Stop, Sort, Burn, Bury - incineration in the waste hierarchy: independent review

Report and supporting documents relating to the Independent Review of the Role of Incineration in the Waste Hierarchy in Scotland.

7 Improving Carbon Performance

What can be done to improve existing residual waste treatment facilities in terms of carbon performance?

7.1 Climate Change Impacts

Burning residual waste releases carbon dioxide. The IPCC estimates that every tonne of waste incinerated releases 0.7-1.2 tCO2e[63], a range that is consistent with the figure adopted by UKWIN[64] of ~1 tCO2e per tonne of waste. For global climate reporting purposes, only "climate-relevant" GHG emissions are considered. These come from the combustion of fossil carbon, which for residual waste is normally in the form of plastic. Emissions from biogenic[65] carbon (paper, card, food, natural textiles, etc) are not counted. Therefore, the greater the proportion of plastic in the residual waste, the worse the outcome for climate change from incinerating it.

By contrast, biodegradable waste decomposes anaerobically[66] in landfill sites, leading to the release of methane, which is a many times more potent GHG than carbon dioxide. Plastics and other forms of fossil carbon generally do not decompose in landfill to release GHGs.

One of the major drivers therefore of whether incineration or landfill emits the least climate-relevant GHG is the proportion of the waste that is biogenic. According to figures from Defra, in 2011 the biogenic content of municipal residual waste in England was 51%, down from 68% previously[67], though data from WRAP[68] in 2017 put it at 63%. The study by Zero Waste Scotland[69] suggests that the biogenic fraction in Scotland in 2018 was 15% and the fossil content 11%; another study showed HH waste only in Scotland[70] was 74% biogenic content in 2014-15. Given that the relative carbon impact of different options depend on it, this uncertainty in the composition of residual waste is unhelpful (see Recommendation 2).

The difference between the amount of GHG emitted for the energy generated via incineration and that generated by other sources is also relevant. Therefore, as the electricity grid decarbonises, the relative carbon benefit of incineration (without additional measures) decreases.

Currently, where energy is recovered, GHG emissions from incineration are categorised alongside other forms of energy generation in line with international standards. However, as pointed out by stakeholders, this obscures the true contribution of incineration to Scotland's GHG emissions. If policy and technology choices are made on this basis, those choices may not in fact be the right ones[71]. To address this situation, these emissions should be identified separately, a point already made by the Climate Change Committee[72].

Recommendation 12 The Scottish Government should report greenhouse gas emissions from incineration separately from other energy-related emissions as soon as possible, ideally from the 2021 data onwards.

7.2 Decarbonisation Of Existing Residual Waste Management Infrastructure

Unfortunately, given the short timescale of the Review, it has not yet been possible to explore fully all the issues related to decarbonisation of residual waste treatment in Scotland. The Review is grateful to the stakeholders who have provided evidence on this topic and has sought to draw some provisional conclusions and recommendations based on that. However, an additional piece of work has been commissioned on this Topic, which is expected to take a further six to nine months and which will be subject to review by the Climate Change Committee. This evidence will be made public in due course and may justify revision of these provisional recommendations at that point. However, the Review and its Chair do not expect this to delay the publication of the existing Report or accompanying evidence document, nor inhibit the Scottish Government's decision making ability based on this Report.

This section must not be taken as providing reasons to build more incineration facilities. Rather, it is considering how to deal with the GHG emissions from those facilities that, for waste management reasons, need to exist.

7.3 Incineration

Historically, incineration facilities have been a better option for treating residual waste than landfill in terms of GHG emissionsError! Bookmark not defined., which is one reason why energy recovery appears higher up the waste hierarchy than disposal. However, as more organic waste is either avoided or separately collected for recycling, and other sources of energy generation decarbonise, this balance will continue to change and may well flip at some point without other action. Additionally, as noted above, we are currently in the growth phase, but if Scotland is to meet its resource and waste management and climate change mitigation targets, there will be a corresponding future phase down. For at least some electricity-only facilities, this could start before their currently planned end of life[73].

At a strategic level, it could be advantageous for incineration to be included in the UK Emissions Trading Scheme, as this would help provide a set of incentives on operators to reduce their GHG emissions. Indeed, the four UK administrations have recently opened a consultation including this very question[74].

