anaerobic digestion (small-scale)

Anaerobic Digestion (Small-scale)

Anaerobic Digestion (Small-acale)

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Dorothee Spuhler, seecon gmbh


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Contents

1. Concept2. How can it optimise SSWM3. Design principals4. Treatment efficiency5. Operation and maintenance6. Applicability7. Advantages and disadvantages8. References



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BackgroundSmall-scale anaerobic biogas reactors are very common in agricultural regions in industrialised as well as developing countries.Because this plants not only allow the treatment of wastes (manure, green waste, toilet products) but also result in the on-site production of a renewable energy source, such plants have been widely disseminated by many rural developing programmes in the past 30 years.In Nepal for instance more than 200’000 such plants have been constructed in the past 20 years.The main features of small-scale anaerobic biogas reactors are:

•Requires animal dung (rich in organic matter and high productions yields) to produced sufficient energy for the household

•Can co-treat toilet products and kitchen or garden waste (green waste)•Depend on relatively high daily mean temperature as anaerobic

digestion, the process which produces biogas slows down drastically with decreasing temperatures.

1. Concept



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Background1. Concept

Toilet, Kitchen and Garden Waste

+ Manure

Adapted from: http://www.seco.cpa.state.tx.us/energy-sources/biomass/images/manure-biogas.gif [Accessed: 30.05.2010]

On-site recycling of nutrients and energy



… Airtight reactors, typically designed to produce biogas at the household or community level.Biogas gas is produced by the conversion of green waste by a process called anaerobic digestion.During anaerobic digestion, microorganism transform organic matter contained in the wastes into biogas The produced biogas can be used either directly for coocking, heating or lightening or be transformed into combined heat and power (CHP) in small cogeneration plants.With time the reactors fill up and digested sludge (sludge which organic fraction was already converted to biogas) accumulates in the bottom.Nutrients remain in the sludge, which is a well-balanced soil amendment.Toilets can be linked to the reactors and co-digested with the animal dung, but biogas production from human manure is only low and therefore animal dung and green wastes are required to cover a familiy’s needs.

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What are Small-Scale Anaerobic Digesters?1. Concept



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1. Concept

Cattle Dung / Manure

Toilet Products (Excreta, Faeces)Kitchen /

Garden Organic Waste

(Green Waste)

Coocking

Lightning

Fertiliser

Electricity

Fuel

Biogas

What are Small-Scale Anaerobic Digesters?

Heating

D. Spuhler (2010), Adapted from: www.kristianstad.se/; http://www.newseedadvisors.com/2009/09/10/invest/; http://www.hydroharrys.com/hydroharrys_about_fertilizer.php and www.clker.com [Accessed: 02.06.2010]

“The Ecocylce of biogas”



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Possible Benefits for Users:Under the right conditions a biogas plant yields several benefits to end-users

• Social:◦ Improved sanitation: reduction of pathogens, worm eggs and flies◦ Reduction of workload: less firewood collection, better cooking

performance◦ Improved indoor air quality: less smoke and harmful particle emission

of biogas stove compared to wood or dung fuels;• Environmental

◦ Production of green energy◦ Reduction of greenhouse gas emission◦ Organic fertilizer production

• Economical:◦ Better Health more work capacity◦ Fertilizer, better crop yields, better Health◦ Fuel substitution

1. Concept



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Possible Benefits for Users: Reduced indoor pollution1. Concept

Coocking with fuelwood Biogas stove

Source: M. WAFLER Source: M. WAFLER



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What is Anaerobic Digeastion ? (1/3)Degradation of organic material by bacteria. In the absence of air (anaerobic). Four stages:•Hydrolisis

◦ Cleavage of a chemical compound through the reaction with water.◦ Insoluble complex molecules are bracken down to short sugars, fatty acids and

amino acids.•Fermentation (Acidogenesis)

◦ Products from hydrolysis are transformed into organic acids, alcohols, carbon dioxide (CO2), hydrogen (H) and ammonia (NH3).

•Acetogenesis◦ Organic acids and alcohols are converted into hydrogen (H2), carbon dioxide

(CO2) and acetic acid (CH3COOH). Therefore, oxygen is consumed and anaerobic conditions are created

•Methanogenesis◦ Methanogenic bacteria (methanogenesis), transform the acetic acid, carbon

dioxide and hydrogen into biogas.

