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Microbiology

Microbiology. Microbiology of biogas. Anaerobic digestion utilizes a consortium of microbes in four distinct phases Products of one phase are feedstocks for next phase (serial process) For optimal performance, each rate keeps up with previous Microbial populations are ever-evolving.

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Microbiology

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  1. Microbiology

  2. Microbiology of biogas • Anaerobic digestion utilizes a consortium of microbes in four distinct phases • Products of one phase are feedstocks for next phase (serial process) • For optimal performance, each rate keeps up with previous • Microbial populations are ever-evolving

  3. What is anaerobic digestion?(Biochemistry perspective) • Aerobic organisms use oxygen as their electron acceptor • Anaerobic organisms utilize alternative electron acceptors • Facultative organisms are aerobic or anaerobic

  4. What is anaerobic digestion?(Biochemistry perspective) • Anaerobic electron acceptors (oxidizers) • NO3-, Fe3+, Mn3+, SO43+, CO2 • Significantly different energy output • 30 ATP (aerobic) vs. 2 ATP (anaerobic) • Anaerobic metabolism occurs throughout nature (hydric soils, ruminants, etc.)

  5. Phases of digestion • Hydrolysis • Acidogenesis • Acetogenesis • Methanogenesis

  6. Long chain fatty acids, intermediates Digestion Process Carbohydrates, lipids, proteins Hydrolysis Sugars, fatty acids, amino acids Acidogenesis Acetogenesis Acetate H2, CO2 Methanogenesis Methane (Biogas)

  7. Hydrolysis • Large organic compounds are broken down into simpler compounds • Performed by many organisms • Bacteria, fungi, protists • Facilitated by extracellular enzymes • H2 and CO2 also produced Carbohydrates, lipids, proteins Sugars, fatty acids, amino acids Vibrio Hartmanella

  8. Sugars, fatty acids, amino acids Acidogenesis • Products of hydrolysis are fermented into volatile fatty acids • Also termed fermentative bacteria • Trace oxygen consumed by facultative bacteria • Also produces acetate, H2, and CO2 Propionibacterium Lactobacillus Long chain fatty acids, intermediates

  9. Acetate, CO2, H2 Acetogenesis • Long-chain volatile fatty acids are converted to acetate, H2, and CO2 • Metabolizes intermediates (proprionate, butyrate) • Two groups of acetogens • Obligate hydrogen-producing acetogens (OHPA) – more dominant • Homoacetogens – less dominant Long chain fatty acids, intermediates Syntrophomonas

  10. Acetogenesis (OHPA) • Produce acetate, CO2 and H2 from fatty acids • Metabolize in low-H2 environments • Mutualistic relationship with methanogens (Syntropy) • Methanogens consume H2, OHPA produce acetate and consume fatty acids • Positive feedback cycle if balance disturbed • Homoacetogens produce acetate from CO2 and H2 • Also assist in reducing H2

  11. Methanogenesis • Final metabolic phase • Methanogens produce methane gas from acetate, H2 and CO2 • 2/3 of methane produced is derived from acetate • Often the rate limiting step in anaerobic digestion • Can lead to accumulation of acids Acetate H2, CO2 Methane (Biogas)

  12. Methanogens • All are Archaebacteria • Obligate anaerobes • Optimum performance at neutral pH (7) • Many genera convert H2 and CO2 to methane (Hydrogenotrophic) Methanospirillum Methanococcus

  13. Methanogens • Two known genera convert acetate to methane (Acetoclastic) • Methanosarcina – Favor high concentration • Methanosaeta – Favor low concentration Methanosarcina Methanosaeta

  14. Questions?

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