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Dry Anaerobic Digestion (AD) for High Solids Manures
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Dry Anaerobic Digestion (AD) for High Solids Manures


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Anaerobic digestion of animal manure has generally been limited to wet digestion where total solids are less than 12%. This has restricted adoption of biogas production primarily to dairy and hog operations, or required substantial water usage to dilute manures with higher solids content. The DRANCO-Farm dry anaerobic digestion technology processes solid manures and other dry crop residues on a continuous basis with solids content in the digester up to 45%.

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  • High net energy yield per hectare is an indispensable prerequisite for an economic operation of an energy crop digestion plant. This includes high biomass yields and low energy requirement for plant cultivation, harvest and processing. From practical experience, on average, about 50% of the total energy requirement is spent for fertilizer production, minor amounts are required for machinery (22%), transport fuel (15%) and pesticides (13%).
  • The consolidated results from data acquisition and analysis are given in Table 2. Although just representing a minimum number of selected parameters, the broad range of results obtained can be clearly recognized. The amount of substrate processed varied between less than 1 t/d in the smallest installations up to 55 t/d in large plants. The biogas productivity ranged from 0.24 to 2.3 m3 m-3 d-1. Correspondingly, the biogasyield varied between 0.42 and 1 m3 kg-1 VSS. A similarly broad range of corresponding results was found in the evaluation of the business economic parameters. The electrical efficiency was as low as 18% in the worst case, while over 38% was achieved in well operating installations. The degree of heat utilization of about 15% (median) was generally low. Best performing plants could use more than 40% of heat, while many of the installations did not make any use of the waste heat from power generation. Fourteen installations produce 100 kW, 11 produce 500 kW and 8 produce 250 kW electrical power. Five were very small installations (50 kWel) and three were bigger than 1 MW. About 71 % of 59,000 t dry organic substance, used annually in the 41 plants considered, originate from energy crops, 12 % from manure and 17 % from other biogenic byproductsand wastes. With a share of 53 %, maize dominates the crops used in digesters. Together with corn cob mixture (22 %) and maize corn (2 %) the overall share of maize amounts 77 %, followed by grass (9.4 %), grain (5.5 %) and several other crops (sun flower, wheat, clover). Concerning manure, pigs dominate (45.6 %), followed by cattle- (36.6 %), chicken- (7.9 %), horse- (6.3 %) and turkey manure (3.6 %). Food leftovers(20 %) dominate the co-substrates used, followed by flour mill by-products (14.4%), oil processing- (11.3 %), sugar beet-(10.8 %), potato- (7.4 %) and various other wastes of minor quantity. The majority of 99 plants considered runs 2-step digesters (85 %), 12 % use 3-step-, theremaining more than 3 digester steps. About 29 % of the plants run at 42C, 27 % at 40C and 22 % at 38C. Just 10 % operate at 48C and 12 % at 55C. The most common residence time is 100 days (32%), followed by 150 days (24 %), 200 days (15 %). Anyhow, 10 % of the installations use 250 days and 15 % even more than 250 days. Just 5% use less than 50 days residence time. The resulting organic loading amounts 4 kgVSS m-3 d-1 (32 %), 5 kg in 22 % and 3 kg in 20 % of the 41 plants considered. Seventeen plants use loadings between 6-8 kg, and 10 use loadings below 2 kg VSS m-3 d-1.
  • Braun et al. (2007) collected the data from 41 energy crop digesters in Austria (of which 20% are thermophilic); Table 3 shows the results of this study. Compared with these 41 installations, the DRANCO-FARM concept has the highest overall efficiency (highest loading rate and biogasproductivity), while maintaining a very good biogas yield of 0.65 Nm³/kg VS.
  • Comparing DRANCO-FARM to other energy crop digestersIn a later study, Braun et al. (2009) compared three installations digesting energy crops in Germany, one of which is the DRANCO-FARM installation of Nustedt. Table 2 summarizes some characteristics of these installations. The results for the DRANCO-FARM installation in this publication are valid for the situation when the electrical output was still 500 kWel. Since then, the electrical output has gone up to 1000 kWel, while still working very stable. These results were collected by OWS and are also represented in Table 2. From this table the high efficiency of the DRANCO-FARM installation is very clear. Where installation 2 needs a reactor volume of almost 4 000 m³ at a loading rate of 4.4 kg VS/m³R/d to obtain an electrical output of 1 000 kWel, the DRANCO-FARM installation obtains the same electrical output with a reactor volume of only 1 200 m³ at a loading rate of 16-17 kg VS/m³R/d. By working at a high total solids content at thermophilic temperature and by continuous monitoring and optimizing the installation, it was possible to obtain a loading rate almost 4 times as high as for an installation working at a low total solids content.
