cluster memberships.

Pearson chi2(19) = 25.5411 Pr = 0.143

Table 1 – Data distribution of REPPCR GEC data
Pre-AD Post-AD
Grouping Susceptible Resistant Susceptible Resistant
1 2 — 2 3 (Am*)
2 2 5 (2 – Am, Cf, S, G, Te) (Am, S, Te) (Te)
(Amc, Am, Cf)		 1 3 (Cf)
(2 – C, S, G, Te)
3 — — 6 —
4 5 3 (2 – G, Te)
(Cf, C, S, G, Te)		 9 —
5 1 — 2 1 (Amc, Am, Cf,  S, G, Te)

*Am = Ampicillin, C= Chloramphenicol, CF = Ceftiofur, S = Streptomycin, G = Sulfasoxizole, Te = Tetracycline, Amc = Amoxycillin clavulanic acid

(fisher.test(tbl, simulate.p.value = TRUE, B = 1e5)

Fisher’s Exact Test for Count Data with simulated p-value (based on 1e+05 replicates)

p-value = 0.104

If no selection is occurring, output equals input, so at P < 0.1 is a trend for a selective process.

Table 2 – Salmonella – Number of susceptible or resistant bacteria
Serogroup Pre-AD Susceptible Pre-AD Resistant Post-AD Susceptible Post-AD Resistant
B 6 1 1 10
C1 12 4 14 0
C2 1 8 0 0
E1 34 0 50 0
K 4 2 2 2
Total 57 65 29 12
% 47 53 71 29

Configuration 1 SeroGrp*ABResist = best fits – association (interaction) of serogroup and resistance

Configuration 2 SeroGrp*PrePost = best fits – association (interaction) of serogroup and pre- post AD, but is conditioned by whether it is resistant

Goodness-of-fit Summary Statistics

Statistic Chi-Sq DF P
Pearson 6.91 5 0.2276
Likelihood 8.67 5 0.1230
Freeman-Turkey 8.28 5 0.1416

Number of Near Zero Expected Cells     4

Three observations were made:

      • a serotype may become more resistant as it goes through the AD
      • a serotype may become less resistant, or
      • a serotype may not survive.

Authors

J. H. Harrison – Livestock Nutrient Management Specialist, Department of Animal Sciences, Washington State University Puyallup Research and Extension Center
jhharrison@wsu.edu

Additional Authors

J. Gay – Department of Veterinary Clinical Medicine, Washington State University, Pullman, WA
R. McClannahan – Facility Manager – Integrated Research and Innovation Center – University of Idaho, Moscow, ID
E. Whitefield – Research and Outreach Specialist Department of Animal Sciences, Washington State University Puyallup Research and Extension Center

References

Aitken M. D., M. D.Sobsey, M. D., N. A.Van Abel, K. E.Blauth, D. R.Singleton, P. L.Crunk, C.Nichols, G. W.Walters, and M.Schneider. 2007. Inactivation of Escherichia coli O157:H7 during thermophilic anaerobic digestion of manure from dairy cattle. Water Res. 41:1659-1666. doi:10.1016/j.watres.2007.01.034.

Chiapetta, H., Harrison, J. H., Gay, J., McClanahan, R., Whitefield, E., Evermann, J., Nennich, T., Gamroth, M. (2019). Reduction of pathogens in bovine manure in three full scale commercial anaerobic digesters. Water, Air, and Soil Pollution, 230:111.

Frear C., W.Liao, T.Ewing, and S.Chen. 2011. Evaluation of co-digestion at a commercial dairy anaerobic digester. Clean—Soil, Air, Water. 39:697-704. doi:10.1002/clen.201000316.

Guan T. Y., and R. A.Holley. 2003. Pathogen survival in swine manure environments and transmission of human enteric illness—a review. J. Environ. Qual. 32:383-392.

Manyi-Loh C. E., S. N.Manphweli, E. L.Meyer, A. I.Okoh, G.Makaka, and M.Simon. 2014. Inactivation of selected bacterial pathogens in dairy cattle manure by mesophilic anaerobic digestion (balloon type digester). Int. J. Environ. Res. Public Health. 11:7184-7194. doi:10.3390/ijerph110707184.

