Projections of GHG emissions and effects of policies and measures in the waste sector in the United Kingdom Presented by Robert G Gregory

Introduction The UKs National Assessment Model for assessing methane emissions from landfills was constructed in 1999 It was updated and revised in 2002 New estimates of national emissions and forecasts were made under a number of waste management scenarios The approach taken is consistent with IPCC Guidelines and IPCC Good Practice guidance (IPCC, 1996; 2000) It takes account of the flexibility allowed in the IPCC guidance for site/country specific data/information and sound scientific principles to be accommodated

Background to the UK model The model implements the IPCC (1996) Tier 2 equations Additional enhancements come from the following: Three methane generation rate constants, k, are adopted for different degradabilities of waste Commercial and Industrial (C&I) waste streams have been introduced alongside municipal solid waste (MSW) Different methane generating potential terms are used for MSW and C&I wastes

Background to the UK model Four different landfill site types are simulated each has different degrees of engineering and gas collection these represent the evolution of landfill engineering and landfill gas management in the UK since 1945

Alignment with GasSim The Environment Agency for England and Wales uses GasSim for the regulation of all its operational landfills GasSim is a state of the art model GasSim has been described by Iain Whitwell on Day 1 of this Workshop The 2002 revisions to the National Assessment Model aligns this model with the scientific principles implemented in GasSim

Waste Related Revisions Waste degradation rate constants are now aligned with GasSim The methane generating potential, L0(x), is a function of Organic Carbon (DOC) and Fraction Dissimilated (DOC F ) DOC and DOC F are specific to the individual components of the waste (e.g. paper, textiles, food waste, etc) DOC and DOC F are now calculated for the individual waste components in the waste stream and then summed values were based on well-documented US research for the USEPAs life-cycle programme, adapted to UK conditions

Methane Oxidation Model A methane oxidation model was built on a number of simple underlying concepts: the surface soil cover must be sufficiently thick and/or the methane flux must be sufficiently low to permit a significant amount of methane oxidation to take place within the cap methane oxidation takes place in the soil cap if the soil depth > 0.3m for modern lined landfills, or If the soil depth > 1.0m for old unlined landfills If neither condition is met, no methane oxidation will take place The methane available for oxidation in the cap is determined after the quantity that is utilised or flared (i.e. recovered) is subtracted from the methane generated

Methane Oxidation Model No oxidation in fissure flow Cap with a maximum oxidising capacity Small source term Large source term Small or large source term

Methane Oxidation Model The methane available for oxidation is defined as: where Avail oxd cap = methane available for oxidation in year x fissure = fraction of methane lost through fissures CH4 generated(x) = methane generated in year x (kt/y) R(t) = methane recovered in year x (kt/y) The model output is most sensitive to the values for field oxidation efficiency and the fraction lost through fissures

Methane Oxidation Model The fraction of methane that is oxidised can be limited by either the sink capacity of the soil (the methane oxidising capacity of the soil cover) or the quantity of methane available for potential oxidation

Landfill Gas Management Installed flare capacity suggests that only 1/3 of all capacity is associated with power generation facilities Growth in installed flare capacity

Landfill Gas Management Installed generation capacity is greater than back-up flaring capacity Power generation facilities do not have equal capacity of back-up flaring Growth in installed generation capacity

Scenario Development Eight MSW scenarios were developed to investigate various waste management options Achieving LD targets with current material recycling rates Achieving LD targets with emphasis on paper/compost recycling Achieving LD targets with emphasis on paper recycling Achieving LD targets with emphasis on EfW/CHP/AD Achieving Waste Strategy 2000 targets with emphasis on glass metals and plastics recycling Higher growth rate, achieving LD targets with current material recycling rates and excess EfW/CHP/AD Higher growth rate, achieving LD targets with excess material recycling rates Current (2000) trends in diversion continued (Base case) – unlikely to achieve LD target

Scenario Development Five additional C&I scenarios were developed Baseline - current landfill 15% diversion based on food wastes, paper & card and other biodegradables to AD, EfW and recycling (lose readily degradables from total C&I excluding C&D) 15% diversion based on general biodegradable wastes to combustion (lose readily and moderately degradable organics) 15% diversion based on general biodegradable wastes to recycling (lose readily and moderately degradable organics) 15% diversion through C&D and mineral wastes recycling (lose inerts)

LFG Generated, Emitted, and Measured Historic Landfill Gas Generation/ Emission Forecasts ETSU 1996 AEAT 1999 NPL 1997 emissions calibration data LQM 2002

Calibrating the Methane Oxidation Model Sensitivity of the fissure term in the Methane Oxidation Model The IPCC 10% oxidation default exceeds observed data Fissures could account for 1% to 30% of the losses and be within the window of measured data

Calibrating the Methane Oxidation Model Effect of the field efficiency term in the Methane Oxidation Model Field efficiency could be between 40% and 100% and be within the window of measured data

Results of Scenario Modelling The effect on Methane Generation/ Emissions resulting from the various future MSW Scenarios 1 – 8 (with C&I Scenario 1 fixed) period 1945 – 2025

Results of Scenario Modelling The effect on Methane Generation/ Emissions of resulting from the various C&I Scenarios 1 – 5 (with MSW Scenario 8 fixed) period 1945 – 2025

LFG recovery is the greatest sink LFG utilisation is encouraged by the Landfill Directive and Renewable Energy subsidies This far outweighs the impact of future diversion policies in the UK because of the size of the existing LFG resource

Summary All the MSW strategies considered achieved some benefit in methane emissions reduction compared with the base cases (Business as Usual) The most significant scenario is paper recycling a 19% reduction in residual methane emissions by 2025 (31 kt CH 4 abated)

Summary The effects of the diversion strategies were not as significant as the impact on emissions reduction due to flaring or gas utilisation methane abated by flaring or utilisation is 1750 kt in 2000, rising to 2465 kt in 2005 The impact of any of the C&I scenarios compared to the base case were negligible in terms of methane emissions abatement.