Waste legislation classification of bottom ash from household waste incineration
Differentiating analysis allows conclusions to be formed regarding chemical bonding forms
Slag from household waste incineration ("HMV bottom ash") is the most important residual material of waste incineration, accounting for around 20 % of the waste quantity. In 2016, around 610,000 t bottom ash was produced in Bavarian waste incineration plants; most of this ash was recovered (recycled).
HMV bottom ash contains metals, which on the one hand have recoverable potential and on the other hand, heavy metals are a risk to the environment.
Depending on their hazardous substances content, HMV bottom ash can be "non-hazardous" (waste code number (EWC) 19 01 12) or they must be classified as hazardous waste (EWC 19 01 11*). in general, the risk-relevant property HP 14 proves to be critical for the classification: "hazardous to the environment", which from July 2018 must be evaluated according to the new provisions of the Waste Framework Directive. The total content of the copper, zinc and lead elements at around 1 % (in total) is so high that HMV bottom ash must be classified as hazardous waste, if the classification is based on the total content and the assumption of high toxicity. This would probably have serious effects on the recovery options.
Large fractions of cooper zinc and lead exist in HMV bottom ash in metallically pure form or as alloys. But compact metals are not to be considered dangerous (under waste legislation), so that only correct determination of these fractions is important for the classification. Further differentiation is possible by type of chemical bonding: For example, copper and zinc in mixed oxides with spinel structure and in several silicates are so tightly bonded that they are not released into the environment and therefore do not have an ecotoxic effect.
bifa has developed a sampling and analysis schema, which enables differentiation between substance groups with different ecotoxicity for correct determination of the critical heavy metal fractions present as metals and to differentiate between bonding forms. Therefore, differentiated consideration of the bonding forms is possible and provides the basis for more detailed classification.
The bottom ash examined by bifa to date using the new analysis schema can be classified as "non-hazardous waste".