Pilot-scale road subbase made with granular material formulated with MSWI bottom ash and stabilized APC fly ash: environmental impact assessment

Categorization of leaching behaviors of elements from commercially treated incineration bottom ash in Singapore

Leaching of potentially hazardous substances, especially the heavy metals from Incineration Bottom Ash (IBA) is a major problem in its recyclable usage. To address this concern, treatment of IBA is indispensable before it can be reused. IBA subjected to laboratory-scale treatment typically yields clearer conclusions in terms of leaching behaviors, benefiting from the controlled laboratory environment. However, the leaching behaviors of commercially treated IBA appear to be more ambiguous due to the complex and comprehensive nature of industrial-scale treatments, where multiple treatment techniques are involved concurrently. Furthermore, treatment efficiencies vary among different plants. In this study, three types of commercially treated IBA were sampled from leading waste treatment companies in Singapore. Characterization and leaching tests were performed on the treated IBAs in both standardized and modified manners to simulate various scenarios. Besides deionized water, artificial seawater was used as a leachant in leaching tests for simulating seawater intrusion. The results reveal the promoting effect of seawater on the leaching levels of several elements from three types of treated IBA, which may require special attention for IBA application and landfill near the coast. Furthermore, the elements examined in these three types of commercially treated IBA generally comply with the non-hazardous waste acceptance criteria outlined in Council Decision, 2003/33/EC (2003), except Sb. By combining two leaching tests, the elements were categorized into different types of leaching behavior, making it possible to prepare and respond to the concerning leaching scenarios in future engineering applications.

MSWIFA and cement cooperate in the disposal of soft soil - experimental study on silty sand and silty clay

Municipal solid waste incineration fly ash (MSWIFA) can be reused as a positive additive to strengthen soft soil. In this study, MSWIFA was initially used as a supplementary solidification material in combination with ordinary Portland cement to prepare fly ash cement-stabilized soil (FACS) with silty sand and silty clay, respectively. The ratio of MWSIFA to total mass was 5%, 10%, and 15%, and the cement content was set as 10% and 15%. The mechanical properties of FACS were evaluated by unconfined compressive strength test. The heavy metal-leaching test was conducted to estimate the environmental risk of FACS. The scanning electron microscope was used to test the micro-structure of FACS. The X-ray diffraction was performed to analyze material composition of FACS. The result indicates that the collaborative solidification of soft soil with MSWIFA and cement is feasible. Regarding the silty clay, the FA had positive effects on the silty clay in the service age (between 50 and 100% with 15% MSWIFA), as the MSWIFA reformulated the initial silty clay structure, resulting in interconnection and pore fill between particles. It can be founded that C-S-H and ettringite are the main products of MSWIFA and cement hydration, which are formed by the hydration of C3S and C2S. Regarding the silty sand, the MSWIFA decreased the peak strength (between 35 and 48% with 15% MSWIFA) but increased the ductility of the stabilized cement. Under the same mix proportions, the leaching toxicities of Zn and Pb in FACS of silty clay were obviously lower than were those of silty sand. Generally, the leaching concentrations of tested metals under all the mix proportions were well below the limit value set by GB 18598-2019 for hazardous waste landfill. Thus, the reuse of MSWIFA in cement-stabilized soil would be one of the effective methods in soft soil treatment and solid waste reduction.

Characterization of contaminant leaching from asphalt pavements: A critical review of measurement methods, reclaimed asphalt pavement, porous asphalt, and waste-modified asphalt mixtures

In recent years, the pavement industry has been seeking sustainable development through recycling reclaimed asphalt pavement and reusing other waste materials as replacements for asphalt mixture constituents. Incorporating waste material into asphalt mixture and the presence of pollutants such as exhaust fumes and gasoline due to vehicle traffic may lead to contaminants leaching from asphalt pavements to underlying soil layers and groundwater aquifers, posing serious risks to ecosystems and the environment. To cast light on contaminant leaching from asphalt pavements, this article presents a comprehensive review of the literature that is divided into four research areas: evaluation of leaching measurement methods, leaching from recycled asphalt materials, leaching characteristics of porous asphalt pavements, and waste-modified asphalt mixtures. Moreover, a critical discussion of bibliometric data, literature content and knowledge gaps in this domain is provided to help highway agencies and environmental scientists address contaminant leaching from asphalt pavements. Finally, some potential research directions are suggested for future research works.

