Evaluation of leachate emissions from crushed rock and municipal solid waste incineration bottom ash used in road construction

Optimizing MSW incineration bottom ash reuse: A study on treated wastewater washing and leaching control

The current study introduces an innovative methodology by utilizing treated wastewater (TWW) from an effluent treatment plant as a washing agent to enhance the characteristics of incineration bottom ash (IBA). This approach addresses sustainability concerns and promotes the circular economy by reusing wastewater generated in municipal solid waste incineration facilities. Previous research has underscored the challenges of open IBA reuse due to elevated leaching of chlorides, sulfates, and trace metal(loid)s. Thus, the experimental setup explores various combinations of washing, with or without screening, to optimize the properties of soil-like material (SLM < 4.75 mm) and overall material (OM < 31.5 mm) fractions of IBA for unrestricted applications. Batch leaching tests were conducted on treated samples, and leaching characteristics were evaluated in accordance with regulatory standards, primarily the Dutch standard for unrestricted IBA reuse. The findings reveal that washing in isolation proves insufficient to enhance IBA properties; however, washing followed by screening, specifically for removing fines (<0.15 mm), proves effective in reducing contamination. The study identifies that multiple steps of washing and screening (with recirculation) process render OM and SLM fractions suitable for unrestricted reuse with a cumulative liquid-to-solid ratio of 6 L/kg and a total washing time of 15 min. The multi-step treatment was found effective in reducing sulfate contamination by 65-74 % and chloride contamination by 83-89 % in IBA fractions. This approach offers a promising solution for overcoming the limitations associated with IBA leaching, thereby promoting sustainable waste reuse practices.

An integrated characterisation of incineration bottom ashes towards sustainable application: Physicochemical, ecotoxicological, and mechanical properties

Environmental protection is a central concern regarding municipal solid waste incineration bottom ash (IBA) management, but the assessment of waste Hazardous Property HP14 (ecotoxicity) is still under debate. Civil engineering applications may be a suitable management strategy. This work aimed at evaluating IBA regarding mechanical behaviour and environmental hazardous potential, including a biotest battery for ecotoxicity assessment (comprising miniaturised tests), to explore its potential for safe utilization. Physical, chemical, ecotoxicological (Aliivibrio fischeri, Raphidocelis subcapitata, Lemna minor, Daphnia magna, Lepidium sativum), and mechanical (one-dimensional compressibility, shear strength) analyses were performed. The low leaching for potentially toxic metals and ions complied with European Union (EU) limit values for non-hazardous waste landfills. No relevant ecotoxicological effects were found. The biotest battery seems suitable for ecotoxicological assessment in the aquatic ecosystem, providing wide information on waste impact on different trophic/functional levels and chemical uptake routes, simultaneously involving short-duration tests and reduced amounts of waste. IBA presented more compressibility than sand, but its mixture with sand (30%:70%) was closer to sand compressibility. IBA (lower stresses) and the mixture (higher stresses) showed slightly higher shear strength than sand. Overall, IBA presented the potential for valorisation as loose aggregates from an environmental and mechanical viewpoint in a circular economy framework.

An innovative reuse of bottom ash from municipal solid waste incinerators as substrates of constructed wetlands

The incineration of municipal solid waste has been important in waste management, but it raises another environmental issue concerning residue treatment. This study describes an innovative use of naturally aged incineration bottom ash (AIBA) as an alternative substrate for horizontal subsurface flow (HSSF) constructed wetlands (CW). Although experimental results from a period lasting for 396 days only revealed slightly higher removal ratios in HSSF with AIBA (HSSF-E) than in HSSF-traditional pebble beds (HSSF-C), increasing from 67% to 76% for BOD, 44%-51% for TKN, 47%-54% for NH₃-N, and 44%-52% for TN. The data indicate that the use of AIBA in HSSF CW can achieves a certain removal efficiency of BOD and nitrogen species. Interestingly, the total phosphorus removal rates also increased significantly from 20% in HSSF-C to 36% in HSSF-E. These observations on the use of AIBA in HSSF CW confirmed that AIBA is a suitable alternative for use as a substrate for HSSF CWs and identified an additional way to reuse incineration bottom ash. Design criteria for a CW using AIBA as a partial substrate is proposed to improve the pollutant removal performance of HSSF CWs.