1. Concept



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What is Anaerobic Digestion ? (2/3)1. Concept

D. SPUHLER (2010)



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1. ConceptWhat is Anaerobic Digestion ? (3/3)

Source: http://water.me.vccs.edu/courses/ENV149/changes/Feat11_picII-1.jpg [Accessed: 02.06.2010]



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What is Biogas ?

Biogas is a mixture of methane and carbon dioxide.The properties of biogas are similar to the ones of natural gas.Biogas is the common name for the mixture of gases released from anaerobic digestion.Typically biogas is composed of:

Methane is the valuable part of the biogas. Biogas that contains about 60 to 70 % of CH4 has a calorific value of about 6 kWh/m3 what corresponds to about half an L of diesel oil. (ISAT/GTZ 1999, Vol. I)

1. Concept

Sources: YADAV & HESSE (1981); FAO (1996); PIPOLI (2005); GTZ (2009

Methane (CH4) 50 to 75 %Carbon Dioxide (CO2) 25 to 50 %Hydrogen (H) 5 to 10 %Nitrogen (N2) 1 to 2 %Hydrogen sulphide (H2S) Traces

Source: MUENCH (2008)



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Examples:Small-scale Biogas plants

1. Concept

Biogas plant for cow dung, Padli village (India)

Source: M. WRIGHT, Ashden Awards





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Examples: Small-scale Biogas Plants1. Concept

Biogas lamp



Adding greywater to the biogas reactor to

optimise moisture conditionss



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Examples Small-scale Biogas Plants1. Concept

The“Mudbooste

r”PlantSource: UNKNOWN



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Examples Small-scale Biogas Plants1. Concept

Source: C. RIECK (2009)

The manhole is filled with water to keep the clay sealing wet and gas

tight. Gas leackage would be indicated by bubbles.

Source: C. RIECK (2009)

Wet clay is used to fit the concrete lid of the manhole gas-tight.

Source: SuSanA

Biogas outlet and manhole with remouvable cover from a

underground biogas plant Installed by the NGO TED in Maseru, Lesotho

(Susana)



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2. How it can optimize SSWM

D. SPUHLER (2010), adapted from: http://www.terranet.or.id/mitra/dewats/photo/masukan1256.jpg; http://www.borda-sea.org/modules/cjaycontent/index.php?id=6; http://whrefresh.com/wp-content/uploads/2010/01/potato_field.jpg; http://www.greenspec.co.uk/images/energy/CHP/chp2.gif]; http://peda.gov.in/eng/images/rural-biogas-plant_179.jpg; [Accessed: 30.05.2010], BPO (2006) and BUNNY (n.y.)

Biogas plants transform traditional manure

management; reducing CH4 and CO2 emission

Biogas substitutes

conventional energy sources,

reducing reliance on fossil fuel and

firewood (CO2)

Digested sludge can substitute chemical fertiliser

Biogas plants can contribute to sustainable

sanitation



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Examples: Biogas Appliances

1. Concept

Chang Mai

K.P. Pravinjith

M. Wafler

Biogas generator Biogas rice cooker

Biogas boiler

Biogas lampsBiogas cooking stoves

PBO (2006)

Krämer (TBW)

Source: UNKNOWN



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Basics: Process Parameters

Anaerobic digestion = Biological system of bacteriaOptimal conditions required that bacteria feel wealthy…•Temperature

◦ Performance◦ Retention time

•pH: Wide range,but methanogenesis requires neutrality (6.5-7.5). (MES et al. 2003)

•Total solid (TS)◦ Solids for digestion (organics) - Liquid for fluidity of slurry.◦ Optimal TScontent: 5 to 10%. (SASSE 1988; NIJAGUNA 2002)

•COD: Chemical oxygen demand: Methane production potential

3. Design Principals



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Basics: Daily manure yield for different cattle3. Design Principals

Sources: OEKOTOP; WERNER et al. (1998)



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Basics: Gas yields for different feedstocks3. Design Principals

