Landfill Design – Above Ground
Note: ca. 30 monitoring points for this site
Slide 1
Landfill Design – Cross Section
Gas Vent
Vegetation
Filter Layer
Topsoil
Drainage System
Barrier Layer
Drainage Layer
Protective Layer
Solid Waste
Perimeter
collection pipe
Top Liner
Filter layer
Leachate Collection
System
Bottom Liner
Leak Detection system
Gas Extraction Pipes
Slide 2
Compacted Soil
Aspects of landfill design
• Landfills are lined with a polyethylene sheet. This is to
prevent migration of landfill gas and leachate to adjacent
soil. It also prevents gas from escaping out of the landfill
before it is extracted and flared off.
Slide 3
Leachate
Leachate is defined as any liquid, including any
suspended components in the liquid, that has
percolated through or drained from hazardous
waste.
Leachate is stored and treated before being added
to the sewerage system.
Leachate will contain dissolved methane and
concentrations of the same toxins found in landfill
gas. It cannot be added directly to the sewerage
system because of the potential of explosion from
methane and the health hazard of harmful
substances to sewerage workers.
Slide 4
Leachate storage and removal
Where there is no treatment facility onsite, the
leachate is removed for treatment.
Most large sites have their own biological leachate
treatment plant. The reed bed (right), absorbs
some of the more harmful pollutants converting
them into less harmful components. The cleaned
leachate can then be added to the sewerage
system.
Slide 5
Landfill gas extraction and use
Landfill gas is used as a fuel if it contains >50% methane. The
gas is extracted using underground pipes. If the rate of landfill
gas production is slow, then the taps can be turned off until there
is a build-up of gas for flaring or using as a fuel.
In most small landfills in Ireland, landfill gas is flared off.
Slide 6
Monitoring on the site
• Monitoring of the landfill gas, ground water and leachate
takes place at bore-hole wells along the perimeter at 5 - 45
m distance once a month. A probe from the analyser is
inserted into a valve protected by the metal pipe and a
measurement manually taken and recorded.
Slide 7
Types of gas monitoring
1. Landfill gas generation
–
–
–
Landfill gas sampled from wells around the perimeter of the site
Grab and analysis sampling techniques
Labour intensive, costly, time intensive but necessary
2. Emissions from the landfill
–
–
–
–
The emissions are sampled at varying depths up to 1 m from the surface of
the landfill
This measures the success of gas extraction to the flare or fuel generation
Grab and analysis techniques and hand-held detectors used
Labour intensive, costly, time intensive and necessary
3. Monitoring at the soil/gas boundary
–
–
–
This is an indication of how much landfill gas (greenhouse gas) is being
emitted to the atmosphere
Hand held detectors and plume analysis methods of detection used
Currently, labour intensive, costly, time intensive and necessary. But
changes are afoot
Slide 8
Types of leachate monitoring
Leachate samples are taken from wells at the
perimeter of the landfill.
These are checked once a month for migration of
leachate into ground water near the landfill site.
No realtime monitoring takes place. Samples are
taken for laboratory analysis where gravimetric,
titrimetric and other testing is carried out for:
Total dissolved solids
Total dissolved oxygen
Metal content
Dissolved methane content
Ammoniacal nitrogen content
Bacterial growth
pH
Slide 9
Current methods of landfill gas detection
Hand – held detection
• FID (Flame Ionisation
Detector)
• PID (Photo Ionisation Detector)
• IR (Infra-red Spectroscopy)
Grab and analysis techniques
• Adsorbent Tubes
• Pre-evacuated teflon coated
‘tedlar’ bags
• Chamber Flux Method - using a
polythene tent
• Samples analysed using GCMS, GC-PID, GC-FID, IR
Plume analysis
Tracer Flux Method
Open Path IR based on IR
lasers
Increasing interest in IR
cameras
Solid State detection
Pellistor Detector
Metal oxide semiconductor
sensors
Slide 10
Pellistors
Slide 11
Pellistor Sensor
CH4 + O2
CH4 + O2
CO2 + HEAT
i
Catalytic Material
•
•
•
•
•
•
•
•
•
CO2
Pt wire
Pt wire
i
Non-catalytic Material
Pt wire resistance is very sensitive to temperature
Current is passed through the wire - heats it up to ca. 500C
Flammable gases like methane are catalytically combusted on the hot catalytic surface (left), generating
more heat which causes the resistance to increase
Reference element (right) has no catalyst - no combustion - temperature difference generated, manifests
as a resistance difference
Resistance difference is measured very accurately in a Wheatstone Bridge resistance network
Very low cost, reliable, rugged, but not selective
Lifetime up to five years
Can be poisoned e.g. by halogen compounds
Requires supply of oxygen to function - use is restricted to at/near the surface
Slide 12
IR Plume Analysis
The Tracer Flux Method uses Open Path IR to
analyse the components of a gas plume (top,
opposite)
Pro - Can be monitored from up to 1 km away
Pro - Can be coupled to a GPS system or a
thermal imaging system for plume tracking
Con - Needs a plume emission from the landfill
and tracer gas mixing; requires steady gas
generation
Con - Time intensive
Con - Reliant on the weather
IR Imaging cameras beginning to gain popularity
- generates a spectral image (below); each pixel
in image contains an IR spectrum See
http://www.psicorp.com/products/airis.shtml
Slide 13
IR Spectra
Slide 14
Model Gases and Characteristic Bands
Infrared sensor must be tuned to specific bands of
component gases
Interference between components will be a problem
Need to cover broad spectrum of components in first phase
– greenhouse gas, toxic gases, odorous gases.
