This paper is based on studies on the effects of accelerated ageing on refuse-derived-fuel (RDF) fly ashes, in experiments under controlled laboratory conditions, intended to derive models to predict the stability of RDF fly ashes used in a landfill liner and the mineralogi-cal changes that occur in them. A reduced factorial design was applied, followed by multivariate data analysis, to evaluate the effects of five factors — carbon dioxide (CO2) levels, temperature, relative air humidity (RH), time and the quality of added water — on mineral transformations within the ashes, and leaching behaviour. The pH values of these ash specimens ranged from 7.2 to 7.6, indicating advanced carbonation. Ageing decreased pH values from 12.4 to 7.2, conse-quently affecting the leaching behaviour of most chemicals measured in the leachates. Levels of Ba, Ca, Cl, Cr, Cu, Pb, K and Na decreased over the study period while those of Mg, Zn and SO4 increased. Clay minerals could not be detected neither in fresh nor in aged ashes. However, geo-chemical modelling indicated that such minerals may precipitate.

The landfilling ban for combustible waste in EU countries and the extended use of bio fuels in heat and electricity production will result in an increasing generation of incineration residues, such as fly ash and bottom ash. Instead of landfilling, ashes used as a construction material in, e.g., roads or landfill covers can result in saving natural resources and economical advantages. The main aim of this work is to assess how ashes used in landfill cover construction affect the environment and how the potential environmental impact can be assessed. The main pollution pathway of using ashes in landfill cover construction is leaching. Laboratory leaching tests can be used as a tool to assess the possible environmental impact of ashes before their use in a landfill cover. Solubility leaching tests, e.g. batch leaching test, pH-stat test and percolation test, can be useful tools to predict contaminants that can be released from ashes used in a protection and drainage layer. The diffusion leaching test together with the availability test are suitable to assess the release from ash used as liner material. However, predicting contaminant release in the field is difficult due to the complexity of the processes occurring in the field. Leachate and drainage water are two types of water generated in landfill cover. Leachate samples were mainly contaminated by As, Mo, Cl and N. Drainage water contained high concentrations of Ni, Cl and N with the addition of As, Cu, Mo, Pb and Zn in the areas where bottom ash is in the protection layer. Since leaching of most pollutants showed no clear tendency to decline over time, assessing how long leachate and drainage water need treatment is difficult. However, it is expected that salt forming elements will be depleted from ashes within some decades. A lower release of other trace elements, such as Cu, Pb and Zn, to ash leachate is expected due to immobilization by Al/Fe hydr(oxides) and clay minerals.

About 66% of all heat energy generated in Sweden originates from the incineration of municipal solid waste and biofuels such as wood, cardboard and peat. In addition to heat energy, incinerators generate about 1.7 Mt of ashes each year, of which 500 000 t are air pollution control (APC) residues. APC residues from municipal solid waste incineration are usually landfilled whereas those from biofuel incinerators are used in roads, as soil fertilizers, and as amendments for stabilizing APC residues classified as hazardous waste. The physico-chemical properties of compacted APC residues are such that they could be viable alternatives to clay in landfill cover liners, and could also replace cement in cases where a solidified structure is desired. However, APC residues are classified as waste and their use may rise concern due to the release of harmful substances into the environment. This thesis examines the environmental impact of APC residues when used together with other waste materials (e.g. sewage sludge, bottom ash, compost) in a landfill cover. In addition, the suitability of APC residues as amendments for stabilizing contaminated soil and their effect on the stability of treated soil under landfill conditions was investigated. The environmental impacts of alternative landfill cover were evaluated by field and laboratory tests that examined two water streams: the landfill cover’s drainage water and its leachate. The drainage water that seeps above the landfill cover liner and is drained away from a landfill cover was contaminated with Cl-, N, TOC and the trace elements As, Cu, Mo, Ni, Se, Pb and Zn. This water stream will need treatment for at least three to four decades. The amounts of landfill cover leachate that percolated through the liner in the field test ranged from 3 to 30 l (m2 y)-1, which was below the legal limit on the leachate flow in non-hazardous waste landfills (

