Tom marshall

989 views
925 views

Published on

Published in: Technology, Business
0 Comments
2 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
989
On SlideShare
0
From Embeds
0
Number of Embeds
1
Actions
Shares
0
Downloads
0
Comments
0
Likes
2
Embeds 0
No embeds

No notes for slide

Tom marshall

  1. 1. Biogas Basics presented byTom Marshall, Ph.D., P.E.Operator Training Committee of Ohio CLASS III & IV WORKSHOP THURSDAY, AUGUST 13, 2009 RAMADA PLAZA HOTEL & CONFERENCE CENTER 4900 Sinclair Road Columbus, OH 43229
  2. 2. Bringing Biogas to Your Community Could Bring Energy Stimulus Money, Jobs and Energy Independence• This presentation is intended to provide a basic process overview of anaerobic digestion and biogas production• A solid technical background provides a platform upon which further investigation into the feasibility of biogas-to-energy facilities in your community can be explored Dr. Thomas Marshall (marshall.15@osu.edu)
  3. 3. Process Overview• Anaerobic Sludge Digestion• Biological Activities in Anaerobic Digestion• Practical Applications Dr. Thomas Marshall (marshall.15@osu.edu)
  4. 4. Anaerobic Sludge Digestion– Process Description– Operational Parameters Dr. Thomas Marshall (marshall.15@osu.edu)
  5. 5. Anaerobic Sludge Digestion Process Description• Involves a complex mixed culture of anaerobic organisms to hydrolyze, ferment and convert to methane the fats, proteins and polysaccharides in organic sludge solids• Organic solids are typically reduced by 50% Dr. Thomas Marshall (marshall.15@osu.edu)
  6. 6. Anaerobic Sludge Digestion Process Description• Batch Process – Supernatant Withdrawal• High-Rate Process – Continuous flow – No Supernatant Withdrawal• Semi-Batch Process – Intermittent flow• Single stage or two stage Dr. Thomas Marshall (marshall.15@osu.edu)
  7. 7. Anaerobic Sludge Digestion Operational Parameters• Temperature – Psychrophilic Range (less than 68 degrees F) • Typically Unheated – Mesophilic Range (between 77 and 104 degrees F) • Requires Heat • Most Common Process – Thermophilic Range (between 122 and 158 degrees F) • Unusual Set of Microorganisms Dr. Thomas Marshall (marshall.15@osu.edu)
  8. 8. Anaerobic Sludge Digestion Operational Parameters• Retention Times – Mesophilic and Thermophilic Range • Typically 25-35 days • Can be as low as 12-15 days – Psychrophilic Range • In excess of 100 days • Requires large storage volume Dr. Thomas Marshall (marshall.15@osu.edu)
  9. 9. Anaerobic Sludge Digestion Operational Parameters• Substrate Loading – Normally expressed as lbs/cu ft - day of volatile solids – Typical loading rates are .1 - .2 lbs/cu ft - day • Assumes Primary or Blended Sludge Dr. Thomas Marshall (marshall.15@osu.edu)
  10. 10. Biological Activities in Anaerobic Digestion– Microbial Composition of Digesting Sludge– Survival of Pathogens– Biochemistry of Anaerobic Digestion– Microbial Growth Parameters Dr. Thomas Marshall (marshall.15@osu.edu)
  11. 11. Biological Activities in Anaerobic Digestion Microbial Composition of Digesting Sludge• Process depends exclusively on bacterial activity (fungi and protozoa contribute little to the process)• Bacteria Types are classified as – Hydrolytic – Fermentative – Methanogenic• The most significant of the strict anaerobes are of the genus Bacteroides • Found at densities of 1010 per gram in feces Dr. Thomas Marshall (marshall.15@osu.edu)
  12. 12. Biological Activities in Anaerobic DigestionMicrobial Composition of Digesting Sludge• Some fermentative organisms are facultative in anaerobic digestion but the predominate population is that of obligate anaerobes such as Clostridium• Reducing conditions release hydrogen sulfide – Sulfate is reduced by Desulfovibrio desulfuricans• The methanogenic population is also strictly anaerobic Dr. Thomas Marshall (marshall.15@osu.edu)
  13. 13. Biological Activities in Anaerobic Digestion Survival of Pathogens• Salmonella is often used as indicator organism for pathogen survival – Survival rates are low with infrequent detection• Vibrio cholerae and Giardia are largely destroyed• Viruses can survive• Survival depends on temperature, detention time and process Dr. Thomas Marshall (marshall.15@osu.edu)
  14. 14. Biological Activities in Anaerobic Digestion Biochemistry of Anaerobic Digestion• While anaerobic digestion is typically described in terms of acid formers and methane producers, there are actually four distinct phases: – Hydrolysis – Fermentation – Acetogenisis – Methanogenisis Dr. Thomas Marshall (marshall.15@osu.edu)
  15. 15. Biochemistry of Anaerobic Digestion Dr. Thomas Marshall (marshall.15@osu.edu)
  16. 16. Biological Activities in Anaerobic Digestion Biochemistry of Anaerobic Digestion• Hydrolysis – The initial phases of the hydrolysis of a substrate occur extracellularly – Only a few bacteria are able to produce degradation enzymes for large polymer substrates Dr. Thomas Marshall (marshall.15@osu.edu)