At a practical level, based on the evidence the Review has considered, the following practical options for decarbonising incineration facilities exist:

1. Reducing the proportion of residual waste that is made up of carbon from fossil sources. In most practical senses, this means ensuring less plastic is present in the material when it is burned.

2. Ensuring that all possible wastes and by-products of combustion are recycled or reused.

3. Extracting the maximum energy from each tonne of waste incinerated through harnessing both power and heat (Combined Heat and Power, CHP) wherever possible.

4. Where practicable, using carbon capture technology to ensure the GHGs are not released to the atmosphere (Carbon Capture, Use and Storage, CCUS).

7.4 Removing Fossil Carbon

Fossil carbon in residual waste is largely from plastics[75],[76], [77] such as used in packaging, toys, building products and clothing. As emphasised before, avoiding this material entering residual waste in the first place is best, but where that has been unsuccessful, pre-treatment before incineration can play a role[78], as for example at Levenseat. Because this can be applied to any incineration facility (either on site or before delivery) and uses well-established sorting technology that can be put in place fairly rapidly, it is the most feasible of the options to implement reasonably quickly. Regulation 29[79] of the Pollution Prevention and Control (Scotland) Regulations 2012 already tasks SEPA to require a degree of pre-treatment to extract hard plastics and non-ferrous metals from municipal waste destined for incineration 'where practicable'. However, since SEPA's Thermal Treatment of Waste Guidelines 2014[80] describes hard plastics as PET and HDPE, not all plastics are covered. In addition, exemptions can also be granted for various reasons.

Several stakeholders who commented on the decarbonisation of incineration, including Friends of the Earth Scotland (FOES) and SESA, agreed that reducing the amount of plastics in residual waste (both by stopping them entering it or by pre-treatment once they have) before incineration was essential for this purpose.

Recommendation 13 (Provisional) The Scottish Government should immediately strengthen existing requirements for pre-treatment and work with local authorities and industry to apply them to all existing and future incineration facilities to remove as much recyclable material as feasible, with a particular focus on plastics.

Clearly, there needs to be reprocessing options for the recyclable material obtained through pre-treatment, and this must be considered as part of the wider resource and waste management system. This might well be an area where so-called 'chemical recycling'[81] of plastics could help, though that too can have its issues[82].

7.4.1 Recycling more by-products

Incinerator bottom ash (IBA) is increasingly recycled into secondary aggregate or other construction materials and the metals found in it can also generally be extracted and recycled. Uses for boiler or fly ash are also being developed, as are approaches to recycle air pollution control residues (APCR). If each of these replaces a higher-carbon virgin resource, this will help improve the carbon balance for incineration. However, some of these materials can contain hazardous substances so care must be taken in how they are recycled and it may not always be the best environmental outcome to do so.

7.4.2 Higher efficiency through Combined Heat and Power

Most incineration plants in Scotland (and the UK more broadly) use the heat from combustion to create steam that then drives a turbine to generate electricity. This process is not hugely efficient, with efficiency percentages in the low twenties being considered normal. As the ratio of fossil carbon to biogenic carbon increases, greater efficiency is required for the process to be better in climate-relevant GHG emission terms than landfill. Figure shows the relationship graphically.

Figure 5: Net efficiency of EfW required as a function of biogenic C content of a range of waste [83]

The most common and practicable method to improve efficiency is to use the steam to provide heat to another user, such as a district heat network or a large industrial facility. In this mode, efficiency can be doubled or more, reaching 55-65%. Almost all incineration plants in Scotland in operation[84] or in planning are required to be 'CHP ready'. However, historically in the UK very few have then gone on to actually be connected to some form of heat user. Stakeholders generally agreed that this is for several reasons, many of which apply to any district heat network but some of which are specific to incineration:


  • The planning process and other factors can mean incineration plants are often not sited near potential heat users.
  • The incineration operator's responsibility for CHP ceases at the facility boundary, so if there is not an organisation prepared to make the running, often nothing will happen.
  • Operating a heat network requires a different skill set than operating and incineration plant, so even if the plant operator is keen they may not be equipped to do so.
  • Heat demand is often seasonal, but waste production happens all year round.