Pandey P. K., and M.L.Soupir. 2011. Escherichia coli inactivation kinetics in anaerobic digestion of dairy manure under moderate, mesophilic, and thermophilic temperatures. AMB Express. 1:18. doi:10.1186/2191-0855-1-18.

 

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

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Characterization of Nutrients and GHG Emissions from Separated Dairy Manure

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

What did we do?

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

equations

       Where:

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

What have we learned?

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

Future Plans

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

 

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

AD

SLS

Feedstock
1

Mixed plug flow

Screw press

Dairy manure
2

No

ABRU

Dairy manure
3 Complete Mix

Screw press with blower

Dairy manure
4

Mixed plug flow

Screw press

Dairy manure
5

Mixed plug flow

Screw press

Paunch manure, food waste
6

Mixed plug flow

Screw press

Dairy manure
7

Mixed plug flow

Screw press

Dairy manure
8

Complete Mix

Centrifuge

Dairy manure, ethanol byproduct, FOG
9

No

ABRU

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

 

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

Authors

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

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

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

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

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Revenue Streams from Poultry Manure in Anaerobic Digestion (AD)

DUCTOR Corp. has developed a biological process that separates and captures nitrogen (ammonia) from organic waste streams. The biogas industry is a natural platform for this biotechnology as it solves the problem of ammonia inhibition, which has long bedeviled traditional anaerobic digestion (AD) processes. DUCTOR’s technology allows for stabilized and optimized biogas production from 100% high nitrogen feedstocks (such as poultry manure) and significantly strengthens the economics of biogas facilities: relatively inexpensive inputs, optimized gas production as well as new, higher value revenue streams from the organically produced byproducts—a pure Nitrogen fertilizer and a high Phosphorus soil amendment. DUCTOR’s mission is to promote biogas as a renewable energy source while securing efficient waste management and sustainable food & energy production, supporting the development of circular economies.

Purpose

Figure 1. High Nitrogen Feedstock-molecular structure
Figure 1. High Nitrogen Feedstock

High concentrations of ammonia in organic waste streams have been a perpetual challenge to the biogas industry as ammonia is a powerful inhibitor of biogas production. In typical methanogenic communities, as ammonia levels exceed 1500mg/L Ammonia-N, the inhibition of methane production begins until it reaches toxic levels above 3000mg/L. Traditionally, various mechanical and chemical methods have been deployed to lower ammonia concentrations in high nitrogen organic feedstocks prior to or following biodigestion (Figure 1). These methods have proven cumbersome and operationally unstable. They either require dilution with often costly supplemental feedstocks, are fresh water intensive, waste valuable nutrients, or require caustic chemicals injurious to the environment. Without the application of these methods, nitrogen levels will build up in the digester and negatively affect the efficiency of biogas (methane) production. DUCTOR’s proprietary process revolutionizes ammonia removal with a biological approach, which not only optimizes the operational and economic performance of biogas production, it also allows for the ammonia to be recaptured and recycled as an organic fertilizer product (a 5-0-0 Ammonia Water). This biotechnical innovation represents a significant advancement in biogas technology.  

What did we do?

DUCTOR’s innovation is the invention of a fermentation step prior to the classic anaerobic digestion process of a biogas facility (Figure 2).  During this fermentation step in a pre-treatment tank, excess nitrogen is biologically converted into ammonia/ammonium and captured through a physical process involving volatilization and condensation of the liquid portion of the digestate.

 

Typical DUCTOR facility layout
Figure 2. Typical DUCTOR facility layout

We ran a demonstration biogas facility with these two steps in Tuorla, Finland for 2000 hours using 100% poultry litter as fermenter feedstock without experiencing ammonia inhibition of the methanogenesis process. While the control, a single-stage traditional digester, showed increased buildup of toxic ammonia, the fermented material coming out of the first stage of the DUCTOR process (having ~50-60% of its nitrogen volatilized and removed) exhibited uniform levels of nitrogen below the inhibition threshold (Figure 3). This allowed a stable and efficient digestion by the methanogenic microbial community in the second stage digester. The fermentation step effectively eliminates the need for co-digestion of poultry manures with other higher C/N ratio substrates.

Figure 3: Ammonium concentration & Methane quantities in treated and untreated substrates
Figure 3: Ammonium concentration & Methane quantities in treated and untreated substrates

What we have learned?