Methane
Ammonia
Methyl Mercaptan
Benzene
3657 cm-1
(2.734 µm)
3414 cm-1
(2.929 µm)
3015 cm-1
(3.316 µm)
1600 cm-1
(6.250 µm)
3019 cm-1
(3.312 µm)
3336 cm-1
(2.997 µm)
2948 cm-1
(3.392 µm)
1500 cm-1
(6.666 µm)
1533 cm-1
(6.523 µm)
2605 cm-1
(3.838 µm)
1311 cm-1
(7.628 µm)
Slide 15
Laser Technologies
• Infrared Spectroscopy
There are a variety of different instrument layouts for infrared
sensors depending on the number of gas components to be
analysed and the environment in which they are being analysed.
In all sensors, filters are tuned to the frequency of the gas under
study. A number of filters are used where there is more than one
gas component to be studied such as the hand held IR analysers
where both CH4 and CO2 are analysed.
Slide 16
Electrochemical Gas Sensor
e.g. CO, H2S
capillary
Working Electrode
Body
Charcoal
Filter
Glass Fibre
separator
Electrolyte
Reference and counter electrodes
Porous Spacer
•
•
•
•
•
•
•
•
Three electrode system - working, reference and counter electrodes
Electroactive gases diffuse through the capillary entrance and charcoal filter (removes potential
interferents such as alcohols)
CO is oxidised at the working electrode surface
CO + H2O => CO2 + 2H+ + 2eThe reduction reaction happens at the counter electrode
O2 + 4H+ + 4e- => 2H2O
Current flows between the working and reference electrodes; the reference electrode is always
totally immersed in the electrolyte and therefore maintains a constant potential
Low cost, reasonably reliable, requires presence of oxygen, can be poisoned, not specific
(responds to any electroactive gas), eventually becomes exhausted
Slide 17
Portable GC-MS Systems starting to
Appear
•
•
•
•
See HAPSITE: http://www.inficonchemicalidentificationsystems.com/en/index.html
http://www.microsaic.com/products.html
Will have the potential to deliver high quality, multicomponent analysis - but still relatively
expensive for multiple deployments
However, this technology is developing very rapidly, mainly due to US-Military sponsored
R&D
Slide 18
ASG Smart Landfill Plan - Primary
Transmitter
Computer
Polyethylene tent
collects gas emissions
for sampling
Pump
Filter and
drying tube
Sensor e.g. Pellistor
Landfill gas
emissions
Gas extraction for
flaring and power
generation
CO2
CH4
Landfill gas
generation
VOCs
Slide 19
Best options of detection for current project
1. Infrared
–
–
Pros:
• Can detect a wide range of components
• Can be tuned to specific bands to reduce complexity of spectrum
Cons:
• Moisture in the sample will pose a problem
• Expensive and need to be tuned
2. Metal oxides (Semi-conductor Sensors)
–
–
Pros:
• Relatively cheap and commercially available for the more common landfill gas
components
• Have a long life (2-5 years)
Cons:
• Only semi-selective. Will react with other similar gases
3. Pellistor devices (Catalytic Bead Sensors)
–
–
Pros:
• Relatively cheap and commercially available
• Have longevity (5 + years)
Cons:
• Only detect combustible gases
• Can be poisoned by chloride, sulfides, etc.
• Need good supply of oxygen present for oxidation of catalyst to take place
Slide 20
Validation of results
When developing a new analytical technique, validation must be
carried out using a known and proven technique. A number of
variables must also be noted at the time of the experiment such as
sudden or significant changes in temperature, humidity or atmospheric
pressure.
For the project, GC-MS analysis at a certified lab will be carried out.
Sampling of the gas onto carbon adsorbent tubes is undertaken as the
new sensor is gathering information. The tube is sent to the laboratory
where the gas components are thermally desorbed and analysed using
GC-MS.
Real-time testing using hand held detectors (IR/PID/FID) will also
give an immediate indication of the content of the gases present at the
time of sampling.
Finally, all the data can be collated and any false readings or false
positives for the sensor data can be better explained and hopefully
removed for the next phase of testing.
Slide 21
Issues related to ‘Autonomous’
environmental monitoring
Deployment of instrumentation
IS regular calibration needed after deployment
Maintenance access if something goes wrong
Vandalism/Theft
Real problem for sites near towns/cities
Weather
Corrosion, flooding, overheating, freezing
Interference with wireless signal
Power consumption
Battery – finite life
Solar – needs access to sunlight
Indigenous life
People
Animals
Slide 22
Looking Ahead…..
• Low cost gas sensors are available - ‘mature’
technology, rugged, reliable
• Easily integrated into distributed sensor
network - providing information from many
locations
• Best use is to detect and report ‘out of spec’
situations
• More detailed information requires more
sophisticated techniques
– IR methods already being deployed
– Portable GC-MS systems starting to appear
– Both relatively costly, but price performance index will
continue to drop e.g. due to breakthroughs arising from
MEMs technologies (e.g. GC-MS on a chip)
Slide 23
Additional information
• Smart Landfill Team (DCU):
• Breda Kiernan, Conor Slater, Kim Lau, Dermot Diamond
•
•
For more information on Smart Landfill:
www.dcu.ie/chemistry/asg/kiernab
•
•
•
•
•
Additional information on waste management and landfill:
www.epa.ie
www.epa.gov
www.environment-agency.co.uk
www.atsdr.cdc.gov
Slide 24