Biodegradation and biodegradability of substrate
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The document discusses the biodegradation process of organic matter by microorganisms, focusing on anaerobic fermentation and its microbiology, which includes the transformation of compounds and the kinetics of biodegradation. It outlines various biodegradation types, the significance of recalcitrance in plant cell walls, and the steps involved in anaerobic fermentation such as hydrolysis and methane formation. Additionally, it explores the oxidative reduction potential and the environmental parameters affecting biogas production.
Biodegradation and biodegradability of substrate
- 1. Lecture 2 Biodegradation and biodegradability of substrate – BOD – Biochemistry of Anaerobic Fermentation (AF) - Microbiology of AF - Kinetics of AF
- 2. Biodegradation • Breakdown of organic matter by microorganisms, such as bacteria and fungi • Depends on the composition of digester feeds • 100% biodegradable – rare - imperfect physico chemical factors, - non – degradable compounds (recalcitrant) • Recalcitrant - natural resistance of plant cell walls to microbial and enzymatic deconstruction • Delignification • Increase in lignin by 1% - drop in biodegradability by 3%
- 3. Biodegradation – Types • Primary biodegradation (transformation) - completely changes the characteristics of a compound - biodegraded compound : no longer responds to analytical procedures - alteration in the chemical structure of a substance, brought about by biological action, resulting in the loss of a specific property of that substance • Ultimate biodegradation - Level of degradation achieved when the test compound is totally utilised by micro-organisms resulting in the production of carbon dioxide, water, mineral salts and new microbial cellular constituents • Environmentally acceptable biodegradation - minimum alteration of the original compound to remove its undesirable characteristics
- 4. Biodegradability • Degree of biodegradation of a chemical compound • Fermentation – wet / dry • Wet fermentation - digester contents mixed with excessive water - portion of dry matter : less than 10% - animal wastes • Dry fermentation - agricultural plant materials - mixing and scum formation - no free water - total solids 25 – 30%
- 5. Biodegradability of Substrates A, B, C and D
- 6. K – reaction velocity coefficient at 20°C - sewage 0.4 /day - industrial waste 0.15 – 0.75 / day
- 7. Oxidative Reduction Potential • Measure of the tendency of a chemical species to acquire electrons from or lose electrons to an electrode and thereby be reduced or oxidised respectively • Measured in volts or millivolts • Ability of a lake or river to cleanse itself or break down waste products, such as contaminants and dead plants and animals • When the ORP value is high, there is lots of oxygen present in the water • Biogas yield, ORP, volatile acids, anaerobic environment • Methane forming bacteria – sensitive to oxygen • Biogas plant - initially aerobic - later – anaerobic - facultative bacteria : survive in aerobic & anaerobic environment • Initially, ORP – higher • Fermentation progresses • Starts declining – stabilises around 10th day of fermentation - acid forming phase to methane forming phase
- 8. Biochemistry of Anaerobic Fermentation Hydrolysis phase - break down large molecules into smaller ones Acid phase - proteins, fats, carbohydrates - organic acids Methane forming phase - Anaerobic oxidation of hydrogen & CO2 - Reduction of CO2 to methane
- 9. Microbiology of Anaerobic Fermentation • Methane bacteria - rod - coccus - sarcina - spiral • Morphological group of methane bacteria - rod-shaped sporulating cells (Methanobacillus) - rod-shaped non-sporulating cells (Methanobacterium) - spherical cells in sarcina arrangement (Methanosarcina) - spherical cells in non-sarcina arrangement (Methanococcus) Methanobacterium Methanosarcina Methanococcus
- 10. • Reproductive cycle time of methane bacteria : 4 – 6 days • Methanobacterium, thermoautotrophicum, M.arbophicum, Hungattii • Temperature and oxygen
- 11. Kinetics of Anaerobic fermentation
- 12. β = βm . S0 / KS + S0 • Monod Model • P. Y. Yang Model
- 14. Reference • Mittal, K.M. 1996. Biogas system: principles and applications. New age international (P) Ltd., New Delhi. P.No: 26 - 37