In addition to solving the problem of ammonia inhibition, DUCTOR’s innovation realizes the separation of valuable recycled nutrients in a manner that can produce additional revenue streams. The result of the fermentation process in the first stage digestion tank is an organically produced non-synthetic ammonia (NH4OH), which is condensed and collected. This ammonia water product can be marketed and sold as an organic fertilizer as it is the result of a completely biological process with no controlled chemical reactions. The non-synthetic ammonia produced comes from the digestion of poultry litter by ammonifying microorganisms in anaerobic conditions. Furthermore, this ammonia water is in a plant available form that can be metered onto fields based on crop demands and thus reduce the amount of excess nitrates leaching into the water table and surrounding watershed.

The solids byproduct that results from the completion of the anaerobic digestion process has a large fraction of phosphorus and potash. This digestate can be dried and pelleted to produce a high-phosphorus soil amendment. While recognizing demand for this product would vary by region based on existing phosphorus levels in the soil, it offers a transportable & storable way to return these valuable elements to the nutrient cycle.

nutrient life cycle

Finally, the importance of gas production as a form of sustainable, renewable energy cannot be understated. With 2/3rds of the world’s greenhouse gas emissions coming from the burning of fossil fuels for energy or electricity generation,1 biogas derived from anaerobic digestion can displace some of those processes and reduce environmental greenhouse gas emissions.2 Currently, there are many state and federal policies focusing on renewable energy credits and low carbon fuel standards to incentivize this displacement.3 With the ability to unlock poultry litter as an additional AD feedstock, biogas facilities can offer greater volumes of biogas production per ton of manure than either dairy or swine.

Future plans

We have several commercial projects that will feature the DUCTOR technology at various stages of development in North America. The demonstration facility at Tuorla has been disassembled and shipped to Mexico where it will be reassembled as part of a larger commercial project there. In cooperation with our Mexican partner, we will demonstrate successful operations under a new set of conditions, including different climate and a new source of poultry litter from different regional growing practices. We further intend to demonstrate the highly efficient water use of the process in a drought-prone area.

Additionally, we have received approval from the North Carolina Utilities Commission for entry into their pilot program for injecting biomethane into North Carolina’s natural gas pipelines. Our first project there is expected to begin construction in Spring 2019 to be completed and operational by early 2020. These projects, and others in development, will bring a very attractive and new manure management option to poultry farmers, while recycling nutrients from the waste stream and returning them to the soil in a measurable and sustainable manner.

Author

Bill Parmentier, Project Development, DUCTOR Americas

bill.parmentier@ductor.com

Additional information

https://www.ductor.com

 

1Global Greenhouse Gas Emissions Data, US Environmental Protection Agency (EPA), https://www.epa.gov/ghgemissions/global-greenhouse-gas-emissions-data

2Sources of Greenhouse Gas Emissions, US Environmental Protection Agency, https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emissions

3Methane is a potent greenhouse gas that is over 20 times more damaging on the environment than carbon dioxide. Anaerobic digestion stops the release of methane into the environment by capturing it and using it for energy production or transportation fuel.

Federal incentives include the Rural Energy for America Program (REAP), Alternative Fuel Excise Tax Credit, & Federal Renewable Energy Production Tax Credit to name a few. Examples of state level incentives include various states Renewable Portfolio Standards (RPS) as well as California’s Low Carbon Fuel Standard (LCFS) or Oregon’s Clean Fuels Standard (CFS).

 

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

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Impact of Anaerobic Digestion on Solids, Nitrogen, Phosphorous, Potassium, and Sulfur Concentrations of Swine Manure

Anaerobic digestion of swine manure is a treatment process that can be used to reduce odor emissions, generate bioenergy, and reduce methane emissions. Studies and models are available that can be used to quantify methane production, and volatile solids (VS) reduction rates. Few provide information on the plant nutrient contents of digested manure. Such information is needed to develop nutrient management plans to use digester effluent to produce crops, biomass, or as a nitrogen source for making compost in an environmentally responsible manner.  The objective of this study was to observe the reductions and transformations of solids (TS, VS), nitrogen, phosphorous, potassium, and sulfur resulting from anaerobic digestion.

What did we do?

