Life cycle assessment and residue leaching: the importance of parameter, scenario and leaching data selection

Sustainable use of composted sewage sludge: Metal(loid) leaching behaviour and material suitability for application on degraded soils

Composted sewage sludge was investigated as a promising material for the reclamation or remediation of degraded sites. Using sewage sludge as soil amendment provides environmental benefits and risks while supporting circularity and waste minimisation. This study aims to comprehensively assess the suitability of locally available low-cost sludge treatment for sustainable and environmentally safe topsoil disposal in a brownfield area affected by coal mining. A nine-month composting was conducted before field application to the soil environment. The objectives were to assess: (i) composting time-dependent and pH-dependent metal(loid) leachability from composted sludges, (ii) the effect of sludges on metal(loid) leachability from soil over the first six months, and (iii) metal(loid) plant uptake during the first vegetation season as well as the bioaccumulation and translocation factors. The set of standardised leaching experiments confirmed the positive effect of compost maturity, i.e. despite some fluctuations over time, metal(loid) availability from the final composts was very low. Some metals showed unusual pH-dependent behaviour with the highest leachability at pH 8 due to excessive release of dissolved organic matter from the not-yet-stabilised matrix. Ecotoxicity testing confirmed the safety of the final composts for further soil application. The sludge-amended plots displayed similar metal(loid) leaching and pH evolution in time compared to the control biomass-amended plot. However, plant species (Artemisia vulgaris L.) that formed the natural vegetation cover of the experimental plots showed cumulative metal(loid) uptake. Cadmium and zinc were identified as the critical metals possibly related to the applied sludges, yielding high bioaccumulation and translocation factors. Yet, the quality of the compost feedstock, heterogeneity, and background values of the brownfield site need to be considered. Nevertheless, soil respiration indicated no adverse effects on soil health six months after sludge application. Overall, the composted material demonstrated potential suitability for remediation application in the studied area.

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.

Ashes from challenging fuels in the circular economy

In line with the objectives of the circular economy, the conversion of waste streams to useful and valuable side streams is a central goal. Ash represents one of the main industrial side-products, and using ashes in other than the present landfilling applications is, therefore, a high priority. This paper reviews the properties and utilization of ashes of different biomass power plants and waste incinerations, with a focus on the past decade. Possibilities for ash utilization are of uttermost importance in terms of circular economy and disposal of landfills. However, considering its applicability, ash originating from the heat treatment of chemically complex fuels, such as biomass and waste poses several challenges such as high heavy metal content and the presence of toxic and/or corrosive species. Furthermore, the physical properties of the ash might limit its usability. Nevertheless, numerous studies addressing the utilization possibilities of challenging ash in various applications have been carried out over the past decade. This review, with over 300 references, surveys the field of research, focusing on the utilization of biomass and municipal solid waste (MSW) ashes. Also, metal and phosphorus recovery from different ashes is addressed. It can be concluded that the key beneficial properties of the ash types addressed in this review are based on their i) alkaline nature suitable for neutralization reactions, ii) high adsorption capabilities to be used in CO2 capture and waste treatment, and iii) large surface area and appropriate chemical composition for the catalyst industry. Especially, ashes rich in Al2O3 and SiO2 have proven to be promising alternative catalysts in various industrial processes and as precursors for synthetic zeolites.

Characterization of Dioxins and Heavy Metals in Chelated Fly Ash

Municipal solid waste incineration (MSWI) fly ash contains highly toxic heavy metals and polychlorinated dibenzo dioxins/furans (PCDD/Fs), which are a type of hazardous waste. The pollution characteristics of fly ash have changed with the development of stoker grate incinerators and the fly ash treatment technology; however, no research has been focused on this in recent years. In this study, 12 fly ash samples were collected from 9 grate power plants in southeastern China, and their PCDD/Fs and heavy metal concentrations were determined and compared to previous fly ash data. The PCDD/Fs concentration in fly ash was in the range of 0.002–0.051 ngI-TEQ/g, with an average of 0.027 ngI-TEQ/g. Furthermore, 1,2,3,4,6,7,8-HpCDD and OCDD made the most significant contributions to PCDDs. The distribution of 10 dioxins exhibited bimodal, unimodal, and normal characteristics. Linear fitting demonstrated a strong correlation between toxicity and 1,2,3,7,8-PentaCDD, 1,2,3,7,8-PentaCDF, and 2,3,4,7,8-PentaCDF. Concerning heavy metals, Pb poses a significant environmental risk. This is the first time that fly ash treated with a chelating agent has been thoroughly analyzed, which is vital for understanding the pollution level and treatment of fly ash derived from current power plants.

