Decarbonisation of residual waste infrastructure: report

4 Decarbonisation Options

What are the possible options to decarbonise residual waste infrastructure?

What are the most effective and feasible options to improve existing waste management infrastructure in terms of carbon performance?

What combination of options is the most feasible for Scotland?

4.1 Emissions Trading and Taxation

Any policy measure that places a cost on emitting GHGs could be used to promote the various approaches to decarbonising residual waste management infrastructure. One example that is currently under discussion is the proposed expansion of the UK emissions trading scheme (UK ETS)^[34] to include incineration. Inclusion of incineration in the UK ETS could play a role in incentivising the three main options to decarbonise the incineration sector (preventing the incineration of plastics, the deployment of heat networks and the use of CCUS).

Another approach would be to introduce a wider carbon tax across the full economy. This could be economically the most efficient approach, but without some form of carbon border adjustment mechanism (CBAM)^[35] could have negative impacts on Scottish and UK industrial competitiveness and seems currently unachievable for political and administrative reasons. While the relative merits of a carbon tax or ETS approach are debatable, the UK ETS is the main approach for carbon pricing across the UK and there is currently an opportunity to extend the scope of the ETS to waste.

The Review therefore concludes that extension of the UK ETS to incineration should be supported by the Scottish Government as one element of the approach to decarbonising incineration:

Recommendation 16: The Scottish Government should support inclusion of incineration (with or without energy recovery) in the UK Emissions Trading Scheme as one important decarbonisation policy tool.

However, as noted in the First Report, the waste sector is a complex system, and no part can be considered in isolation. Applying an ETS to the incineration sector is likely to have impacts on other parts of the waste management system and some consideration of what those impacts may be and how to mitigate those impacts is warranted, including further expansion of the UK ETS to other parts of the waste sector.

4.2 Preventing Residual Waste

As noted in the First Report, the best form of residual waste treatment is preventing it from occurring in the first place. Where waste does occur, preventing it from entering the residual waste stream by collecting it for reuse or recycling is preferable to any disposal option. When a product is made from virgin materials, significant GHG emissions are associated with that production process from extraction, refining, transport, manufacture and distribution. If a product is made from recycled materials, there is no extraction; refining is generally lower energy; and often (but not always) transport distances are lower. This means using recycled materials creates lower GHG emissions than using virgin materials.

Where residual waste enters landfill, the degradation of biodegradable waste is responsible for the majority of emissions (as methane) and where it is incinerated, burning fossil carbon is particularly important for emissions^[36]. Fossil carbon in residual waste is largely contained in plastics such as that from packaging, toys, building products and clothing.

Preventing biodegradable (e.g. food waste) and plastics from entering the residual waste is, therefore, likely to be the most impactful and reliable strategy to reducing the carbon impact of residual waste management^[37].

4.3 Advanced Sorting

The Scottish Government accepted the First Report final recommendations, including the need to rapidly seek further reductions in the proportion of recyclable material entering the residual waste stream to the greatest extent possible^[38].

However, even with improved kerbside collections, it is likely that a proportion of recyclable material will enter the residual waste stream with current collection methodologies. Data from households suggest currently that up to 60% of what is put into general waste bins can be recycled using existing recycling services^[39]. In addition, contamination of materials collected for recycling makes managing recycling collections more costly and in extreme cases can mean all collected recycling in that load has to be diverted for incineration or landfill. For example, just under a fifth of everything put out for recycling by householders is currently non-recyclable^[40].

Therefore, where efforts to prevent waste occurring and prevent materials entering the residual waste stream have been unsuccessful, advanced sorting^[41] to recover recyclable materials may play a role in decarbonising the sector. Moreover, separating these different elements will allow a greater recovery of valuable materials, the amount of material sent to landfills to be minimised, and recyclable materials to find a new purpose. It also supports Scotland in reaching its recycling targets, particularly in areas where recycling targets might be more difficult to reach, for example in more rural areas or those with a high density of flatted properties.

A wide range of sorting and separating technologies can be used to separate key recyclable material streams, based on characteristics of the targeted items. Overall, most technologies are well established across Europe¹⁰. It can help to reduce climate change emissions in two ways:

• Emission benefits from the recycling activity – which results in avoided emissions from the primary production of materials
• For materials that contain fossil carbon (mostly plastics), emissions benefits also arise because of the reduction in this material within the incinerator feedstock.

