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

International audienceThe 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 CO2. 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

Environmental assessment of construction with recycled materials

The use of industrial residues as raw materials in construction raises concerns over the potential leaching and dispersal of hazardous constituents from them into the environment. Their leaching behaviour has been studied in laboratory assays, but leaching processes in the field over larger spatial and temporal scales are more complex due to variations in the conditions the materials are exposed to, and less well understood. Hence, estimates of the potential environmental loads associated with the use of such materials based on laboratory tests may be inaccurate. This thesis addresses the environmental implications of using recycled materials in road and landfill cover constructions. The focus is primarily on the leaching of inorganic constituents from six types of materials: incineration ashes, copper smelter slag, blast-furnace slag, recycled concrete, natural rock and contaminated soil. The leaching behaviour of constituents from these materials were assessed in both laboratory batch leaching tests and monitoring programs in which the water percolating through them in field applications were sampled over one to ten years. Leaching data were evaluated using statistical and geochemical modelling. In addition, assessment methods and criteria to judge the environmental suitability of substituting natural materials for recycled materials in construction were reviewed. It was found that leachates from recycled materials in the constructions contain higher concentrations of several constituents than natural water and leachates from conventional materials. However, the rates and extent of constituent leaching were affected by the application methods in various ways that are explored and discussed. The results of simplified leaching tests did not always reflect the leaching behaviour in the field, which highlight the importance of developing assessment methods that allow case-specific factors to be taken into account. The environmental impacts of leaching must also be considered in relation to the expected impacts of the default alternative, i.e. landfilling of industrial residues and exploitation of natural resources. Combinations of case-specific assessments and system analyses would be the ideal approaches to evaluate impacts at both local and regional scales.Användningen av industriella restprodukter som konstruktionsmaterial inom anläggningsbyggande väcker frågan om möjlig utlakning och spridning av förorenande ämnen från materialen till omgivande miljö. Materialens lakningspotential bestäms vanligen genom lakförsök utförda under kontrollerade förhållanden i laboratorium. Lakningsprocesser i fält sker dock över större rums- och tidskalor och är mer komplexa på grund av variationer i miljön som materialen exponeras för. Uppskattningar av materialens möjliga miljöpåverkan baserade på laboratorietester kan därför vara felaktiga. Den här avhandlingen handlar om den miljömässiga betydelsen av att använda återvunna material som konstruktionsmaterial i vägar och deponisluttäckningar. Fokus är i huvudsak på utlakningen av oorganiska ämnen från sex typer av material: förbränningsaskor, kopparslagg, hyttsten, återvunnen betong, naturligt berg och förorenad jord. Utlakningen från dessa material undersöktes med hjälp av både skakförsök i laboratorium och kontrollprogram där vatten som perkolerade materialen i fältapplikationer (sk. lakvatten) provtogs under ett till tio år. Lakvattendata utvärderades med hjälp av statistisk och geokemisk modellering. Dessutom granskades olika bedömningsmetoder och kriterier som kan användas för att bedöma den miljömässiga lämpligheten av att använda återvunna istället för naturliga material i anläggningskonstruktioner. Lakvatten från återvunna material i de undersökta konstruktionerna innehöll högre koncentrationer av flera ämnen än naturliga vatten och lakvatten från naturliga material. Dock var hastigheten och omfattningen av utlakningen beroende av hur materialet användes, vilket har undersökts och diskuteras i avhandlingen. Resultaten från förenklade skakförsök överensstämde inte alltid med observationerna i fält, vilket understryker vikten av att utveckla bedömningsmetoder där fallspecifika faktorer kan tas i beaktande. Miljöpåverkan orsakad av lakning måste också ses i relation till den påverkan som kan uppstå om restprodukterna istället deponeras och naturliga material exploateras. Kombinationer av fallspecifika och systemövergripande analyser skulle därför vara det ideala sättet att utvärdera både lokala och regionala effekter av en möjlig användning av återvunna material.Godkänd; 2008; 20081003 (ysko)</p

