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TRANSCRIPT
Gas Collection Strategies for Bioreactor Landfills:Issues for Developed and Developing Countries
Timothy G. Townsend, PhD, PEProfessor
Department of Environmental Engineering SciencesUniversity of Florida
Bioreactor Landfill WorkshopUS EPA National Risk Management Laboratory and World Bank
November 13, 2007
0 10 20 30 40Time (Years)
Gas
Vol
ume
Bioreactor Landfill
Traditional Landfill
Yard Trash from 20‐yr Waste
Gas Collection from Bioreactor Landfills
• Current status of gas management– Developed nations
– Developing nations
• Concerns with gas collection at wet landfills
• Bioreactor landfill gas collection strategies
• Landfill gas capture in developing countries
Landfill gas capture and energy production as part of green energy program
Landfill Gas Management in Developed Countries
• Landfills are designed, constructed and operated to protect environment from leachate
• Depending on size of landfill, at some point landfill will be required to capture and treat landfill gas
Installation of Vertical Gas Wells
Typical Landfill Gas Well (active system)
Waste
Cap
Gas Extraction Pipe
GravelPack
PerforatedPipe
WellHea
d
Geomembrane Cap
Boot
Wellhead
Control ValveFlow
MeasurementDevice
Newly ConstructedLandfill Gas Well
Horizontal Wells
It is very common to use horizontal gas wells in some locations
At some landfills, you wait until the facility reaches grade and theninstall gas collection wells. At others, you continually build and expandthe gas collection network.
The landfill may have a complex system of collection pipes by the completion of the project.
Collection ManifoldCentrifugal Blowers
A vacuum is applied to the manifold system to extract gas from the landfill.
The landfill gas field has to beregularly “tuned” to make surethe appropriate amount ofvacuum is applied.
EnclosedFlare
CandlestickFlare
At a minimum, the gas is flared.
Management of Condensate is a Major Design Issues
CondensateKnock‐out
Gas Engine for Electricity Generation
Gas Turbine for Electricity Generation
Landfill Gas Used for Heating Leachate
Landfill Gas for Leachate Evaporation
Gas well in Costa Rica
Fuente: Hernández Barrios, Claudia P.; Wehenpohl, Gunther. Manual para la rehabilitación, clausura y saneamiento de tiraderos a cielo abierto en el Estado de México. México, D.F., Secretaria de Ecología, 2000. Fotografía: G. Wehenpohl.
Gas Collection at Bioreactor Landfills‐ Gas is produced more rapidly‐ How do you collect it?
0 10 20 30 40Time (Years)
Gas
Vol
ume
Bioreactor Landfill
Traditional Landfill
Issues with Gas Collection at Bioreactor Landfills
• If gas is produced more rapidly, then systems must be in place to collect it.
• Design issues:– Larger pipes, more capacity– More “condensate” to manage
• Environmental issues:– Atmospheric emissions– Seeps– Fires
Lessons From Alachua County SW Landfill
Lessons From Alachua County SW Landfill
Leachate
Gas
Lessons From Alachua County SW Landfill
Leachate
Gas
Lessons From Alachua County SW Landfill
Leachate
Gas
Problems with Traditional Gas Collection
• Vertical wells often become flooded. The presence of this water hinders gas collection efficiency.
• Horizontal collectors can become flooded as well.
• This problem occurs at many traditional landfills (especially in wet climates) and becomes exacerbated when liquids are purposefully added to the waste.
Gas Well
Soil Layer
PerchedLiquids
Issues with Gas at Bioreactor Landfills
Before Liquids Addition After Liquids Addition
Landfill gas well equipped with liquidpumping system
Pump repairand maintenance
Strategies for Collecting Gas in Bioreactors
– Use leachate collection system– Let the cap serve as a primary gas
collector– Smart of use of leachate recirculation
devices– Strategic use of vertical wells
MSW Landfill
Leachate collection pipe
Leachate wet well
Geomembrane cap
Geomembrane liner
Vertical gas collection wells
Horizontal gas collection wells
Landfill gas pressure
Landfill gas generation and flow
Use Leachate Collection System
• The leachate recirculation system can successfully used as a gas collection system.
• The driving force of gas out of the landfill is pressure. If the pressure in the leachate collection system is near atmospheric, gas will migrate in that direction.
