Fly ash from biofuel incineration and slags from steel production were used in two full scale applications of cover constructions on municipal solid waste (MSW) landfills. The long-term stability of the cover materials is studied in a designed laboratory experiment. The impact of six environmental factors on accelerated carbonation is investigated over a period of three years. Leaching behaviour, acid neutralization capacity, mineral composition (XRD) and thermo gravimetrical behaviour (TG) are tested after different periods of ageing under different conditions. By now samples were taken after three and ten months of ageing. Multivariate data analysis was used for data evaluation. The results indicate the factors material, ageing time and carbon dioxide content of the atmosphere to be most relevant.
Steel slags from high-alloyed tool steel production were used in a full scale cover construction of a municipal solid waste (MSW) landfill. In order to study the long-term stability of the steel slags within the final cover, a laboratory experiment was performed. The effect on the ageing process, due to i.e. carbonation, exerted by five different factors resembling both the material characteristics and the environmental conditions is investigated. Leaching behaviour, acid neutralization capacity and mineralogy (evaluated by means of X-ray diffraction, XRD, and thermogravimetry/differential thermal analysis, TG/DTA) are tested after different periods of ageing under different conditions.Samples aged for 3 and 10 months were evaluated in this paper. Multivariate data analysis was used for data evaluation. The results indicate that among the investigated factors, ageing time and carbon dioxide content of the atmosphere were able to exert the most relevant effect. However, further investigations are required in order to clarify the role of the temperature.
The waste management is in need of a reliable and economical treatment method for metals in fly ashes from municipal solid waste incineration (MSWI). However, no state-of-the-art technique has gained wide acceptance yet. This Doctoral Thesis aimed at assessing the possibilities and limitations of carbonation as a stabilization method. Factors that were studied are the partial pressure of carbon dioxide, the addition of water, the temperature, and the reaction time. Laboratory experiments were performed applying methods such as factorial experimental design, thermal analysis, scanning electron microscopy (SEM), x-ray diffraction (XRD), and leaching assays including titration at static pH and sequential extraction. Leaching data were verified and complemented using chemical equilibrium calculations. Data evaluation was performed by means of multivariate statistics such as multiple linear regression, principal component analysis (PCA), and partial least squares (PLS) modeling. It was found that carbonation is a good prospect for a stabilization technique especially with respect to the major pollutants lead (Pb) and zink (Zn). However, a mobilization of cadmium (Cd) was observed, which requires further research on possible countermeasures such as e.g. metal demobilization through enhanced silicate formation.
The potential to damage the environment is the major motive to treat solid wastes. One main group of pollutants comprises metals such as cadmium, chromium, copper, mercury, nickel, lead, and zinc. This paper is a synthesis of five elsewhere published investigations focusing on the possibilities and limits to control the flux of metals from solid wastes using anaerobic processes. In particular, the treatment of sulfide forming elements and hexavalent chromium (Cr(VI)) were studied at both bench-, pilot-, and full-scale. It was found that two-step processes have the potential to significantly improve the quality of solid wastes. In a first step, metals were leached and transferred to the process water. In a second step, the metal-enriched process water was treated under methanogenic conditions facilitating metal trapping through precipitation as sulfides or hydroxides. Anaerobic hydrometallurgy is judged to be a promising technique that has the potential to gain wide acceptance in the treatment of metal-containing solid wastes from a wide variety of sources.
Waste management is in need of a reliable and economical treatment method for metals in fly ashes from municipal solid waste incineration (MSWI). However, no state-of-the-art technique has gained wide acceptance yet. This paper is a synthesis of five elsewhere published investigations covering a project which aimed to assess the possibilities and limitations of adding carbon dioxide (CO2) to fly ash as a stabilization method. Carbonation factors that were studied are the partial pressure of carbon dioxide (CO2), the addition of water, the temperature, and the reaction time. Laboratory experiments were performed applying methods such as factorial experimental design, thermal analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), and leaching assays including pHstat titration and sequential extraction. Leaching data were verified and complemented using chemical equilibrium calculations. Data evaluation was performed by means of multivariate statistics such as multiple linear regression, principal component analysis (PCA), and partial least squares (PLS) modeling. It was found that carbonation is a good prospect for a stabilization technique especially with respect to the major pollutants lead (Pb) and zinc (Zn). Their mobility decreased with increasing factor levels. Dominating factors were the partial pressure of CO2 and the reaction time, while temperature and the addition of water were of minor influence. However, the treatment caused a mobilization of cadmium (Cd), requiring further research on possible countermeasures such as metal demobilization through enhanced silicate formation.