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.

Chemical stabilization of heavy metals in municipal solid waste incineration fly ash: a review

Sufficient attention should be attached to the large amount of fly ash containing high levels of toxic heavy metals generated after municipal solid waste incineration. Because heavy metals could be leached out of the fly ash under specific conditions, it is necessary to stabilize the heavy metals in fly ash before landfill disposal. Processing technologies of incineration fly ash include solidification/stabilization technology, thermal treatments, and separation processes. This study reviewed the current treatment technologies of municipal solid waste incineration (MSWI) fly ash, with the main focus on the treatment of heavy metals in fly ash with chemical stabilization. Chemical stabilization processes involve chemical precipitation of heavy metal and chelation of heavy metals. In multiple studies, chemical stabilization technology has shown practical feasibility in terms of technology, economy, and effect. In addition, the combination of two or more stabilization agents broadens the general applicability of the agents to heavy metals and reduces the cost. The application of joint processing technology realizes the remove of soluble salt from fly ash. To minimize pollutants while increase their usable value, effective use of waste and co-disposal of several kinds of wastes have gradually become the research hotspots. New developments in chemical stabilization are progressively moving towards the sustainable direction of harmlessness and resource utilization of MSWI fly ash.

Life cycle assessment of air-pollution-control residues from waste incineration in Europe: Importance of composition, technology and long-term leaching

Air pollution control residues (APCr) are hazardous materials generated from municipal solid waste incineration and require appropriate management. This life cycle assessment (LCA) study investigates the environmental impacts of current and alternative management options, considering the possibility of a cascading management of APCr, where one treatment technology is followed by another. In total, 14 base case scenarios and 30 sensitivity scenarios were evaluated. The effects of APCr composition, leaching, time horizon, and uncertainties were investigated. The APCr management options with the lowest environmental impacts and the smallest uncertainties were i) backfilling of underground salt mines and ii) neutralization treatment followed by backfilling (Langøya, Norway). These options were followed by iii) scenarios that included Zn extraction, iv) cement stabilization of fresh APCr followed by landfilling and v) production of cement aggregates made from carbonated APCr followed by their utilization in construction works. Recovery of salts from APCr required further performance optimizations before being environmentally competitive with other options. Long-term leaching emissions of Zn, Cr and As were among the largest contributors to toxicity-related impacts, emphasizing the need for management strategies that minimize their leaching. The investigated scenarios demonstrate that increased "processing" and cascading utilization of the residues, contribute with increased uncertainty of the results compared to landfilling and may not necessarily lead to decreased environmental impacts. LCA studies of APCr management should address the full management chain, rather than just the first treatment. Overall, the results of this study were found robust, also considering potential changes in the surrounding energy system.

Municipal solid waste incineration residues recycled for typical construction materials-a review

Focusing on the great potential of municipal solid waste incineration (MSWI) residues in the construction sector, the applications of recycling MSWI residues in construction materials are discussed in this review. Incineration is a promising method for managing the great quantity of municipal solid waste (MSW). Careful handling of incineration residues including fly ash, air pollution control (APC) residues, and bottom ash is required for this approach. The yield of these residues is large, and they contain many toxic and harmful substances. On the other hand, these residues contain valuable components such as SiO₂, CaO, Al₂O₃, MgO, which are important components of building materials. Therefore, MSWI residues present huge opportunities for potential recycling and reuse in the construction and building industry. This paper summarized and discussed the application of MSWI residues in four typical building materials including cast stone, glass-ceramic, cement, and concrete. Before utilization, three types of pretreatment methods can be used to reduce the toxicity of the residues and improve the performance of the products. In addition, the current issues and the prospects of this field, and the environmental impacts of this application were discussed. It was concluded that MSWI residues can be used to prepare building materials after proper treatment which can improve the mechanical and chemical properties of the residues. The recycling can gain significant economic and environmental benefits at the same time. However, further researches on treatment methods for fine particles are needed.

