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4.4 Biogas – a way to solve sanitation problems

4.4 Biogas – a way to solve sanitation problems. Anaerobic fermentation is a natural and unavoidable process . How much biogas can be produced from excreta and biomass? How safe is the process and its sludge? ?.

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4.4 Biogas – a way to solve sanitation problems

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  1. 4.4 Biogas – a way to solve sanitation problems Anaerobic fermentation is a natural and unavoidable process How much biogas can be produced from excreta and biomass? How safe is the process and its sludge?? Learning objectives: to know about the fundamental processes in biogas production, and get an overview of biogas generation in the world Jam-Olof Drangert, Linköping university, Sweden

  2. Spying on Nature – What can we learn from cows? Inlet Outlet Biogas digester Cows convert biodegradable plants and water to milk, cow dung and urine – and gases Pedro Kraemer, BORDA, India

  3. A new look at the cow – and bull The Biogas Plant Outlet Biogas digester Inlet Pedro Kraemer, BORDA, India

  4. A biogas plant operates though anaerobic digestion of organic material The Biogas Plant Biogas Inlet Outlet Biogas digester Pedro Kraemer, BORDA, India

  5. Integrating biogas in agriculture Pedro Kraemer, BORDA, India

  6. Some examples of biogas plants Pedro Kraemer, BORDA, India

  7. Where is biogas technology applied? Approximate numbers of biogas units in selected countries: 99% of all systems do not use pumps, agitator, and heating Pedro Kraemer, BORDA, India

  8. Available human excreta in India compared to the need of fertiliser Excreta viewed as waste: N-P-K: X Y Z R … or as a resource Pedro Kraemer, BORDA, India

  9. Slurry application in agriculture Pedro Kraemer, BORDA, India

  10. Energy balance – for composting and digestion • Aerobic conversion (composting): • C6 H12 O6 + 6O2 6 CO2 +6 H2 O • E= -3,880 kJ/mol Anaerobic conversion (digestion): C6 H 12 O6 + 2H2 O  3 CO2 + 3CH4 + 2H 2O • E= - 405 kJ/mol • Burning of biogas: • 2CH4+ 6O2 CO2 + 6 H2 O • E = -3,475 kJ/mol Pedro Kraemer, BORDA, India

  11. Biogas appliances Pedro Kraemer, BORDA, India

  12. Bacterial mass Bacterial mass H2 , CO2, acetic acid Methan + CO2 Bacterial mass Propionic acid Butyric acid Alcohols, Other components H2 , CO2 acetic acid Biochemical process of anaerobic fermentation/digestion Step 1: Hydrolysis + Acidogenesis Step 2: Acetogenesis Step 3:Methanogenesis Organic waste Carbohydrates Fats Protein Water Fermentative bacteria Acetogenic bacteria Methanogenic bacteria Pedro Kraemer, BORDA, India

  13. What parameters affect anaerobic digestion? The most important determinants of good living conditions for anaerobic bacteria and therefore efficient gas production, are: • Temperature • Retention Time • pH-level • Carbon/Nitrogen ratio (C/N ratio) • Proportion of dry matter in substrate = suitable viscosity • Agitation (mixing) of the substrate If any one of these determinants is outside acceptable range, the digestion may be inhibited Pedro Kraemer, BORDA, India

  14. Substrate temperature in the digester Anaerobic fermentation can work in an ambient temperature between 3oC and 70oC and, if colder, the reactor has to be insulated and/or heated. Common temperature ranges for bacteria: • Psychrophillic bacteria below 20oC • Mesophillic bacteria 20 – 40oC • Thermophillic bacteria above 40oC Methane production is very sensitive to changes in temperature Pedro Kraemer, BORDA, India

  15. 30 20 10 50 100 150 Biogas production with continuous feeding Litres of biogas per litre of slurry Hydraulic retention time in days Pedro Kraemer, BORDA, India