Multivariate data analysis (MVDA), a new statistical approach in terms of landfill research, was performed at the evaluation of data sets from three investigations. The interrelationships among variables as well as variation between observations could be examined. Causal relations between experimental factors and response variables have been identified using scatterpott interpretation. The ease of using MVDA at data evaluation is proved. MVDA techniques as follows were applied: principal component analysis (PCA), partial least squares modelling (PLS) and partial least squares discriminant analysis (PLS-DA).
Multivariate data analysis (MVDA), a new statistical approach in terms of landfill research, was performed on the evaluation of three investigations. It gains advantage over classical statistical methods when multiple variables and their interactions have to be considered. In addition, it is tolerant for incomplete datasets. MVDA techniques as follows were applied: principal component analysis (PCA), partial least squares modelling (PLS) and partial least squares discriminant analysis (PLS-DA). The interrelationships among variables as well as variation between observations could be examined and illustrated by a few plots.
In Japan, expenses for landfilling yield about 400 US$ per t of ash, which gives an incentive to reduce the amount of landfilled ash. At NIES (National Institute for Environmental Studies) in Tsukuba, Japan, the AMT process (Accelerated Mineralization Technology) was developed aiming at the treatment of ashes and production of soil-like material for reuse. The objective of the project EJA was to evaluate the AMT process on the basis of available information and the possibilities the process could offer with respect to the conditions present in Sweden.With support of researchers at NIES, available literature including unpublished manuscripts on the AMT process was compiled, translated and evaluated. During treatment, the ashes are washed, aged and mixed with up to 5 weight-% of biodegradable organic matter. The material is stabilized at landfill. During up to several decades, metals are demobilized through a combination of three mechanisms, viz. carbonation, clay formation, and humification. Also persistent organic pollutants (POP) are demobilized due to humification products or they are degraded anaerobically. When the treatment is completed, the reuse of the material is envisaged.Due to the long treatment period, the AMT method might not be favored by ash producers in Sweden. In the future, landfill companies could be interested in the technology, since they are experienced to handle waste at long sight. This, however, requires that the legislation does not pose any hindrance for the implementation of the method, e.g. regarding the requirement to add organic matter to the ash. Above all, it remains several years of research on the AMT process to fully understand and evaluate the underlying biological and chemical processes as well as their interaction.
Increasing amounts of municipal solid waste incineration (MSWI) residues are treated prior to landfilling or reuse. In Japan, electric arc melting is used for bottom ash vitrification that generates a glasslike slag. The objective of this paper was to assess this pretreatment technique with respect to its effect on metal mobility and metal content. Both bottom ash and slag were sampled and analyzed on total solids (TS), fixed solids (FS), particle density (P), specific BET surface area, particle size distribution, and total element content. A six-step wet sequential extraction procedure was used for assessing metal mobility. The results were qualitatively verified by scanning electron microscopy. The major conclusion was that the availability of various metals was affected differently by electric arc vitrification. Metals were solidified, stabilized, and/or separated from the slag. The mobility of Cr, Cu, Zn, Pb, and Ca was reduced. In slag, major fractions of these elements were found in moderately reducible phases or in the residual slag lattice. The approximately three-fourths of Pb [174 ± 7 mg (kg of FS)-1] and half of Zn content [676 ± 352 mg (kg of FS)-1] were most likely removed from bottom ash through evaporation. The total content increases of Al, Cr, Ni, and Cd (51 ± 3, 621 ± 27, 138 ± 19, and 99 ± 32%, respectively) were probably caused by the wear of furnace refractories.
I förbränningsanläggningarnas flygaska koncentreras föroreningar från det avfall som förbränts. För att förhindra att dessa föroreningar sprids i samband med deponering kan askan stabiliseras. I Luleå utvecklas en ny metod för stabilisering av flygaska där koldioxid används i en process, så kallad karbonatisering, för att förhindra utlakning av bland annat miljöstörande metaller. Metoden utnyttjar den höga pH-halten i askan. Det är en betydligt enklare och billigare metod än de som tidigare prövats.
