Treatment of MSWI bottom ash (BA) helps to save resources in the sense of recovering valuable metals while simultaneously minimizing the environmental risk as a result of upgrading the quality of the residue fraction (through decreasing metals, organic content, salts in the case of washing, etc.).
The possible environmental risks are mainly related to the composition of bottom ash, handling, transport, utilization and disposal of bottom ash due to leaching, dust and gas emissions.
Leachate which is generated may have an impact on the environment (ground water, surface water, etc). This may occur during the temporary storage, treatment or reuse as well as during the final disposal of the material.
Dust emissions are due to a high content of fine particles in MSWI bottom ash. Those particles typically contain chloride and sulfate salts as well as heavy metals such as lead, copper and zinc. These contaminants may create health risks to workers and to the public, and may contribute to soil contamination.
Temperature and gas emissions result from the corrosion of metals (e.g. aluminium hydration=>hydrogen production) or the hydration of alkaline and alkaline earth oxides or the carbonation of portlandite. This effect could result in explosive combustion.