  16. pH –value is crucial for a good result pH is a central parameter for controlling the anaerobic process • Optimal production when pH 7.0 – 7.2 • Inhibition (due to acids) if pH < 6.2 • Inhibition (due to ammonia) if pH > 7.6 • Deviation from the optimum range results in: • Lower gas yield • Inferior gas quality Pedro Kraemer, BORDA, India

  17. C/N ratio is important Microorganisms need N (nitrogen) and C (carbon) for their metabolism Methanogenic organisms prefer a C/N ratio of between 10:1 and 20:1 • N must not be too low, or else • shortage of nutrient Recommendation: Mix different substrates Pedro Kraemer, BORDA, India

  18. Nitrogen inhibition If N concentration is too high(>1,700 mg/l of NH4-N) and pH is high, then growth of bacteria is inhibiteddue to toxicity caused by high levels of (uncharged) ammonia Methanogens, however, are able of adapt to 5,000 - 7,000 mg/l of NH4-N given the pre-requisite that the uncharged ammonia (NH3 controlled by pH) level does not exceed 200-300 mg/l Pedro Kraemer, BORDA, India

  19. Changes in dry matter (DM) concentration inside the digester Pedro Kraemer, BORDA, India

  20. Behaviour of the substrate inside the digester Pedro Kraemer, BORDA, India

  21. Stirring the substrate Stirring improves the efficiency of digestion by: • Removing metabolites (gas removal) • Bringing fresh material in contact with bacteria • Reducing scum formation and sedimentation • Preventing temperature gradients in the digester • Avoiding the formation of blind spots (short cuts) However, excessive stirring disturbs the symbiotic relationship between the different bacteria species Simple biogas units normally do not have mechanical stirring devises Pedro Kraemer, BORDA, India

  22. Efficiency of a biogas unit Input: 1 kg of dry (95%) cattle dung will produce 2.5 kWh (rule of thumb) 1 kg dry (100%) matter can generate 2.5/0.95 = 2.63 kWh Slurry contains 10% dry matter, thus 1 litre can generate 0.263 kWh 1 litre slurry (27oC, 90 days retention) releases 27 litre biogas 1 m3 of biogas can generate 6 kWh (rule of thumb) So, 1 lit of slurry generates 0.027*6 = 0.162 kWh ActualkWh Potential kWh 0.162 0.262 = = 0.62 Efficiency = 62% efficiency and the other 38% energy remains in the slurry Pedro Kraemer, BORDA, India

  23. Check-list if gas production is lower than expected Check Response Add water and take pH after one hour Yes Is pH >7.5 ? No Add urine or ash (kg/m3) and wait 1 day Yes Is pH < 6.8 ? Try to insulate digester, less feed, heat substrate. Wait one day Temperature fallen? Yes No Add lime (acute action) and wait one day Yes Too much feed or of skewed composition? Drangert & Ejlertsson, Linkoping university, Sweden

  24. Principles for design and construction Continuous feeding orbatch feeding • Gas collector: • fixed dome, or • floating dome Further treatment or direct use Pedro Kraemer, BORDA, India

  25. Fixed-dome biogas digester 2 1 3 4 Bird´s eye view 4 1 2 slurry 3 Pedro Kraemer, BORDA, India

  26. Floating-drum unit with water-jacket Pedro Kraemer, BORDA, India

  27. Anaerobic filter(off-plotsystem) Pedro Kraemer, BORDA, India

  28. Off-plot system Anaerobic Baffled Reactor Anaerobic baffled reactor Pedro Kraemer, BORDA, India

  29. Public toilet with hidden treatment unit Pedro Kraemer, BORDA, India

  30. A public toilet with a biogas digester Jan-Olof Drangert, Linköping University, Sweden

  31. Faeces Urine Rainwater Organic waste System border Groundwater recharge Liquid urine Toilet units & showers Bio-digester Faeces biogas washwater Flush Ablution water Faeces Liquid urine Slurry Slurry compost Urine drying-bed Aerobic pond Soil conditioner Urine powder Liquid fertilizer Material flows in the toilet complex Jan-Olof Drangert, Linköping University, Sweden

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