Sources: OEKOTOP; WERNER et al. (1998)



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Basics: Biogas Guideline data3. Design Principals

Adapted from WERNER et al. (1998); ISAT/GTZ (1999), Vol. I; MANG (2005)

Suitable digesting temperature

20 to 35 °C

Retention time 40 to 100 daysBiogas energy 6kWh/m3 = 0.61 L diesel fuelBiogas generation 0.3 – 0.5 m3 gas/m3 digester

volume per day

Human yields 0.02 m3/person per dayCow yields 0.4 m3/Kg dungGas requirement for cooking

0.3 to 0.9 m3/person per day

Gas requirement for one lamp

0.1 to 0.15m3/h



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Types of Digester: Bag or Rubber Balloon Biogas Plants (1/2)


Batch mode: emptying once every few yearsPlug-flow reactor: the slurry moves through continuously much like a train a tunnel

Huge common plastic bag (e.g. PVC): sludge settles on the bottom and biogas is collected in the top. Gas is transported by the pressure from the elasticity of the balloon (can be enhanced by placing weights on the balloon).

• Most simple design, easy and low-cost ( if material locally available)

• Temperature enhanced when exposed to sun• Simple to clean but lifespan generally limitedPlastic

bag

Layer of compacted backfill

To reuse or further

treatment (e.g. drying

bed)

Source: adapted from FAO (1996)

Gas pipe

Inlet

Leveled surface

Biogas accumulates in the top of the bag



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Types of Digester: Bag or Rubber Balloon Biogas Plants (2/2)


Source: http://www.habmigern2003.info/biogas/Baron-digester/Baron-digester.htm [Accessed: 02.06.2010]

Underground plug-flow reactor bag biogas plant () and balloon biogas collection

chamber (). (Philippines, Garry Baron)



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Types of Digester: Fixed-dome Biogas Plants (1/3)Airtight underground reactor out of concrete or brick work (most often round), with a fixed (also airtight) dome in which gas is collected. Gas pressure is absorbed by the slurry which is displaced into a compensation tank.

• Most widely disseminated• Long life-spam• Underground: safes space and protect from temperature changes• Construction must be supervised




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Types of Digester: Fixed-dome Biogas Plants (2/3)3. Design Principals

Removable cover

Overflow tank /

compensation chamber

Seal

Slurry

Biogas accumulates in the dome

Biogas collection

Inlet

Source: adapted from http://peda.gov.in/eng/images/rural-biogas-plant_179.jpg [Accessed: 02.06.2010]

Fixed-dome



Source: K.P. PRAVVIJITH Source: K.P. PRAVVIJITH

Source: K.P. PRAVVIJITH Source: K.P. PRAVVIJITH

Types of Digester: Fixed-dome Biogas Plants (3/4)3. Design Principals



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Plastic dome 3. Design Principals

Any pit can be filled with organic waste and

covered airtight with a plastic sheet in order to

collect biogas

Source: ISAT/GTZ (1999, Vol. I)



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Floating-drum Biogas Plants3. Design Principals Floating-

drum

Biogas

Slurry

Inlet Outl

et

Floating-drum plants consist of an underground digester and a moving gasholder (mostly of made out of steel).The gasholder floats either directly on the fermentation slurry or in a water jacket of its own. The gas is collected in the gas drum, which rises or moves down, according to the amount of gas stored. The gas drum is prevented from tilting by a guiding frame.

• Easy to and to control operation• Material costs are high• High risk of corrosion and

rusting (short lifespam).



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Floating-drum Biogas Plants3. Design Principals

MUELLER (2007)

MUELLER (2007)

Open gasholder

Different design of floating drum plants

Floating drum plant with inlet from the the NGO BIOTECH (India)



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Toilet linked Biogas Reactors

Co-digestion of toilet products (nightsoil or blackwater) is a sustainable solutions for

•Hygienically safe on-site treatment of toilet excreta

•Production of fertiliser

•Production of renewable energy

The mixing of animal dung with blackwater increases its fluidity and results in optimal moisture conditions for the anaerobic digestion.

Human manure has a lower content in organic matter and thus a limited biogas yield.




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Toilet linked Biogas Reactors3. Design Principals

Source: ???