Long-term evaluation of geotechnical and environmental properties of ash-stabilised road

In 2009, a low-volume gravel road in Sweden was stabilised using fly ash from a local paper mill. The objective was to examine whether fly ash could be used to enhance the stability of the road and how the nearby environment would be affected. The technical and environmental properties of the road have been monitored for two, six, and eleven years. Because the construction costs are higher for ash upgrading than for conventional upgrading, knowing for how long the improved properties will remain is relevant. Strength development was studied using a falling weight deflectometer and compressive strength tests. Environmental properties were studied by chemical analysis of road samples, soil, soil pore water, and vegetation. The results showed that the ash sections had higher stiffness than the reference sections. Leaching tests of road samples showed that the mobility of potassium, sodium, chloride, and sulfate decreased with time. Trace element concentrations in soil samples, except barium, were below the Swedish guideline values for sensitive land use. Chromium, lead, and copper were as high or even higher along the reference section than along the ash section. After 11 years, the pH closest to the ash section was slightly enhanced. Concentrations of zinc and cadmium in the soil pore water were the lowest closest to the ash road, although the total concentrations in the soil were at their highest at the same distance. No toxic levels of trace elements were found in the vegetation close to the road, although a clear difference was observed between plants from the ash section and the reference section, using multivariate data analysis. The positive effects on the geotechnical road properties from ash stabilisation remained after 11 years. The environmental impacts on nearby soil and vegetation can be considered low and acceptable. This study demonstrates that the use of biofuel fly ash in infrastructure projects can contribute to the circular economy and effective use of resources because the demand for pristine materials will be reduced.

Contaminants of concern (CoCs) pivotal in assessing the fate of MSW incineration bottom ash (MIBA): First results from India and analogy between several countries

Present study characterizes municipal solid waste incineration bottom ash (MIBA) from three incineration plants in Delhi with an intent to serve the dual objectives: a) assessing the disposal/reuse options for Delhi MIBA, b) evaluating variability in results across the countries (including India) and assessing if is significant enough to influence the fate of MIBA of varied origin. A review on leaching studies of MIBA (50 research papers) was conducted which aided in achieving both the objectives. Delhi MIBA samples were analysed for chemical composition. The two commonly adopted leaching tests i.e., TCLP and EN 12457-2, were conducted and the results were checked against regulatory threshold levels (RTLs) to achieve the first objective. Leaching concentration of the contaminants was compared with the compiled literature and RTLs to accomplish the second objective. The compendium of literature most importantly revealed the physicochemical parameters which are pivotal in determining the fate of MIBA but have been missing from many studies. Ten such parameters were identified: Cr, Cu, Mo, Sb, Cl^-,SO₄^2-, Cd, Pb, Ni and Zn and are referred as contaminants of concern (CoCs). Delhi MIBA was found suitable for disposal to non-hazardous waste landfills and unsuitable for unrestricted reuse. CoCs identified in Delhi MIBA were identical to those observed in literature (except Cd, Pb and Zn). The variability in leaching concentration of CoCs, observed from comparative assessment of results, spanned nearly 2 to 3 log₁₀ magnitudes for Cu, Cr, Pb, Sb and Zn while 1 to 2 log₁₀ magnitudes for Mo, Cl^-andSO₄^2-.