Driving Force for Gas is Pressure
Gauge Pressure (cm of water column)
-15 -10 -5 0 5 10 15
z/L
0.0
0.2
0.4
0.6
0.8
1.0
mLmk
smkgM
z
2010
104.4
212
37
==
×=
−
−γ+β+α−= zzp 2
ωμ
+α=βz
j kRT2z2
i2i
2i zzp β−α+=γ
MkRT
z
μ=α
Source: Townsend, T., Wise, W., Jain, P. (2005). “One‐dimensional Gas Flow Model for Horizontal Gas Collection Systems at Municipal Solid Waste Landfills.” Journal of Environmental Engineering, ASCE 131(12), 1716‐1723.
Top of Landfill
Bottom of Landfill
Design Considerations
• The landfill should be designed from the beginning with the idea of collecting gas from the leachate collection system
Leachate collection system manholeretrofitted for gas collection
Gas Collection from LCS
MSW Landfill
Gas flow
Leachate clean‐out line
To flare
Leachate collection pipe
Leachate wet well
Leachate level
Pump
Gas flow
Leachate clean‐out line
To flare
MSW Landfill
Leachate collection pipe
Leachate wet well
Minimum leachate level
Gas collection system being constructed on topof sand drainage blanketat Polk County NCLF.
Photos: Jones Edmunds(www.jonesedmunds.com)
LCS Gas Collection System at New River Regional Landfill
LCS Gas Collection System at New River Regional Landfill
Capping Systems for Gas Collection
• Use a cap system with a geomembrane as a gas collector.– Composite liner
– Buried geomembrane
– Exposed geomembrane
Geomembranes for Gas Collection
Liner
LCS
MSW
Geomembrane
Creative Use of Leachate Recirculation Devices
• Use leachate recirculation devices as gas collectors, but don’t count on them as primary collectors.
• Exception: Horizontal trenches on the surface of the landfill.
• Also, use unused recirculation devices as gas collectors to collect gas being produced from other recirculated areas.
• Only use horizontal trenches for liquids addition when you an active level of gas collectors above.
Strategic Use of Vertical Wells
• Vertical well still have a place, but their location and design should be planned with the wet condition of the landfill in mind.
• It would counter productive to put wells in the middle of areas that are planned to be very wet.
• Target for areas not well serviced by other devices.
• Shorter wells in greater number.
Timing of Liquids Addition• Given the challenges presented by liquids addition and gas collection, one option is to prolong the start of bioreactor activity until the landfill is filled, and then start liquids addition.
• Advantage: Gas collection should be more efficient
• Disadvantages:– Limited leachate recirculation capacity
– Harder to inject into deeper lines
Limitations for Developing Countries
• Let’s separate the issues– What techniques can be used by developing countries to collect gas, whether they are a bioreactor or not.
– What role should bioreactors play in waste management in developing countries
Techniques for Gas Collection
• Important factors– Operating landfill or closed landfill
– Lined landfill or unlined landfill
• For newer modern landfills, use similar strategies as presented for developed countries– Key: The landfill should be designed and constructed with gas collection in mind
Techniques for Gas Collection
• When landfills are developed with only limited resources, utilize less elaborate and costly methods for gas extraction.– Something simple enough for the operators to install themselves
– Creative use of recycled materials
– Think collection from the bottom up and from the beginning
– Leverage gas value for site improvements
Crushed glass for drainage media
Shredded tires for drainage media
The Role of Bioreactor Landfills in Developing Countries
• Depending on the composition of the waste stream, sufficient water may already exist, and it may be essentially a bioreactor already!
• For lined landfills, bioreactor techniques, if done correctly can optimize methane recovery and value.
• For unlined landfills, the benefits of liquids addition must be weighed against impact to the environment.
Discussion Topic
• Should leachate recirculation be allowed in unlined landfills?
Discussion Topic
• How do landfills with methane recovery compare with composting?
Summary
• Gas collection is critical to the operation of a bioreactor. It is not really a “bioreactor” in the true sense of the word if gas is not managed well.
• Standard gas collection techniques do not always work well with bioreactors. Alternative approaches should be considered.
• In developing countries, gas collection should be integrated into landfill design, construction and operation, whether a bioreactor or not.
• Additional discussion is needed on whether landfills operated for the purpose of methane recovery are appropriate for developing countries.
Contact info
• www.ees.ufl.edu/homepp/townsend
• www.bioreactor.org
• hinkleycenter.org