CHARACTERISTICS, TREATMENT AND UTILIZATION OF RESIDUES FROM MUNICIPAL WASTE INCINERATION

Transcription

1 February 200 ECN-RX CHARACTERISTICS, TREATMENT AND UTILIZATION OF RESIDUES FROM MUNICIPAL WASTE INCINERATION H.A. van der Sloot* D.S. Kosson** O. Hjelmar*** * ECN Soil & Waste Research, P.O. Box, 755 ZG Petten, The Netherlands **Vanderbilt University, Box 83 Station B, Nashville, Tennessee, USA *** VKI, Agernallee, 2960 DK Hørsholm, Denmark A B Revisions Made by: Approved: ECN-Clean Fossils Soil & Waste Research H.A. van der Sloot Checked by: G.J. de Groot Issued: C.A.M. van der Klein

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3 CHARACTERISTICS, TREATMENT AND UTILIZATION OF RESIDUES FROM MUNICIPAL WASTE INCINERATION Abstract H.A. van der Sloot*, D.S. Kosson** and O. Hjelmar*** * ECN Soil & Waste Research, P.O. Box, 755 ZG Petten, The Netherlands **Vanderbilt University, Box 83 Station B, Nashville, Tennessee, USA *** VKI, Agernallee, 2960 DK Hørsholm, Denmark Beneficial utilization of residues from municipal solid waste incineration is an important objective for integrated waste management in many jurisdictions. When residues are to be used as an aggregate substitute in construction applications, the release of constituents of concern to soils and water through leaching is an important environmental consideration. In this paper, residue characteristics that control constituent leaching and testing approaches for evaluating leaching are discussed. Quality control and potential improvement in case of beneficial application are addressed. Keywords: Leaching, Treatment, Waste incineration, Residues, Environmental impact, Ash Introduction From waste-to-energy conversion of municipal solid waste, in which high standards of emission control are reached, solid residues remain, including bottom ash, fly ash and air pollution control residues, that need to be dealt with in an environmentally acceptable manner. Advanced air pollution control measures in incinerators shift constituents of concern from air emissions to solid residues, which potentially may lead to soil and water pollution. The evaluation of the environmental quality of such residues is necessary before decisions can be taken on the utilization, treatment or disposal of the residues. The quality of the residues from Waste-To- Energy conversion is very diverse, as has been detailed in the International Ash Working Group s (IAWG) book Municipal Solid Waste Incinerator (MSWI) Residues []. Management practices for incinerator residues are very different in different jurisdictions. As a result of recent developments in waste management, consideration is given to recycling and reuse of residues in construction. This necessitates a judgement on the short and long-term environmental acceptability of such utilization scenarios. In addition to the environmental aspects, the new material will have to meet technical specifications similar to those of natural materials traditionally used for the same purpose. In Europe, utilization of MSWI bottom ash is either practised (e.g. Netherlands, Denmark, Germany, France) or increasingly considered as a viable option (e.g. Belgium). National legislation has been implemented to regulate utilization of MSWI bottom ash in the Netherlands [2] and in France [3]. In the Netherlands, bottom ash is placed in a special category, because bottom ash as currently produced does not always meet the regulatory requirements. It is anticipated that improvement in ash quality will bring the material within the regulatory specifications [2]. Quality control programs and certification of bottom ash are in progress to ensure production of a marketable product [4]. In this paper recent developments in characterization of environmental properties of MSWI residues are discussed. Leaching data and relevant information from field studies are interpreted to reach conclusions on how to predict long-term environmental impact. Since MSWI residues as produced often do not meet environmental criteria, treatment options are discussed. One of the options is to control the input through waste acceptance criteria. For this latter aspect, the relationships between input and ultimate leaching behaviour of residues are needed. ECN-RX

4 Materials and Methods The work mainly deals with MSWI residues. Some earlier published data[] have been used as reference for more recent results. The sampling of MSWI residues was carried out in accordance with the recommendations of the IAWG []. The leaching test methods applied are preliminary versions of the dependence leaching test [5] and the percolation test [6] now standardized in CEN TC 292 Characterization of waste - Working Group 6. Environmental Quality of Residues The main leaching character of MSWI residues has been largely outlined in the IAWG book []. Since the time of publication, more detailed information has been generated following this same basis of characterization by using the dependence leaching test and percolation tests [5,6]. Also a stronger emphasis has been placed on modelling leaching behaviour to identify the