Evaluating the Performance of Lateritic Soil Stabilized with Cement and Biomass Bottom Ash for Use as Pavement Materials

From the perspective of sustainable waste management and its environmental impact, waste biomass bottom ash (BA) remains problematic and challenging to use as a recycling material for civil engineering infrastructures. This study evaluated the performance of lateritic soil (LS), stabilized with cement and biomass BA, as a subbase material. BA has been considered a replacement material in LS prior to the introduction of hydraulic cement stabilization means. The geotechnical engineering tests comprised the modified Proctor test, the California Bearing Ratio (CBR) test, and the unconfined compression test. X-ray fluorescence (XRF) and X-ray diffraction (XRD) tests were conducted to investigate the mineralogical properties of the stabilized soil samples. The leachate test was performed with a permeability mold to measure the release of heavy metals. Finally, the benefits of using the stabilized subbase material were assessed using the mechanistic–empirical (M–E) pavement design approach. Based on the results obtained, the strength and stiffness characteristics of the stabilized soils indicate that the efficiency of the mix satisfied the Thailand highway specification. The admixture of 80% BA and 5% cement is suggested for use as a soil–cement subbase material for flexible pavements, due to its good engineering and environmental properties. The results of the M–E design demonstrate the effectiveness of the stabilized soil presented herein. The study’s outcomes are predicted to promote the utilization of waste BA as a promising pavement material.

Durability and Sustainability of Cement-Stabilized Materials Based on Utilization of Waste Materials: A Literature Review

The utilization of waste materials in cement-stabilized materials (CSMs) is an important way to promote the sustainable development of road engineering construction and solve the environmental problems caused by the accumulation of waste materials. With the increasingly prominent global environmental problems, the exploitation of natural aggravate and the production of cement are subject to strict management and restrictions. Different waste materials, such as industrial and mining wastes, construction and demolition wastes, municipal wastes, waste rubber and waste fiber, are utilized in CSMs, and this is beneficial to promote the sustainable development of CSMs. In order to promote the rational application of waste materials in CSMs, this paper systematically reviews the research on the durability and sustainable development of CSMs. The types and mixing forms of waste materials reutilized in CSMs are discussed. The effect of different waste materials on the durability of CSMs is objectively evaluated. The potential challenges of sustainable development of CSMs are proposed. This review may help to alleviate the apprehension of road workers about the utilization of waste materials in CSMs and provide useful suggestions for the large-scale application of different waste materials.

The use of calcium sulfo-aluminate cement as an alternative to Portland Cement for the recycling of municipal solid waste incineration bottom ash in mortar

Municipal solid waste incineration generates large quantities of bottom ash that should be recycled. Current use of municipal solid waste incineration bottom ash (MSWI-BA) in cementitious materials is mostly in Ordinary Portland Cement (OPC). This paper considers using MSWI-BA as sand substitution in Calcium Sulfoaluminate Cement (CSA) as an alternative to OPC. A comparison between OPC and CSA mortars containing 0-2 mm MSWI-BA is conducted. The MSWI-BA used was treated to remove the ferrous and non-ferrous metals in order to obtain a better mineral fraction. Different percentages (0%, 25%, 50%, 75%, and 100%) of standard sand were substituted by MSWI-BA based on equivalent volume. Experimental results showed that the compressive strength and porosity of the CSA mortars were superior to OPC after substitution at 1, 7, 28, and 90 days. The compressive strength of OPC mortars with 25% substitution decreased by 40% compared to 11% for CSA mortars at 90 days. This is due to the difference in pH between the two cement pastes as OPC in contact with the MSWI-BA leads to a reaction with the aluminum content which releases hydrogen gas, increases the porosity, and decreases the compressive strength.

