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

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Presentation on theme: "4.4 Biogas – a way to solve sanitation problems How much biogas can be produced from excreta and biomass? How safe is the process and its sludge?? Learning."— Presentation transcript:

1 4.4 Biogas – a way to solve sanitation problems 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 Anaerobic fermentation is a natural and unavoidable process 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 Inlet Outlet Biogas digester The Biogas Plant Pedro Kraemer, BORDA, India

4 A biogas plant operates though anaerobic digestion of organic material The Biogas Plant Inlet Outlet Biogas digester Biogas 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: CountryNo of units Volume >100 m 3 China12,000,000 x0 India (in 2004) 3,600,000 ? Nepal (in 2007) 200,000 ? Vietnam, Thailand, Tanzania, Bangladesh, Burundi, Brazil x,000 3,400 (2006) in Germany Kenya, Mexico, Cuba, Guyana x00 ? Morocco, Ghana, Zimbabwe, Nicaragua, Jamaica, Bolivia x0 DK, NL, S, Thailand, 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 Dry org. matter (DS)90,000 t/day Nitrogen (N)15,000 t/day Phosphorus (P 2 O 5 )5,000 t/day Potassium (K 2 O)3,000 t/day Carbon (C)35,000 t/day Calcium (CaO)5,000 t/day Potential biogas50 mil m 3 day … or as a resource Excreta viewed as waste: Faeces 250,000 tons/day Urine1,000,000 m 3 /day N-P-K: X Y Z R Pedro Kraemer, BORDA, India

9 Slurry application in agriculture Pedro Kraemer, BORDA, India

10 Energy balance – for composting and digestion Aerobic conversion ( composting ): C 6 H 12 O 6 + 6O 2 6 CO 2 +6 H 2 O E= -3,880 kJ/mol Anaerobic conversion ( digestion ): C 6 H 12 O 6 + 2H 2 O 3 CO 2 + 3CH 4 + 2H 2 O E= kJ/mol Burning of biogas: 2CH 4 + 6O 2 CO H 2 O E = -3,475 kJ/mol Pedro Kraemer, BORDA, India

11 Biogas appliances Pedro Kraemer, BORDA, India

12 Biochemical process of anaerobic fermentation/digestion Acetogenic bacteria Fermentative bacteria Methanogenic bacteria Organic waste Carbohydrates Fats Protein Water Bacterial mass H 2, CO 2 acetic acid Bacterial mass Methan + CO 2 Bacterial mass Propionic acid Butyric acid Alcohols, Other components H 2, CO 2, acetic acid Step 1 : Hydrolysis + Acidogenesis Step 2 : Acetogenesis Step 3 : Methanogenesis 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 Common temperature ranges for bacteria: Psychrophillic bacteriabelow 20 o C Mesophillic bacteria20 – 40 o C Thermophillic bacteriaabove 40 o C Anaerobic fermentation can work in an ambient temperature between 3 o C and 70 o C and, if colder, the reactor has to be insulated and/or heated. Methane production is very sensitive to changes in temperature Pedro Kraemer, BORDA, India

15 Biogas production with continuous feeding Hydraulic retention time in days Litres of biogas per litre of slurry Pedro Kraemer, BORDA, India

16 pH –value is crucial for a good result Optimal production when pH 7.0 – 7.2 Inhibition (due to acids) if pH < 6.2 Inhibition (due to ammonia) if pH > 7.6 pH is a central parameter for controlling the anaerobic process 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 Recommendation: Mix different substrates N must not be too low, or else shortage of nutrient Pedro Kraemer, BORDA, India

18 Nitrogen inhibition If N concentration is too high ( >1,700 mg/l of NH 4 -N ) and pH is high, then growth of bacteria is inhibited due to toxicity caused by high levels of (uncharged) ammonia Methanogens, however, are able of adapt to 5, ,000 mg/l of NH 4 -N given the pre-requisite that the uncharged ammonia (NH 3 controlled by pH) level does not exceed 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 kWh 1 litre slurry (27 o C, 90 days retention) releases 27 litre biogas 1 m 3 of biogas can generate 6 kWh (rule of thumb) So, 1 lit of slurry generates 0.027*6 = kWh Actual kWh Potential kWh Efficiency = = = % 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 Is pH >7.5 ? Yes Add water and take pH after one hour No Too much feed or of skewed composition? Temperature fallen? Yes Try to insulate digester, less feed, heat substrate. Wait one day Add lime (acute action) and wait one day No Is pH < 6.8 ? Add urine or ash (kg/m 3 ) and wait 1 day Yes Drangert & Ejlertsson, Linkoping university, Sweden

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

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


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

28 Anaerobic filter (off-plot system) Pedro Kraemer, BORDA, India

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

30 Public toilet with hidden treatment unit

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

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

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