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Laboratory leaching tests may be used for source term determination as a basis for risk assessment for soilgroundwater pathway (leachate forecast) on contaminated sites in Germany. Interlaboratory comparisons on the evaluation of the reproducibility of column percolation tests were conducted within the framework of an integrated R + D program using three waste reference materials.
The interlaboratory comparisons of column percolation tests showed good reproducibility of the results for inorganic and organic parameters as well as for the accompanying parameters. This is due to the stipulations concerning the time of contact between leachant and sample material as well as the sample placement in the columns. Different column dimensions used by the participants of the interlaboratory comparisons did not have any substantial influence on the column test results.
Laboratory leaching tests may be used for source term determination as a basis for risk assessment for soilgroundwater pathways on contaminated sites. In order to evaluate different leaching procedures, batch extraction tests and percolation tests were performed using three reference materials produced from contaminated soil, demolition waste and municipal solid waste incinerator bottom ash. Emphasis was placed on the investigation of the leachability of the heavy metals copper and chromium, polycyclic aromatic hydrocarbons (PAHs) and the anions chloride and sulfate. Significant discrepancies between column experiments and batch/extraction tests were found for the release of PAHs and to a lesser extent for the heavy metals Cu and Cr. Additionally interlaboratory comparisons were conducted based on different leaching tests with the reference materials and evaluated using the criteria of comparability and reproducibility. The best reproducibility was achieved for all investigated substances in column tests. The reproducibility of batch tests was acceptable except for PAHs. The results from the experimental work will help establish standardized and feasible laboratory procedures as fundamental for substance specific risk assessment of contaminated sites.
This article presents a snapshot of key issues regarding characterization of granular waste materials with respect to their reuse as alternative construction materials, and the factors that need to be considered in their reutilization in order to comply with soil and groundwater protection regulations.
When reusing or disposing of contaminated granular waste materials there is a need to evaluate how the contaminants will interact on the pathway soil-groundwater and the effect this interaction will have on the surrounding environment. While column testing can provide a closer approximation to field percolation conditions than batch testing, there is still a need to develop column testing procedures that consider the requirements of practical testing time frames. This study evaluates the effect of different column contact times (2.5, 5, and 16 h) on the release of inorganic constituents from bottom ash and demolition waste, two commonly reused granular materials. Leaching data for representative constituents of concern, such as copper, chromium, sulfate and chloride, as well as pH and electrical conductivity was compared for all different contact times studied.
Results for the materials investigated in this study showed that variations in contact time have no significant effect on the release of the selected constituents and leaching parameters at low liquid to solid ratios. However, after a liquid to solid ratio of 1 L/kg, the effect is more noticeable, and higher contact times show lower pH values as well as a reduction in the release of constituents of concern from bottom ash. In the case of demolition waste, the variation of contact time did not have a strong effect on the leaching behavior.
A sustainable recycling of photovoltaic (PV) thin film modules gains in importance due to the considerable growing of the PV market and the increasing scarcity of the resources for semiconductor materials. The paper presents the development of two strategies for thin film PV recycling based on (wet) mechanical processing for broken modules, and combined thermal and mechanical methods for end-of-life modules. The feasibility of the processing steps was demonstrated in laboratory scale as well as in semi-technical scale using the example of CdTe and CIS modules. Pre-concentrated valuables In and Te from wet mechanical processing can be purified to the appropriate grade for the production of new modules.
An advantage of the wet mechanical processing in comparison to the conventional procedure might be the usage of no or a small amount of chemicals during the several steps.
Some measures are necessary in order to increase the efficiency of the wet mechanical processing regarding the improvement of the valuable yield and the related enrichment of the semiconductor material.
The investigation of the environmental impacts of both recycling strategies indicates that the strategy, which includes wet mechanical separation, has clear advantages in comparison to the thermal treatment or disposal on landfills.
Leaching tests are fundamental tools for the assessment of long-term impact of contaminated waste materials on the soil-groundwater pathway. Experiments were carried out in the framework of standardization and validation of column percolation and batch test procedures, in particular concerning the stipulation of the experimental setup. The colloid release of column and batch experiments was compared and the influence of different column filling heights (12.5–50 cm) on the release of polycyclic aromatic hydrocarbons (PAH) from soil was studied, as well as the effect of varying contact times (2.5–16 h) on the release of chromium from construction and demolition (C&D) waste and municipal solid waste incineration (MSWI) bottom ash. The results indicate that filtration of the eluate, which is required for batch tests, does not always allow the simulation of the actual colloid amount in soil pore water. Medium column heights four times the inner diameter of the column seemed to provide reasonable equilibrium adjustment conditions and avoid major biodegradation. The release of chromium was only marginally affected by the contact time, varied between 0.115 and 0.150 mg/kg for demolition waste eluate at a liquid-to-solid ratio of approximately 5 L/kg.
Raw material supply is essential for all industrial activities. The use of secondary raw material gains more importance since ore grade in primary production is decreasing. Meanwhile urban stock contains considerable amounts of various elements. Photovoltaic (PV) generating systems are part of the urban stock and recycling technologies for PV thin film modules with CdTe as semiconductor are needed because cadmium could cause hazardous environmental impact and tellurium is a scarce element where future supply might be constrained. The paper describes a sequence of mechanical processing techniques for end-of-life PV thin film modules consisting of sandblasting and flotation. Separation of the semiconductor material from the glass surface was possible, however, enrichment and yield of valuables in the flotation step were non-satisfying. Nevertheless, recovery of valuable metals from urban stock is a viable method for the extension of the availability of limited natural resources.