  • In another study, Weiland et al. (2009) collected data from 61 installations digesting energy crops in Germany (including the installation in Nüstedt). Of these 61 installations, 16 operated under dry conditions, and 11 worked thermophilic. Table 4 shows for some parameters the range for dry mesophilic installations, for wet thermophilic installations and for dry thermophilic installations, compared to the DRANCO-FARM installation at the time of the report and the situation at the beginning of 2010. Again, the DRANCOFARM concept has the highest organic loading rate of all installations reviewed. The loading rate of the DRANCO-FARM installation is 3 times higher than the second highest dry thermophilic installation and 5 times higher than the highest wet mesophilic installation. Only one dry mesophilic installation has a loading rate that is comparable to the situation in Nüstedt at the end of 2008, but is still 1/3 lower than the current situation. The average loading rate of all 61 installations was ± 3 kg VS/m³R/d, which means that the DRANCO-FARM reactor is 5 times more efficient than the average installation.
  • Transcript

    • 1. FußzeileDry AD for High Solids ManuresNorma S. McDonaldWaste to Worth Conference – April 5, 2013
    • 2. PRESENTATION HIGHLIGHTS• High solids feedstock characteristics andmarket dynamics• European research on operating plants• In-depth look at dry continuous digestion• Example economics
    • 6. LESS WATER,LESS CAPACITY REQUIRED –within ammonia concentration limitsNOMINAL 1 MW ENERGY POTENTIALANIMALS NUMBERMANURETONS/YRTOTALSOLIDSFRESHAT5% TOTALSOLIDSAT12%TOTALSOLIDSAT 35%TOTALSOLIDSBeef Cows 10,600 45,580 35% N/A 1,746,876 598,929Dairy Cows 4,800 182,646 8% 4,800,000 2,000,000 685,714Hogs 60,000 109,588 5% 2,304,000 960,000 N/AChickens 1,050,000 49,823 25% 3,273,381 1,363,909 467,626REQUIRED WORKINGCAPACITY (GAL)20 DAY RETENTION
    • 8. COMPARINGMETHANE YIELDON A VOLATILESOLIDS BASISHIGHEST:Barley, Triticale, Beets, Alfalfa, Rhubarb, Rye, Grass, Maize
    • 9. COMPARING METHANEYIELD PER ACREHIGHEST:Potatoes, Maize, Beets, Kale,Sorghum, Alfalfa
    • 10. NET ENERGY YIELD PROVIDES AN INDICATION OFSUSTAINABILITYBut ~50% of energy requirement is now fertilizer manufacturing
    • 11. Presented atEuropean Biogas workshop and study tourThe Future of Biogas in Europe III14th -16th of June 2007University of Southern Denmark, Niels Bohrs Vej9, 6700 EsbjergEsbjerg - Denmark
    • 12. Comparison of 41 Austrian digestion plants processing manureand energy crops – 2005
    • 13. Comparison of 41Austrian digestion plantsprocessing manure and energy crops – 2005*The data for DRANCO Farm was not included in the Study and are from OWS records
    • 14. Installation 1 Installation 2 DRANCO-FARM Nüstedt500 kWel 1 MWel*Energy crops t/year 9 500 11 000 10 500 21 000Manure t/year - 7 300 830 1 700Total input t/year 9 500 18 300 11 330 22 700Installed electrical power kWe 500 1000 500 1000Reactor volume m³ 3000 3850 1200 1200Temperature °C 49.5 39 55 55Retention time days - 77 29 20Loading rate kg VS/m³/d - 4.4 9.7 16-17Biogas productivity Nm³/m³R/d 1.72 2.86 6.0 10.4TS-content reactor % < 10 < 10 15-16 15-16*The data for 1 MW was not included in the Study and are from OWS recordsBiogas from energy crop digestion / IEA BioenergyTask 37R. Braun / P. Weiland / A. Wellinger (2009)
    • 15. Fermentation gas-measuring program IIComparison of 61 Digester OperationsP. Weiland u.a. / Fachagentur Nachwachsende Rohstoffe e.V.* The data for 1 MW was not included in the Study and are from OWS recordsMesophilicDryThermophilicWetThermophilicDryDRANCO-FARM2009 2010*# installations - 11 6 4 **Reactor volume m³ 881-5 626 1 100-8 900 845-3 400 1 200 1 200Loading rate kg VS/m³RV/d 1.1-9.8 1.8-3.4 1.9-4.8 9.7 15-16Retention time days 35-289 80-164 78-163 29 203-5X Loading Rate5X Digestion Efficiency<1/4 Digester Capacity