Long-Term Leaching Behavior of Organic and Inorganic Pollutants after Wet Processing of Solid Waste Materials

The recycling of mineral materials is a sustainable and economical approach for reducing solid waste and saving primary resources. However, their reuse may pose potential risks of groundwater contamination, which may result from the leaching of organic and inorganic substances into water that percolates the solid waste. In this study, column leaching tests were used to investigate the short- and long-term leaching behavior of “salts”, “metals”, and organic pollutants such as PAHs and herbicides from different grain size fractions of construction & demolition waste (CDW) and railway ballast (RB) after a novel treatment process. Specifically, silt, sand and gravel fractions obtained after a sequential crushing, sieving, and washing process (“wet-processing”) of very heterogeneous input materials are compared with respect to residual contamination, potentially limiting their recycling. Concentrations in solid fractions and aqueous leachate were evaluated according to threshold values for groundwater protection to identify relevant substances and to classify materials obtained for recycling purposes according to limit values. For that, the upcoming German recycling degree was applied for the first time. Very good agreement was observed between short and extensive column tests, demonstrating that concentrations at L/S 2 ratios are suitable for quality control of recycling materials. Different solutes showed a characteristic leaching behavior such as the rapid decrease in “salts”, e.g., SO₄²⁻ and Cl⁻, from all solid fractions, and a slower decrease in metals and PAHs in the sand and silt fractions. Only the gravel fraction, however, showed concentrations of potential pollutants low enough for an unlimited re-use as recycling material in open technical applications. Sand fractions may only be re-used as recycling material in isolated or semi-isolated scenarios. Leaching from heterogeneous input materials proved harder to predict for all compounds. Overall, column leaching tests proved useful for (i) initial characterization of the mineral recycling materials, and (ii) continuous internal (factory control) and external quality control within the upcoming German recycling decree. Results from such studies may be used to optimize the treatment of mixed solid waste since they provide rapid insight in residual pollution of material fractions and their leaching behavior.

Calcium leaching characteristics in landfill leachate collection systems from bottom ash of municipal solid waste incineration

Calcium leaching is a critical factor in the clogging of leachate collection systems (LCS), a phenomenon that affects landfill stability and operation. The bottom ash (BA) of municipal solid waste (MSW) incineration plants contains large quantities of calcium-based compounds. Landfilling is the main disposal method for BA in China that intensifies the consequences of LCS clogging. The factors influencing BA calcium leaching were investigated using simulated leachate. The results showed that fine BA particles, low pH values, high temperature, and ratios of leachate to BA solids were conducive to calcium leaching. Calcium leaching was found to be higher in actual leachate than in simulated leachate. At pH = 5, the cumulative calcium dissolution ratios (CDRs) were 83.36% and 31.49% after 20 days of leaching in the actual and simulated leachate, respectively; at pH = 6, the values were 50.67% and 12.06%, respectively. The introduction of landfill gas could decrease the calcium dissolution and leaching rates. When the ratio of leachate to BA solid was 20:1 mL/g, the accumulative CDR values were 45.98% (pH = 6) and 5.80% (pH = 8) without landfill gases, and 4.59% (pH = 6) and 0.48% (pH = 8) with landfill gases. These results provide the scientific basis for clogging risk prediction with respect to calcium leaching in the LCS of landfills. BA landfilling in old landfill areas with relatively high leachate pH and low chemical oxygen demand, as well as when leachate mixed with an appropriate amount of landfill gases, could be feasible measures to reduce calcium leaching and further prevent clogging in LCS.

The environmental performance of enhanced metal recovery from dry municipal solid waste incineration bottom ash

This study assesses the environmental performance of the municipal solid waste (MSW) incineration bottom ash (IBA) treatment plant in Hinwil, Switzerland, a large-scale industrial plant, which also serves as a full-scale laboratory for new technologies and aims at an optimal recovery of metals in terms of quantity and quality. Based on new mass-flow data, we perform a life cycle assessment that includes the recovery of iron, stainless steel, aluminium, copper, lead, silver and gold. Fraction-specific modelling allows for investigating the effect of the metal fraction quality on the subsequent secondary metal production as well as examining further metal recycling potentials in the residual IBA. In addition, the implications on the landfill emissions of IBA residues to water were quantified. The impact assessment considered climate change, eco- and human toxicity and abiotic resource depletion as indicators. Results indicate large environmental savings for every impact category, due to primary metal substitution and reduction of long-term emissions from landfills. Metal product substitution contributes between 75% and >99% to these savings in a base scenario (1'000-year time horizon), depending on the impact category. Reductions in landfill emissions become important only when a much longer time horizon was adopted. The metal-based analysis further illustrates that recovering heavy non-ferrous metals - especially copper and gold - leads to large environmental benefits. Compared to the total net savings of energy recovery (215 kg CO₂-eq per tonne of treated waste, average Swiss plant), enhanced metal recovery may save up to 140 kg CO₂-eq per tonne of treated waste.

