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

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

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

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

Integrating biogas in agriculture Pedro Kraemer, BORDA, India

Some examples of biogas plants Pedro Kraemer, BORDA, India

Where is biogas technology applied? Approximate numbers of biogas units in selected countries: Country No of units Volume >100 m3 China 12,000,000 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 DK, NL, S, Thailand, 99% of all systems do not use pumps, agitator, and heating Pedro Kraemer, BORDA, India 7

Available human excreta in India compared to the need of fertiliser Excreta viewed as waste: Faeces 250,000 tons/day Urine 1,000,000 m3/day Dry org. matter (DS) 90,000 t/day Nitrogen (N) 15,000 t/day Phosphorus (P2O5) 5,000 t/day Potassium (K2O) 3,000 t/day Carbon (C) 35,000 t/day Calcium (CaO) Potential biogas 50 mil m3 day N-P-K: X Y Z R … or as a resource Pedro Kraemer, BORDA, India

Slurry application in agriculture Pedro Kraemer, BORDA, India

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

Biogas appliances Pedro Kraemer, BORDA, India

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

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

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

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

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

Methanogenic organisms prefer a 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

Nitrogen inhibition If N concentration is too high (>1,700 mg/l of NH4-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 - 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

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

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

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

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 Actual kWh Potential kWh 0.162 0.262 Efficiency = = = 0.62 62% efficiency and the other 38% energy remains in the slurry Pedro Kraemer, BORDA, India

if gas production is lower than expected 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

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

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

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

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

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

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

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

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