A Review on Cementitious Materials Including Municipal Solid Waste Incineration Bottom Ash (MSWI-BA) as Aggregates

Waste management is a vital environmental issue in the world today. Municipal solid wastes (MSWs) are discarded in huge quantities on a daily basis and need to be well controlled. Incineration is a common method for reducing the volume of these wastes, yet it produces ashes that require further assessment. Municipal solid waste incineration bottom ash (MSWI-BA) is the bulk byproduct of the incineration process and has the potential to be used in the construction sector. This paper offers a review of the use of MSWI-BA as aggregates in cementitious materials. With the growing demand of aggregates in cementitious materials, MSWI-BA is considered for use as a partial or full alternative. Although the physical and chemical properties of MSWI-BA are different than those of natural aggregates (NA) in terms of water absorption, density, and fineness, they can be treated by various methods to ensure suitable quality for construction purposes. These treatment methods are classified into thermal treatment, solidification and stabilization, and separation processes, where this review focuses on the techniques that reduce deficiencies limiting the use of MSWI-BA as aggregates in different ways. When replacing NA in cementitious materials, MSWI-BA causes a decrease in workability, density, and strength. Moreover, they cause an increase in water absorption, air porosity, and drying shrinkage. In general, the practicality of using MSWI-BA in cementitious materials is mainly influenced by its treatment method and the replacement level, and it is concluded that further research, especially on durability, is required before MSWI-BA can be efficiently used in the production of sustainable cementitious materials.

Acid washing of incineration bottom ash of municipal solid waste: Effects of pH on removal and leaching of heavy metals

This study systematically investigated the acid washing of incineration bottom ash (IBA) of municipal solid waste, focusing on the removal and leaching of heavy metals (Pb, Zn, Cr, Cd, Cu, and Ni), as well as their pH-dependent behavior. A series of small-scale laboratory acid washing tests with different nitric acid concentrations and washing periods were conducted. The concentrations of metals in the washing water were measured to evaluate the metal removal efficiency. Then, one stage batch leaching test was conducted for washed IBA to evaluate the leaching reduction efficiency of washing. The results showed that the maximum metal removal efficiencies for Zn, Cu, and Ni (62-76%) were higher than those for Pb, Cr, and Cd (17-25%), which were reached at the highest acid addition for most of the metals. Increasing the washing period did not always increase the metal removal efficiency. The maximum leaching reduction efficiencies were higher for Zn, Cr, and Cu (93-98%) than those for Pb, Ni, and Cd (73-79%). Both washing and leaching processes showed a similar metal concentration-pH profile for each metal. For Pb, Zn, Cr, and Cd, the metal concentration-pH profile generally followed the metal hydroxide solubility versus pH curves. For Cu and Ni, the concentration of metal decreased with the increasing pH first and then kept at a stable concentration higher than the solubility of the hydroxide, indicating that Cu and Ni in the IBA washing water and leachates did not exist dominantly as their hydroxides.

Incineration Fly Ash and Its Treatment to Possible Utilization: A Review

Incineration has gained popularity over landfill as a key solution for the reduction of massively increasing volumes of municipal solid waste (MSW) generation worldwide and in particular China. However, it is not the end solution. The disposal of the incineration residues, which are enriched with a wide range of heavy metals and soluble salts, has become a challenge for the environmental managers. The aim of this study was to review the increasing urbanization and its repercussion on waste generation in China; waste management options were compared for possible environmentally friendly considerations. Treatment techniques of incineration fly ash were discussed to determine the effectiveness of obtaining environmentally stable material, and, finally, possible applications of incineration fly ash for utilization were discussed based on identifying the processing suitability, performance and environmental impact of incineration fly ash for its applications.