Assessing the environmental performance for more local and more circular biowaste management options at city-region level

Biomass, biobased materials and food waste are considered priority areas for Europe's transition towards a circular economy (CE). Waste management is a central activity for this transition and offers multiple CE implementation options which should be evaluated from environmental perspective. The purpose of this work was to analyze the environmental consequences when redirecting biowaste flows from conventional to more circular management systems and to identify the CE option with the best environmental performance. We were particularly interested in studying the combined management of green and food waste, analyzing the challenges when introducing separate collection and different treatment processes, and evaluating the substitution potential for by-products. To determine environmental impacts, we performed a life cycle assessment (LCA) based on local data. Following the purpose analyzing a change in the system, we applied a consequential LCA and compared impacts from processes that are replaced with impacts from alternative management options such as co-composting, anaerobic digestion (AD) and decentralized composting. The LCA results show clear advantages for impacts on ecosystems and resource use for the local AD system with separate combined collection. The decentralized system shows reductions in resource use, whereas the industrial co-composting system has higher or similar impacts than the baseline scenario. We conclude that local systems with combined food and green waste management can show benefits if process emissions are properly managed and if by-products are used in applications with high substitution potentials. However, a change towards a CE does not necessarily result in environmental benefits. Our research highlights the complexity of biowaste systems and proposes a novel combination of local data, databases and models to handle this issue. With this research we are further contributing to the understanding of the combined management of food and green waste, which is a relevant, but so far under-researched, management option for cities.

The contents and release behavior of heavy metals in construction and demolition waste used in freeway construction

A large volume (more than 4.0 million m³) of treated construction and demolition waste (CDW) is planned to be used in the construction of the Xi'an-Xianyang north loop line freeway in West China. These CDW were preliminarily separated into broken concretes, bricks, and porcelains in the treatment plants. In this study, a total of 190 CDW samples including 80 concretes, 80 bricks, 20 porcelains, and 10 mixed samples were collected from five treatment plants. Five farmland soil samples near treatment plants were collected as controls. The contents of 10 elements including cadmium (Cd), arsenic (As), copper (Cu), nickel (Ni), zinc (Zn), chromium (Cr), lead (Pb), manganese (Mn), silver (Ag), and mercury (Hg) in these samples were measured. The contents of 8 elements (Cu, Ni, Zn, Cr, Pb, Mn, Ag, and Hg) in all CDW samples were qualified for the third-level criterion of the Standard of Soil Environment (GB15618-2008). However, Cd contents in 37 concretes, 34 bricks, 6 porcelain samples, and 4 mixed CDW samples exceeded the national third-level standards (1 mg/kg) in GB15618-2008. And As contents in 28 concretes, 21 bricks, 5 porcelain samples, and 3 mixed CDW samples were higher than the national third-level standards (40 mg/kg). The total exceeding standard rates (ESRs) of Cd and As were 42.6% and 30%, respectively. The leaching tests for Cd and As were also done due to their higher ESRs. The results showed that the release amounts (μg/kg) of Cd and As from CDW were increased with increasing liquid to solid ratio (0.4-10 l/kg) but decreased with increasing pH (4-7). The leached concentrations of Cd and As from four types of CDW samples were both in a descending order: brick, mixed materials, concrete, and porcelain. The measured concentrations (μg/L) of Cd and As in leachate were all lower than second-grade criteria of Standard for Groundwater Quality (GB3838-2002). By comparing the leached concentrations of Cd and As with the value in European criteria (EU Council Decision 2003/33/EC) for hazardous wastes, all the CDW samples should be classified as inert or non-hazardous wastes. Thus, it could be concluded that heavy metals in these CDW would not pollute surrounding soil, surface water, and groundwater environment when applied in freeway construction.

Material- and Site-Specific Partition Coefficients for Beneficial Use Assessments

Partition coefficient (K_d) values available in the literature are often used in fate and transport modeling conducted as part of beneficial use risk assessments for industrial byproducts. Because element partitioning depends on soil properties as well as characteristics of the byproduct leachate, site-specific K_d values may lead to more accurate risk assessment. In this study, contamination risk to groundwater of beneficially reused byproducts was assessed using batch leaching tests on waste to energy bottom ash and coal combustion fly ash. Leachates were equilibrated with eight different soils to obtain the waste-soil-specific K_d,exp values for the metals of interest. The K_d,exp values were used as inputs in the Industrial Waste Management Evaluation Model to demonstrate the degree to which K_d estimates affect risk assessment outcomes. Measured K_d,exp values for the most part fell within the large range of K_d values reported in the literature, but IWEM results using default K_d values for some types of soils resulted in overestimated risk compared to those derived from K_d,exp values. Modeled concentration at the receptor location was much lower for some elements for those soils with high concentrations of iron and aluminum.