The removal of plastics from the residual waste stream is likely to be the priority for decarbonisation of incineration infrastructure since fossil carbon in residual waste is largely from plastics^[42]. Almost all plastic is fossil carbon locked up in polymer form^[43]. Composition changes and the reduction of plastic in residual waste can, therefore, have a significant effect on incineration carbon emission.

One stakeholder noted that removing plastic from the residual waste stream prior to combustion is a promising route towards reducing EfW emissions and increasing the material available for recycling. Trials at two of their facilities in Scotland have indicated an ability to remove 16% of waste (70% in the form of plastics), thereby reducing the fossil emissions of a tonne of black bag waste by up to 281kgCO₂e i.e. it reduces the fossil emissions by more than half^[44]. However, the trials also reinforce some of the challenges associated with Advanced Sorting, such as the poor quality of contaminated materials.

The Eunomia report therefore looked at advanced sorting to remove recyclable plastic. It found (Pathway 1) that advanced sorting alone would reduce annual direct GHG emissions from incineration by 56% from the modelled business as usual (BAU) baseline of 747ktCO₂e to 329ktCO₂e. Even where significantly less plastic is ending up in residual waste (the BES-P scenario), the reduction from advanced sorting is 49% 496 to 252ktCO₂e.

The arguments for advanced sorting to remove recyclable plastic are clear. Therefore, this Second Report confirms the First Report’s provisional position:

Recommendation 13: 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 possible, with a particular focus on plastic.

However, it is also the case that burning fossil-based plastics^[45] – whether recyclable or not – creates climate-impacting GHG emissions and needs to be avoided if Scotland is to reach its net zero targets. In other words, for some or all incineration plants (depending on the deployment of carbon capture technologies, see Section 4.7), net zero is not possible if plastic remains in the feedstock.

This Second Report therefore goes further:

Recommendation 17: The Scottish Government and SEPA should put in place by 2025 robust arrangements to stop fossil-based plastic from being incinerated in Scotland from the beginning of 2030, except where required for hazardous waste disposal.

Industry and local authorities have the ability and direct levers (e.g. through contracts) to prevent the incineration of fossil-based plastics and should take action as soon as possible to do so. However, it will necessarily fall to Scottish Government and SEPA to ensure that robust arrangements are in place to prevent plastics from being incinerated in Scotland.

Currently, Scotland and the rest of the UK are heavily reliant on exports^[46] for managing plastic waste. Recent estimates suggest that the UK exports around 60% of its packaging waste^[47]. While some exports currently ensure the value of material is maximised, this trade is fraught with problems and is increasingly seen as unsuitable^[48]. It is also not consistent with Scotland’s desire to be self-sufficient in its waste management for it to send any significant quantity of its waste out of the country.

Recommendation 18: In implementing the recommendations of the Review, the Scottish Government should do what is within its powers to ensure that there is no increase (and ideally a significant decrease) in the export of plastic waste from Scotland.

Plastics fractions contained in complex waste streams may not be easily sortable or available in sufficient amounts or at the sufficient quality to make mechanical recycling a viable solution from both an economic and environmental standpoint. Black plastics are particularly hard to sort as their colour makes them difficult for machines to spot, plastic films are problematic due to their capacity to jam sorting machinery, and low-density polythene needs to be chemically recycled.

There are also limited options for off-takes of the lower quality plastics that are sorted from residual waste. Industry experience of plastics recovered from residual waste in Scotland has highlighted that they are very poor quality with low market acceptability^[49]. Furthermore, alternative options such as chemical recycling also come with technical complexities and other challenges.

Overcoming the barriers to handling plastic waste domestically will require action and investment across the plastics supply and management chain. The UK Plastics pact Annual Report 2021/22^[50] suggests that although the UK’s plastics reprocessing capacity has grown 50% over the past 5 years, it will require an additional 440,000t/y of domestic plastics reprocessing capacity to achieve the UK Plastic Pact target of boosting plastics recycling to 70% by 2025. It also notes that certainty on key policy is needed to ensure this capacity will be available to the market in time.