Discusses the two-step anaerobic degradation (TSAAD) system of the Boras plant in Sweden. Reasons for the decision of the municipality of Boras to choose the source separation refuse system; Anaerobic digestion technology used by the Boras plant; How the TSAAD works; Results of the evaluation of the operation.
Fly ash from municipal solid waste incineration (MSWI) is considered as hazardous waste that calls for a robust, reliable, and reasonable treatment technique. This investigation aims to assess the impact of CO2 partial pressure, water addition, time, and temperature on the stabilization of MSWI fly ash with particular emphasis on Pb, Zn, Cd, and Cr. Carbonation and element mobility were studied by applying thermal analysis and leaching assays on fly ash samples treated according to a 24 factorial design. The relationship between the factors and the response variables was evaluated using partial least squares modeling. Chemical equilibrium calculations were performed so as to complement the experimental findings. Decalcification of carbonated fly ash in a typical Swedish landfill was estimated at 0.13 mm.yr(-1) Treatment through carbonation reduced the availability of Pb and Zn about 100 times and also the carbonate alkalinity of 7.4 eq. (kg.FS)(-1) (FS represents the fixed solids) was remedied successfully. However, shortcomings that need to be resolved are the remobilization of Cr with time and the mobilization of Cd.
Dry scrubber residue from municipal solid waste incineration (MSWI) was characterized to identify critical inorganic pollutants and to suggest a conceptual treatment method. The key methods used were thermal analysis, including thermogravimetry (TG) and differential thermal analysis (DTA), pHstat titration, qualitative X-ray diffraction (XRD), scanning electron microscopy (SEM), chemical equilibrium calculations, and statistics such as error propagation, principal component analysis (PCA), and empirical modeling based on factorial designs. Based on EU directives, the major inorganic pollutants Cd, Cr, Pb, and Zn were found. In addition, the pH was too high. With dry scrubber residue stabilization in mind, the impact of carbonation and hydration was assessed and judged to be encouraging. In particular, chemical equilibrium calculations showed that carbonation has considerable potential to lower the pH and the availability of Pb, Zn, and Cr. The impact of carbonation on the mobility of Cd was found to be small. During carbonation, a metal-trapping calcium aluminosilicate hydrate (C–A–S–H) phase is also formed. Both processes together have the potential to lead to a robust, reliable, and reasonable stabilization method for dry scrubber residue. However, to control these processes, the decisive factors need to be identified and their effects need to be quantified. Ca, Cl, Na, and K might be abundant components which would be mobile even after stabilization.
Solid residues from municipal solid waste incineration (MSWI) can be categorized as air pollution control residues (AR) and bottom ash (BA). Both categories pose a particular environmental threat on account of the risk of the release of dioxins and metals. In Japan, handling of MSWI residues is of major concern and the treatment of AR prior to landfilling is stipulated. Accepted treatment: techniques are melting, cementitious S/S (stabilization and solidification), stabilization with a chemical agent and acid extraction. These methods are reviewed and evaluated in this paper with respect to: quality; quantity and utilization of end products; treatment costs; energy demand and process reliability. Thermal processes are superior regarding dioxin removal as well as material recovery and reuse, but treatment costs can be as high as 60 000 Y t(-1), i.e. one order of magnitude higher than for other processes. Cementitious SIS and chemical stabilization are characterized by the ease of operation, but the solid waste mass is increased by up to 40 and 10 wt.-%, respectively. Acid extraction is a proven and reliable technique and is inexpensive: nevertheless, it has the smallest share of the market.
Dissolved organic carbon (DOC) may affect the transport of pollutants from incineration residues when landfilled or used in geotechnical construction. The leaching of dissolved organic carbon (DOC) from municipal solid waste incineration (MSWI) bottom ash and air pollution control residue (APC) from the incineration of waste wood was investigated. Factors affecting the mobility of DOC were studied in a reduced 26-1 experimental design. Controlled factors were treatment with ultrasonic radiation, full carbonation (addition of CO2 until the pH was stable for 2.5 h), liquid-to-solid (L/S) ratio, pH, leaching temperature and time. Full carbonation, pH and the L/S ratio were the main factors controlling the mobility of DOC in the bottom ash. Approximately 60 weight-% of the total organic carbon (TOC) in the bottom ash was available for leaching in aqueous solutions. The L/S ratio and pH mainly controlled the mobilization of DOC from the APC residue. About 93 weight-% of TOC in the APC residue was, however, not mobilized at all, which might be due to a high content of elemental carbon. Using the European standard EN 13 137 for determination of total organic carbon (TOC) in MSWI residues is inappropriate. The results might be biased due to elemental carbon. It is recommended to develop a TOC method distinguishing between organic and elemental carbon.