Review of leaching behavior of municipal solid waste incineration (MSWI) ash

Incineration is widely adopted in modern waste management because it provides an effective way to minimize municipal solid waste that needs to be disposed of in landfills. The ash residue is often disposed by landfilling. Alternatively, the incineration ash may be recycled and reused for various applications. The crucial issues, however, are the leaching of harmful elements during the use and the end-of-life phases. This review summarizes extensive studies on leaching behavior of municipal solid waste incineration ash. Specifically, pollutants generated through leaching, factors governing leaching, methodologies to study leaching, leaching mechanisms, and treatments to reduce leaching. Many types of pollutants are generated through leaching from municipal solid waste incineration ash, in which heavy metals and organic contaminants are the most toxic and concerned. Ash properties, pH and liquid to solid ratio are the main factors governing municipal solid waste incineration ash leaching. Leaching behavior of municipal solid waste incineration ash is complicated and existing methods to evaluate leaching may not be able to represent the field conditions. Solubility and sorption are the two major leaching mechanisms. Many treatment methods have been proposed. However, not all methods are effective and some approaches are associated with high energy and high cost, which makes them less economically feasible and attractive.

Improving the Life Cycle Impact Assessment of Metal Ecotoxicity: Importance of Chromium Speciation, Water Chemistry, and Metal Release

Investigations of metal ecotoxicity in life cycle assessment (LCA) and life cycle impact assessment (LCIA) are becoming important tools for evaluating the environmental impact of a product or process. There is, however, improvement needed for LCIA of metal ecotoxicity in order to make this assessment more relevant and robust. In this work, three issues within the LCIA of metal ecotoxicity are investigated, mainly focusing on topics related to stainless steel manufacturing. The first issue is the importance of considering regional water chemistry when constructing the characterization factor (CF). A model freshwater of relevance for stainless steel manufacturing in a region of Sweden was created with chemistry different from available options. The second issue is related to the lack of consideration on changes in speciation of Cr(VI) in freshwater for a given emission, as Cr(VI) to some extent will be reduced to Cr(III). Two new options are suggested based on relationships between the Cr(VI)–total Cr ratio as a way to improve the relevancy of LCIA for Cr(VI) in freshwater. The last issue is how to treat metal release from slags in LCIA. Metal release from slags was shown to vary significantly between different ways of modelling slag emissions (differences in total metal content, slag leaching tests, estimated emissions to groundwater).

A large-scale field trial experiment to derive effective release of heavy metals from incineration bottom ashes during construction in land reclamation

Recycling of incineration bottom ashes (IBA) is attracting great interest as it is considered as a vital aspect for closing the waste loop to achieve sustainable development at the growing cities around the world. Various laboratory-testing methods are developed to assess the release potential of heavy metals - one of the most important concerns of using IBA, by reflecting the release conditions of heavy metals from IBA based on the targeted land reclamation application scenarios and corresponding environmental conditions. However, realistic release of the concerned elements in actual application with the presence of complex environment could possibly deviate from the outcomes produced by leaching tests carried out in the laboratory. Hence, a set of large-scale column trial experiments was performed to experimentally determine the effective release of heavy metals, when IBA is used as a filling material in land reclamation. 20 tons of IBA and 320 m³ of seawater were used in six column trial experiments. The release of 13 heavy metal elements was analyzed through multiple aspects which included kinetics of release, distribution of elements in seawater and the impacts of two different dumping methods, with and without application of a chute. After dumping of IBA into the seawater, almost instantaneous release of heavy metals with uniform horizontal dispersion was observed. Higher concentration of these elements was observed near the bottom of the column, especially when a chute was applied. Comparative analysis was then carried out to establish relationships between the results obtained from the column trial with batch leaching test carried out in the laboratory. Distinctive relationships were observed for different heavy metals which suggests the need of pursuance of further understanding on leaching of IBA in real application scenario and complex environment.