Fresh swine manure was obtained from the gestation barn at the Starkey Swine Center at Clemson University (Figure 1), and large supernatant samples were obtained from the lagoon on-site. The solid manure from the gestation floor was diluted with supernatant from the lagoon to obtain three total solids (TS) concentrations. The target total solids concentrations were 1%, 1.2%, and 2%. Dilutions in this range were selected because they were representative of common ranges of liquid swine manure removed from modern production facilities. This also provided three levels of organic load (OL) that was defined by the VS concentration of the mixtures (g VS/L). The dilutions that were actually achieved were 0.9%, 1.2%, and 1.9% total solids with volatile solids (VS) concentrations of 6.10, 9.05, and 13.75 g VS/L.

Since lagoon water was used for dilution in a manner similar to the operation of a recycled flush system no additional seed material was needed. The microorganisms needed for anaerobic digestion already existed in the manure.

Figure 1. Naturally ventilated gestation barn at the Starkey Swine Center at Clemson University.
Figure 1. Naturally ventilated gestation barn at the Starkey Swine Center at Clemson University.

Batch Anaerobic Digestion

The three mixtures of swine manure and lagoon water were anaerobically digested using 1.8L batch reactors that were maintained at 35 C in a heated water tank as shown in Figure 2. Three 1.8L bottles were used for each of the three liquid swine manure mixtures to give a total of 9 reactor bottles. Complete details of the batch method used is provided by Chastain and Smith (2015).

Figure 2. Aquarium used to provide a heated water bath (35°C) that held the nine, 1.8-L batch reactors.
Figure 2. Aquarium used to provide a heated water bath (35°C) that held the nine, 1.8-L batch reactors.

The reactor bottles were digested for 56 to 74 days. The pH of the bottles was measured daily and was used as the primary parameter to monitor digestion progress. Biogas production was also monitored by collecting it in 3-L Tedlar® bags, one per reactor bottle. The day on which the gas collection bags were emptied was recorded and provided a secondary parameter to determine when digestion was complete. Anaerobic digestion is a two phase process. During the first phase, called the acid forming phase, microorganisms create volatile fatty acids (VFA) and the pH falls rapidly to 6 or less. During the second phase the methanogens increase in population and consume the VFAs causing the pH to rise. Digestion was complete once the pH hovered around 7.5 for several days, and biogas was no longer produced. A graph of the variation in pH for the reactors is provided in Figure 3.

Figure 3. Variation of pH with respect to process time for three organic loading rates used. Each point is the mean of three 1.8-L batch reactor bottles.
Figure 3. Variation of pH with respect to process time for three organic loading rates used. Each point is the mean of three 1.8-L batch reactor bottles.

Solids and Plant Nutrients Measured Before and After Anaerobic Digestion

Well-mixed samples of the three liquid swine manure mixtures were obtained before and after anaerobic digestion. Since nitrogen and phosphorous in swine manure exist in soluble and organic forms the reductions and transformations of soluble and organic forms of these nutrients were also observed. The samples were analyzed to determine the following using standard techniques:

  • The total solids (TS),
  • The fixed solids (FS) or ash content,
  • The volatile solids (VS = TS – FS)
  • Total Kjeldahl nitrogen (TKN = Org-N + TAN)
  • Total ammonical nitrogen (TAN = NH4+-N + NH3– – N),
  • Organic nitrogen (Org-N = TKN – TAN),
  • Nitrate nitrogen (NO3-N),
  • Mineral nitrogen (Min N = TAN + NO3-N),
  • Total nitrogen (TN = TKN + NO3-N),
  • Total phosphorus (TP),
  • Soluble phosphorous (Sol-P),
  • Total potassium (TK), and
  • Sulfur (S).

What did we learn?

The first important observation was related to the completeness of anaerobic digestion. The mean VS reduction ratio (g VS destroyed/g VS added) for all nine reactors was measured, and was 0.62 on the average. This  and was in excellent agreement with the literature value of 0.63 for swine manure (Hill, 1991), and indicated that anaerobic digestion was complete. The rate of TS destruction was 0.45 g TS destroyed / g TS added.

