Can waste help us get to net zero?

Carbon emissions generated by burning waste could be prevented from entering the atmosphere by fitting carbon-capture technology into EfW facilities. This has been recognised by the Climate Change Committee, and in its Sixth Carbon Budget Report, the committee stated that "any new EfW facilities… should be built with CCUS (carbon capture, usage and storage) or be CCUS-ready and that retrofits of existing EfW facilities should be required to install CCUS". 

EfW is a well-proven technology where residual waste, which is not suitable for reusing or recycling, is combusted to reduce its mass and volume and produces energy in the form of electricity and heat. Adding carbon capture to EfW facilities is particularly attractive for two reasons:

1. Operational consistency. EfW facilities typically operate continuously for more than 8,000 hours per year and for more than 25 years, providing a concentrated source of recoverable carbon emissions. In contrast, gas-fuelled power stations are increasingly used intermittently, filling gaps when renewables are insufficient.

2. Biogenic matter. The waste processed by EfW facilities contains a proportion of biogenic matter (from organic sources), such as food waste, paper, cardboard and wood. Carbon capture from EfW can produce negative carbon, as the carbon captured using energy from biogenic sources is considered renewable. This means that it can offset other emissions, and there are limited alternatives for producing negative carbon.

Industry and the Department for Energy Security and Net-Zero (DESNZ) typically estimate that residual waste has a 50 per cent biogenic energy content. This means that 50 per cent of the energy in the waste, which can be converted during combustion or other treatment processes, arises from organic sources. The biogenic energy content is generally considered renewable.

EfW was historically seen as a green source of energy, when compared, for example, to oil and gas, given that it was from approximately 50 per cent renewable sources. However, with the rising contribution of other renewable energy sources to our electricity mix, the ranking of EfW as a clean energy source has declined. This is reflected in recent regulation — it is proposed that, from 2028, EfW will be subject to carbon taxes for emissions related to non-renewable carbon sources.

Where EfW is used according to the waste hierarchy, processing only material that cannot be recycled, it is logical that the amount of organic material in the waste should reduce over time. Key drivers include:

• Source segregation. Food and garden waste should be source-segregated and composted or processed in anaerobic-digestion facilities. By 2026, most local authorities in England must offer separate collections. In Wales, all businesses producing more than 5 kilograms of food waste must separate it for collection.

• Dry mixed recyclables. Paper, card, and some plastics, metals and glass should continue to be collected separately, with minimal changes expected in the short term.

Extended producer responsibility. This aims for businesses to cover the full costs of managing waste produced, increasing financial incentives to reduce packaging materials and recycle more. As cardboard is a significant portion of packaging waste, less of it should end up in the residual waste stream. Less packaging waste would also mean less plastic waste, but the plastic packaging currently used is typically not easily recyclable, so this is likely to be residual waste until other options are available.

The actual biogenic energy fraction of waste feedstocks will vary by the minute, hour and season, as well as from facility to facility, depending on the type of waste processed, the amount of pre-treatment and even the weather. Currently, we do not have comprehensive data for all facilities using the testing method that will be required as part of the Emissions Trading Scheme (ETS). The current consultation (ending August 2024) includes a suggestion to use analysis of the levels of carbon-14 in flue gas for larger facilities, but the requirements are not yet clear.

In 2023, data for 48 EfW facilities in England indicated a biogenic energy content of 53.5 per cent. However, the method for reporting that figure is different from what will be required as part of the ETS. A 2020 report for BEIS showed an extrapolated decline in the percentage of biogenic content of residual waste, decreasing to 43 per cent by 2050.  A reduction has climate implications and major financial impacts, which need to be worked through.

Carbon-capture developers and EfW operators have an incentive for their facilities to process as much biogenic carbon as possible, reducing carbon tax and increasing negative carbon. However, they may be competing with circular-economy legislation, anaerobic-digestion facilities, and as technology develops, hydrogen producers.

This means that the organic fraction of the waste will become increasingly sought after, with the residual non-recycled, fossil-based materials less appealing.

It is possible that carbon taxes will have the desired effect and that changes to waste practices will see less plastic in the residual waste stream, keeping the overall proportion of biogenic energy in EfW feedstocks constant while the total amount of waste reduces. However, unless the competing factors are managed and legislation is written cohesively, there is a risk that projected carbon benefits are miscounted at the design stage. This could lead, at best, to higher costs and, at worst, to facilities designed to be carbon-negative actually becoming carbon emitters, when taking into account the energy required to actually capture the carbon.

It is essential to monitor the biogenic content of residual waste being processed in EfW facilities so that business models can be developed using accurate data. When modelling for the future, it is important to consider the multiple aspects of waste management, from education, social practices, collection and treatment, to the development of new materials with different compositions.