ANAEROBIC DIGESTION
Break the ice
Sergi Astals & Joan Mata
EPROBIO - Foggia - June 2011
BA
DEPARTAMENT D’ENGINYERIA QUÍMICA
GRUP DE RECERCA EN
BIOTECNOLOGIA AMBIENTAL
IT
XARXA DE CENTRES
DE SUPORT A LA
INNOVACIÓ TECNOLÒGICA
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INDEX OF CONTENTS
What is anaerobic digestion?
Anaerobic digestion advantages
Which waste can be digested?
What is biogas?
Biogas as a renewable source of energy
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What come to your mind when you listen anaerobic digestion?
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What is anaerobic digestion?
• AD is a biological technology which, in the absence of oxygen,
decomposes organic matter.
• The breakdown of the biodegradable organic matter produce stable
organic residues and biogas (a mixture of methane (CH4) and carbon
dioxide (CO2)).
• Anaerobic conditions requires the absence of oxidizers compounds*:
- Oxygen (O2)
- Nitrate (NO3-) and nitrite (NO2-)
- Sulphates (SO42-)
* Substances that have the ability to oxidize other substances. They gain electrons, they are reduced, so other
compounds have to loss it (oxidized).
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What is anaerobic digestion?
• AD take place in the nature where organic matter is present and the
oxygen concentration is negligible:
- Stomachs of ruminants
- Sediments of lakes
- Landfills
- Sewers
-…
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Anaerobic digestion advantages
• The main advantages of the AD technology are:
- Stabilize organic matter
- Feasible for a wide variety of waste and flow rates
- Reduce greenhouse gases emission Æ global warming
- Low sludge production
- Positive energy balance
· Energy from biogas
· Low operational cost
- No or very little use of chemicals
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Which wastes can be anaerobically digested?
• AD has long been used to stabilize organic wastes before its final
disposal.
• Today, AD is a consolidated technology used to stabilize:
- Sewage sludge from wastewater treatment plants
- Municipal solid wastes (MSW)
- Industrial wastewaters
- Agricultural wastes
- animal manure
- crops waste
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What industrial wastewaters are anaerobically digested?
• AD is used as an end of pipe treatment for:
Agro-food industry: Sugar, potato, starch, fruit, vegetables, dairy, bakery
Beverage: Beer, soft drinks, wine, fruit juices, coffee
Pulp and paper industry: mechanical pulp, straw, bagasse
Others: pharmaceutical, chemical, municipal sewage, landfill leachate
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What is biogas?
Biogas is a methane rich flammable gas that results from the
decomposition of organic waste materials.
Which gases can be found in biogas:
> Mayor compounds:
- Methane (CH4) [60 – 70 %]
- Carbon dioxide (CO2) [40 – 30%]
> Minor compounds:
- Hydrogen sulphide (H2S) > odour problems
- Ammonia (NH3)
> odour problems
- Hydrogen (H2)
-…
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Biogas energy value
• Biogas can be used in a combustion heat and power unit (CHP) to
produce electricity and another form of energy (steam or hot water).
> Methane lower heating value is 35,800 KJ/m3
> Natural gas* heating value is 37,300 KJ/m3
Biogas lower heating value range from 21,300 to
23,400 KJ/m3 as function of the % CH4
An estimation of the lower heating value of
biogas can be done by:
Biogas heating value (kJ/m 3 ) =
35,800
⋅100
% CH 4
* Natural gas is a mixture of methane, propane and butane.
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Biogas energy value
Exercise a:
How much water can be heat to 80 ºC with 1 m3 of
biogas?
Exercise b:
How much water can be boil with 1 m3 of biogas?
Exercise c:
How much water can be boil with 1 m3 of biogas is
the burner efficiency is 0.75?
Data of water:
Initial temperature = 25 ºC
Latent heat vaporization (λ)= 2,260 KJ/m3
Heat capacity (C) = 4.18 KJ/(Kg · ºC)
Biogas lower heating value = 22,400 KJ/m3
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Biogas energy value
Exercise a:
⎛ KJ ⎞
⎟⎟ ⋅ (100 − 20 º C ) ⋅ X(kg ) = 22,400 KJ
4.18⎜⎜
⋅
Kg
º
C
⎝
⎠
X = 66.99 Kg
Exercise b:
⎛ KJ ⎞
⎛ KJ ⎞
⎟⎟ ⋅ (100 − 20 º C ) ⋅ X(kg ) + 2260⎜⎜
⎟⎟ ⋅ X(Kg ) = 22,400 KJ
4.18⎜⎜
Kg
⋅
º
C
Kg
⎠
⎝
⎝
⎠
X = 8.64 Kg
Exercise c:
⎛ KJ ⎞
⎛ KJ ⎞
⎟⎟ ⋅ (100 − 20 º C ) ⋅ X(kg ) + 2260⎜⎜
⎟⎟ ⋅ X(Kg ) = 22,400 KJ ⋅ 0.75
4.18⎜⎜
⋅
Kg
º
C
Kg
⎝
⎠
⎝
⎠
X = 6.48 Kg
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Energy conversion factors
1 KWh = 3600 KJ
1 KJ
= 2.34 · 10-11 ktep*
1 KWh
= 0.84·10-7 ktep
* tep: tonne of oil equivalent (the amount of energy released by burning one tonne of crude oil)
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Biogas uses
Biogas, as a renewable source of energy, is becoming more
important as petrol cost continue to rise.
Even some AD plant still burn the biogas in flares, digester gases are
used as fuel for:
- Heating anaerobic digesters and plant buildings
- To operate cogeneration unit
- To operate blowers, pumps,…
Household and/or communities
AD can use biogas for:
- heat water
- cook
EurObserv’ER 2002
- light
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Biogas as renewable source of energy
Energy crisis of 1970s and 2000s promoted the development of the AD.
While the interest for the environment protection, mainly the depuration of the
surface water is increasing.
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EurObserv’ER 2008
Landfill gas
Urban sewage and industrial
effluents
Agricultural waste, MSW,
OFMSW, co-digestion plants
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EurObserv’ER 2008 and 2010
Landfill gas
Urban sewage and industrial
effluents
Agricultural waste, MSW,
OFMSW, co-digestion plants
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EurObserv’ER 2010
9 The biogas sector has never before aroused so much attention as it does today.
9 Interest has been fired by the introduction of regulatory directives
- Council Directive 1999/31/EC of 26 April 1999on the landfill of waste
- Council Directive 2008/98/EC on waste
- Council Directive 2009/28/EC of 23 April 2009 on the promotion of the use of
energy from renewable sources
9 Biogas is mainly produced form waste treatment. However, energy crops are growing
9 Biogas production has been stimulated to farm holders to reduce their energy
dependency and diversify their incomes.
9 Countries want to reduce their dependency on natural gas, purify biogas to obtain
“biomethane” which can be injected in the natural gas grid
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Biogas price
Country
Spain
Germany
Austria
France
Installed Power (kW)
€ / kWh
Bonus
< 500
0,140
> 500
0,100
< 150
0,117
plus 0.07€/kWh using energy crops
150 - 500
0,092
plus 0.01€/kWh if a 30% of manure is used
500-5000
0,083
plus 0.03€/kWh for CHP unit
5000-2000
0,078
< 100
0,165
100 - 500
0,145
500 - 1000
0,125
> 1000
0,103
< 150
0,093
> 2000
0,078
minus 25% for co-digestion
plus 0,02 for methanisation
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