Incinerator Bottom Ash (IBA)
The ash resulting from the controlled combustion of waste, Incinerator Bottom Ash (IBA) is frequently only considered in relation to the residue from Residual Waste Incinerators. In this context it represents around 20% of input tonnage and includes Incinerator Bottom Ash Metals (IBAm) - which are later removed and recycled - and can be produced into a secondary aggregated called Incinerator Bottom Ash Aggregate (IBBA).
The residues from the combustion of waste associated with the removal of fine particulates and neutralisation of flue gases are more generaly knowm as Air Pollution Control (APC) Residues. Boiler ash residues are generally included in this stream.
Nature of Incinerator Bottom Ash
The nature of IBA can vary considerably according to the type of material combusted ranging from a quite granular material (for example from the combustion of MSW waste) through to a fine particle size ash (for example from the combustion of wood).
IBA can be classified as hazardous or non-hazardous in nature, reflective of the waste and any residual heavy metals, for example, and in some cases reflective of the process (i.e. where APC ash is sometimes incorporated into the IBA).
In one case in the UK at present (Hooton Biopower) the gasification approach produces a vitrified glass-type material also termed a 'vitrified slag'.
Biochar can be produced from a pyrolysis approach to wood-based materials, and can be appled to land if the input feedstock is clean (generally not waste materials).
Tonnage
Not only can the nature of IBA vary, the tonnage left after the combustion process can also vary consdierably (see table below).
Generally Clinical and High Temperature Incinerators have lower percentages of IBA and higher percentgaes of APC (the reverse being the case for generally 'cleaner' biomass feedstock).
The total tonnage of Residual Waste EfW IBA was 6.3 million tonnes in 2024. The total IBA from all other incinerators listed in WikIWaste and referred to in the table was just under 200,000 tonnes in 2024.
Only IBA from Municipal Incinerators[1] (those generally listed as Residual Waste Incinerators in WikIWaste) can be used to produce IBAA if it is non-hazardous in nature.
Incinerator Bottom Ash % by Type of Incinerator
Type of Incinerator | Average (%) | Maximum (%) |
|---|---|---|
18.2 | 26.2 | |
4.2 | 20.4 | |
14.1 | 24.2 | |
11.6 | 15.7 |
Notes
- The figures come from analysis of individual incinerators' annual reports in 2024[2] and is the IBA divided by the Total Combusted
- The percentage can vary considerably based on the waste incinerated and the type of combustion approach
- The high temperature analysis includes only East Kent , Ellesmere Port, and Fawley
- Cement Kilns are not included in the table as the ash produced is essentially the clinker used in the production of cement