The aim of this study was to evaluate the drainage water quality from a landfill cover built with secondary construction materials (SCM), fly ash (FA), bottom ash (BA) sewage sludge, compost and its changes over time. Column tests, physical simulation models and a full scale field test were conducted. While the laboratory tests showed a clear trend for all studied constituents towards reduced concentrations over time, the concentrations in the field fluctuated considerably. The primary contaminants in the drainage water were Cl−, N, dissolved organic matter and Cd, Cu, Ni, Zn with initial concentrations one to three orders of magnitude above the discharge values to the local recipient. Using a sludge/FA mixture in the protection layer resulted in less contaminated drainage water compared to a sludge/BA mixture. If the leaching conditions in the landfill cover change from reduced to oxidized, the release of trace elements from ashes is expected to last about one decade longer while the release of N and organic matter from the sludge can be shortened with about two–three decades. The observed concentration levels and their expected development over time require drainage water treatment for at least three to four decades before the water can be discharged directly to the recipient.

An alternative to virgin and artificial materials in landfill cover can be various types of waste materials like ashes and sewage sludge. From the environmental point of view, the most interesting question to study is the quality of the drainage water generated above the liner in landfill cover built with waste materials. Thus, the main aim of this paper is the evaluation of drainage water quality and time required for its treatment. Results from a full scale test, physical models and a column test were used in the evaluation of the drainage water quality development. The main contaminants identified in drainage water were N-tot, As, Cu, Cd, Pb, Zn and Ni. The laboratory tests showed higher concentrations of N-tot, NH4-N, TOC, As and Pb, but lower values of Cl, Zn, Ba and Ni in comparison with drainage water from the field.  It was probably a result of different factors that may have influence on leaching but interactions of the protection layer with the vegetation layer and the liner surface are expected to influence the results from the field. According to results from the laboratory experiments, drainage water will probably need treat­ment for at least two-three decades after covering.

Large amounts of construction materials will be needed both in Sweden and other European countries for capping landfills that will be closed in the near future. In order to reduce exploitation of virgin materials and to save natural resources, an option can be utilization of various types of secondary construction materials (SCM) e.g. ash, slag, sand from fluid bed incineration and compost. However, at the same time this may represent potential risks due to the release of trace elements and other pollutants into environment. The main aim of this work is to evaluate the environmental impact of water that discharges from different parts of a landfill cover built with ashes and other SCM.From 2003 to 2005, a four hectares large test area was established at Tveta landfill, southwest of Stockholm, Sweden. Test area is divided into six sub areas with regard to different recycled materials used in different layers of the cover construction (Figure 1).Figure 1. Design of the landfill cover test area at the Tveta landfill. BA = Bottom ash; FA = Fly ash; FC = Friedland clay Infiltrating water through the landfill cover either drains off in the drainage layer as drainage water or percolates through the liner into landfill body as leachate. At Tveta landfill, leachate amounts between 1 l (m2 yr)-1 and 30 l (m2 yr)-1 have been observed below highly compacted ash liner. Results show that leachate samples have higher pH, salt forming elements (e.g. K, Na, Ca and Cl) and concentrations of Cd, Ba As, Al, and Mo, and lower concentrations of Mn, Zn, Mg, Fe, Ni, and Pb compared to drainage water. The concentrations of Cr and total N are in the same range in leachate and drainage water while NH4-N is higher in leachate. Leachate of areas 1 and 4 shows higher content of organic matter than drainage water in these areas. A strong correlation is observed between EC, K, Na and Cl as well as between Cu and TOC. The comparison of the leachate and drainage water quality with different limit values showed that the leachate had elevated concentrations of As, Mo, Cl and nitrogen while the drainage water was mainly contaminated by Ni, Zn, Cl and nitrogen with the addition of As, Cu, Mo, and Pb in areas 2 and 4.Following conclusions can be drawn by now:The hydraulic properties of the landfill cover satisfy legislative requirements for non hazardous waste landfills; in some cases/areas also for hazardous waste landfills.Most of the infiltrating water through the landfill cover is discharged as drainage water. Thus, the design of layers above the liner is most important with regard to the environmental impact of the construction. Both leachate and drainage water need treatment before discharge into the local recipient. Organic matter in the protection layer is likely to contribute to the mobilization of Cu and Ni in short term.The sea might be a suitable recipient in cases where ashes are used in landfill covers be­cause both leachate and drainage contain salt forming elements in elevated con­cen­tra­tions which may harm groundwater or freshwater but do not pose a risk to salt-water.The leaching of most pollutants did not show any clear tendencies during first three years. Thus, assessing the time period for treatment needs is difficult. However, it is expected that the contaminants in the drainage water will be depleted within few decades.Leachate might be contaminated by salt forming and trace elements for one hundred years. However, generated leachate amounts are low and it is expected that leachate from landfill cover will not influence overall landfill leachate with full extent.The ageing of the ashes in connection with mineral transformations is an important process that is expected to reduce the release of pollutants. Further research is needed with regard to long term changes of the material properties and the treatment needs for water.