solubility controlling phases and binding mechanisms. In the framework of the European Standardization Committee (CEN) Technical Committee (TC) 292 Characterization of Waste, the two leaching procedures - dependence test and percolation up-flow test - identified as forming the basis for characterization of MSWI residues are now being standardized (Working Group 6). In the framework of this Working Group a methodology guideline (ENV 2920) has been described for the assessment of long-term leaching behaviour [7]. It advocates evaluation of utilization and disposal options based on the specific management scenario. This aspect will be addressed in more detail later. Comparison of leaching behaviour of different MSWI residues and treated residues is possible through the information generated by the dependence test. Figure presents the leaching behaviour of Cd from different MSWI residue streams. The different leaching curves of Cd as a function of are largely related to the chloride content in the residue for greater than 7. The amount released at less than 5 usually reflects the total content of Cd in the residue stream, as almost all Cd present is leachable. Refuse Derived Fuel (RDF) ash and vitrified MSWI fly ash are included for comparison. The danger of indiscriminate use of an extraction test, which provides data at only one condition, is illustrated through the results of a single extraction test at the own of the material. Clearly, this very limited evaluation could result in erroneous classification of a material. If local equilibrium is assumed, the actual release can be quantified from the dependence leach curves of Cd with varying Cl levels. Figure illustrates that, if the would decrease over the long-term as a result of external influences, the leachability of Cd from RDF ash and MSWI fly ash may increase dramatically. A compensating factor for this dramatic increase may occur if Cl - is released under high conditions when Cd is not leachable, and by the time the decreases no Cl - is left to mobilize the Cd. In this case, the dynamics of leaching can lead to a substantially lower release in practice. Such processes illustrate the need to carry out more detailed characterization tests such as percolation tests for some cases. Batch leaching tests will not always clarify such interrelated mechanisms. However, no extent of characterization will result in a perfect prediction of future environmental performance and a balance must be maintained to obtain information necessary for a sufficiently, but not overly, conservative decision and excessive testing requirements should be avoided. The consistency of data from different sources both in time and place is illustrated in figures 2 and 3. For the elements Cd, Cr, Mo and Zn, the characteristic behaviour of MSWI bottom ash and MSWI fly ash is clear. In case of Cd the leaching from fly ash is similar in shape but shifted due to the Cl - concentration and total Cd content in the material (note that the plateau is at <7 for high Cl concentrations but <5 for low Cl concentrations). For Cr the difference in leaching behaviour of bottom ash and fly ash at > 5 is attributed to the presence of Cr as chromate in flue gas cleaning wastes, whereas in bottom ash Cr is present as Cr III due to its The own of a material is the final of the leaching solution when the material is extracted with deionized water. 4 ECN-RX

5 initial slightly reducing properties. In case of Mo, the leaching behaviour as a function of is typical for an oxyanion [8]. In fly ash, the Mo level is increased relative to bottom ash but the shape of the curve is similar, indicating no significant difference in chemical speciation between the two types of residues. The difference between different MSWI residues is not very marked at 8 2 in spite of large differences in total composition. At > 7 the level available for leaching is reached (plateau) with a difference of only a factor of 2 to 3 between fly ash and bottom ash. The dependence leaching test provides a very good means of mutual comparison of MSWI residues as well as a comparison of leaching behaviour within one and the same type of MSWI residue. Parameter settings in dependence and column tests In the studies carried out to provide a basis for parameter setting in these standards worked out by CEN TC 292 Working Group 6, MSWI bottom ash has been used as a reference material, which owing to its heterogeneous nature cannot be considered a simple choice. Aspects such as particle size, contact time and percolation rate have been addressed. In figure 4 the aspects percolation rate and contact time are highlighted. Results of column tests performed at different flow velocities (particle size: 95% < 4mm) and dependence tests at different contact times (particle size: 95% < 2 mm) are shown in figures 4 and 5, respectively. These results indicate that the hydraulic retention time within the column is not a critical parameter within the range of retention times evaluated. From V and Mo leachability as a function of and as a function of contact time further conclusions can be