Müllverbrennungsschlacken: umwelt- und verwertungsrelevante Eigenschaften: Fid-Bau Portal

Müllverbrennungsschlacken: umwelt- und verwertungsrelevante Eigenschaften

Riedel, H.

Re-utilization of municipal solid waste incineration (MSWI) bottom ash in civil engineering requires compliance with quality standards defined in terms of bulk and leachate concentrations. In addition, solid phase properties (shear strength, compactability, resistance to freeze/thaw cycles etc.) comparable to natural construction materials are necessary. Addressing the perspectives and possible constraints of bottom ash recycling, this study includes the results of laboratory analyses, a field leaching experiment (6 m³ bottom ash), and a survey of several construction projects in which MSWI bottom ash was used as a grounding material. Special attention was put on the effects of ageing processes on pollutants' mobilities. Solid phase organic and inorganic contaminant levels scatter considerably, but typically meet the standards of LAGA bulletin M19 for bottom ash recycling. In terms of both the solid and aqueous phase (according to DIN 38414 part 4), concentrations are higher in the fine-grained fraction (to 8 mm) than in the coarse-grained fraction (8 to 32 mm). Mineral reactions during bottom ash ageing increase the specific surface area, carbonate contents and loss on ignition. Although being most intense during the first three months, ageing processes remain detectable for two years. They may be enhanced by process-integrated operations (e.g. carbon dioxide-flushing, moisturing, and/or storage at minimized heat loss). After ageing, the leachates of the coarse-grained bottom ash fraction meet the limit values of LAGA. However, this does not apply to the fine-grained fraction, particularly owing to excess chloride concentrations. Laboratory and field leaching tests show ambiguous results: While peak pollutant concentrations in the seepage water (field) are severely underestimated by the static batch test (lab), medium-term contaminant loads are adequately predicted. The survey of several construction projects shows that chemical properties of the bottom ash body are unaffected by the time elapsed since building operations while a positive effect was observed for the leachability of contaminants. Thus, to further minimise leachate emissions, storage periods longer than the prescribed three months may be recommendable. Mechanical soil properties of compacted bottom ash bodies are comparable to natural materials used in earth-moving and foundation works. Concluding, recycling of MSWI bottom ash in civil engineering may be a suitable re-utilization strategy. Precautions to be taken include: long-term quality management by the manufacturer, careful handling by executing companies, optimum moisture content to assure a high degree of compaction and prevent dust emissions during transport, handling, and construction. After completion, access of precipitation should be hindered.