Assessment of the total content and leaching behavior of blends of incinerator bottom ash and natural aggregates in view of their utilization as road base construction material

The total and leachable metal content from mixtures of weathered municipal solid waste incinerator bottom ash (MSWI BA) and conventional natural or recycled aggregates was investigated with a focus on utilization of MSWI BA as a partial component in a road base. Two weathered bottom ashes were combined with various aggregates in multiple replacement percentages of up to 85% traditional aggregate, with the goal of mitigating leaching and direct human exposure risk. Al leaching was found to decrease proportionally to the mass of bottom ash included in the blended products, with over 90% reduction in blends with 85% recycled concrete aggregate (RCA). Release of Sb from the bottom ashes was predominantly controlled by solubility. Sb concentrations were reduced from 0.043 and 0.037 mg/L to 0.006 and 0.007 mg/L for facility A and B respectively blended with the highest tested proportion of RCA, near compliance drinking water standards of 0.006 mg/L. The high pH and presence of calcium-bearing minerals in recycled concrete appeared to facilitate significant immobilization of Sb in comparison to other aggregates. Similar results were observed for several other elements and material blends. Results indicate that blending MSWI BA with conventional aggregates is a feasible recycling application. Blending effectively mitigates environmental risk associated with the un-encapsulated use of MSWI BA in road construction.

Leaching behaviour of incineration bottom ash in a reuse scenario: 12years-field data vs. lab test results

Several types of standardized laboratory leaching tests have been developed during the past few decades to evaluate the leaching behaviour of waste materials as a function of different parameters, such as the pH of the eluate and the liquid to solid ratio. However, the link between the results of these tests and leaching data collected from the field (e.g. in disposal or reuse scenarios) is not always straightforward. In this work, we compare data obtained from an on-going large scale field trial, in which municipal solid waste incineration bottom ash is being tested as road sub-base material, with the results obtained from percolation column and pH-dependence laboratory leaching tests carried out on the bottom ash at the beginning of the test. The comparisons reported in this paper show that for soluble substances (e.g. Cl, K and SO₄), percolation column tests can provide a good indication of the release expected in the field with deviations usually within a factor of 3. For metals characterized by a solubility-controlled release, i.e. that depends more on eluate pH than the liquid to solid ratio applied, the results of pH-dependence tests describe more accurately the eluate concentration trends observed in the field with deviations that in most cases (around 80%) are within one order of magnitude (see e.g. Al and Cd). The differences between field and lab-scale data might be in part ascribed to the occurrence in the field of weathering reactions (e.g. carbonation) but also to microbial decomposition of organic matter that modifying leachate pH affect the solubility of several constituents (e.g. Ca, Ba and Cr). Besides, weathering reactions can result in enhanced adsorption of fulvic acids to iron/aluminum (hydr)oxides, leading to a decrease in the leaching of fulvic acids and hence of elements such as Cu, Ni and Pb that strongly depend on DOC leaching. Overall, this comparison shows that percolation column tests and pH-dependence tests can represent a reliable screening tool to derive data that could be employed in risk-based analysis or life cycle assessment (LCA) frameworks for evaluating potential environmental impacts deriving from specific disposal/reuse options for waste materials.

Phytotoxicity and groundwater impacts of leaching from thermal treatment residues in roadways

The use of coal fly ash (CFA), municipal solid waste incinerator bottom ash (MSWIBA) and flue gas desulfurization residue (FGDR) in road construction has become very common owing to its economical advantages. However, these residues may contain toxic constituents that pose an environmental risk if they leach out and flow through the soil, surface water and groundwater. Therefore, it is necessary to assess the ecotoxicity and groundwater impact of these residues before decisions can be made regarding their utilization for road construction. In this study, the physico-chemical characteristics, leaching and phytotoxicity of these residues were investigated. Specifically, multivariate analyses were used to evaluate the contributions of the leaching constituents of the CFA, MSWIBA and FGDR leachates to the germination index of wheat seeds. B, Ba, Cr, Cu, Fe and Pb were found to be more toxic to the wheat seeds than the other heavy metals. Furthermore, the leached concentrations of the constituents from the CFA, MSWIBA and FGDR were below the regulatory threshold limits of the Chinese identification standard for hazardous wastes. Analyses conducted using a numerical groundwater model (WiscLEACH) indicated that the predicted field concentrations of metals from the CFA, MSWIBA and FGDR increased with time up to about 30years at the point of compliance, then decreased with time and distance. Overall, this study demonstrated that the risks resulting from MSWIBA, CFA and FGDR leaching could be assessed before its utilization for road construction, providing crucial information for the adoption of these alternative materials.

