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Anaerobic Digestion: Co-Digestion and Operational Issues
The document discusses the optimization of anaerobic digesters, emphasizing their benefits such as energy independence, reduced greenhouse gases, and potential revenue streams. It outlines the anaerobic digestion process, critical parameters for optimal performance, the importance of feedstock evaluation, and lessons learned from case studies. Key takeaways include that digesters require careful management, mixing is vital yet variable, and operators must understand the system for effective optimization.
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Anaerobic Digestion: Co-Digestion and Operational Issues
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- 2. Why install adigester? • Energy independence • Reductions in green house gases • Flexibility in manure management • Reduced odors & pathogens • Reduction in other environmental impacts • Potential for additional asset streams (?) • Bedding • Tipping fees • Environmental credits • Do I dare say profits? • What can’t digesters do?
- 3. Anaerobic Digestion inthe U.S. USEPA AgSTAR, 2011
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- 6. Anaerobic Digestion ProcessFlow Slurry Biogas SeparatorDigestate Filtrate (liquid) Fiber (solid) Feedstock's
- 7. Characterized by rapid bacterial growth “Weaklink” in the process of producing biogas Goal?...Avoid inhibition, maintain stabilization! Stage Three: Acetogenesis Stage One: Hydrolysis Stage Two: Acidogenesis Stage Four: Methanogenesis CO2 reducing methanogens aceticiastic methanogens acetogens (H2 producing) fermentative bacteria fermentative bacteria PROPIONATE, BUTYRATE, etc. (Short-chain volatile organic acids) fermentative bacteria fermentative bacteria COMPLEX POLYMERS (Proteins, polysaccharides, etc.) MONOMERS AND OLIGOMERS (Sugars, amino acids, peptides) acetogens (H2 consuming) H2 + CO2 ACETATE CH4, CO2 Source: Syed Hashsham, PhD, lecture notes, Michigan State University The Biological Process of Producing Biogas
- 8. Key Parameters • Temperature– sensors, controls (~100°F, ~135°F) • pH (methanogens 6.4-8.2; manure = good buffer) • Microorganism populations • Feedstocks/Loading • Mixing • Limit Toxicity • Micro/Macro Nutrients • HRT – engineering design
- 9. Different Digester OrganismsResult in Different Biogas Yields Control = Seed biomass microbial community Active = Different microbial community (bioaugmented) Source: Kaushik Venkiteshwaran, Ph.D. student, Marquette University 15% more methane
- 10. Anaerobic Digestion Feedstocks CheeseWhey Swine Manure Dairy Manure Cattle Manure Cucumber Waste Yard Clippings Municipal Organics Human Waste Food Processing Waste Vegetables Grasses
- 11. Gas Yields ofDifferent Feedstocks Kestutis Navickas. 2007. Bioplin Tehnologija in Okolje,
- 12. Additional Substrates • Whatto use? • Avoid toxicity – trust your supplier (now have brokers) • Producers range – smart ones are cautious • Evaluate additional substrates • What will substrates do to the digestate? • Rule of thumb – must be worth more than the cost of spreading (some use the idea that tipping fees must be ≥ application costs) • Load slowly Electrical $ 420,000 Bedding $ 275,000 Fertilizer $ 440,000 Heating $ 30,000 Carbon C $ 125,000 Tipping $ 75,000 Tax Credit $ 40,000 Total $1,384,000 Revenues from Digester
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- 15. Cheese Whey andCheese Whey Permeate • Evaluated in triplicates • 0% (control – all manure), 20%, 40%, 80%, and 100% substrate additions • Varying performance • Generally < 40% reached a maximum biogas production
- 16. Mixing • Microorganisms mustcome into contact with the food • Benefits of mixing • Speeding up the breakdown of the volatile solid • Increase in biogas production • There is a cost associated with mixing! • Still done on a trail and error basis
- 17. Case Study: Optimizinga Small Scale Digester
- 18. Case Study • Don’tassume anything! • Make operators record EVERYTHING 1.Verify temperature throughout tank 2.Take measurements (pH, VS, COD, etc.) over time 3.Don’t change things quickly, allow time to stabilize • Lower gas production than predicted • Made lots of changes to feedstocks and feed operations • Contemplated design changes • Retention time was too short, found through low destruction • Increased temperature resulted in 2-3x the biogas production
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- 21. Take Away • Manythings affect digester performance, optimize one by one, may need to go back • Feedstocks need to be evaluated on an individual basis • Mixing is still a trail and error process • Digesters require operators and farm employees to understand the system • Make the simple and low cost adjustments first, typically have the highest pay back • Future: • Mixing impacts to methanogens and modeling to reduce build-up (we will finish eventually)
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Editor's Notes
- #7 T