drawn with respect to mechanisms of release, which in turn can be used to guide activities to improve ash quality and in assessing short and long term environmental impact. Mo is leached as molybdate (oxyanion) and its mobile fraction is almost completely washed out within L/S=2 l/kg. Molybdenum is therefor an example of availability controlled leaching. When the percolation test data are plotted in the dependence graph (test carried out at L/S=0 l/kg) the cumulative leached amounts approach the stat curve (determined at L/S=0 l/kg) at the relevant from L/S=2 l/kg onwards. This indicates consistency between the two fully independent leaching tests. Obviously, when concentration data from the column test at low L/S are plotted in comparison to the dependence curve, greater concentrations are observed from the column test. However, this is also relevant information, as it will indicate what concentrations may be expected in leachate in the short term or even long term, depending on the level of infiltration. The relation between L/S (in l/kg) and time is given by [9]: L/S= I. t / (ρ. h) with I is the net infiltration of precipitation in mm/year, t the time in years, ρ the dry bulk density of the material in kg/m 3 and h the height of the application in m. For open applications with a height of 0.5 meter and an infiltration rate of 200 mm per year, an L/S of about 0 l/kg is reached in about 00 years, whereas in a situation with top cover for a height of 5 meters and a substantially reduced infiltration, an L/S of l/kg may only be reached in more than 000 years. In the case of V, solubility controls release, which is reflected by the horizontal line in the plot of concentration in percolate versus L/S and the slope of about (dotted line in the middle figure in figure 4) in the cumulative release versus L/S curve []. Residence times (shortened to RT in the graphs) have been calculated as respectively 2.7, 5.6 and 40.5 hours for the fast, normal and slow flow rates in the percolation test. The percolation rate is apparently not a very critical factor as the percolation rates differ significantly between the three experiments, whereas the differences between element concentrations are not as large [0]. ECN-RX

6 The may also be a factor, which should not be forgotten in this type of comparison. The ranges in the fast, normal and slow column are respectively , and Clearly, the tends to become lower as the percolation time increases. Whether this is caused by reactions in the material matrix itself or is caused by external influences (atmosphere) is at present not clear. The contact time has been varied in the dependence test. In figure 5 the data are given for V and Mo, that indicates under specific conditions (Mo at 4 and 6) reactions are continuing after 48 hours, which is now identified as the standard condition for testing. The bottom ash is still reactive at 4 and 6 as indicated by the acid addition needed to maintain the respective levels constant (figure 6). It is therefore not surprising to see that Mo is still reacting. For Mo and V, it is likely that slow sorption reactions (iron oxide phases) are responsible for the observed decrease with time because otherwise one would expect an increase in Mo leachability as a result of more acid consumption. The more critical values (4 and 6) in terms of reaching stable conditions are relevant from a leaching behaviour and modelling point of view. These conditions are less important for the evaluation of environmental impact as due to carbonation (calcite buffer formation) in MSWI bottom ash it is not likely that these values will be reached under field exposure conditions. Impact evaluation from leaching data In the framework of the network Harmonization of Leaching/Extraction Tests interrelations between different test methods have been addressed [,2]. Through the acid neutralization capacity (ANC) and base neutralization capacity (BNC) information generated in the dependence test, the external stresses on a material in a given environmental setting can be addressed. These include acidification resulting from for instance degradation of organic matter, sulphide oxidation, buffering capacity of natural waters, acid rain and atmospheric CO 2. In figure 7 a typical ANC curve is illustrated. As can be concluded from this graph, it takes about 0.3 mol/kg of acid equivalent to reach around 8. This can come from the uptake of CO 2 from the atmosphere as well as from degradation of organic matter generating CO 2. Based on this information and conditions specific to the application, which can be site specific, the relevant boundaries for the application can be identified. In the case of MSWI bottom ash, the lower boundary is set by the calcite buffering around 8. In figure 8 the domain relevant for application of granular MSWI bottom ash in road base or embankment is given. This can be set against hypothetical regulatory criteria at a specified L/S ratio as indicated with the dotted lines. For Cr no problems are expected to occur as the actual leaching level is well below the critical value. In case