Construction of an interim storage field using recovered municipal solid waste incineration bottom ash: Field performance study

The leaching of hazardous substances from municipal solid waste incineration (MSWI) bottom ash (BA) has been studied in many different scales for several years. Less attention has been given to the mechanical performance of MSWI BA in actual civil engineering structures. The durability of structures built with this waste derived material can have major influence on the functional properties of such structures and also the potential leaching of hazardous substances in the long term. Hence, it is necessary to properly evaluate in which type of structures MSWI BA can be safely used in a similar way as natural and crushed rock aggregates. In the current study, MSWI BA treated with ADR (Advance Dry Recovery) technology was used in the structural layers of an interim storage field built within a waste treatment centre. During and half a year after the construction, the development of technical and mechanical properties of BA materials and the built structures were investigated. The aim was to compare these results with the findings of laboratory studies in which the same material was previously investigated. The field results showed that the mechanical performance of recovered BA corresponds to the performance of natural aggregates in the lower structural layers of field structures. Conversely, the recovered MSWI BA cannot be recommended to be used in the base layers as such, even though its stiffness properties increased over time due to material aging and changes in moisture content. The main reason for this is that BA particles are prone for crushing and therefore inadequate to resist the higher stresses occurring in the upper parts of road and field structures. These results were in accordance with the previous laboratory findings. It can thus be concluded that the recovered MSWI BA is durable to be used as a replacement of natural aggregates especially in the lower structural layers of road and field structures, whereas if used in the base layers, an additional base layer of natural aggregate or a thicker asphalt pavement is recommended.

Environmental impact assessment of wood ash utilization in forest road construction and maintenance--A field study

The ever increasing use of wood material as fuel for green energy production requires innovative, environmentally safe strategies for recycling of the remaining wood ash. Utilizing wood ash in forest road construction and maintenance to improve mechanical stability has been suggested as a feasible recycling option. To investigate the environmental impact of wood ash application in forest road maintenance, a two-year field experiment was conducted at two Austrian forest sites (Kobernausserwald (KO) (soil pH 5.5) and Weyregg (WE) (pH 7.7)) differing in their soil chemical properties. Two different ashes, one produced by grate incineration (GA) and the other by fluidized bed incineration in a mixture with 15 vol% burnt lime (FBA), were incorporated in repeated road sections at a 15:85% (V/V) ash-to-soil rate. Leaching waters from the road body were collected and analyzed for 32 environmentally relevant parameters over two years. Upon termination of the experiment, sub-road soil samples were collected and analyzed for ash-related changes in soil chemistry. Even though a larger number of parameters was affected by the ash application at the alkaline site (WE), we observed the most pronounced initial increases of pH as well as Al, As, Fe, Mn, Ni, Co, Cu, Mo, and NO2(−) concentrations in leachates beneath GA-treated road bodies at Kobernausserwald due to the lower soil buffer capacity at this site. Despite the observed effects our results indicate that, when specific requirements are met (i.e. appropriate ash quality, sufficient soil buffer capacity below the road body, and single time-point ash incorporation within several decades), wood ash application in forest road construction is generally environmentally acceptable.

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.

Valorization of unauthorized sea disposal dredged sediments as a road foundation material

The main objective of this study is to show the ability of fine dredged material (mainly silty material) to be used in road construction project. This paper is divided into three parts. In the first part, the physical, the mineralogical and the mechanical characteristics of the used fine dredged sediments, as well as their chemical composition and environmental impacts are presented. In the second part, the methodology developed to design the road made from dredged fine sediment is developed. The third part of the paper focuses on the presentation of the road construction and the interpretation of analyses made on cores drilled samples from the road and measurements of the deflection of the road. The environmental assessment, based on leaching tests, is also performed at different issues.

