Valuing Feedstocks for Anaerobic Digestion – Balancing Energy Potential and Nutrient Content

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Proceedings available at: http://www.extension.org/67610 To improve the energy production and revenue generation, many farm digester operators are including off-farm feedstocks in the blend. Off-farm feedstocks are raw materials with high carbon concentrations that can be degraded anaerobically. Common off-farm feedstocks include food service or retail waste, food processing byproducts, residuals from biofuels production and FOG (fat, oil & grease) resulting from food preparation. Typically, off-farm feedstocks have a higher energy potential when compared to manure. Manures generally have biogas potential in the range of 280 to 500 L of biogas/kg of VS, compared to off-farm feedstocks which can range from 300 to 1,300 L of biogas/kg of VS [1]. In addition to the increased biogas production, revenue can also be generated from tipping fees collected for feedstock brought onto a farm. The tipping fee is typically comparable to the cost of disposing of the material at a landfill or wastewater treatment plant.

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<ul><li> 1. Valuing Feedstocks for AnaerobicDigestion Balancing EnergyPotential and Nutrient ContentApril, 2013Dana Kirk, Ph.D., P.E.Louis FaivorSteve Safferman, Ph.D., P.E.Wei Liao, Ph.D., P.E.Anaerobic Digestion Research and Education CenterBiosystems and Agricultural Engineering</li></ul> <p> 2. Industry growth on-farm anaerobic digesters2012 192 operating systemsUp from 151 systems in 2010 3. Revenue generation Low value of products Assessing value of environmental benefits Access to markets Location Utilities Capital cost Manure &amp; nutrient management Feedstock availability Technological gaps Nutrient recovery CNG vehicle conversionChallenges with anaerobic digestion 4. Pros &amp; cons Energy potential Nutrients Tipping fees Infrastructure Regulatory ManagementNon-farm feedstock as a way to address revenue 5. Disclaimer 6. Energy Potential 7. ADREC classification of feedstockValuesFeedstock Count (n) Avg, TS raw (%) Avg, VS raw (% of TS)Avg of Normalizedper Initial VS, BiogasProduction (mL/mg) Max Methane (%)Acid food 3 5.74% 58.77% 0.427 70.67%Algae 1 1.01% 50.29% 0.051 60.00%Bakery 1 92.86% 71.51% 0.169 15.91%BlendBeef 6 92.86% 71.51% 0.433 66.92%Chicken 3 0.85% 59.04% 0.477 60.33%Dairy 141 14.01% 68.56% 0.466 63.19%Pomace 16 0.135 25.81%Swine 16 0.110 25.83%Undisclosed 3 19.54% 88.07% 2.913 70.67%Blend Total 185 16.94% 68.87% 0.445 56.92%DairyCheese whey 3 28.16% 82.19% 1.204 70.28%Whey 3 6.06% 68.38% 1.218 64.17%Dairy Total 6 17.11% 75.29% 1.211 67.23%Dairy food 1 6.60% 74.63% 0.452 75.00%Food manufacture 10 25.63% 80.96% 1.469 69.20%Food wasteCafeteria(blank)Cafeteria - breakfast 1 20.31% 77.04% 0.451 74.00%(blank) Total 1 20.31% 77.04% 0.451 74.00%Cafeteria Total 1 20.31% 77.04% 0.451 74.00%Food waste 6 27.37% 80.32% 1.445 59.11%Food waste Total 7 26.20% 79.78% 1.303 61.24%Formic acid 1 0.17% 78.70% 0.199 0.00% 14 general categories of non-farm substrate 558 data points as of June, 2012 8. Energy potential of non-farm feedstock05,00010,00015,00020,00025,00030,00035,000BiogasPotential(ft3/tonVS)Substrate 9. FeedstockBiogas Potential (ft3/ton VS) TS VSLow High % %Liquid dairy manure 16,018 3.3% 2.3%Cheese Whey 22,746 32,000 5.3% 4.5%Fish offal 28,833 35.4% 29.2%FOG/food grease 15,378 29,794 60.2% 58.3%Mixed food waste 14,417 20.3% 15.6%Food processing waste 21,785 26,590 52.3% 50.6%Fruit &amp; Vegetable waste 16,659 18,902 11.2% 10.6%Glycerin 27,872 32,000 29.8% 26.8%Switchgrass, fresh 10,892 51.0% 48.8%Waste Potatoes 17,300 23.2% 16.5%Energy potential of non-farm feedstock 10. Energy potential of non-farm feedstock02000400060008000100001200014000160001800020000BiogasPotential(ft3/tonasis)Substrate 11. Digester feedstocks &amp; nutrients 12. FeedstockP2O5(lb/ton)TN(lb/ton)Fish offal 59 317FOG 3 to 16 24 to 37Mixed food waste 20 to 118 116Food processing waste 8 to 43 32 to 42Glycerin 19 to 33 38Meat 31 to 69 69 to 300+Milk 51 44Nutrient composition of non-farm feedstock 13. Feedstock nutrients: benefit or liability?Acres Needed to Utilize P2O5Feedstock P2O5(lb/ton offeedstock)Alfalfa(8 ton/ac)Corn Grain(180 bu/ac)Corn Silage(20 ton/ac)Soybean(60 bu/ac)Wheat(75 bu/ac)Fish offal 59 0.6 0.9 0.9 1.2 1.3FOG 3 to 16</p>