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Biogas production

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  1. Gas out Biomas in Biomas out (Digestate) Biogas production

  2. Where are we?Why do we want?How do we manage?What do we need?From where should we start?What do we want to know?

  3. Biogas knowledge piramide

  4. Biogas plant concept Pig slurry Biomas out (Digestate) Fe • Additional income for the farmers • Clean energy (kitchen) • Digestate is an excellent fertilizer • Less odour • Sanitaion

  5. Biomasse: Animal manure Organic waste Hydrolysis Dissolved substrate Acidogenesis VFA>C2 Acetognesis H2+CO2 CH3-COOH Methanogenesis CH4+H2O+ CO2 The microbiology process

  6. Biomasse: Animal manure Organic waste Hydrolysis Dissolved substrate Acidogenesis VFA>C2 Acetognesis H2+CO2 CH3-COOH Methanogenesis CH4+H2O+ CO2 Methane produktion • Hydrolysis is process rate controlling • VFA transformation reduced due to: • High NH3 • Sudden changes in environment • High H2 concentration • Feedback: • High VFA conc. reduces hydrolysis

  7. COMPOSITE MATERIAL MACROMOLECULES • Physical process: Disintegration • Lysis • Non enzymatic decay • Phase separation • Physical breakdown (shearing) Physical process

  8. MACROMOLECULES SIMPLE SUBSTRATES Hydrolysis (chemical) A→B1+B2 (H2O is used) Hydrolytic enzymes (biological/chemical) Made by micro-organisms – same outcome Biological and chemical process

  9. SIMPLE SUBSTRATES VOLATILE FATTY ACIDS ACETATE & HYDROGEN Acidogenesis: (biological) Volatile fatty acids are generated from monosaccarides, fat and aminoacids. (sugar-degraders & aminoacid-degraders) Acetogenesis: (biological) Acetate is generated from LCFAs. (lcfa-degraders) and from sugar (sugar-degraders)

  10. ACETATE & HYDROGEN BIOGAS Methanogenesis (biogas production) Acetoclastic methanogenesis CH3COOH → CH4 + CO2 Hydrogenotrophic methanogenesis CO2 + 4H2 → CH4 + 2H2O

  11. Biogas knowledge pyramideInhibition

  12. H2inhibition Acetic acid VFA component

  13. Ammonia inhibition • Ammonia inhibition: 1,5 – 2,5 g N/L, after adaptation inhibition at 4 g N/L (Angelidaki og Ahring 1998)

  14. Ammonia chemistry • pH= -log(H+) • Thus if the concentration of [H+] is • Neutral: 10-7 mol then pH = –log(10-7)=7 • Acid: 10-2 mol then pH = –log(10-2)=2 • Basic: 10-10 mol then pH = –log(10-10)=10

  15. Ammonia-ammonium equilibrium

  16. Ammonia inhibition • In literature ammonia inhibition has been assessed relating biogas production to • Reactive ammonium (NH3) • Total Nitrogen • Ammonium How is NH3 related to NH4+ How would you recommend that the inhibition is expressed (reactive ammonium, total nitrogen or ammonium

  17. Inhibition at high and low pH SH2 NH3

  18. VFA inhibition • Inhibition at a ratio of propionic acid to acetic acid at 1.4:1 • Inhibition at 2 g VFA Ltr-1

  19. TemperatureBacteria adaptation Batstone et al. 2002

  20. SIMPLE SUBSTRATES VOLATILE FATTY ACIDS ACETATE & HYDROGEN Acidogenesis: (biological) Volatile fatty acids are generated from monosaccarides and aminoacids. (sugar-degraders & aminoacid-degraders) Acetogenesis: (biological) Acetate is generated from LCFAs. (lcfa-degraders) and from sugar (sugar-degraders) What happens if the temperature suddenly drops?

  21. Metane production as affected by NH4+ koncentration interacting with temperature 20 days retention time in CSTR digester

  22. Biogas knowledge piramideDigestibilty

  23. Definitioner • VS (Volatile solids): • The fraction of dry matter (DM) in slurry that is transformed to gas at high temperature/incineration (550oC) for one hour • How would you measure VS? • Methane productivity: • CH4 production pr. unit VS • CH4 production pr. unit COD

  24. Source of energy in animal slurry

  25. Energy production Biogas, CH4 +CO2 CH4 - source

  26. Characterisation of biogas potential • In the biological process the maximum biogas production BMP • (liter CH4 kg(VS)-1) • Volume of methane produced when residence time is in principle very long Biomas Inoculum BMP is estimated in batch fermentation at 35oC Fermentation time 70-100 days

  27. Anaerobic Digestibility • The theoretical biogas productioncanbecalculated from knowing the chemicalcomposition of the biomass:TBMP • In the biologicalprocess the maximum biogas production: BMP • Anaerobicdigestibility =BMP/TBMP • Question • - BMP/TBMP ↑ digestibility?? • - BMP/TBMP ↓ digestibility ??

  28. Biodegradability (BMP/TBMP) examples

  29. Lignocellulose • Low digestibility • lignin : Non degradable in anaerobic environments • hydrolysis of cellulose blocked by lignin. • Lignin • glue to hold lignocellulosic matrix • protective coat • used to assess digestibility of feed in animal science

  30. Lignocellulose in VS (volatile solid)

  31. Fermentation result - animal manure

  32. Digestability of the biomass CH4 L kg(VS)-1

  33. Energy potential of biomass Why is biogas energy production of straw so low

  34. Methane produkcion crops and organic waste

  35. Biogas production estimates • With the Hashimoto equation one can assess production of biogas as affected by: • temperature, • hydraulic retention time, • micro-organism activity • biomass composition

  36. Hashimoto equation

  37. Hashimoto model predictions’

  38. Summarising • Biogas is efficient in producing energy from biomasses with a high water content • Biogas transform the biomas reducing VS and thus reduced GHG emission potential of the slurry • Biogas transform biomas organic N into ammonium that is an efficient fertilizer