The second set of observations were related to the impact of anaerobic digestion on nitrogen. The mass of total N was not changed by anaerobic digestion, but the mass of organic nitrogen was decreased by 36% as it was mineralized to TAN. The TAN was increased by a factor of 1.84, and the mineral N (TAN + NO3-N) was increased by a factor of 1.8 on the average. The initial nitrate-N concentrations were small and evidence of denitrification was observed as indicated by a reduction in nitrate-N by 59%. The impact of N transformations was to increase the fraction of total-N that was in the total ammonical form from 33% before digestion to 59% after digestion which highlights the need to store and land apply anaerobically digested manure so as to reduce ammonia volatilization.

Anaerobic digestion was also observed to have mixed results on the mass of P, K, and S.  The mass of total-P was not significantly impacted by anaerobic digestion. On the average, 73% of the soluble-P was converted to organic P by microbial activity, and was believed to remain in the microbial biomass. There was no impact on TK by digestion as expected. The mass of S was reduced by 7% on the average presumably by the formation of small amounts of H2S.

Authors

  • John P. Chastain, Ph.D. Professor and Extension Agricultural Engineer, Clemson University, Department of Agricultural Sciences, Agricultural Mechanization and Business Program, McAdams Hall, Clemson, South Carolina 29634 USA. jchstn@clemson.edu 1-864-656-4089
  • Bryan Smith, BSAE, MSCE, Area Extension Agent – Agricultural Engineer, Clemson Extension Service, 219 West Laurens Street, Laurens, South Carolina 29360 USA.

References

Chastain, J.P. and W.B. Smith. (2015). Determination of the Anaerobic Volatile Solids Reduction Ratio of Animal Manure Using a Bench Scale Batch Reactor. Presented at the 2015 ASABE Annual International Meeting. Paper No. 152189216. ASABE, 2950 Niles Rd., St. Joseph, MI 49085-9659

Hill, D.T. (1991). Steady-State Mesophilic Design Equations for Methane Production from Livestock Wastes. TRANSACTIONS of the ASAE, 34(5):2157-2163.

Acknowledgements

This study was supported by the Clemson Extension Confined Animal Manure Managers Program and by a grant from the South Carolina Energy Office.

 

 

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

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Anaerobic Digestion Policy Analysis: Understanding Perceptions, Knowledge and Implementation

Anaerobic digestion (AD) is a growing technology that uses a series of microbial activities to breakdown organic material such as food waste and manure, to produce biogas for renewable energy, digestate for nutrient recycling as fertilizer, and large reductions in greenhouse gas (GHG) emissions and odors. Currently there are millions of AD systems in China and India, with a vast majority of these systems operating on a small-scale basis, while European nations such as Germany and Italy, have thousands of agricultural- based AD systems, that are large scale and more technologically advanced. Europe with over 17,000 biogas plants has steady increases in AD adoption each year, as more countries are setting sustainability goals that include increasing renewable energy use and reducing GHG emissions. The US however, has less than 300 agricultural-based AD systems and 1500 AD systems at wastewater treatment facilities. An in depth analysis was performed of US policies related to AD adoption and how these policies compare to policies in other countries with higher AD adoption rates. A survey was developed for farmers, policy makers, and extension associates to understand policy effects on AD adoption rates and identify challenges to increasing AD adoption rates in the US. The survey data, along with the AD policy analysis, was used to compare and contrast policies, programs and overall legislative climate between countries and understand the timeline in which policies were administered. While policy is the product of a multitude of variables, including general perceptions, institutional involvement, legal framework, and societal /economic benefits, the survey and subsequent analyses seek to understand how these variables interact. The results of the survey and policy analysis will be presented to detail the general perceptions around AD policies, challenges with AD adoption, operation, and maintenance, and overall perceptions of the AD field in the US.  

Authors

Carlton Poindexter, University of Maryland-College Park, cpoindex@umd.edu  

Lansing, Stephanie (University of Maryland-College Park)

 

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

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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.

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Renewable Energy Set-asides Push Biogas to Pipeline

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Purpose

Deriving the most value from the harvesting of organic wastes, particularly waste produced through farming operations, can be quite challenging. This paper describes an approach to overcome the challenges of realizing the best value from harvested farming wastes through aggregation. Included in this description is an overview of the first swine waste-to-energy project in North Carolina based on aggregation of the value stream rather than aggregation of the feedstock, or manure. Also included in the description are an overview of the challenges encountered, approaches to overcome these challenges, and the solutions developed for this breakthrough approach that will foster further development of successful ventures to maximize the value derived from recycled farming wastes.