  17. 17. Biological Activities in Anaerobic Digestion Biochemistry of Anaerobic Digestion• Hydrolysis – Lipid hydrolysis is not well understood • Clostrdia and micrococci appear to produce most of the extracellular lipases • Some of these enzymes are very specific while others will also hydrolyze proteins Dr. Thomas Marshall (marshall.15@osu.edu)
  18. 18. Biological Activities in Anaerobic Digestion Biochemistry of Anaerobic Digestion• Hydrolysis – Polysaccharides include cellulose, pectins and starch – Polysaccharides are degraded extracellularly by a variety of different bacterial genre Dr. Thomas Marshall (marshall.15@osu.edu)
  19. 19. Biological Activities in Anaerobic Digestion Biochemistry of Anaerobic Digestion• Fermentation – Amino acids and sugars are the most readily fermentable substrates – Sugars are fermented to alcohols – Pyruvate is an important intermediate in the fermentation of amino acids from which formate and acetate are formed Dr. Thomas Marshall (marshall.15@osu.edu)
  20. 20. Biological Activities in Anaerobic Digestion Biochemistry of Anaerobic Digestion• Fermentation – Acidogenic fermentation results in acetate – Carbon dioxide and molecular hydrogen are also fermentative end-products Dr. Thomas Marshall (marshall.15@osu.edu)
  21. 21. Biological Activities in Anaerobic Digestion Biochemistry of Anaerobic Digestion• Acetogenesis – For many years is was assumed that methanogens could convert all of the fermentative end-products directly to methane. However, there is an important intermediate step in which acetate and hydrogen are produced with OHPA bacteria • Obligatory Hydrogen-Producing Acetogenic bacteria Dr. Thomas Marshall (marshall.15@osu.edu)
  22. 22. Biological Activities in Anaerobic Digestion Biochemistry of Anaerobic Digestion• Methanogenesis – Methanosarcina bareri is the only species that can produce methane directly from acetate – Twice as much methane is generated from acetate than from the reduction of carbon dioxide Dr. Thomas Marshall (marshall.15@osu.edu)
  23. 23. Biological Activities in Anaerobic Digestion Biochemistry of Anaerobic Digestion• Process stability – Hydrolysis and fermentation processes proceed slowly but the micro-organisms are robust – Acetate and hydrogen are present in low concentrations during stable operations – Overload of carbohydrates will result in elevated concentrations of acetate – Acetate accumulation results in low pH and process inhibition Dr. Thomas Marshall (marshall.15@osu.edu)
  24. 24. Biological Activities in Anaerobic Digestion Biochemistry of Anaerobic Digestion• Process stability – OHPA bacteria are inhibited by their own metabolic product, hydrogen, which is removed by the methanogens – Early detection of elevated volatile fatty acid concentrations (2000 – 5000 mg/l) is an early warning to process upset. – pH adjustments can counter process failure Dr. Thomas Marshall (marshall.15@osu.edu)
  25. 25. Biological Activities in Anaerobic Digestion Biochemistry of Anaerobic Digestion• Process stability – Methanogenic inhibition is also caused by: • Heavy metals • Chloromethane • Detergents Dr. Thomas Marshall (marshall.15@osu.edu)
  26. 26. Biochemistry of Anaerobic Digestion Dr. Thomas Marshall (marshall.15@osu.edu)
  27. 27. Biological Activities in Anaerobic Digestion Microbial Growth Parameters• It is commonly thought that the slow growth rate of the methanogens limits the rate of anaerobic digestion, however, the OHPA bacteria have a slower growth rate (1/10 of the rate of methanogens)• The detention time must be sufficient to allow the OHPA bacteria to produce acetate• The yield coefficients for anaerobic bacteria are 50% of aerobic bacteria due to organic carbon being converted to gas rather than biomass Dr. Thomas Marshall (marshall.15@osu.edu)
  28. 28. Practical Applications• Typical gas production value is approximately 15 cubic feet of gas (65% methane) per pound of volatile solids• Typical biogas has 650 BTU/cu ft• H2S is undesirable and can be removed with scrubbers Dr. Thomas Marshall (marshall.15@osu.edu)
  29. 29. Practical Applications• Gas can be used to directly provide heat, run internal combustion engines or micro-turbines• Operating gas pressures are typically 12-15 inches of water head• Cogeneration is cost effective for communities with 1 MGD or higher wastewater flows• If electrical costs double, payback period for biogas facilities is divided by a factor of 2 Dr. Thomas Marshall (marshall.15@osu.edu)
  30. 30. Conclusion• This presentation was intended to provide a basic process overview of anaerobic digestion and biogas production• A solid technical platform provides a basis upon which further investigation into the feasibility of biogas-to-energy facilities in your community can be studied• Bringing Biogas to Your Community Could Bring Energy Stimulus Money, Jobs and Energy Independence Dr. Thomas Marshall (marshall.15@osu.edu)
  31. 31. Biogas Basics presented byTom Marshall, Ph.D, P.E.Operator Training Committee of Ohio CLASS III & IV WORKSHOP THURSDAY, AUGUST 13, 2009 RAMADA PLAZA HOTEL & CONFERENCE CENTER 4900 Sinclair Road Columbus, OH 43229

×