At the beginning of this month, Zero Waste Scotland – a not-for-profit environmental organisation funded by the Scottish Government and European Regional Development Fund – published a report describing the climate change impacts of burning residual municipal waste in Scotland.

In the report, the carbon intensity and greenhouse gas (GHG) emissions of all six Energy from Waste (EfW) plants burning residual municipal waste in Scotland in 2018 have been calculated.  Measuring carbon intensity allows a comparison with other energy production technologies.  Life Cycle Analysis has been used to calculate the net GHG emissions per tonne of waste input for EfW and landfill as an alternative waste management option.  Incineration and landfill are reserved for residual waste once all other, less environmentally damaging options, such as prevention, reuse and recycling, have been exhausted.

Burning residual municipal waste in EfW plants in Scotland in 2018 had an average carbon intensity of 509 gCO₂/kWh.  Electricity-only incinerators and gasifiers have an average carbon intensity of 524 gCO₂/kWh – nearly twice that of the UK marginal electricity grid average (270 gCO₂/kWh in 2018).  The carbon intensity of the only heat-only incinerator operating in Scotland in 2018 was lower, at 325 gCO₂/kWh, although this was still higher than the UK marginal heat average (267 gCO₂/kWh).

Sending one tonne of residual municipal waste to EfW in Scotland in 2018 emitted 219 kgCO₂e, which is 15% less GHG emissions per tonne than the emissions from sending the waste to landfill instead.

A sensitivity analysis was conducted to explore the impact of two critical variables in the model: the composition of waste and the potential of technological solutions.  The results show that changes in waste composition and technology can considerably alter the climate change impacts of waste management.

Both incinerator and landfill impacts are very sensitive to the composition of the waste input.  Increasing the plastic content of municipal waste increases the Net Calorific Value (NCV) but also the GHG emissions of EfW plants, as a higher proportion of fossil carbon is burnt and released into the atmosphere.  If the proportion of plastic in residual municipal waste increases from 15% to 17%, GHG emissions per tonne for incinerators rises to the same level as landfill.  Converting to combined heat and power (CHP) systems reduces the carbon intensity of EfW plants significantly, but not below the UK average for marginal grid electricity.

A ban on Scottish biodegradable municipal waste (BMW) is due to come into force in 2025 with the aim of reducing GHG emissions from biodegradable material sent to landfill.  This study includes an assessment of the potential carbon impacts of meeting the ban in three different ways:

• Incinerate all waste in facilities which operate at 2018 efficiency levels;
• Incinerate all waste in facilities which operate as CHPs; or
• Upgrade all incinerators to CHPs and pre-treat the waste sent to landfill (the tonnage split between incineration and landfill remaining at 2018 levels).

In 2018, management of residual municipal waste had a GHG impact of 332,016 tCO₂e.  If all waste was sent to electricity-only incineration plants (the default scenario), the impact would be lowered slightly by 7% to 310,125 tCO₂e.  If all waste was sent to CHP plants instead, the impact would fall further (27% below the 2018 baseline) to 225,910 tCO₂e.  If incinerators were upgraded to CHPs and pre-treatment added to landfill, much greater savings are possible.  The annual impact would be reduced by 79% to 71,104 tCO₂e.

The savings from landfill pre-treatment are illustrative only and further, more detailed research is required to understand the exact savings required.

This study has implications for how long-term infrastructure and policy decisions are made.

The report concludes that whilst EfW plants have been successful, to date, in reducing GHG emissions from residual municipal waste, there is a risk that these savings will be lost if current trends and policies continue.  This is due to the changing nature of waste composition and because of the successful decarbonisation of the UK and Scottish energy grids.  As a consequence, the authors believe that decarbonisation of the grid has been so successful that “EfW technologies can no longer be considered low-carbon solutions”.  They go on to state that “decisions on future management must be based on the most current and accurate data possible to ensure climate change impacts are minimised.  Waste policy should be adapted to take advantage of significant opportunities to reduce the climate change impacts of waste further.  This study can inform policy decisions in this area”.

It will be interesting to see how the EfW industry reacts to this report…