of Zn, the leachability may become critical, when the drops to below 7.5, which is however unlikely under natural conditions. This type of evaluation is helpful in deciding which elements need to be addressed in quality control and for which elements improvement or additional controls may be needed. It helps to define the relevant range of as a result of external stresses and internal changes (mineralization, organic matter degradation). To create durable material improvements in ash quality it is essential to base measures on understanding of the controlling mechanisms by using characterization data for evaluation of treatment. Therefore, it is important to relate changes to the input, changes to the conversion process and changes after treatment to the basic characterization as described before. Firstly to avoid solving one problem and creating a new one, and secondly, to ensure that a reduced leaching level is durable and not counteracted by exposure to the environment. Field studies Several field verification studies have been carried out [3]. Meima [4], in particular, has provided information on cores taken from a 20-year old MSWI bottom ash deposit. Results from field work (8 year old road base of MSWI bottom ash [3] and 20 year old landfill [4]) indicate that MSWI bottom ash is neutralized under unsaturated conditions. This observation 6 ECN-RX

7 leads to the question which testing conditions are most relevant for MSWI bottom ash: the high resulting from crushing fresh ash or the longer term stable condition of carbonated and neutralized material (which can be mimicked by = 8 control in testing). Upon weathering new phases may be formed [5]. Such effects are included in the field weathered samples that were tested. Thus ageing of MSWI bottom ash leads primarily to a significant change with its inherent changes in leachability. Field verification studies [3] have revealed that leachable Cu is fractionated between a labile dissolved organic matter (DOC; likely low molecular weight organic acids) and a more stable DOC complex (more humic matter like) in MSWI bottom ash, as roughly 40 % of the leachable Cu is retained in the soil directly underneath an application of MSWI bottom ash as a road base stabilization layer. The labile Cu complex is either degraded or destroyed though exchange with soil organic matter. About 60% has been transported to the groundwater as a water soluble organic complex. This type of Cu fractionation in MSWI bottom ash has also been identified in laboratory studies [6]. Johnson et al [7], Baranger et al [8] have also modelled MSWI bottom ash leaching, thus providing an increasingly better understanding of controlling factors under field conditions. Quality control Once sufficiently well defined data are obtained through characterization, reduction of the testing effort can be achieved by limiting the number of leaching steps that need to be measured and by limiting the effort to constituents that are really relevant for the material being evaluated. Figure 9 shows quality control data relative to characterization data providing clues for action. For example, reductions in Mo may be possible through control of the waste sources and Cu leaching may be controlled through reduction in residual organic matter content. In contrast, the behavior of Pb and Zn leaching from different facilities appears to be controlled only by the material s own. This type of approach provides a basis for QA/QC testing and eventually certification, when proven to be sufficiently stable. By presenting the QA/QC data in perspective to previous characterization the power of decision based on a single data point increases drastically. This aspect is grossly overlooked in current practice. In several cases, a crucial parameter as is not even measured, which makes such regulatory leaching data useless. New developments in this area provide a sound basis for quality control [9,20], in which no more testing is done than needed. However, as soon as results appear to be out of specification the level of testing needs to be increased. Treatment of MSWI residues MSWI bottom ash does not always comply with regulatory criteria for utilization. This implies that treatment prior to utilization may be required. A commonly applied method to stabilize material properties is a minimum sample storage period of several weeks up to a few months to age the material. However, this treatment may not be sufficient and additional treatment to remove critical components e.g. through washing of salts, Cu and Mo may prove necessary. The main issue in relation to MSWI fly ash and Air Pollution Control (APC) residues is the content of soluble salts []. Several options have been evaluated to treat these residues. Controlled containment of the stabilized salt containing residues is an option for treatment. Removal of the soluble salts makes the remaining inorganic residue much more manageable. However, it is unlikely to lead to a marketable product. Vitrification for fly ash has been tested and is practised on a small scale. The process is more costly than other solutions and also requires further treatment of salt concentrates (salts can not be vitrified). In many cases impact assessments carried out in accordance with the environmental assessment principle specified in the Methodology Guideline ENV 2920 [7] will show that MSWI residues cannot be utilised or even landfilled without prior treatment. Various treatment options exists, several of which are already part of the common MSWI management practice. Nearly all the available treatment methods are based on one or more of three treatment principles: physical or chemical ECN-RX

