1. Small-Scale Conversion of Biogas to Electricity
Dexter Lo, Shierlyn S. Paclijan, Peter Andres Gamones, Xavier University

2. Copy it, adapt it, use it – but acknowledge the source!
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Copy it, adapt it, use it – but acknowledge the source!
Copyright
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3. Contents
Concept
How it can optimize SSWM
Applicability
Advantages and Disadvantages
References

4. 1. Concept
Background
Biogas is a mixture of methane, carbon dioxide, water and hydrogen sulphide produced during the anerobic decomposition of organic matter.
Biogas is a combustible gas mixture produced during the anaerobic digestion of organic matter in a biogas reactor.
Composition:
Methane (65-70%)
Carbon dioxide (25-30%)
Varying quantities of water and hydrogen sulphide
Other compounds such as ammonia, hydrogen, nitrogen and carbon monoxide
(adapted from ASHDEN (2004), TILLEY et al. (2008))
Anaerobic Biogas Reactor Source: TILLEY et al. (2008)

5. 1. Concept
Background
Biogas energy may be derived from methane and other combustible gases. It is considered a renewable form of energy production.
The heating value correlates with the methane content. The methane in biogas is generally equivalent to Btu/ft3 and can be utilized directly as a heat source or to produce electricity (MDCSEO 2003).
Biogas must be dehumidified and purified before combustion; otherwise it can damage the gas engine.
In principle the chemical energy of the combustible gases is converted to mechanical energy in a controlled combustion system.
This mechanical energy then activates a generator to produce electrical power.
Gas turbines and internal combustion engines are the most common technologies used in this kind of energy conversion.

6. Cogeneration/ Combined Heat and Power (CHP)
1. Concept
Cogeneration/ Combined Heat and Power (CHP)
The most efficient way of using biogas is in a cogeneration process that simultaneously generate both electricity and useful heat.
Thermal power plants and heat engines, do not convert all of their thermal energy into electricity. In most heat engines, a bit more than 50% is lost as excess heat
By capturing the excess heat, CHP uses heat that would be wasted in a conventional power plant, potentially reaching an efficiency of up to 89%, compared with 55% for the best conventional plants (WRAPAI 2009).
The heat output can be reused to run the CHP to produce electricity again.
Byproduct heat at moderate temperatures ( °C) can also be used in absorption chillers for cooling (WRAPAI 2009).
Micro-Cogeneration: less than 5 kWe (WRAPAI 2009)
Mini-Cogeneration: more than 5 kWe and less than 500 kWe (WRAPAI 2009).

7. 1. Concept
Example
Micro CHP in the home. Source: P. Bance, Ceres Power

8. 1. Concept
Example
Combined Heat and Power (CHP) unit “micro size” in Germany. Source: GTZ Ecosan

9. 1. Concept Technologies Used
Various cogeneration technologies on household level are available.
Micro- and Mini-Cogeneration installations use five different technologies:
Microturbines
Internal combustion engines
Stirling engines
Closed cycle steam engines
Fuel cells
Micro-CHP based on Stirling engines is considered to be one of the most cost effective of the so called micro-generation technologies in abating carbon emissions.

10. 2. How it can optimize SSWM?
Small-Scale Conversion of Biogas to Electricity can help in optimizing your local water management and sanitation system and make it more sustainable by:
Providing an environmental friendly way of energy production by making use of the energy content of excreta
Having a positive impact on climate change. In fact, the contribution of a methane molecule (CH4) to the greenhouse effect is 21 times greater than that of a carbon dioxide molecule (SUSANA 2009). Therefore burning methane, even though producing CO2, reduces its impact on the environment.
Providing a source of income generation (if sold back to the grid)

11. 3. Applicability Micro Cogeneration Mini Cogeneration
This technology is easily adaptable and can be applied at household or community level. To minimize distribution losses, the reactors should be installed close to the CHP where the gas can be used.
Biogas cogeneration is also extensively used in rural China, Nepal, Vietnam and other nations where waste management and industry closely interface.
Micro Cogeneration
Useful for a single house or small business because of the low power output.
The electricity can be used within the home or business or, if permitted by the grid management, sold back into the electric power grid.
Mini Cogeneration
Installation is usually more than the micro cogeneration and supplies electricity for more than one household.
Mini-CHP has a large role to play in the field of carbon reduction in buildings where more than 14% of carbon can be saved by 2010 using CHP in buildings (WRAPAI 2009).

12. Combined Heat and Power (CHP)
4. Advantages and Disadvantages
Combined Heat and Power (CHP)
Advantages:
Generation of a renewable, valuable energy source
Low operating costs
Underground construction minimizes land use
Long life span
No/low electrical energy required
Positive impact on greenhouse gas emissions
Increases income by selling back electric energy to electric power grid
On site use of heat
Disadvantages:
Requires expert design and skilled construction
Gas production below 15°C, is no longer economically feasible
High capital costs
Expert maintenance required

13. 5. References
COELHO S. T., GONZALEZ VELASQUEZ S. M. S., MARTINS O. S., ABREU F. C. DE (2006): Biogas from Sewage Treatment used to Electric Energy Generation, by a 30 kW (ISO) Microturbine. Sao Paulo, Brazil: Brazilian Referenze Center on Biomass (CENBIO)
MDCSEO (2003): Minnesota’s Potential for Electricity Production Using Manure Biogas Resources. Minnesota, USA: Minnesota Department of Commerce State Energy Office (MDCSEO)
SCHALLER M. (2007): Biogas electricity production hits GWh a year in Europe. In: Engineer Live, p
SUSANA (2009): SuSanA fact sheet 09/2009. Links between sanitation, climate change and renewable energies. Sustainable Sanitation Alliance (SuSanA)
TILLEY, E., LÜTHI, C., MOREL, A., ZURBRÜGG, C., SCHERTENLEIB, R. (2008): Compendium of Sanitation Systems and Technologies. Switzerland: Swiss Federal Institute of Aquatic Science (EAWAG) & Water Supply and Sanitation Collaborative Council (WSSCC)
WRAPAI (2009): Document 8, Data Management Document, Appendix S 06 - Energy Research. Australia: Waste Refinery Australia Project Association Incorporated (WRAPAI)

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