Environmental perspectives of recycling various combustion ashes in cement production - A review

Recycling different types of ashes for cement production has gained increasing attentions worldwide in a bid to close the waste loop. It minimizes waste landfilling and meanwhile produces useful secondary materials with reduced costs. Ascribed to the presence of elevated metal concentrations, however, it also receives negative inclination for their reuse. Herein, recycling various combustion ashes, such as municipal solid waste incineration fly ashes (MSWI FA), municipal solid waste incineration bottom ashes (MSWI BA), coal fly ashes (CFA), coal bottom ashes (CBA), blast furnace slags (BFS), biomass ashes (BIOA), sewage sludge ashes (SSA) and different co-combustion ashes (CCA), were comprehensively reviewed, from environmental perspectives combined with statistical data analysis (e.g. bulk components, trace metals, leaching potential, and etc.), to quantitatively explore their feasibility during cement production. It was unveiled that pozzolanic contents were predominant which highly fluctuated in their composition based on the ash type, limiting the replacement at maximum of 5-10 wt%. Considering total metal criteria, heavy metal contents posed challenges as secondary raw materials for blended cements. However, in consideration of metal leaching criteria, exothermic pozzolanic reactions in the second phase of blended cement would sufficiently alleviate their leaching potential, ensuring the environmental feasibility. Apart from the above, treatment costs have to be evaluated in nexus of multiple factors, whereas government policies play significant roles in valorization of recycling ashes. From sustainability perspective, life cycle assessment promises the overall strategy on ash utilization in cement industry.

Comparative Life Cycle Assessment of possible methods for the treatment of contaminated soil at an environmentally degraded site

This study reports on the assessment of the environmental sustainability of different management practices for an environmentally degraded site in Slovenia: the Old Zinc-Works in the town of Celje. Life Cycle Assessments (LCAs) were applied in order to evaluate possible trade-offs by comparing a proposed in situ remediation scenario with two other reclamation scenarios (scenario 2: incineration, metal extraction, underground disposal and reclamation of the site by refilling it with replacement material, and scenario 3: underground disposal and reclamation of the site by refilling it with replacement material) and with a no-action scenario. The results of the comparisons performed show that in the case of the in situ remediation scenario, the consumption of resources is smaller by a factor of 51 compared to that in the second scenario and by a factor of 7 compared to that in the third scenario. The impacts on human health and ecosystem quality are approximately 30 and 3.5 times less in the first scenario than in the second and third scenarios, respectively. Compared to the impact of the no-action scenario, the impact on human health of the in situ soil remediation scenario is approximately 6 times less, whereas its impact on the ecosystem is approximately 4 times less. The results confirmed that the in situ soil remediation scenario is the most sustainable practice from an environmental point of view. Its main advantage lies in the achieved conservation of natural resources. Despite the recovery of valuable metals (Zn, Pb, Cu, and Ni) from the bottom ash, the second scenario is significantly more environmentally burdensome compared to both the first and third scenarios. This outcome is due to the significantly high impacts related to the consumption of fuels needed to support the incineration of low-calorific contaminated soil and to electricity consumption. The present study demonstrates that the results of LCA studies, in addition to technological, economic and social indicators, yield important information about the sustainability of different management practices and therefore should be an important part of decision-making when approaching the reclamation of environmentally degraded sites.

Statistical comparison of leaching behavior of incineration bottom ash using seawater and deionized water: Significant findings based on several leaching methods

Bottom ashes generated from municipal solid waste incineration have gained increasing popularity as alternative construction materials, however, they contains elevated heavy metals posing a challenge for its free usage. Different leaching methods are developed to quantify leaching potential of incineration bottom ashes meanwhile guide its environmentally friendly application. Yet, there are diverse IBA applications while the in situ environment is always complicated, challenging its legislation. In this study, leaching tests were conveyed using batch and column leaching methods with seawater as opposed to deionized water, to unveil the metal leaching potential of IBA subjected to salty environment, which is commonly encountered when using IBA in land reclamation yet not well understood. Statistical analysis for different leaching methods suggested disparate performance between seawater and deionized water primarily ascribed to ionic strength. Impacts of leachant are metal-specific dependent on leaching methods and have a function of intrinsic characteristics of incineration bottom ashes. Leaching performances were further compared on additional perspectives, e.g. leaching approach and liquid to solid ratio, indicating sophisticated leaching potentials dominated by combined geochemistry. It is necessary to develop application-oriented leaching methods with corresponding leaching criteria to preclude discriminations between different applications, e.g., terrestrial applications vs. land reclamation.

