Ligia Tiruta-Barna

Long-term prediction of the leaching behavior of pollutants from solidified wastes

Abstract A methodology based on three experimental tests and a behavioral model was developed for the assessment of inorganic contaminant release from cement-based waste materials placed in an ‘immersed scenario’. The experimental ‘toolbox’ consists of the Pore water test (PWT), the Acid neutralization capacity test (ANC), and the Monolithic leaching test (ML). The experimental data supplied by the tests (leaching–available quantity, pore water composition, solubility vs. pH, released mass at the end of each leaching sequence) are the necessary input parameters for the behavioral model. The leaching model takes into account the transport phenomena coupled with main physico-chemical reactions in the saturated pore system of the material as well as in the eluate. The model, adapted to different scenarios, provides the concentration and the cumulative quantities released for each species. The methodology was applied on the wastes containing lead and stabilized/solidified with different hydraulic binders: two cements and a coal fly ash with lime. The stabilization of lead was better in the case of cement-based materials. The 10 years simulation of Pb release in the case of the particular scenario example, i.e. a water-storage reservoir built with the waste materials show that the lead concentration in stored water is higher than the accepted limit. Pb precipitation in the eluate can occur.

Environmental behaviour of a construction made of a mixture of hydraulic binders and air pollution control residues from municipal solid waste incineration Part 1. Physico-chemical characterisation and modelling of the source term

Abstract The reuse of waste materials requires the development of assessment methods for the long-term release of pollutants (source term) from wastes (or materials containing wastes) in contact with water. These methods depend on the scenario conditions: characteristics of the materials (especially physical structure and composition), contact with water. The scenario studied here is a water storage reservoir for fire fighting. The reservoir construction is made of a mixture of hydraulic binders and air pollution control (APC) residues from a municipal solid waste incinerator (MSWI). The modelling of the source term is performed in 5 steps ranging from the physico-chemical characterisation of the material to the validation of the proposed model by means of field simulation devices. This article presents the first steps of the methodology: physico-chemical characterisation of the source term, identification of the main transfer mechanisms and laboratory scale modelling of the source term. During the physico-chemical characterisation, it has been shown that the solidified waste shows a high basic capacity and that a relative decrease in pH during leaching favours retention of the main pollutants. During the first leaching sequences, the dynamic leaching tests show that the release of pollutants such as cadmium, arsenic, zinc and lead is extremely low but that the release of alkaline species (sodium and potassium) and chloride is very high from the beginning, whereas the release of calcium remains very high even after 3600 h of leaching. Identification of the main transfer mechanisms concludes that the release of soluble pollutants is the combined result of diffusional transfer of pollutants in the solution and the physico-chemical specificity of the species. The modelling based on these features enables a good simulation of the release but reveals a deviation from the experimental results after 500 h for alkaline species and 1000 h for Ca and Cl leaching. However, this deviation only appears after release of the major part of these elements.

Prediction of inorganic pollutant release from various cement based materials in disposa/utilisation scenario based on the application of a multi-parameter leaching tool box

The aim of this study is to assess the long term release of contaminants from cement based stabilised wastes. According to the methodology proposed by the European standard ENV 12 920, the impact of waste in disposal/utilisation scenarios has to be evaluated before being exposed to the environment. For this objective we propose a combined experimental and modelling procedure. Firstly a “tool box” consisting of some tests as the Pore Water simulation test (PW), the Maximum Leachable Fraction test (MLF), the Acid Neutralisation Capacity test (ANC), and the Monolithic Leaching Test (MLT) is used to characterise the waste containing material. Secondly the results of the tests are the necessary input parameters for the coupled physico-chemical leaching model that provides the long-term leaching behaviour. For applying the tool box and the model validation, Ordinary Portland Cement with additives was used to prepare the samples containing 25% of binder, 1% of Pb, and sand. The release mechanisms are described. The model provides the long-term release amounts of pollutants as well as the expected concentrations of pollutants in surrounding natural water over several centuries in the considered scenario conditions.

Accounting for the Emergy Value of Life Cycle Inventory Systems: Insights from Recent Methodological Advances

Emergy, due to its unique ability to translate into a single metric the memory of the geobiosphere exergy (environmental work) supporting any (technological or natural) system, has the potential to offer a new perspective of environmental assessment to support decision-making. Previous work by a number of researchers has pointed out the expected advantages of taking a hybrid approach combining Emergy Evaluation (EME) and Life Cycle Assessment (LCA). In particular, emergy calculation using Life Cycle Inventory (LCI) databases and LCA matrix-based formulation is claimed to have the potential to increase the reliability of emergy-based evaluations and thereby the applicability of the emergy concept in environmental decision-making. The paper points out the main obstacles to overcome in order to reach this consistent integration, highlighting the progresses made so far in this direction, until the most recent practical and operational advancements.

Environmental behaviour of a construction made of a mixture of hydraulic binders and air pollution control residues from municipal solid waste incineration Part 2. Simulation tests and validation of the source term modelling

Abstract The reuse of waste materials requires the development of assessment methods for the long-term release of pollutants (source term) from wastes (or materials containing wastes) in contact with water. These methods depend on the scenario conditions: characteristics of the materials (especially physical structure and composition), contact with water… The scenario studied here is a water storage reservoir for fire extinguishing. The reservoir construction is made of a mixture of hydraulic binders and air pollution control (APC) residues from municipal solid waste incinerator (MSWI). The modelling of the source term is performed in five steps ranging from the physico-chemical characterisation of the material to the validation of the proposed model by means of field simulation devices. This paper follows a first publication on source term modelling using laboratory tests which therefore concerns the comparison of the results obtained with the previously established model. The first laboratory scale simulation test aims at taking into account the role of the leachate carbonation in the leaching behaviour of the studied material. The results obtained show that air carbonation of the leachate does not fundamentally change mass transfer mechanisms of easily soluble species (especially for alkaline metals). For these species, the use of the apparent diffusional model (model proposed in the previous paper) is, therefore, at first, a satisfactory solution for the prediction of long term leaching behaviour. The field scale test enables us to validate and calibrate the release model determined on a laboratory scale basis.

Assessing the potential environmental hazards of concrete made using recycled aggregates (RAs)

This chapter starts with widely recommended and used methodologies for environmental assessment, with an overview of their application to construction materials. The concept of pollutant emission by leaching and its dependence on the materials involved is introduced, along with the parameters influencing the leaching process. The manner in which water contact with materials causes transfer, transport and dispersion of the contained contaminants is explained. Then the most relevant experimental tools dedicated to hazard identification and environmental performances are presented. These tools comprise laboratory leaching tests whose suitability for future standardisation in the field of construction materials is considered. Ecotoxicology tests could potentially be adapted to this standard testing method. The second part discusses recent research and discoveries concerning the leaching properties and potential hazards of materials of concern. The chemical behaviour of several pollutants in cement matrix is explained and examples of results obtained by leaching studies on concrete materials are discussed. Examples of studies on recycled aggregates (RA) from demolition as well as new concrete materials containing these wastes are also presented.