Emissions to Air from Landfill and Landfill Gas EnginesAlan RosevearEnvironment Agency Science Group

Typical Landfill Operation

Post Landfill Directive� Required to Control, Collect and Treat landfill

gas. Where possible utilise the gas, the remainder to be flared.

� A step change in management of landfill gas at permitted sites.

� Combustion of methane reduces greenhouse gas potential

� Renewable fuels obligation (10% electricity from renewables such as landfill gas by 2010)

The Regulatory Framework

� Old Legacy sites - pre CoPA with no control, little monitoring but probably low gas production. Now Contaminated Land under Part IIA

� Old Waste Management Licensed sites - some control and monitoring - significant gas

� Sites permitted under PPC - well engineered, contained, gas utilised

The Holistic View

Source - Pathway - ReceptorGASSIM provides a conceptual model

Raw Gas Emission Rates

� Each tonne of waste will generate 6 cubic metres of landfill gas a year over first 10 years

� A modern permitted site contains several million tonnes of waste

� Passive venting no longer acceptable� Gas collection efficiency 85% on capped/controlled areas

Fugitive emissions of raw gas� the capped surface� lateral migration� leaks & failures in collection system� active tipping area� uncapped active cells

Surface Emissions Monitoring1. identify high permeability area2. Rectify faults3. Quantify with an array of flux boxes

Standards for Emission of Raw Gas� Surface emissions of raw gas - from

permanently capped area 10-3 mg methane per m2 per sec.

� Only achieved with a well engineered cap and good gas management.

Raw Gas� Methane� Carbon dioxide� Trace Components (less than 1% in total)� Air (oxygen depleted)

� Global warming potential and calorific value from methane (ca 60% v/v in source gas)

� Odour and potential health impact from a few of the 550 trace components

Median and mean concns of trace components - recent typical sites

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Potential impacts of raw gas� Acute - explosive risk from methane

accumulation in voids (lateral migration)� Acute - odour due to trace components in the

gas; principally sulphur compounds� Global - methane as greenhouse gas� Chronic - potential health impact from trace

components such as chlorethene, carbon disulphide and benzene.

Combustion Products - Engines & Flares� Carbon dioxide and water diluted with excess air� Products of incomplete combustion of methane

(Carbon monoxide, unburnt methane, VOCs such as formaldehyde, dioxins?)

� Products from combustion of traces in raw gas (sulphur dioxide, hydrogen chloride, hydrogen fluoride)

� Products of high temperature (nitrogen oxides)

Impact is on local air quality

Gas Utilisation in Engines

Gas use may be in an adjacent compound and managed separately from the landfill

Central facility - variation in scale� Single Unit with balancing flare� Multiple units with single, high stack

Enclosed Landfill Gas Flares

Stack Emissions Monitoring

Principal Standards Emissions to be Assessed for ComplianceEmission Engine

(mg/Nm3)TypicalUncertainty

Flare(mg/Nm3)

TypicalUncertainty

NOx 650 30% 150 30%

CO 1500 20% 100 20%

Total VOC 1750 40% 10 40%

NMVOC 150 40% 5 40%

Impact of Combustion on Local Air Quality� Landfills often near major transport corridors � NOx background already close to annual

mean AQ objective of 40 micrograms/ m3

� Flares and engines are point sources with relatively low velocity at small height (low plume rise), close to site boundary

� Compliant engines and flares must also take account of local air quality

Air Quality Objectives� NOx from Combustion - additional contribution from

two compliant engines may breach air quality objectives at nearest receptor (2005) and even more likely at site boundary (2010)

less significant - site specific� Benzene in Raw Gas - surface emission has potential

to breach air quality objectives at nearest receptor (2005) and site boundary (2010)

� SO2 from Combustion - small potential on some sites for breach at nearest receptor

In ConclusionLandfill Gas emission from permitted landfills is

controlled and relatively low; less control at older landfills.

� Raw Gas: global warming potential of methane; risk of explosion from gas migration and risk of odour or health impact from aerial emission of trace components.

� Combustion Products: engines could impact local air quality, particularly for NOx.