Electrodialytic extraction of Cr from water-washed MSWI fly ash by changing pH and redox conditions

Electrodialytic process offers a range of possibilities to waste management by electrodialytic separation (EDS) of heavy metals, depending on how the process is designed. Using three EDS cell setups (two two-compartment and one three-compartment) and their combinations, the extraction of Cr from municipal solid waste incineration fly ash by changing pH and redox conditions was investigated in the present work. The experiments were designed into single, two and three steps, based on the number of setups (by changing EDS cells) or effective setups (by shifting working electrode pairs) used. Prior to EDS the ash studied went through pretreatments such as water-washing and dry-sieving with a 50 µm sieve. The results showed that Cr was strongly bound in the ash, and the major fraction remained bound after the different treatments. Two/three-step treatment, which obtained the maximum Cr extraction rate of 27.5%, is an improvement on the single-step that extracted maximum 3.1%. The highest extraction was obtained due to the combined extraction of Cr(III) under low pH (accompanied with high redox) conditions and Cr(VI) under high pH (low redox) conditions subsequently. The Cr leaching from the treated ashes with acidic pH was lower than from those with alkaline pH; after the three-step treatment, Cr leaching was much lower from the coarse fraction (> 50 µm), as compared to the fine (≤ 50 µm) or the unsieved ash. As for the coarse fraction, two/three-step treatment reduced the leaching of Cr compared to the single-step in the same pH range (either acidic or alkaline).

A risk-based approach for assessing the recycling potential of an alkaline waste material as road sub-base filler material

In this work we present an integrated risk-based approach that can be used to evaluate the recycling potential of an alkaline waste material such as incineration bottom ash (BA) as unbound material for road sub-base construction. This approach, which is aimed at assessing potential risks to the groundwater resource (in terms of drinking water quality) and human health associated to the leaching of contaminants from the BA, couples the results of leaching tests for the estimation of source concentrations with the fate and transport models usually adopted in risk assessment procedures. The effects of weathering and of the type of leaching test employed to evaluate eluate concentrations were assessed by carrying out different simulations using the results of laboratory leaching tests. Specifically, pH-dependence and column percolation leaching tests were performed on freshly collected and 1-year naturally weathered BA samples produced from a grate-fired incineration plant treating Refuse Derived Fuel (RDF). To evaluate a broad span of possible scenario conditions, a Monte Carlo analysis was performed running 5000 simulations, randomly varying the input parameters within the ranges expected in the field. In nearly all the simulated conditions, the concentrations of contaminants in the groundwater for the specific type of BA tested in this work were well below EU and WHO drinking water quality criteria. Nevertheless, some caution should be paid in the case of the establishment of acidic conditions in the field since in this case the concentration of some elements (i.e. Al, Pb and Zn) is expected to exceed threshold values. In terms of risks to human health, for the considered utilization scenario the probability of exceeding the acceptable reference dose for water ingestion was usually less than 1% (except for Cr and Pb for which the probability was lower than 3.5% and 7%, respectively).

Life-cycle assessment of a Waste-to-Energy plant in central Norway: Current situation and effects of changes in waste fraction composition

Waste-to-Energy (WtE) plants constitute one of the most common waste management options to deal with municipal solid waste. WtE plants have the dual objective to reduce the amount of waste sent to landfills and simultaneously to produce useful energy (heat and/or power). Energy from WtE is gaining steadily increasing importance in the energy mix of several countries. Norway is no exception, as energy recovered from waste currently represents the main energy source of the Norwegian district heating system. Life-cycle assessments (LCA) of WtE systems in a Norwegian context are quasi-nonexistent, and this study assesses the environmental performance of a WtE plant located in central Norway by combining detailed LCA methodology with primary data from plant operations. Mass transfer coefficients and leaching coefficients are used to trace emissions over the various life-cycle stages from waste logistics to final disposal of the ashes. We consider different fractions of input waste (current waste mix, insertion of 10% car fluff, 5% clinical waste and 10% and 50% wood waste), and find a total contribution to Climate Change Impact Potential ranging from 265 to 637gCO₂eq/kg of waste and 25 to 61gCO₂eq/MJ of heat. The key drivers of the environmental performances of the WtE system being assessed are the carbon biogenic fraction and the lower heating value of the incoming waste, the direct emissions at the WtE plant, the leaching of the heavy metals at the landfill sites and to a lesser extent the use of consumables. We benchmark the environmental performances of our WtE systems against those of fossil energy systems, and we find better performance for the majority of environmental impact categories, including Climate Change Impact Potential, although some trade-offs exist (e.g. higher impacts on Human Toxicity Potential than natural gas, but lower than coal). Also, the insertion of challenging new waste fractions is demonstrated to be an option both to cope with the excess capacity of the Norwegian WtE sector and to reach Norway's ambitious political goals for environmentally friendly energy systems.

