Abstract
Knowledge of the long-term leaching behavior of potentially harmful substances is crucial for the assessment of the environmental compatibility of reusing municipal solid-waste incineration bottom ash (MSWI BA) in construction, i.e., as a road base layer. BA fractions obtained from wet-processing aiming at the improvement of environmental quality were used to investigate the mobility of relevant substances. Eluates from laboratory-scaled leaching procedures (column percolation and lysimeters) were analyzed to learn about the long-term release of substances. Unsaturated conditions and artificial rainwater (AR) were used in the lysimeter tests to simulate field conditions. In addition, batch test eluates were generated at usual liquid-to-solid ratios (L/S) for compliance testing purposes. A variety of cations and anions was measured in the eluates. The wet treatment reduces the leaching of chloride and particularly sulfate by more than 60%. The release of typical contaminants for the treated MSWI BA such as the heavy metals Cu and Cr was well below 1% in the conducted leaching tests. An increase in the Sb concentration observed in the lysimeter experiments starting at L/S 0.75 L/kg and in the column experiment at L/S 4 L/kg is assumed to be related to decreasing concentrations of Ca and thus to the dissolution of sparingly soluble calcium antimonate. The same leaching mechanism applies with V, but the concentration levels observed are less critical regarding relevant limit values. However, on the long term the behavior of Sb could be problematic for the application of MSWI BA in construction.Graphic
Highlights
68 million tonnes of municipal solid waste were incinerated in 2017 in the EU-28 countries [1] which resulted in about 15 million tonnes of municipal solid-waste incineration bottom ash (MSWI BA) and represents a valuable source for secondary raw materials
Following DIN 19528, a flow rate of 4.35 mL/min was applied to obtain 5 h contact time between leachant and sample. Whereas such column percolation tests are usually performed up to an liquid-to-solid ratios (L/S) of 4 L/kg, the tests in this study were extended to an L/S of approximately 10 L/kg to make it possible to compare the release of substances with the other leaching tests and especially to study the long-term behavior of Sb
The process was realized in two plants in Germany, one near a waste incineration plant and a second where the ash material was delivered by combined ship and truck transport
Summary
68 million tonnes of municipal solid waste (about 27% of total amount) were incinerated in 2017 in the EU-28 countries [1] which resulted in about 15 million tonnes of MSWI BA and represents a valuable source for secondary raw materials. We performed accompanying investigations regarding the mass balance of the process and the leaching behavior of the various processed fractions [21] In this manuscript, eluate analyses from batch leaching, column percolation, and lysimeter tests in laboratory scale were thereby discussed to learn more about the long-term release of hazardous substances from bottom ash in civil engineering applications, e.g. road construction [2, 22]. Following DIN 19528, a flow rate of 4.35 mL/min was applied to obtain 5 h contact time between leachant and sample Whereas such column percolation tests are usually performed up to an L/S of 4 L/kg, the tests in this study were extended to an L/S of approximately 10 L/kg to make it possible to compare the release of substances with the other leaching tests and especially to study the long-term behavior of Sb. In contrast to the lysimeter experiments, saturated conditions prevailed in the laboratory column tests. ICP-MS measurements were performed from tenfold dilutions with a Thermo Scientific iCAP Qc [42]
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