Value-added wood processing : Building and living with wood

Godkänd; 2012; 20110505 (soli)Lean Wood Engineerin

Environmental assessment of construction with recycled materials

The use of industrial residues as raw materials in construction raises concerns over the potential leaching and dispersal of hazardous constituents from them into the environment. Their leaching behaviour has been studied in laboratory assays, but leaching processes in the field over larger spatial and temporal scales are more complex due to variations in the conditions the materials are exposed to, and less well understood. Hence, estimates of the potential environmental loads associated with the use of such materials based on laboratory tests may be inaccurate. This thesis addresses the environmental implications of using recycled materials in road and landfill cover constructions. The focus is primarily on the leaching of inorganic constituents from six types of materials: incineration ashes, copper smelter slag, blast-furnace slag, recycled concrete, natural rock and contaminated soil. The leaching behaviour of constituents from these materials were assessed in both laboratory batch leaching tests and monitoring programs in which the water percolating through them in field applications were sampled over one to ten years. Leaching data were evaluated using statistical and geochemical modelling. In addition, assessment methods and criteria to judge the environmental suitability of substituting natural materials for recycled materials in construction were reviewed. It was found that leachates from recycled materials in the constructions contain higher concentrations of several constituents than natural water and leachates from conventional materials. However, the rates and extent of constituent leaching were affected by the application methods in various ways that are explored and discussed. The results of simplified leaching tests did not always reflect the leaching behaviour in the field, which highlight the importance of developing assessment methods that allow case-specific factors to be taken into account. The environmental impacts of leaching must also be considered in relation to the expected impacts of the default alternative, i.e. landfilling of industrial residues and exploitation of natural resources. Combinations of case-specific assessments and system analyses would be the ideal approaches to evaluate impacts at both local and regional scales.Användningen av industriella restprodukter som konstruktionsmaterial inom anläggningsbyggande väcker frågan om möjlig utlakning och spridning av förorenande ämnen från materialen till omgivande miljö. Materialens lakningspotential bestäms vanligen genom lakförsök utförda under kontrollerade förhållanden i laboratorium. Lakningsprocesser i fält sker dock över större rums- och tidskalor och är mer komplexa på grund av variationer i miljön som materialen exponeras för. Uppskattningar av materialens möjliga miljöpåverkan baserade på laboratorietester kan därför vara felaktiga. Den här avhandlingen handlar om den miljömässiga betydelsen av att använda återvunna material som konstruktionsmaterial i vägar och deponisluttäckningar. Fokus är i huvudsak på utlakningen av oorganiska ämnen från sex typer av material: förbränningsaskor, kopparslagg, hyttsten, återvunnen betong, naturligt berg och förorenad jord. Utlakningen från dessa material undersöktes med hjälp av både skakförsök i laboratorium och kontrollprogram där vatten som perkolerade materialen i fältapplikationer (sk. lakvatten) provtogs under ett till tio år. Lakvattendata utvärderades med hjälp av statistisk och geokemisk modellering. Dessutom granskades olika bedömningsmetoder och kriterier som kan användas för att bedöma den miljömässiga lämpligheten av att använda återvunna istället för naturliga material i anläggningskonstruktioner. Lakvatten från återvunna material i de undersökta konstruktionerna innehöll högre koncentrationer av flera ämnen än naturliga vatten och lakvatten från naturliga material. Dock var hastigheten och omfattningen av utlakningen beroende av hur materialet användes, vilket har undersökts och diskuteras i avhandlingen. Resultaten från förenklade skakförsök överensstämde inte alltid med observationerna i fält, vilket understryker vikten av att utveckla bedömningsmetoder där fallspecifika faktorer kan tas i beaktande. Miljöpåverkan orsakad av lakning måste också ses i relation till den påverkan som kan uppstå om restprodukterna istället deponeras och naturliga material exploateras. Kombinationer av fallspecifika och systemövergripande analyser skulle därför vara det ideala sättet att utvärdera både lokala och regionala effekter av en möjlig användning av återvunna material.Godkänd; 2008; 20081003 (ysko)</p

Trästäder visar vägen mot hållbart byggande

Godkänd; 2010; 20100519 (soli

Leaching behaviour of air-cooled blast-furnace slag under intermittent and continuous wetting

