Field Studies Of MSWI Bottom Ash As Aggregate For Unbound Base Course Mixtures

In the European Union, about 30–40 million tonnes of residues known as municipal solid waste incinerator (MSWI) bottom ash is generated and landfilled annually. To address the continuous growth of landfills and to implement zero waste and circular economy policies, researchers are researching ways to turn MSWI bottom ash into a useable resource. The conducted studies show that MSWI bottom ash is suitable for civil engineering, especially for roads, however there is a lack of field studies. As a result, MSWI bottom ash was used to construct unbound base course in heavy vehicles parking lot in 2018 and two pedestrian paths in 2018 and 2020 in Vilnius (Lithuania). This paper focuses on the structures composition and performance of those unbound base courses in terms of stability of particle size distribution, bearing capacity and permeability. The conducted study showed promising results for MSWI bottom ash as aggregate (mixture) to construct unbound base course.

A Study of State Parameters for Road Construction of MSWI Bottom Ash

The current work tries to valorize the bottom ash from Municipal Solid Waste Incineration (MSWI). The bottom ash from waste incineration consists of atypical granular materials. They are industrial by-products resulting from the incineration of domestic waste and the way of the considered valorization is road gravel. In this paper, we present the state parameters of bottom ash taken from a recycling company in the North of France. These features can help us evaluate our bottom ash according to the technical guide of realization of embankments and subgrades.

Effects of enhanced metal recovery on the recycling potential of MSWI bottom ash fractions in various legal frameworks

In recent years, complex new bottom ash treatment processes for enhanced metal recovery have been implemented in Switzerland, producing residual bottom ash fractions with various qualities. This study focusses on three different treatment processes by characterizing all arising fractions in detail. Thereby the factors influencing the composition of these fractions are identified and their recycling potential in Switzerland is investigated. However, high legislative requirements on total contents of heavy metals represent a high barrier for bottom ash recycling in Switzerland. Therefore, the recycling potential is further evaluated based on the waste legislation applied in the Netherlands, where recycling of bottom ash has a long tradition. There, threshold values for bottom ash recycling are based on leachate concentrations and not on total contents as in Switzerland. However, Swiss Waste Legislation also knows threshold values based on leachate concentrations for certain waste materials. The leaching tests applied in these two countries, however, are different. The comparison of both leaching tests reveals that the setup and conditions, especially the considered pH range, significantly influence the leaching of heavy metals. With emphasis on problematic pollutants, the possibilities for new applications of these fractions are evaluated based on Swiss and Dutch legal threshold values. The comparison within the legal frameworks of these two countries allows recognizing opportunities and risks related to bottom ash recycling.

Assessing The Impacts of Wet Treatment On Leaching Toxicity of Municipal Solid Waste Incineration Bottom Ash

Wet-treatment is usually employed to recover metals from bottom ash (BA). However, its effectiveness on regulating the leaching behavior of BA and minimizing environmental impact is still unquantified when BA is used as engineering materials. This study investigated the leaching behavior of targeted pollutants including Cu, Zn, Ni, SO42- and Cl- in fresh bottom ash (FBA) and treated bottom ash (TBA) using batch, standard column up-flow leaching and simulated rainfall down-flow leaching tests. It was firstly noted by the batch leaching that the potential ecological risk of MSWI bottom ash could not be ignore during its reutilization, and wet treatment enabled reduce the leaching concentration of Cu, Zn, Cl- and SO42- by 7.1%, 33.8%, 46.3% and 18.9%, respectively. The leaching concentrations of the targeted ions in FBA are generally higher than those of TBA. Furthermore, when BA was applied in water dynamic system such as rainfall environment, its toxicity leaching should be paid more attention onto the early leaching stage with a very high water dissolved salts release, such as Cl- and SO42-. The leaching concentration of Cu particularly exceeded the limit value before L/S=1. Meanwhile, it was also found that the leaching of SO42-, Ni, Cu and Zn in water dynamic system were directly proportionate to the liquid-to-solid (L/S) ratio. The leaching concentration of the pollutants obtained from the simulate rainfall down-flow tests was usually 4-6 times higher than those from the standard up-flow column when at the same ratio of liquid and solid.

Performance of concrete mixtures containing MSWI bottom ash

In the European Union, each inhabitant annually generates about 500 kg of municipal waste. About 30 % of this are incinerated in waste-to-energy plants. It results in approximately 20 million tonnes of residues known as municipal solid waste incinerator (MSWI) bottom ash, which is typically landfilled. To address the continuous growth of landfills and to implement zero waste and circular economy policies, researchers are focusing on possibilities to use MSWI bottom ash in civil engineering instead of landfilling. One of them is to replace natural aggregates in concrete mixtures applicable for roads with MSWI bottom ash. Therefore, the subject of this research is the performance of concrete mixtures containing different amount (0–100%) and fraction (0/5–0/16) of MSWI bottom ash. Four specimens with similar aggregate gradations were designed. Each of them was mixed with two different amount (340 kg/m3 and 300 kg/m3) of cement (CEM I 42.5 R). In total eight different concrete mixtures were tested and analysed. The performance of designed concrete mixtures containing different amount of MSWI bottom ash was evaluated according to density and compressive strength after 28 days. The results showed good MSWI bottom ash performance as a substitute for natural aggregates. The compressive strength after 28 days varied from 21 MPa to 29 MPa depending on the aggregate type and amount of MSWI bottom ash and cement. For concrete mixtures made only of MSWI bottom ash at least 340 kg/m3 of cement is required to achieve compressive strength higher than 20 MPa.

Positive Influence of Liquid Sodium Silicate on the Setting Time, Polymerization, and Strength Development Mechanism of MSWI Bottom Ash Alkali-Activated Mortars

Setting time and mechanical properties are key metrics needed to assess the properties of municipal solid waste incineration (MSWI) bottom ash alkali-activated samples. This study investigated the solidification law, polymerization, and strength development mechanism in response to NaOH and liquid sodium silicate addition. Scanning electron microscopy and X-ray diffraction were used to identify the formation rules of polymerization products and the mechanism of the underlying polymerization reaction under different excitation conditions. The results identify a strongly alkaline environment as the key factor for the dissolution of active substances as well as for the formation of polymerization products. The self-condensation reaction of liquid sodium silicate in the supersaturated state (caused by the loss of free water) is the major reason for the rapid coagulation of alkali-activated samples. The combination of both NaOH and liquid sodium silicate achieves the optimal effect, because they play a compatible coupling role.