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

A granular material (GM) to be used as road sub-base was formulated using 80% of weathered bottom ash (WBA) and 20% of mortar. The mortar was prepared separately and consisted in 50% APC and 50% of Portland cement. A pilot-scale study was carried on by constructing three roads in order to environmentally evaluate the performance of GM in a real scenario. By comparing the field results with those of the column experiments, the overestimations observed at laboratory scale can be explained by the potential mechanisms in which water enters into the road body and the pH of the media. An exception was observed in the case of Cu, whose concentration release at the test road was higher. The long-time of exposure at atmospheric conditions might have favoured oxidation of organic matter and therefore the leaching of this element. The results obtained showed that immobilization of all heavy metals and metalloids from APC is achieved by the pozzolanic effect of the cement mortar. This is, to the knowledge of the authors, the only pilot scale study that is considering reutilization of APC as a safe way to disposal.

Aggregate material formulated with MSWI bottom ash and APC fly ash for use as secondary building material

The main goal of this paper is to obtain a granular material formulated with Municipal Solid Waste Incineration (MSWI) bottom ash (BA) and air pollution control (APC) fly ash to be used as secondary building material. Previously, an optimum concrete mixture using both MSWI residues as aggregates was formulated. A compromise between the environmental behavior whilst maximizing the reuse of APC fly ash was considered and assessed. Unconfined compressive strength and abrasion resistance values were measured in order to evaluate the mechanical properties. From these results, the granular mixture was not suited for certain applications owing to the high BA/APC fly ash content and low cement percentages used to reduce the costs of the final product. Nevertheless, the leaching test performed showed that the concentrations of all heavy metals were below the limits established by the current Catalan legislation for their reutilization. Therefore, the material studied might be mainly used in embankments, where high mechanical properties are not needed and environmental safety is assured.

MSWI bottom ash used as basement at two pilot-scale roads: comparison of leachate chemistry and reactive transport modeling

The recycling of municipal solid waste incineration bottom ash as aggregates for road basement requires assessing the long-term evolution of leachate chemistry. The Dåva (Sweden) and Hérouville (France) pilot-scale roads were monitored during 6 and 10 years, respectively. Calculated saturation indices were combined to batch test modeling to set a simplified geochemical model of the bottom ash materials. A common reactive transport model was then applied to both sites. At Hérouville, pH and the concentration of most elements quickly drop during the first two years to reach a set of minimum values over 10 years. The decrease is less pronounced at Dåva. The evolutions of pH and major element concentrations are fairly well related to the following pH-buffering sequence: portlandite, C-S-H phases or pseudo-wollastonite and, finally, calcite in equilibrium with atmospheric CO(2). Al(OH)(3), barite, ettringite and monohydrocalcite may also control leachate chemistry. Cu release is correctly modeled by DOM complexation and tenorite equilibrium. Temperature has no significant effect on the modeling of leachate chemistry in the range 5-30°C, except at high pH. Effects at road edges and roadside slopes are important for the release of the less reactive elements and, possibly, for carbonation processes.

Recovery of MSWI and soil washing residues as concrete aggregates

The aim of the present work was to study if municipal solid waste incinerator (MSWI) residues and aggregates derived from contaminated soil washing could be used as alternative aggregates for concrete production. Initially, chemical, physical and geometric characteristics (according to UNI EN 12620) of municipal solid waste incineration bottom ashes and some contaminated soils were evaluated; moreover, the pollutants release was evaluated by means of leaching tests. The results showed that the reuse of pre-treated MSWI bottom ash and washed soil is possible, either from technical or environmental point of view, while it is not possible for the raw wastes. Then, the natural aggregate was partially and totally replaced with these recycled aggregates for the production of concrete mixtures that were characterized by conventional mechanical and leaching tests. Good results were obtained using the same dosage of a high resistance cement (42.5R calcareous Portland cement instead of 32.5R); the concrete mixture containing 400 kg/m(3) of washed bottom ash and high resistance cement was classified as structural concrete (C25/30 class). Regarding the pollutants leaching, all concrete mixtures respected the limit values according to the Italian regulation.