What did we do?

Increasingly, our civilization is turning to bioenergy sources as an environmentally-friendly, sustainable alternative to harvesting long-buried fossil fuel sources to supply our energy needs. As the land that farmers have cultivated for years becomes encroached more and more by non-farming land uses, society seeks innovations to address its concerns for our future food needs produced in a manner that addresses environmental concerns associated with modern food production, including nutrient recovery, water conservation and reuse, and controlling odors and emissions from agricultural wastes and manures. Collectively, these innovations have been described as ‘sustainable farming’ approaches.

North Carolina is a significant agricultural producer, and as such, a large producer of agricultural wastes. This state also became the first state in the Southeast to adopt a Renewable Energy Portfolio Standard, and is the only state in the U.S. to require a certain percentage of that renewable energy must be generated from agriculture waste recovery, with specific targets for swine and poultry waste. Naturally, the plentiful resources coupled with a regulatory driver for renewable energy worked together to create attention and efforts toward cost-effective and efficient means of supplying our energy needs through organic waste recovery, or bioenergy approaches.

We are only beginning to see a surge in commercial development for the recovery of additional value stream from the waste, such as through the recovery of nutrients, enzymes, and monetized environmental attributes associated with pollution abatement. While manyOptima-KV swine waste to pipeline RNG project forward-thinking farmers have learned that their waste is valuable for supplying renewable energy, it has been unfortunately difficult for an individual farmer to implement and manage advanced value recovery systems primarily due to costs of scale. Rather, it seems, success may be easier achieved through the aggregation of these products from several farms and through the collaborative efforts of project developers, product offtakers, and policy. A shining example of such aggregation and collaboration can be observed from the Optima-KV swine waste to pipeline renewable gas project, located in eastern North Carolina in an area of dense swine farm population.

The Optima-KV project combines, or aggregates, the biogas created from the anaerobic digestion of swine waste from five (5) adjacently located farms housing approximately 60,000 finishing pigs. The Optima-KV project includes the construction of an in-ground anaerobic digester at each farm. The resulting biogas is captured from each farm, and routed to an adjacent, centralized biogas upgrading facility, or refinery, where the biogas undergoes purification and cleaning to pipeline quality specifications. The renewable natural gas produced from this system will be sold to an electric utility subject to the requirements of the North Carolina Renewable Energy Portfolio Standards, and will result in reduced emissions from both the receiving electricity generating unit and the farms, reduced emissions of odors from the farms, and reduced fossil fuel consumption for the production of electricity. The upgraded biogas (RNG) will be transmitted to the electricity generating unit through existing natural gas pipeline infrastructure.

What have we learned?

The innovative design, permitting, and financing for the project is very different than a conventional feedstock aggregation approach, and thus much has been learned. To deliver the RNG to the end user, in this case, multiple contracts with multiple utilities wereGraphic showing how it works required, which presented challenges of negotiating multiple utility connections and agreements. This learning curve was steepened as, at the time of the inception of Optima KV, the state of North Carolina lacked formal pipeline injection standards, so the final required quality and manner of gas upgrading was established through the development of the project.

The project is currently in the beginning stages of construction, and completion is expected by the end of 2017. Given this schedule, the Optima KV project will provide the first pipeline injection of gas – from any source – in the state of North Carolina (all natural gas presently consumed in the state is sourced from out of state).

Future Plans

North Carolina’s potential for agricultural waste-to-energy projects is enormous, given its vast agricultural resources. Combining the potential from agriculture with the bioenergy potential from wastewater treatment plants and landfills, it is estimated to be third in capacity behind only California and Texas. The unique approach to aggregation of value streams from multiple sources, as exhibited by this project, will open the doors for similar aggregation strategies, including the anaerobic digestion of mixed feedstocks such as food waste, poultry and swine waste, animal mortality, fats, oils and grease and energy crops.

Corresponding author, title, and affiliation

Gus Simmons, P.E., Director of Bioenergy, Cavanaugh & Associates, P.A.