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Collection and

expansions chamber

Gas outlet pipe

Pour-flush toilet

Link of toilet

Inlet for animal waste

Baffle to mix influent with tank contents

Removable cover

annual desludging

Biogas

reactor

Toilet linked Biogas Reactors

Source: adapted from WELL (n.a.)



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Toilet linked Biogas Reactors3. Design Principals

Source: M. WAFLER

Sludge drying bedExpansions chamber

Biogas reactor

Pour-flush toilet

Manure and green waste

mixing chamber

http://www.ashdenawards.org/files/imagecache/large/files/images/biogasnepal05a.jpg [Accessed: 02.06.2010]



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Health aspectsAnaerobic digested sludge are generally pathogen free. Pathogen removal depends temperature and retention time. Generally , at more than 55°C pathogens are killed after a few days. At normal temperatures (mesophilic digestion), longer time is required.

4. Treatment Efficiency

Source: SASSE (1988)

Source: WERNER et al. (1998)

In reality, fresh sludge is always mixed with new sludge and it is very difficult to control retention times. Therefore, caution needs to be taken when emptying and handling sludge manually.



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NutrientsAnaerobic digestion only removes organics, and the main mineral material and almost all nutrients remain in the bottom sludge.

• Phosphorus: almost 100 % • Nitrogen (ammonium): and 50 to 70 % (JOENSSEN et al. 2004)

Biogas Slurry = Fertiliser

Further treaments to increase the safety (pathogen removal)• Composting• Drying beds / Humification

4. Treatment Efficiency

Biogas slurry=Fertilisers



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Start-up

Seeding with living sludge form other anaerobic reactor required. The establishment of the complex biological conditions for anaerobic digestion and biogas production may takes some weeks to months.

5. Operation and Maintenance (O&M)

Operation

No skilled operator is required but households should be trained to understand the system.Regular maintenance includes

•Checking for foaming or scum formation•Checking for air/gas- tightness•Checking for rusting (e.g. floating-drum reactor)



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Small-scale biogas digesters can transform almost any biodegradable waste into biogas.

Household or community scale.

Most often used for biogas production in rural areas from animal dung.

Green wastes (kitchen, garden, etc.) can be added.

If toilets are linked: safe and sustainable sanitation solution.

Underground construction provided: can also be constructed in urban areas.

As anaerobic digestion is limited to moderate to high temperature, only in areas where temperature does not fall short of for any substantial length of time.

6. Applicability



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7. Pros’ and Cons’

Advantages:• Low-cost• Generation of biogas and

fertilizer• Combined treatment of

animal, human and solid organic waste

• Low operation and maintenance

• Underground construction (low space requirement and high acceptance)

• Low risk of odours• Resistance against shock

loads• Long life span if maintained

and operated correctly• Reduces the amount of wood

fuel and improves indoor air quality

Disvantages:• Experts are required for the

design of the reactor and skilled labour is required for the construction of a gastight tank

• Substrates need to contain high amounts of organic matter for biogas production

• Slurry may has to be further treated before reuse (e.g. composting)

• Below temperatures of 15°C, biogas production is economically not interesting (heating required)

• Requires seeding (start-up can be long due to the low growth yield of anaerobic bacteria)



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Thank you for your attention!

Source: ???