Ten-year chemical evolution of leachate and municipal solid waste incineration bottom ash used in a test road site

The use of municipal solid waste incineration (MSWI) bottom ash for road and car-park construction is an appropriate solution to reduce their disposal and the consumption of natural materials. In addition to leaching tests, the environmental impact assessment of such a waste recycling scenario critically needs for reliable long-term field data. This paper addresses a 10-year pilot site where MSWI bottom ashes have been used as road aggregates in Northern France (oceanic temperate climate). The paper focuses on the long-term evolution of leachate chemistry and the mineralogical transformations of MSWI bottom ash over 10 years. Data interpretation is supported by geochemical modeling in terms of main pH-buffering processes. The leachate pH and concentrations in major elements (Ca, Na and Cl) as well as in Al and heavy metals (Cu, Pb and Zn) quickly drop during the first 2 years to asymptotically reach a set of minimum values over 10 years; similar to those of a reference road built with natural calcareous aggregates. SO(4) release makes exception with a slightly increasing trend over time. Carbonation induced by CO(2) inputs, which leads to the successive dissolution of portlandite, CSH and ettringite, is one of the main phenomenon responsible for the geochemical evolution of leachate. On the other hand, mineralogical observations and batch tests demonstrate a relative stability of the MSWI bottom ash inside the subbase layer. In particular, carbonation may be far to be completed and still in progress after 10 years. This is consistent with preferential rainwater flow and dilution at the road edges combined to diffusion inside the subbase layer.

Potential environmental impacts of using refuse derived material for landfill capping

In this study, the potential impacts on leachate emissions of applying a pretreated refuse-derived material as a capping layer on top of a municipal solid waste landfill were researched. Leachate emissions and stability against degradation were investigated with reference to the untreated material. Results from percolation leaching tests were analysed by multivariate data analysis and chemical speciation modelling. During 6 month aerobic pretreatment in composting windrows with forced aeration, the waste was stabilized against aerobic degradation measured as respiration activity down to 15% of the original value. Initial percolation leachate concentrations were reduced by 40% for As, by 50% for Co, by 60% for Ni, Pb, and total sulfur, by 40% for sulfate-sulfur, by 96% for ammonium nitrate, and by 62% for dissolved organic carbon. An increase was observed by a factor of 4 for Cd, by a factor of 150 for Cu, by a factor of 3 for Zn. Principle Component Analysis revealed that the leaching characteristics of the pretreated material developed towards those of a top soil used as reference material. Increasing the flow rate in column percolation experiments led to lower leachate concentrations at liquid to solid ratios of 10. Constructing a capping layer from the pretreated material is likely to have impacts on the leachate treatment system.

Assessing the environmental impact of ashes used in a landfill cover construction

Large amounts of construction materials will be needed in Europe in anticipation for capping landfills that will be closed due to the tightening up of landfill legislation. This study was conducted to assess the potential environmental impacts of using refuse derived fuel (RDF) and municipal solid waste incineration (MSWI) ashes as substitutes for natural materials in landfill cover designs. The leaching of substances from a full-scale landfill cover test area built with different fly and bottom ashes was evaluated based on laboratory tests and field monitoring. The water that drained off above the liner (drainage) and the water that percolated through the liner into the landfill (leachate) were contaminated with Cl(-), nitrogen and several trace elements (e.g., As, Cu, Mo, Ni and Se). The drainage from layers containing ash will probably require pre-treatment before discharge. The leachate quality from the ash cover is expected to have a minor influence on overall landfill leachate quality because the amounts generated from the ash covers were low, <3-30l (m(2)yr)(-1). Geochemical modelling indicated that precipitation of clay minerals and other secondary compounds in the ash liner was possible within 3 years after construction, which could contribute to the retention of trace elements in the liner in the long term. Hence, from an environmental view point, the placement of ashes in layers above the liner is more critical than within the liner.