Practical guidelines on the classification under waste legislation of bottom ash from household waste incineration
Selective extraction provides information on bonding forms
The ITAD and IGAM associations are producing practical guidelines on waste legislation classification of slag and bottom ash from household waste incineration (HMV ash). The “selective extraction” developed by bifa Umweltinstitut for differentiated consideration of bonding forms will be an important part of these guidelines.
Substances with high chronic toxicity for aquatic life (hazard code H410) are primarily relevant for the assessment of how environmentally hazardous HMW ash is. The approach for differentiating between the bonding forms developed by bifa are based on the task of differentiating between substances that are harmful or have low toxicity for aquatic life (H411, H412…) and those with potentially high toxicity. This is done through selective extraction with weak acid at pH 4. Results determined with this method on the fractions to be classified as “non H410”, “potentially 410” and “definitely H410” are now available for many bottom ash samples taken from a range of waste incineration plants. Plants with different grating and furnace design were considered, as well as those which primarily recover substitute fuels energetically. None of the HMV ash samples examined were to be deemed hazardous on differentiated consideration of the substance groups, so that the practical guidelines come to the conclusion that HMV ash is generally not hazardous, but requires periodic checking on a case-by-case basis.
Optimisation of the method with regard to the recovery of substances classified to H410, the reproducibility and separation accuracy produced the best results with maleic acid (1.4 %) as the extractant and an extraction period of 24 h at room temperature.
The approach of differentiating between bonding forms can also be adapted in principle to other issues such as classification with regard to the Hazardous Incident Ordinance; and work on this is already in progress.