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8. ReferencesBPO (2006): Support Project to the Biogas Programme for the Animal Husbandry Sector in some Provinces of Vietnam. BP I Final report. Hanoi: Biogas Project Office (BPO) HanoiBUNNY, H., BESSELINK, I. (n.y.): The National Biodigester Programme in Cambodia. In Relation to the Clean Development Mechanism. National Biogidgester PRobramme and NV Netherlands Development Organisation FAO (1996): Biogas Technology - A Training Manual for Extension. Consolidated Management Services Nepal (P) Ltd. and Food and Agriculture Organization of the United Nations (FAO) Available at: http://www.fao.org/docrep/008/ae897e/ae897e00.HTM [Accessed: 19.04.2010]GTZ (2009): Biogas sanitation for black water or brown water, or excreta treatment and reuse in developing countries. Draft Version.(=Technology review). Eschborn: German Agency for Technical Cooperation GmbH (GTZ) and Sustainable Sanitation Alliance (SuSanA) Available at: http://www.gtz.de/en/themen/umwelt-infrastruktur/wasser/9397.htm [Accessed: 11.03.2010]ISAT/GTZ (1999): Biogas Basics. (=Biogas Digest, Volume I). Information and Advisory Services on Appropriate Technology (ISAT) and German Agency for Technical Cooperation GmbH (GTZ). Available at: http://www2.gtz.de/dokumente/bib/04-5364.pdf [Accessed: 19.04.2010]JOENSSON, H., RICHERT A., VINNERAAS, B., SALOMON, E. (2004): Guidelines on the Use of Urine and Faeces in Crop Production. (= EcoSanRes Publication Series, Report No. 2004-2). Stockholm: Stockholm Environment Institute (SEI)MANG, H.-P., (2005): Biogas Sanitation Systems. (=Ecological sanitation course, Norway, 15.-20. August 2005). Beijing: Chinese Academy of Agricultural EngineeringMES, T.Z.D. de, STAMS, A.J.M, REITH, J.H., ZEEMAN, G. (2003): Chapter 4. Methane production by anaerobic digestion of wastewater and solid wastes. In: REITH, J.H., WIJFFELS, R.H., BARTEN, H.(Eds.) (2003): Biomethane and Biohydrogen. Status and perspectives of biological methane and hydrogen production. Dutch Biological Hydrogen Foundation and the Netherlands Agency for Energy and the Environment (Novem). Available at: http://gasunie.eldoc.ub.rug.nl/FILES/root/2003/3339875/3339875.pdf [Accessed: 25.04.2010]MUELLER, C. (2007): Anaerobic Digestion of Biodegradable Solid Waste in Low- and Middle-Income Countries. Swiss Federal Institute of Aquatic Science (EAWAG), Department of Water and Sanitation in Developing Countries (SANDEC) http://www.eawag.ch/organisation/abteilungen/sandec/publikationen/publications_swm/downloads_swm/Anaerobic_Digestion_high_resolution.pdf [Accessed: 27.04.2010]MUENCH, E. (2008): Overview of anaerobic treatment options for sustainable sanitation systems. In: BGR Symposium „Coupling Sustainable Sanitation and Groundwater Protection“ 14 – 17 Oct 2008, Hannover, Germany. Eschborn: German Agency for Technical Cooperation (GTZ) GmbH Available at: http://www.gtz.de/en/dokumente/en-bgr-conference-biogas-ecosan-muench-2008.pdf [Accessed: 23.04.2010]NIJAGUNA, B. T. (2002): Biogas Technology. New Delhi: New Age International (P) Ltd.PIPOLI, T. (2005): Feasibility of Biomass-based Fuel Cells for Manned Space Exploration. In: Proceedings of the Seventh Eurpean Space Power Conference, Stresa, Italy. 9 to 13 May 2005. SASSE, L. (1988): Biogas Plants. German Appropriate Technology Exchange (GATE) and German Agency for Technical Cooperation (GTZ) GmbH Available at: http://www.borda-net.org/modules/wfdownloads/viewcat.php?cid=5 [Accessed: 25.04.2010] WELL (n.y.): Using Human Waste. (=WELL Technical Briefs, No. 63) Loughborough: Water and Environmental health at London and Loughborough (WELL) Available at: http://www.lboro.ac.uk/well/resources/technical-briefs/technical-briefs.htm [Accessed: 26.04.2010]WERNER, U. STOEHR, U., HEES, N. (1998): Biogas Plants in Animal Husbandry. German Appropriate Technology Exchange (GATE) and German Agency for Technical Cooperation (GTZ) GmbH Available at: http://www.scribd.com/doc/27434211/Biogas-Plant-in-Animal-Husbandry [Accessed: 25.04.2010]YADAVA, L. S., HESSE, P. R. (1981): The Development and Use of Biogas Technology in Rural Areas of Asia (A Status Report 1981). Improving Soil Fertility through Organic Recycling. (=Project Field Document No. 10.). Food and Agriculture Organization (FAO) and United Nations Development Programme (UNEP)

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