    • 16. DRANCO-FARM plant Nüstedt (Germany)DRANCO Farm digesterCSTR3 X 250 KW GENSETS
    • 17. Specific features of the DRANCO FARM procedureENERGYCROPSMIXERPUMPDIGESTATESTORAGEBIOGASUSEDRANCO-FARMDIGESTERPUMPPUMPACTIVEDIGESTATEINACTIVEDIGESTATEINTENSIVEFERMENTATION• Combined feeding, mixing and pump technology• Recirculation of partially digested material from the upper cone areaand integral post-fermentation step in the conical bottom
    • 18. DRANCO-FARM Plant Data• Region: Bassum-Nüstedt• Startup: 2006• Capacity: 500 KW (until 2009)• Expansion: in 2010 increased to 1 MW• Substrates: Maize silage, chicken manure, grasses• MT per year: 21,000 – 22,000 (silage, manure)• TS % of Inputs: ca. 30% (no addition of liquid manure or water!)• TS % in digester: 16-17%• Operation: Thermophilic (55°C)• Destruction: 75% of TS• Biogas production: 185 Nm3/mt~ 4,000,000 Nm3/ yr• Methane Content: 54 - 56%• Parasitic load: ca. 5-7%
    • 19. DRANCO-FARM plant Nüstedt (Germany)
    • 21. DRANCO-FARM plant Nüstedt (Germany)3322111 2 3321.200 5.800 15.400Ton/yearBiogasGAS STORAGEENGINEGENERATORElectricity (1000 kW)Heat (950 kW)DRANCO-FARMDIGESTER1.200 m³EXTRACTIONPUMPSTORAGEInactiveresidueActive residueDOSING UNITDOSING UNITDOSING SCREWDOSING SCREWMIXING UNIT/FEEDING PUMPEnergy crops (& manure)To fieldDigestate has NPKsimilar to manure ondry tonbasis, pumpable, spreadable
    • 22. DRANCO-FARM plant Nüstedt (Germany)ECONOMIC DATA2010 2011Produced kWh electricity 7,899,090 8,728,924Permitted power production 8,760,000 8,760,000% of max capacity 90.2%* 99.6%* First year operation as 1MW-plant
    • 23. Experiences and Conclusions• Study results prove the high efficiency of dry andcontinuous digestion of energy crops, high solidsmanures• High and steady biogas productivity is achieved by:– High TS content– Thermophilic operating temperatures– Optimal and consistent operating parameters• Dry and continuous digestion of energy crops is:– Technically possible– Reliable and highly efficient
    • 24. EXAMPLEECONOMICS- 1PoultryManure @ $10tip feeEnergy Crop@ $45harvested costElectricity soldat $0.10/kWhDigestate sold@ $10/tonDSCR of 4.6CALCULATING THE NET VALUE PER TON OF FEEDSTOCKValue (cost) as Received TPY Value $/ton $/yrManure 10,000 10.00$ 100,000$Energy Crop(s) 45,000 (45.00)$ (2,025,000)$TOTAL 55,000 (35.00)$ (1,925,000)$Variable Costs TPY Cost $/ton $/yrO&M 55,000 (5.45)$ (300,000)$Labor 55,000 (2.65)$ (145,600)$TOTAL 55,000 (8.10)$ (445,600)$Energy Value TPY Value $/ton $/yrManure 10,000 58.03$ 580,305$Energy Crop(s) 45,000 77.37$ 3,481,829$TOTAL 55,000 73.86$ 4,062,134$Digestate Value (Cost) TPY Value $/ton $/yr39,286 10.00$ 392,857$NET VALUE PER INPUT TON (EBITDA)TPY Value $/ton $/yr55,000 37.90$ 2,084,391$
    • 25. EXAMPLEECONOMICS- 2Bedded PackManure @ nocostEnergy Crop@ $45harvested costElectricity soldat $0.10/kWhDigestate @no valueDSCR of 3.5CALCULATING THE NET VALUE PER TON OF FEEDSTOCKValue (cost) as Received TPY Value $/ton $/yrManure 45,000 -$ -$Energy Crop(s) 10,000 (45.00)$ (450,000)$TOTAL 55,000 (8.18)$ (450,000)$Variable Costs TPY Cost $/ton $/yrO&M 55,000 (5.45)$ (300,000)$Labor 55,000 (2.65)$ (145,600)$TOTAL 55,000 (8.10)$ (445,600)$Energy Value TPY Value $/ton $/yrManure 45,000 38.69$ 1,740,914$Energy Crop(s) 10,000 77.37$ 773,740$TOTAL 55,000 45.72$ 2,514,654$Digestate Value (Cost) TPY Value $/ton $/yr39,286 -$ -$NET VALUE PER INPUT TON (EBITDA)TPY Value $/ton $/yr55,000 29.44$ 1,619,054$
    • 26. CURRENT SITUATION• ~195 operating AD plants on/near NorthAmerican farms• Limited to wet digestion• >95% are dairy farmsUNMET MARKET OPPORTUNITY• ~20,000 additional farms with solid and semi-solid manures and crop residuals – >100Xthe volume of volatile solids
    • 27. FußzeileOrganic Waste Systems, Inc.Tel. 513-535-6760Fax 513-233-3395norma.mcdonald@ows.bewww.ows.beThank you!