The aim of this study was to investigate the stability of As, Cr and Cu in contaminated soil treated with air pollution control residues under landfill conditions. The influence of landfill gas and temperature on the release of trace elements from stabilized soil was simulated using a diffusion test. The air pollution control residues immobilized As through the precipitation of Ca–As minerals (calcium arsenate (Ca5H2(AsO4)3 × 5H2O), weilite (CaAsO4) and johnbaumite (Ca5(AsO4)3(OH)), incorporation of As into ettringite (Ca6Al2(SO4)3(OH)12 × 26H2O) and adsorption by calcite (CaCO3). The air pollution control residues generally showed a high resistance to pH reduction, indicating high buffer capacity and stability of immobilized As in a landfill over time. Generation of heat in a landfill might increase the release of trace elements. The release of As from stabilized soil was diffusion-controlled at 60 °C, while surface wash-off, dissolution, and depletion prevailed at 20 °C. The air pollution control residues from the incineration of municipal solid waste immobilized Cr, indicating its stability in a landfill. The treatment of soil with air pollution control residues was not effective in immobilization of Cu. Contaminated soils treated with air pollution control residues will probably have a low impact on overall leachate quality from a landfill.

The aim of this study was to evaluate the stabilization/solidification (S/S) of trace element-contaminated soil using air pollution control residues (APCRs) prior to disposal in landfill sites. Two soil samples (with low and moderate concentrations of organic matter) were stabilized using three APCRs that originated from the incineration of municipal solid waste, bio-fuels and a mixture of coal and crushed olive kernels. Two APCR/soil mixtures were tested: 30 % APCR/70 % soil and 50 % APCR/50 % soil. A batch leaching test was used to study immobilization of As and co-occurring metals Cr, Cu, Pb and Zn. Solidification was evaluated by measuring the unconfined compression strength (UCS). Leaching of As was reduced by 39–93 % in APCR/soil mixtures and decreased with increased amounts of added APCR. Immobilization of As positively correlated with the amount of Ca in the APCR and negatively with the amount of soil organic matter. According to geochemical modelling, the precipitation of calcium arsenate (Ca3(AsO4)2/4H2O) and incorporation of As in ettringite (Ca6Al2(SO4)3(OH)12 · 26H2O) in soil/APCR mixtures might explain the reduced leaching of As. A negative effect of the treatment was an increased leaching of Cu, Cr and dissolved organic carbon. Solidification of APCR/soil was considerably weakened by soil organic matter.

The main aim of this study is to evaluate the stabilization of As-contaminated soil with Fly Ash (FA) and the environmental impact assessment of a soil/ash mixture after treatment. Two soil samples heavily contaminated with As were stabilized with two FA that originate from incineration of biofuels (BFA) and mixture of coal and crushed olive kernel (CFA). The As solubility was reduced between 39 and 93% in soil/ash mixtures. Leaching of As from soils decreased with increased amount of ash. Immobilization of As was positively correlated to pH and negatively correlated to the amount of organic matter in soil. Geochemical modeling showed that the release of As was controlled by Ca3(AsO4)2:4H2O in soil/ash mixtures that can be a possible explanation for the reduced solubility of As from soil/ash mixtures. A negative effect of the treatment was the mobilization of Cu from ashes and Dissolved Organic Carbon (DOC) from soil.

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, <3-30 l (m2 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.