Air-cooled blast-furnace slag is commonly utilised as a construction material in roads, fill and embankments. Materials used in such constructions do not remain continuously wetted, but is often subjected to cyclic wetting and drying under various exposure conditions. However, its leaching behaviour is often assessed based on tests performed under continuous wetting. This work was conducted to evaluate the leaching behaviour of an air-cooled blast-furnace slag under intermittent and continuous wetting. Four different leaching tests were performed, including a static leaching test without leachant renewal and three dynamic leaching tests: a column leaching test with continuous flow of the leachant, a tank leaching test with sequential renewal of the leachant and an intermittent leaching test with periodical flow of leachant. Leaching of the studied material under cyclic wetting and drying led to less alkaline and more oxidised eluates than leaching under continuously wetted conditions. The eluates are expected to maintain a mildly alkaline pH for long time periods during wetting, drying and oxidation of the material because the material has considerable acid neutralising potential. The leaching of soluble elements such as Ca and S was lower under intermittent than under continuous flow of the leachant which could be due to the shorter contact time between the leachant and material, and the precipitation of secondary phases on the particle surfaces during intermittent leaching. During exposure of the BFS to cyclic wetting and drying, the leaching of these elements decreased and the speciation of S in the eluates shifted towards more oxidising forms. The leached amounts of constituents were low in all performed tests, which indicate that the material was resistant to leaching under the conditions that were investigated here.Godkänd; 2011; 20110327 (soli)</p

Environmental assessment of secondary construction materials

Process industry, construction and other comparable activities produce large quantities of waste with potential use in geotechnical applications. Prior to utilisation, an acceptably low risk of contamination to humans and the environment must be demonstrated. This work focuses on the identification and evaluation of critical factors for environmental assessments of secondary construction materials. The market potential and the main barriers for usage of industrial wastes were analysed and showed a good potential especially in urban areas. The main obstacle is the long and complicated permit process involved. Further, the lack of a general procedure to investigate the suitability of intended usage leads to inconsistent assessments. An evaluation of leachate emissions from a large-scale test road demonstrated the importance of construction design and site-specific field conditions on the potential environmental impacts. It was also shown that pollutant concentrations in leachate from secondary construction materials tend to become comparable, or for some pollutants, even lower than from rock materials. Different assessment methods and criteria to judge the acceptability of an intended use were reviewed and various methods were identified. However, a generic method to evaluate materials under various environmental conditions is lacking.Godkänd; 2004; 20070109 (mlk

Assessment of redox-sensitive element mobility : discrepancy between laboratory and field data

Leaching tests have become popular tools to assess the environmental effect of materials containing pollutants e.g. wastes, construction materials, soils. Batch (EN 12457-3) and column (prEN 14405) leaching tests are both standardised. The standardisation regulates how the test should be performed i.e. the procedure, the amount of material to be used and how to handle the leachate. However, standardisation is often misinterpreted as quality insurance that the results of the test are relevant for any type of material and application. The EN 12457-3 test has thanks to the standardisation and its relatively low price become the most popular tests used to assess if waste material could be used in constructions. Basically waste materials fulfilling acceptance criteria for landfill for inert waste are often regarded as acceptable to reuse in the society.The aim of the presentation is to discuss the risk of using tests without a critical assessment of their relevance and limitations. Materials containing sulphides, iron and arsenic are specially challenging to assess as the standard batch leaching test underestimates the risk for leaching.The leaching of arsenic was underestimated by the EN 12457-3 test and the effect of open filtration, sample preparation and test conditions are discussed. The results showed that a material fulfilling criteria for landfill for inert waste leached more arsenic than was acceptable at a landfill for hazardous waste. In the second example, the documented generation of acidic leachate from blast furnace slag in field conditions has never been observed in the laboratory. The main hypothesis is that the development of unsaturated conditions caused the oxidation of sulphidic minerals in the blast furnace slag heap and generation of acid leachate.The selection of appropriate leaching tests should be done with regard to the real conditions that are to be assessed. Standardisation does not mean that the test is automatically adapted to the need. A relevant assessment requires therefore understanding of the geochemical process controlling the pollutant mobilisation and immobilisation in the actual material and its application. Such comprehension is a prerequisite to the selection of appropriate leaching procedures.Godkänd; 2009; Bibliografisk uppgift: Værtspublikationsredaktører: Jacques Mehu; 20090824 (chma

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

The use of municipal solid waste incineration (MSWI) bottom ash in road construction may possess a risk to the environment due to the release of e.g. salt and heavy metals. In this study, two years of leachate data from a test road built of MSWI bottom ash and crushed rock in northern Sweden were evaluated. It was found that Cu, Cr, Al, Na, and Cl- were leached in higher amounts from the bottom ash, while the release of Zn, Mg, Ba, and Ca was higher from the crushed rock. The difference between ash and crushed rock leachates decreased over time, mainly due to changes in the ash leachate composition. The road pavement reduced the release rate of most pollutants from the bottom ash compared to the release from the uncovered parts of the road, whereas the release of pollutants from the crushed rock was less affected by the presence of a pavement.Godkänd; 2005; 20070520 (ysko