Baroness Miller of Chilthorne Domer – 2016 Parliamentary Question to the Department for Energy and Climate Change

The below Parliamentary question was asked by Baroness Miller of Chilthorne Domer on 2016-04-28.

To ask Her Majesty’s Government what is their assessment of how the carbon emissions of waste-fed anaerobic digestion plants compare to those of plants fed by energy crops.

Lord Bourne of Aberystwyth

The carbon emissions from anaerobic digestion (AD) plants have been assessed by adding together; the greenhouse gas emissions from the AD plant including an estimate of their methane leakage rate, the reduction in UK greenhouse gas emissions from the use of biomethane to substitute for natural gas in the gas grid, and where this is relevant, the emissions avoided by no longer needing to dispose of the feedstock. The estimates below are for typical plants and will depend on particular circumstances.

For food waste this net change in greenhouse gas emissions was assessed as a saving of 850 g of carbon dioxide equivalent per kilowatt hour of energy in the biomethane produced (g CO_2eq /kWh). This arises principally from the reduction in emissions from the landfilling of food waste. Animal waste based AD plant save emissions of 704 g CO_2eq /kWh as a result of the reduction in storage emissions of slurries and manures. The use of annual energy crops for AD was assessed as saving 102 g CO_2eq /kWh.

The assumptions behind this assessment are detailed in the Impact Assessment that accompanied the recent consultation ‘The Renewable Heat Incentive: A reformed and refocused scheme’ and did not taken account of any additional carbon emissions impacts relating to indirect land use change, which may arise from changes in agricultural land caused by the expansion of croplands for feedstock production.

This evidence was drawn from the modelling that supported the Impact Assessment for the recent Renewable Heat Incentive consultation that closed on 27th April.

Food waste is estimated to be considerably more cost-effective than agricultural feedstocks because of the ‘upstream’ emissions abatement that is assumed to occur as a result of diverting food waste from landfill to an anaerobic digester. This is despite the controls that are in place at landfill sites to collect and combust landfill gas.

Agricultural wastes are also assumed to produce upstream emission abatement owing largely to avoided emissions from the storage of slurries and manures, although these are less significant than the upstream abatement from food waste. In contrast energy crops do not offer these GHG emission reduction advantages.