  • Building a heat network (which essentially means installing a lot of pipe work) can be disruptive and expensive.
  • Depending on the funding model and what fuel is being replaced, switching to district heat can be more expensive for the user than sticking with their existing solution (for example, natural gas).
  • There is a lack of widespread cultural experience and acceptance of district heating for housing and a perceived loss of individual control.
  • Unplanned downtime for the heat source needs alternative (often expensive) cover.

The provisions on CHP for incineration in the draft NPF4[85] represent a toughening of current requirements and seek to address some of the issues above. However, these will not be relevant for incineration projects that already have planning consent. It will be feasible for some of those to develop heat recovery to boost their overall efficiency, though this will require focused attention from the Scottish Government and local authorities, which are uniquely placed to bring together the different actors needed to make CHP a reality.

Recommendation 14 (Provisional) The Scottish Government and local authorities should continue to work with industry to deploy combined heat and power for as many existing incineration facilities as possible.

For others, where the planning and location decisions already taken make it unlikely that heat recovery will be possible, removal of fossil carbon from their feedstocks is vital if they are to remain beneficial in carbon terms.

7.4.3 Carbon capture

Several technologies[86] have been proposed to capture the carbon dioxide emitted from combustion processes so that it can either be used elsewhere or sent for long term storage underground. Chemical absorption using an amine is the most mature, and physical separation through a range of processes is also already in use for some industrial processes. Less well developed approaches include membrane separation and chemical looping.

Stakeholders raised a number of issues with the application of CCUS to incineration facilities, including:

  • Construction Cost – adding CCUS is thought to require an additional 20-25%.
  • Efficiency – current CCUS technologies require significant amounts of electricity to run. This would mean a reduction in electricity available for export by about a quarter by some estimates.
  • Transport – moving captured carbon dioxide by tanker is very expensive, so either close proximity to a carbon dioxide user or a connection to some form of pipeline is preferable. Only a subset of incineration sites will be well-placed to take advantage of any such users or pipelines.
  • Lead time – the industry's own target is to have CCUS fitted to all incineration plants 'where feasible' by 2040[87].

One recent report[88] suggests that capture costs will range from £66 to £110 per tonne of carbon dioxide captured. Using the figure of ~1 tCO2 per tonne of waste, this could see gate fees increasing by a similar amount, from current levels of £91-£110[89] to £157-£220.At least two projects are underway to deploy CCUS on large incinerators in England[90] and the UK Government is supporting the one in Teesside[91]. Other operators are also looking closely at CCUS options including Viridor for its facility in Dunbar.[92] However, from the evidence received so far, it seems that carbon capture alone is unlikely to be able to deliver the required level of decarbonisation of incineration in time to meet Net Zero. Further research has been commissioned by the Review to investigate this. In the meantime, removal of fossil carbon from the feedstock is a no regrets move, since if CCUS is then implemented it could result in net carbon dioxide removal (also called negative emissions).

7.5 Other Residual Waste Treatment Options

The focus of the Review is on the role of incineration so in its limited time, it has not looked at decarbonisation of other residual waste treatment options such as landfill. However, the additional research it has commissioned will consider this further.

7.6 Provisional Conclusion On Improving Carbon Performance

Reporting of GHG emissions from incineration under the wider energy sector makes sensible decision making more difficult for policymakers and less transparent for stakeholders and should be changed.

Currently, incineration releases fewer climate-relevant GHG than landfill and is therefore the better option from a carbon perspective. However, this balance is dependent on the proportion of residual waste that is biological versus fossil in origin and has probably been shifting in an unfavourable direction over the past decade. The balance is also affected by the comparison of emissions from incineration with emissions from the rest of the energy system. As that wider system decarbonises, the balance becomes less favourable for incineration.

The four routes to redress the balance for incineration are removal of plastics from the waste before burning; greater use of by-products; improved efficiency through use of the waste heat; and capturing carbon emissions. All can play a role, but only the first two are currently applicable to all operational and planned facilities in Scotland. Using waste heat depends on a suitable location and customer. Capturing carbon will take a long time to deploy and it is expensive and probably only worthwhile on larger facilities that are near carbon dioxide users or transport pipelines.



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