The re-use of bottom ash in road construction necessitates a tool to predict the impact of trace metals on the surroundings over the lifetime of the road. The aim of this work was to quantify the effect of environmental factors that are supposed to influence leaching, so as to suggest guidelines in developing a leaching procedure for the testing of incineration residues re-used in road constructions. The effects of pH, L / S (liquid-to-solid ratio), leaching time, and leaching atmosphere on the leachate concentrations of Cd, Cr, Cu, Ni, Pb, and Zn were studied using a two-level full factorial design. The most significant factor for all responses was the pH, followed by L / S, though the importance of pH and L / S is often ignored in leaching tests. Multiple linear regression models describing the variation in leaching data had R2 values ranging from 61-97%. A two-step pH-stat leaching procedure that considers pH as well as L / S and leaching time was suggested.
Secondary materials could help meeting the increasing demand of landfill cover liner materials. In this study, the effect of compaction energy, water content, ash ratio, freezing, drying and biological activity on the hydraulic conductivity of two fly ash - sewage sludge mixes was investigated using a 27-1 fractional factorial design. The aim was to identify the factors that influence hydraulic conductivity, to quantify their effects and to assess how a sufficiently low hydraulic conductivity can be achieved. The factors compaction energy and drying, as well as the factor interactions material×ash ratio and ash ratio×compaction energy affected hydraulic conductivity significantly (α = 0.05). Freezing on 5 freeze-thaw cycles did not affect hydraulic conductivity. Water content affected hydraulic conductivity only initially. The hydraulic conductivity data were modelled using multiple linear regression. The derived models were reliable as indicated by R2adjusted values between 0.75 and 0.86. Independent on the ash ratio and the material, hydraulic conductivity was predicted to be between 1.7 × 10-11 m s-1 and 8.9 × 10-10 m s-1 if the compaction energy was 2.4 J cm-3, the ash ratio between 20 and 75 % and drying did not occur. Thus, the investigated materials met the limit value for non-hazardous waste landfills of 10-9 m s-1.
Carbon in waste can occur as inorganic (IC), organic (OC) and elemental carbon (EC) each having distinct chemical properties and possible environmental effects. In this study, carbon speciation was performed using thermogravimetric analysis (TGA), chemical degradation tests and the standard total organic carbon (TOC) measurement procedures in three types of waste materials (bottom ash, residual waste and contaminated soil). Over 50% of the total carbon (TC) in all studied materials (72% in ash and residual waste, and 59% in soil) was biologically non-reactive or EC as determined by thermogravimetric analyses. The speciation of TOC by chemical degradation also showed a presence of a non-degradable C fraction in all materials (60% of TOC in ash, 30% in residual waste and 13% in soil), though in smaller amounts than those determined by TGA. In principle, chemical degradation method can give an indication of the presence of potentially inert C in various waste materials, while TGA is a more precise technique for C speciation, given that waste-specific method adjustments are made. The standard TOC measurement yields exaggerated estimates of organic carbon and may therefore overestimate the potential environmental impacts (e.g. landfill gas generation) of waste materials in a landfill environment.
COD (chemical oxygen demand) has historically been considered to be an estimate of organic matter, and though this is no longer the case, for most kinds of water it is still a fair approximation. Landfill leachates may, however, be one of the exceptions. Landfill leachate contains many inorganic substances and, in certain circumstances, high concentrations of volatile organic compounds like acetic acid; the COD value may be affected by these conditions. Designed experiments were performed to determine how COD could be affected by the composition of landfill leachates. The factors studied include the content of iron(II), manganese(II), sulphide, ethanol, acetic acid, ammonia, and chloride as well as different aspects of the COD analysis design. The results show that up to about one-third of COD may be due to the inorganic components of leachates. The main conclusion from the experiments is that COD cannot be used solely as a measure of the organic matter of landfill leachate since inorganic substances as well as interactions between substances may interfere with the COD results.