Assessment of the Long-Term Leaching Behavior of Incineration Bottom Ash: A Study of Two Waste Incinerators in Germany

Abstract

The long-term leaching behavior of incineration bottom ash (IBA) was studied with large-scale samples from two German waste incinerators with grate technology. The observation period was up to 281 days. The aging processes proceeded faster in the outdoor storage of the samples. The dominant factor in the leaching behavior is the pH, which starts at values above 12 and decreases to values below 10 (outdoors, <11 indoors). Most heavy metals exhibit minimum solubility in this pH range. The solubility of Sb depends on the prevailing Ca concentration, due to the formation of low-soluble Ca antimonate. The very low sulfate concentrations observed in the leaching tests with fresh IBA could be explained by the presence of ettringite. In the course of the aging reaction, ettringite is transformed into gypsum. The results from batch tests were compared with those from column tests, showing reasonable agreement. Leaching dynamics can be better followed with column tests. All results confirm that the use of IBA is possible under German law.

Sequential Extraction of Incineration Bottom Ash: Conclusions Regarding Ecotoxicity

“…In the cited work, the leachate was prepared with an L/S of 10 L/kg and then diluted by factors of 2, 4, and 8. The leachate of a moderately aged IBA has a pH of 11 [21], and even with a dilution by a factor of 8, the resulting test solution has a pH higher than 8.5, which is, however, recognized as the maximum pH for biotests. At higher pH values, the test organisms already show effects due to the pH.…”

“…Further, setting a cut-off value (here, 0.1%) leads to non-consideration of other heavy metals rather than Cu and Zn. However, a longer list of heavy metals is under consideration for landfilling or utilization of IBA [21].…”

“…In a recent publication [21], it was shown that in Germany, IBA can be landfilled on a landfill class DK I [41] and utilized according to quality class HMVA-2 of the secondary building material ordinance [42].…”

“…Both sulfates of Zn and Cu belong to this group. In a recent publication, it was shown that for the above-mentioned metals the leached amount is well below the cut-off value of 1000 mg/kg even when the stochiometric factors are applied [21]. Substance group 3 includes potential H410 substances.…”