8 separation, stabilization/solidification and thermal treatment. These treatment principles and a number of the corresponding treatment processes or unit operations are listed in table, which also provides an evaluation of the potential applicability of the various methods. Before selecting a treatment process for a given residue and a given scenario, it is important to set target properties, which are in harmony with the short and long term conditions expected for the scenario. When evaluating a given treatment option it is also important to take all new waste streams created by the process into account. In most cases, a particular treatment process will consist of a combination of several of the unit operations shown in table. For instance, it will be very difficult to stabilize acid gas cleaning residues without prior or simultaneous removal of the high content of readily soluble salts, e.g. by aqueous extraction (and subsequent treatment and/or discharge of the extract). In addition to the treatment of residues from traditional mass burn incinerators, new incineration technologies have been developed in which e.g. thermal treatment of the residues are integrated (see for instance [2]). To judge the performance of treatment options, a compliance test (single extraction method) does generally not suffice. A characterization of the changes in leaching behaviour caused by the treatment can be visualized by using the dependence test, as it provides a direct measure for such changes in leachability. Waste input measures and mass balance An important question posed by government and municipal solid waste incinerator (MSWI) operators is how the quality of MSWI residues is influenced by the composition of the waste input to the incinerator. Also operating conditions, which are not discussed here, have been identified as important controlling factors [22,23]. A question linked to the input characteristics is to what extent specific (often smaller) waste streams are responsible for the final quality of the residues. This forms another option to improve the quality of the residues. Besides the chemical composition of the residues, a main aspect for the evaluation of MSWI residue quality is the leaching behaviour. This has been shown to be unrelated to the bulk chemical composition for most elements of interest. Several studies have been carried out to address this question [,23,24,25,9]. Characterization of the waste input to the incinerator into separate sub-streams for their chemical composition is an essential element in answering such a question. Back in 973 the National Public Health Institute (RIVM) conducted a separation of curb collected domestic waste in different sub-streams to be able to quantify both the magnitude of the different contributions to the total waste input as well as the chemical composition of the different streams [25]. An inherent limitation of the study was that the sorting of the waste was carried on integral collected waste. This resulted in a situation, where the composition of the wet organic fraction was significantly biased by other non-organic sub-streams in integral waste, such as vacuum cleaner dust and other fine particulate contributions not originally belonging to the organic fraction. The organic fraction analysed by sorting of integrally collected waste is therefor significantly different from the organic fraction for separately collected organic waste. By comparing the composition of the organic fraction as obtained from sorting integral waste with composition data derived from analysis of pure organic matter the level of contamination can be clearly identified. This is particularly relevant for the elements Cr, Pb, Cu, Cd. At present the leaching behaviour of MSWI residues, in particular, MSWI bottom ash, forms a limitation for the beneficial use of such residues in construction applications. Based on knowledge gained on how the quality of the residues is affected by specific materials or constituents in the input stream, the input to the incinerator could be managed in a manner in which such inputs are minimized or eliminated. Such contaminating waste streams may form a minor fraction of the total throughput, but greatly affect the overall quality. Before such measures will lead to measurable effects it is important to relate the leaching behaviour of MSWI residues to the waste input quality. Based on work carried out in the framework of the IAWG and other studies [,8,], the lack of correlation between composition 8 ECN-RX