LCA of management strategies for RDF incineration and gasification bottom ash based on experimental leaching data

The main characteristics and environmental properties of the bottom ash (BA) generated from thermal treatment of waste may vary significantly depending on the type of waste and thermal technology employed. Thus, to ensure that the strategies selected for the management of these residues do not cause adverse environmental impacts, the specific properties of BA, in particular its leaching behavior, should be taken into account. This study focuses on the evaluation of potential environmental impacts associated with two different management options for BA from thermal treatment of Refuse Derived Fuel (RDF): landfilling and recycling as a filler for road sub bases. Two types of thermal treatment were considered: incineration and gasification. Potential environmental impacts were evaluated by life-cycle assessment (LCA) using the EASETECH model. Both non-toxicity related impact categories (i.e. global warming and mineral abiotic resource depletion) and toxic impact categories (i.e. human toxicity and ecotoxicity) were assessed. The system boundaries included BA transport from the incineration/gasification plants to the landfills and road construction sites, leaching of potentially toxic metals from the BA, the avoided extraction, crushing, transport and leaching of virgin raw materials for the road scenarios, and material and energy consumption for the construction of the landfills. To provide a quantitative assessment of the leaching properties of the two types of BA, experimental leaching data were used to estimate the potential release from each of the two types of residues. Specific attention was placed on the sensitivity of leaching properties and the determination of emissions by leaching, including: leaching data selection, material properties and assumptions related to emission modeling. The LCA results showed that for both types of BA, landfilling was associated with the highest environmental impacts in the non-toxicity related categories. For the toxicity related categories, the two types of residues behaved differently. For incineration BA the contribution of metal leaching to the total impacts had a dominant role, with the highest environmental loads resulting for the road scenario. For the gasification BA, the opposite result was obtained, due to the lower release of contaminants observed for this material compared to incineration BA. Based on the results of this study, it may be concluded that, depending on the type of BA considered, its leaching behavior may significantly affect the results of a LCA regarding its management strategies.

Soil retention of hexavalent chromium released from construction and demolition waste in a road-base-application scenario

We investigated the retention of Cr(VI) in three subsoils with low organic matter content in laboratory experiments at concentration levels relevant to represent leachates from construction and demolition waste (C&DW) reused as unbound material in road construction. The retention mechanism appeared to be reduction and subsequent precipitation as Cr(III) on the soil. The reduction process was slow and in several experiments it was still proceeding at the end of the six-month experimental period. The overall retention reaction fit well with a second-order reaction governed by actual Cr(VI) concentration and reduction capacity of the soil. The experimentally determined reduction capacities and second-order kinetic parameters were used to model, for a 100-year period, the one-dimensional migration of Cr(VI) in the subsoil under a layer of C&DW. The resulting Cr(VI) concentration would be negligible below 7-70 cm depth. However, in rigid climates and with high water infiltration through the road pavement, the reduction reaction could be so slow that Cr(VI) might migrate as deep as 200 cm under the road. The reaction parameters and the model can form the basis for systematically assessing under which scenarios Cr(VI) from C&DW could lead to an environmental issue for ground- and receiving surface waters.

Life cycle assessment of construction and demolition waste management

Life cycle assessment (LCA) modelling of construction and demolition waste (C&DW) management was carried out. The functional unit was management of 1 Mg mineral, source separated C&DW, which is either utilised in road construction as a substitute for natural aggregates, or landfilled. The assessed environmental impacts included both non-toxic and toxic impact categories. The scenarios comprised all stages of the end-of-life management of C&DW, until final disposal of all residues. Leaching of inorganic contaminants was included, as was the production of natural aggregates, which was avoided because of the use of C&DW. Typical uncertainties related to contaminant leaching were addressed. For most impact categories, utilisation of C&DW in road construction was preferable to landfilling; however, for most categories, utilisation resulted in net environmental burdens. Transportation represented the most important contribution for most nontoxic impacts, accounting for 60-95 per cent of these impacts. Capital goods contributed with negligible impacts. Leaching played a critical role for the toxic categories, where landfilling had lower impacts than utilisation because of the lower levels of leachate per ton of C&DW reaching the groundwater over a 100-year perspective. Leaching of oxyanions (As, V and Sb) was critical with respect to leaching. Typical experimental uncertainties in leaching data did not have a pivotal influence on the results; however, accounting for Cr immobilisation in soils as part of the impact assessment was critical for modelling the leaching impacts. Compared with the overall life cycle of building and construction materials, leaching emissions were shown to be potentially significant for toxicity impacts, compared with contributions from production of the same materials, showing that end-of-life impacts and leaching should not be disregarded when assessing environmental impacts from construction products and materials. CO2 uptake in the C&DW corresponding to 15 per cent carbonation could out-balance global warming impacts from transportation; however, carbonation would also likely result in increased toxicity impacts due to higher leaching of oxyanions.