Inhibition on anaerobic digestion
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This document discusses various compounds that can inhibit anaerobic digestion, including: 1. Oxygen, which should be below 0.1 mg/L for methanogens. 2. Sulfur compounds like sulfates and hydrogen sulfide which can inhibit bacteria or decrease pH. Monitoring and removal techniques exist. 3. Organic acids like fatty and amino acids can inhibit methanogens, especially long chain fatty acids and propionic acid. These first three compounds pose the primary threats to anaerobic digestion according to the document. It also briefly mentions other inhibitors like nitrates, ammonia, heavy metals, and miscellaneous compounds.
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Inhibition on anaerobic digestion
- 2. Refferences:
- 3. Oxygen Sulfur Compounds Organic Acids (Fatty Acids & Amino Acids) Nitrate (NO3 -) Ammonium (NH4 +) and Ammonia (NH3) Heavy Metals Other InhibitingThresholds Inhibition Compounds on Anaerobic digestion
- 4. 1. Oxygen • The exclusion of oxygen is not absolutely necessary for acidogens • Avoiding the presence of oxygen more than 0.1 mg L − 1 O 2 for methanogens
- 5. 2. Sulfur Compounds • Sulphate ions inhibits to the process by following this reaction: • Hidrogen sulphide inhibits the metabolic activity of anerobic bacteria.
- 8. • Sulphate is reduced to hydrogen sulfide by sulphate reducing bacteria (SRB) • Hydrogen sulphide is formed by degradating of organic coumponds.
- 9. Monitoring sulphate/sulphide control: • Increasing the pH (caustic soda addition) • Addition precipitation chemicals (iron salt) and Physico-chemical techniques (stripping) The process are coagulation, oxidation, precipitation (Oude Elferink et al., 1994; Song et al., 2001; Chen et al., 2008).
- 10. 3. Organic Acids (Fatty Acids and Amino Acids • Long chain fatty acids (LCFA’s) inhibit on methanogens. Propionic acids performs most inhibitor (Dublein and Steinhauser, 2008) Lauric acids performs most inhibitor (Gerardi, 2003)
- 12. Volatile acids such as acetate, butyrate, and propionate causes a decreasing pH.
- 13. Nitrate (NO3 - ) • The redox potential occure more negative • Gas quality have high portion of nitrogen content
- 14. Ammonium (NH4 +) and Ammonia (NH3) Nitrogen source- providing buffering capacity- (Dublein and Steinhauser, 2008)
- 15. (Gerardi, 2003)
- 16. Controling the ammonia content • ANAStrip-process
- 17. Heavy Metals • They are stimulator the activity of bacteria • But in higher concentration can be toxic • This groups incudes lead, mercury, cadmiun, uranium, iron, zinc, copper, chromium, manganese, molybdenum, nickle, and selenium.
- 19. Other inhibiting thresholds • Disenfectans • Chlorinated hydrocarbons • Benzene ring compounds • Cyanide • Recalcitrant (flavour compounds, essential oil)
Editor's Notes
- In the process of biogas plant, there is a things that make anaerobic digestion going not to be effective. Substrate that contain inhibition compounds can inhibit anaerobic digestion especially in biocenosis. What are inhibition compounds on anaerobic digestion? I want to explain in the next slides.
- The majority of the acidifying bacteria are facultatively anaerobic, so that the exclusion of oxygen is not absolutely necessary for acidifi cation. But methanogenics are obligatorily anaerobic – the inhibition begins at 0.1 mg L − 1 O 2 . They take nitrate, sulfate, or carbonate as the oxygen replacement, i.e. as the hydrogen acceptor. Since under operational conditions the methanogenics always grow in the presence of facultatively anaerobic acidifying bacteria, which consume available oxygen immediately, anaerobic conditions can be maintained in closed reactors. The small amount of air, which is injected frequently for the biotechnological desulfurization of the biogas, usually has no inhibiting effect on the methane formation.
- Due to diffusion through a cell membrane. Non ionized hydrogen sulfide diffuses more rapidly across a cell membrane than sulfide Involving the pH.
- Several genera of anaerobic bacteria reduce sulfate of sulfur to hydrogen sulfide. Ex: desulfuromonas, desulfovibrio. There is competition between SRB and MBP (methane producing bacteria). Sulfur is a nutrient for MBP.
- Work as H2S scavenger (iron salt)
- The fatty acids bind to the cell membrane, protecting the cell and transportation of materials in out ouf the cell. Inhibits more in methanogens Hidrolized to fatty acids and glicerols. Occuring foaming Propionic acids performs most inhibition during concentration of 5 mg/L.
- Propionate is the most toxic of the volatile acids and may exert toxixity at <5 mg/L
- Denitrified in the firs stage of decomposition
- Ammonia and ammonium are formed under biological degradation of nitrogen compounds (proteins, amino acids). Ammonia is nutrient for bacteria as nitrogen source. Free ammonium is toxic. Ammonia forms ammonium in the substrate, due to the pH increasing/ decreasing. Inhibition increasing following increasing temperature. Shifted in favor of NH3
- Interferere with organism’s enzyme system by binding to different groups of these enzymes. Chelating agent for organic compound that make invisible for microorganism