to read the full report - Ecolateral by Peter Jones

Evaluation of Opportunities for Converting Indigenous UK Wastes to Wastes and Energy
AEA/ED45551/Issue 1
Some of the key features of the BEAT systems and the criteria that have been used here are:
• System boundary: In this work the systems begin at the point the waste is available for use as a
resource, taking no consideration of the environmental impacts of creating the waste. Once use
of the waste as a feedstock commences all subsequent stages are incorporated, e.g. emissions
from processing the waste, manufacture of machinery and ash disposal, to cite a few stages.
• GHG Emissions: Emissions of the three main GHGs, carbon dioxide (CO2), methane (CH4) and
nitrous oxide (N2O) are included. While carbon dioxide and, to a lesser extent, methane
emissions are widely publicised, sources of nitrogen giving rise to the emission of nitrous oxide
(N2O) from the soil is a less well known effect. A complex series of reactions and processes
transform some of the nitrogen present into N2O, potentially a critical issue as the global warming
potential of N2O is nearly 300 times that of CO2. Individual GHG emissions are converted into
equivalent CO2 using quoted values of Global Warming Potentials (GWPs).
• CHP: In all cases emissions savings have been derived assuming the displacement of
compressed natural gas, or the displacement of grid electricity.
• Reference system: Reference systems are used here to address the alternative fate of a waste
product. The disposal of a waste product will be avoided if it is used as a biomass feedstock for
energy production. The GHG emissions that would have arisen from disposal are taken into
account by deducting from the total GHG emissions of the pathway.
• Fossil Fuel Displacement: Assumptions about the fossil fuel displaced (e.g. coal, oil, or gas) and
the efficiency of the conversion technology for heat and electricity production can make a
significant difference to the savings calculated.
Using BEAT to follow the two waste disposal scenarios outlined below allow establishment of the
potential GHG reductions that could be achieved were the alternative disposal route to be pursued and
the final products fully utilised.
The results have been presented in terms of the kilograms of GHG saved per tonne of waste, as waste
utilisation is the primary aim, with energy generation the secondary aim.
11.1 Scenario 1: Food Waste
Domestic food waste can be collected separately as part of the MSW disposal route. This waste
represents a resource that can be widely available throughout the UK, although collection and transport
are likely to be more efficient in urban areas. It is estimated that there is potentially 5 million tonnes of
MSW food waste each year, as well as nearly 7 million tonnes of C&I food waste (for England, Wales and
Scotland), although it is unlikely all would be available for collection.
The majority of this waste stream currently goes to landfill, often with energy recovery through landfill gas.
This situation is rapidly changing with the requirement of the Landfill Directive that levels of biodegradable
municipal solid waste (MSW) sent to landfill must be reduced to 75% by 2010, by 50% 2013 and by 35%
by 2020 of 1995 levels. The alternative disposal options available are to compost or anaerobically digest
the waste.
Food waste treated at a compost site will produce a soil conditioner material. The composting process
will be required to be carried out in a sealed container as the material may contain meat or meat
products.
Food waste treated at an AD site will produce an organic digestate output, which can be used as a soil
conditioner. It has been assumed that a compost soil conditioner and a digestate soil conditioner,
although having different physical forms, have the same value as a soil conditioner. In addition biogas
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