Corresponding author email

gus.simmons@cavanaughsolutions.com

Additional information

http://www.cavanaughsolutions.com/bioenergy/

1-877-557-8923

gus.simmons@cavanaughsolutions.com

https://www.biocycle.net/2016/11/10/anaerobic-digest-67/

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

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Manure Management Technology Selection Guidance

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Purpose

Manure is an inevitable by-product of livestock production. Traditionally, manure has been land applied for the nutrient value in crop production and improved soil quality.With livestock operations getting larger and, in many cases, concentrating in certain areas of the country, it is becoming more difficult to balance manure applications to plant uptake needs. In many places, this imbalance has led to over-application of nutrients with increased potential for surface water, ground water and air quality impairments. No two livestock operations are identical and manure management technologies are generally quite expensive, so it is important to choose the right technology for a specific livestock operation. Information is provided to assist planners and landowners in selecting the right technology to appropriately address the associated manure management concerns.

What did we do?

As with developing a good conservation plan, knowledge of manure management technologies can help landowners and operators best address resource concerns related to animal manure management. There are so many things to consider when looking at selecting various manure treatment technologies to make sure that it will function properly within an operation. From a technology standpoint, users must understand the different applications related to physical, chemical, and biological unit processes which can greatly assist an operator in choosing the most appropriate technology. By having a good understanding of the advantages and disadvantages of these technologies, better decisions can be made to address the manure-related resource concerns and help landowners:

• Install conservation practices to address and avoid soil erosion, water and air quality issues.

• In the use of innovative technologies that will reduce excess manure volume and nutrients and provide value-added products.

• In the use of cover crops and rotational cropping systems to uptake nutrients at a rate more closely related to those from applied animal manures.

• In the use of local manure to provide nutrients for locally grown crops and, when possible, discourage the importation of externally produced feed products.

• When excess manure can no longer be applied to local land, to select options that make feasible the transport of manure nutrients to regions where nutrients are needed.

• Better understand the benefits and limitations of the various manure management technologies.

Picture of holding tank

Complete-Mix Anaerobic Digester – option to reduce odors and pathogens; potential energy production

Picture of mechanical equipment

Gasification (pyrolysis) system – for reduced odors; pathogen destruction; volume reduction; potential energy production.

Picture of field

Windrow composting – reduce pathogens; volume reduction

Picture of Flottweg separation technology

Centrifuge separation system – multiple material streams; potential nutrient
partitioning.

What have we learned?

• There are several options for addressing manure distribution and application management issues. There is no silver bullet.

• Each livestock operation will need to be evaluated separately, because there is no single alternative which will address all manure management issues and concerns.

• Option selections are dependent on a number of factors such as: landowner objectives, manure consistency, land availability, nutrient loads, and available markets.

• Several alternatives may need to be combined to meet the desired outcome.

• Soil erosion, water and air quality concerns also need to be addressed when dealing with manure management issues.

• Most options require significant financial investment.

Future Plans

Work with technology providers and others to further evaluate technologies and update information as necessary. Incorporate findings into NRCS handbooks and fact sheets for use by staff and landowners in selecting the best technology for particular livestock operations.

Corresponding author, title, and affiliation

Jeffrey P. Porter, P.E.; National Animal Manure and Nutrient Management Team Leader USDA-Natural Resources Conservation Service

Corresponding author email

jeffrey.porter@gnb.usda.gov

Other authors

Darren Hickman, P.E., National Geospatial Center of Excellence Director USDA-Natural Resources Conservation Service; John Davis, National Nutrient Management Specialist USDA-Natural Resources Conservation Service, retired

Additional information

References

USDA-NRCS Handbooks – Title 210, Part 651 – Agricultural Waste Management Field Handbook

USDA-NRCS Handbooks – Title 210, Part 637 – Environmental Engineering, Chapter 4 – Solid-liquid Separation Alternatives for Manure Handling and Treatment (soon to be published)

Webinars

Evaluation of Manure Management Systems – http://www.conservationwebinars.net/webinars/evaluation-of-manure-management-systems/?searchterm=animal waste

Use of Solid-Liquid Separation Alternatives for Manure Handling and Treatment – http://www.conservationwebinars.net/webinars/use-of-solid-liquid-separation-alternatives-for-manure-handling-and-treatment/?searchterm=animal waste

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

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