Costs for advanced sorting are highly variable and dependent on facility size – with smaller facilities tending to be more expensive on a per tonne basis. The overall balance of costs depends on material revenues and avoided disposal costs – not just the cost of installing and operating sorting processes. Furthermore, transporting, storing, and potentially upgrading intermediates can add significant operational and capital costs.

Given these constraints, implementation of the Review’s Recommendations implies that plastic that is currently not recyclable will need to be stored until a suitable recycling route is developed and implemented. Such storage will need to be regulated appropriately to ensure it is done safely in terms of risks to human health and the environment as well as to enable it to be easily and economically retrieved once recycling is feasible.

Because it is likely that advanced sorting technologies will not be able to deliver Recommendation 15 alone, additional approaches should be examined. Clearly, global work to reduce plastic production and use may have an impact, as will the deployment of extended producer responsibility schemes for packaging and other plastic uses, bans on certain single-use items, etc. In addition, a change to waste collection practices could be beneficial. For example, businesses and households could be required to place all end-of-life plastic items into one ‘bin’, which would then be taken to specialist plastics sorting, recycling and storage facilities that would divert it all away from incineration. This could be easier for waste producers to understand and comply with than other approaches, though would also require investment in the appropriate infrastructure.

Recommendation 19: The Scottish Government should implement Recommendation 17 through policies to reduce plastic production and use, promote source segregation of all plastic wastes, and implement advanced sorting of residual waste.

The point of this recommendation is that all these policy approaches are likely to be relevant and necessary – it is unlikely that any one alone will give the desired result for Scotland.

4.4 Biostablisation

Biostabilisation processes that use in-vessel composting may be able to stabilise waste to a level that is compliant with the landfill ban. However, as noted in the First Report, while it may be technically feasible to stabilise waste to achieve the landfill ban criteria, biostabilisation is unlikely to be a practical treatment option for the majority of residual waste in Scotland.

However, as the First Report highlighted, there are geographies in Scotland where residual waste treatment options may be limited, such as remote and rural areas. In such cases, biostabilisation may have a role as a small-scale treatment option, particularly where food waste collections are limited.

Since biostabilisation is unlikely to be a practical treatment option for the majority of Scottish residual waste, it is unlikely to provide a solution or alternative route to support the decarbonisation of existing and planned infrastructure in Scotland. It was therefore not included in the detailed modelling of options^[10].

4.5 Waste to Fuel and Chemical Recycling Technologies

Stakeholder feedback noted the potential for ATT processes to develop products other than electricity, which might be beneficial to support decarbonisation of other activities, especially as the power grid decarbonises and so the carbon benefit of this kind of electricity generation reduces.

Waste to fuel is an umbrella term for a range of technologies, typically gasification or pyrolysis, that convert mixed municipal waste or single waste streams (eg plastics) into fuel sources such as hydrogen and bioethanol. These have been labelled ‘low carbon fuels’, since they typically displace fossil fuels derived directly from extracted oil.

Scotland currently has two gasification plants in operation, none in development and one with planning permission for the treatment of municipal waste. We understand that it would be difficult for these facilities to convert to waste to fuel processes. It is therefore, unlikely that waste to fuels technologies would be viable options for the decarbonisation of existing and planned infrastructure, particularly for the processing of mixed municipal waste.

Chemical recycling is also an umbrella term for technologies that seek to recycle plastics by changing their material structure^[51], for example, converting them back to their monomers for reformulation into plastics. One form of chemical recycling involves pyrolytic techniques, and there is therefore a cross-over in the type of technologies used in chemical recycling, waste to fuels and in the incineration of mixed municipal waste, considered by the Review.

Waste to fuel and chemical recycling technologies could play a role in allowing the sector to support wider decarbonisation by offering a route for plastics that are difficult (practically or economically) to mechanically recycle and are collected at source or recovered from the residual waste stream. This could facilitate the implementation of recommendations in this Second Report, including the collection of plastics not currently recycled.

We would not expect chemical recycling or waste to fuel technologies to be caught under Recommendation 4^[52] so long as they do not directly emit GHGs. Although they add a small amount of treatment capacity, they will ultimately reduce the need for municipal waste incineration capacity, which could be reflected in a faster reduction in any future capacity cap (Recommendation 5^[53]).