Technologies for the management of MSW incineration ashes from gas cleaning: New perspectives on recovery of secondary raw materials and circular economy

Environmental policies in the European Union focus on the prevention of hazardous waste and aim to mitigate its impact on human health and ecosystems. However, progress is promoting a shift in perspective from environmental impacts to resource recovery. Municipal solid waste incineration (MSWI) has been increasing in developed countries, thus the amount of air pollution control residues (APCr) and fly ashes (FA) have followed the same upward trend. APCr from MSWI is classified as hazardous waste in the List of Waste (LoW) and as an absolute entry (19 01 07*), but FA may be classified as a mirror entry (19 0 13*/19 01 14). These properties arise mainly from their content in soluble salts, potentially toxic metals, trace organic pollutants and high pH in contact with water. Since these residues have been mostly disposed of in underground and landfills, other possibilities must be investigated to recover secondary raw materials and products. According to the literature, four additional routes of recovery have been found: detoxification (e.g. washing), product manufacturing (e.g. ceramic products and cement), practical applications (e.g. CO₂ sequestration) and recovery of materials (e.g. Zn and salts). This work aims to identify the best available technologies for material recovery in order to avoid landfill solutions. Within this scope, six case studies are presented and discussed: recycling in lightweight aggregates, glass-ceramics, cement, recovery of zinc, rare metals and salts. Finally, future perspectives are provided to advance understanding of this anthropogenic waste as a source of resources, yet tied to safeguards for the environment.

Valorization of MSWI bottom ash for biogas desulfurization: Influence of biogas water content

In this study an alternative valorization of Municipal Solid Waste Incineration (MSWI) Bottom Ash (BA) for H₂S elimination from landfill biogas was evaluated. Emphasis was given to the influence of water content in biogas on H₂S removal efficiency by BA. A small-scale pilot was developed and implemented in a landfill site located in France. A new biogas analyzer was used and allowed real-time continuous measurement of CH₄, CO₂, O₂, H₂S and H₂O in raw and treated biogas. The H₂S removal efficiency of bottom ash was evaluated for different inlet biogas humidities: from 4 to 24g_water/m³. The biogas water content was found to greatly affect bottom ash efficiency regarding H₂S removal. With humid inlet biogas the H₂S removal was almost 3 times higher than with a dry inlet biogas. Best removal capacity obtained was 56gH₂S/kgdryBA. A humid inlet biogas allows to conserve the bottom ash moisture content for a maximum H₂S retention.

Construction and demolition waste: Comparison of standard up-flow column and down-flow lysimeter leaching tests

Five samples of construction and demolition waste (C&DW) were investigated in order to quantify leaching of inorganic elements under percolation conditions according to two different experimental setups: standardised up-flow saturated columns (<4mm particle size) and unsaturated, intermittent down-flow lysimeters (<40mm particle size). While standardised column tests are meant primarily to provide basic information on characteristic leaching properties and mechanisms and not to reproduce field conditions, the lysimeters were intended to mimic the actual leaching conditions when C&DW is used in unbound geotechnical layers. In practice, results from standardised percolation tests are often interpreted as estimations of actual release from solid materials in percolation scenarios. In general, the two tests yielded fairly similar results in terms of cumulative release at liquid-to-solid ratio (L/S) 10l·kgTS; however, significant differences were observed for P, Pb, Ba, Mg and Zn. Further differences emerged in terms of concentration in the early eluates (L/S<5l·kg(-1)TS) for Al, As, Ba, Cd, Cu, DOC, Mg, Mn, Ni, P, Pb, Sb, Se, Si, Zn. Observed differences between tests are likely to be due to differences in pH related to crushing and exposure of fresh particle surfaces, as well as in equilibrium conditions. In the case of C&DW, the standardised column tests, which are more practical, are considered to acceptably describe cumulative releases at L/S 10l·kg(-1)TS in percolation scenarios. However, when the focus is on estimation of initial concentrations for (for example) risk assessment, data from standardised column tests may not be fully applicable, and data from lysimeters may be used for validation purposes. Se, Cr and, to a lesser extent, SO4 and Sb were leaching from C&DW in critical amounts compared with existing limit values.