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Potential use of incineration bottom ash in construction – Evaluation of the environmental impact
(2020)
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.
This Special Issue, ‘Measurement of the Environmental Impact of Materials’, is focused on the impact that materials have on the environmental compartments of soil, water and air. Leaching and emission processes, including underlying mechanisms, are a recurring topic in most published articles in the present Special Issue. Contributions have come from three continents and numerous countries (USA, Germany, France, Latvia, Poland, Russia, Japan, Korea and Thailand) indicating the global dimension of the subject.
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.
Half of global material consumption involves mineral material. The circularity is still low so that the enhanced use of secondary building material is required to close loops. Three different secondary building materials are discussed based on exemplary research results: construction and demolition waste (C&D waste), soil-like material, and incineration bottom ash (IBA). Focus was placed on the environmental compatibility of the materials examined mainly by standardized leaching tests. C&D waste was investigated after a wet treatment using a jigging machine, and soil-like material and IBA were characterized with respect to their material composition. Their environmental compatibilities in particular were studied using standard leaching tests (batch tests and column tests).
It was concluded that soil-like material can mostly be utilized even when the precautionary limit values set are exceeded by a factor of less than two. For C&D waste, the fine fraction below 2 mm and the content of brick material is problematic. IBA fulfills quality level “HMVA-2” following German regulations. Improved levels of utilization might be achievable with better treatment technologies.
Antimony in incineration bottom ash – Leaching behavior and conclusions for treatment processes
(2020)
Antimony (Sb) is used in industrial products mainly as flame retardant in plastic material. Due to such additives in plastics, about a half of Sb ends up in municipal solid waste incineration at the end-of-life and consequently in relevant amounts in the generated bottom ash. In contact with water, the initial leachability is low, as antimonates form sparingly soluble compounds with Ca2+. Following the carbonation of the incineration bottom ash (IBA) during the proceeding ageing the pH in the leachates decreases. With decreasing concentration of Ca in the eluate the solution equilibrium changes and antimonates dissolve. In Germany it is intended to regulate Sb in IBA with the planned implementation of the so called Mantelverordnung (MantelVO, containing provisions on the utilisation of mineral waste) in the near future. The limit values set in the draft might be critical for IBA and therefore pose a risk for the utilisation of the mineral fraction of IBA in the well-established recycling routes.
Leaching experiments on the release of heavy metals and PAH from C&D waste and MSWI bottom ash
(2010)
Leaching tests are fundamental tools for the assessment of long-term impact of
contaminated waste materials on the soil-groundwater pathway. Waste materials should be
tested under conditions equal to their actual application in re-use scenarios to achieve reliable
results. Since the standards for leaching procedures available on international level so far are
either not validated or considered inadequate in respect to coarse grained materials, new
standards had to be developed. Therefore column percolation and batch test procedures have
been standardized and validated to enable their introduction to new German regulations
concerning waste management. Practical aspects of the test procedures as well as the
boundary conditions compared to the already existing standards will be described. Examples
including round robin test results will be given to justify the selection of the new
specifications.
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.
The potential release of hazardous substances from polymer-based products is currently in the focus of environmental policy. Environmental simulations are applied to expose such products to selected aging conditions and to investigate release processes. Commonly applied aging exposure types such as solar and UV radiation in combination with water contact, corrosive gases, and soil contact as well as expected general effects on polymers and additional ingredients of polymer-based products are described. The release of substances is based on mass-transfer processes to the material surfaces. Experimental approaches to investigate transport processes that are caused by water contact are presented. For tailoring the tests, relevant aging exposure types and release quantification methods must be combined appropriately. Several studies on the release of hazardous substances such as metals, polyaromatic hydrocarbons, flame retardants, antioxidants, and carbon nanotubes from polymers are summarized exemplarily. Differences between natural and artificial exposure tests are discussed and demonstrated for the release of flame retardants from several polymers and for biocides from paints. Requirements and limitations to apply results from short-term artificial environmental exposure tests to predict long-term environmental behavior of polymers are presented.
Im Zusammenhang mit der Novellierung der Bundes-Bodenschutzverordnung und der Einführung einer Ersatzbaustoffverordnung wurden vom DIN-Normenausschuss Wasserwesen, Unterausschuss "Eluierungsverfahren" zwei Verfahren zur Elution von Feststoffen erarbeitet. Dabei handelt es sich um ein Säulenperkolationsverfahren zur gemeinsamen Untersuchung des Elutionsverhaltens von organischen und anorganischen Stoffen und ein Schüttelverfahren mit einem Wasser-/Feststoff-Verhältnis (W/F) von 2 l/kg zur Untersuchung der Elution von anorganischen Stoffen. Beide Verfahren sind für Bodenmaterialien und mineralische Abfälle mit einer Korngröße bis 32 mm vorgesehen. Der Vergleich der Praktikabilität der beiden Elutionsverfahren soll zur Diskussion zu deren Einsatz im Rahmen der geplanten bundeseinheitlichen gesetzlichen Regelungen beitragen, welche gegenwärtig kontrovers geführt wird.