Challenge: Management of fly ash, air pollution control residue (APCr) and cement kiln dust (CKD)
Most thermal processes used for energy generation by coal combustion, waste-to-energy, and geothermal energy production methods generate fly ash and air pollution control residue (APCr), often characterised by elevated soluble salt and hazardous metals content, requiring removal before safe land disposal, recycle or other beneficial uses.
Other industrial operations producing similar residue include municipal/industrial sewage waste incineration operations, that generate fly ash containing elevated concentrations of soluble salts and heavy metals. Cement manufacturing operations also produce cement kiln dust, often requiring removal of soluble salts and hazardous metals prior to reuse or safe land disposal.
Although there is a global drive towards recycle or reuse of fine residues, a common environmental/cost issue relates to association of soluble salt and metals with such solid residues, which requires washing these residuals with freshwater (prior to recycle/reuse), generating a new saline waste stream. Depending on the local disposal regulatory regime further treatment may be required for safe landfilling of such saline waste or for acceptance by a hazardous waste management facility.