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(Vassilev et al., 2010)

In 2019, the UK burned 2,439,339 tonnes of recycled wood for energy (Ofgem, 2021), around 20% of the total biomass fuel used.

Due to treatments and contamination, waste wood can result in higher emissions than virgin wood (Röder and Thornley, 2018). In the UK, it is categorised A-D in terms of quality, contamination and treatment (WRAP, 2012). Grade A wood is essentially untreated, and can be co-incinerated with virgin wood (Tolvik, 2020), Grade B contains a small amount of non-hazardous contamination such as glues, nails and paint, C contains a larger proportion and Grade D contains hazardous contaminants such as creosote treatment.

As a result of the mineral and metal contamination, alongside pollutants, recycled wood is often classed as hazardous and generates a greater proportion of ash than virgin wood (Vassilev et al., 2010).

Research also indicates potentially high levels of dangerous heavy metal contaminants (Demeyer, Voundi Nkana and Verloo, 2001). Paints and other treatments used on timber might only represent a thin surface layer in use, but when the timber is burned and the organic matter is reduced by an 97.3%, the minerals that make up these treatments can end up highly concentrated in the ashes

(Vassilev et al., 2010)
(WRAP, 2012)
(Tolvik, 2020)