9 and leaching has been unambiguously established. The elements Na, K, Mo, Br and Cl form an exception, as these do show a direct relation between input and leachability due to absence of matrix interaction, and thus are leached within L/S=2 l/kg. A control measure at the input for these elements will lead to a direct and proportional improvement of quality in terms of leaching. However, these elements are also readily removed by washing after the residue is produced. In figure 0 the positive correlation between total composition and leachability is illustrated for Mo. For elements (e.g. metals) controlled by solubility, measures at the input side are meaningless. There may be other reasons to separate metals from the waste stream, but not from an environmental impact evaluation. Only when leachability is controlled by availability, can measures at the input side of the installation be useful. To be able to quantify the contribution of different waste streams to the residue composition, a spreadsheet has been developed, which uses the composition of the separate sub-streams identified in the input to the incinerator, their moisture content, their loss on ignition and their fractional contribution to the total waste stream [25]. Based on these data, the ash composition of respectively bottom ash and fly ash is quantified by assigning the ash resulting from a specific sub-stream in the waste input entirely or partially to either bottom ash or fly ash. The rationale behind this concept is that during combustion materials with a very low ash content release elements almost completely to the gaseous phase which will be carried over to the fly ash. This also applies to elements considered to be non-volatile. Elements from sub-streams with a high ash content are largely or completely assigned to bottom ash. A few materials will be distributed between the two. The resulting predicted compositions can be verified against the average Dutch bottom ash and fly ash composition [9]. The advantage of such a model is that a decision can be taken on the acceptability of new or increased inputs of certain waste streams beforehand. In addition, it points at the gaps in the present information on sub-streams. In table 2 a first comparison of predicted bottom ash and fly ash composition with the average bottom ash and fly ash composition in the Netherlands is made. With this type of comparison a main drawback is the limited number of elements for which composition data are available. This applies in particular for major elements. The Cr content reported for MSWI fly ash is low, which may be related to the type of sample destruction (aqua regia). Data from the Mammoet project [26] point at higher average Cr contents in fly ash (Complete matrix dissolution with HF). In view of the raw nature of the data, the agreement between the prediction and the measured data is quite good for Cd, Mo, Cu, Sb and As. The Zn and Pb levels in bottom and fly ash are clearly underestimated, which may be attributed to an insufficiently described composition of electronic parts in the feed stock. The assessment is particularly interesting to assess the qualities of the fly ash and APC residues as a result of variations in low ash materials in the feedstock. Conclusions General To guide measures in acceptance of waste, in the conversion process and in treatment of residues a more thorough understanding of factors controlling the leachability of MSWI residues is needed. Waste titration to beat a single extraction test is not an acceptable approach, as it will generally lead to undesirable environmental impact. Instead, the emphasis should be on an assessment of the long term behaviour of the materials in their service life and ultimate fate ( end of life ). The tools and associated modelling to make such assessments have grown substantially in recent years and are now subject of standardization. Leaching behaviour of MSWI residues has been shown to be very systematic and has been modelled with a great deal of success in identifying solubility controlling phases. The understanding of controlling factors helps greatly in focusing the quality improvement activities and in defining the necessary quality control for certification purposes. ECN-RX

10 Field verification assists in keeping a balance between laboratory practice and realistic field conditions. Release modelling already has shown potential for prediction purposes. As the understanding grows such assessments may have consequences for the regulatory framework and level setting. In addition, the process of evaluation of environmental properties of materials for recycling and treatment for utilization is not unique to MSWI residues, but also applies to other industrial residue streams. Specific The dependence leaching test provides a very good means of mutual comparison of MSWI residues as well as a comparison of leaching behaviour within one and the same type of MSWI residue Ageing of MSWI bottom ash leads primarily to a significant change with its inherent changes in leachability. The more critical values (4 and 6) in terms of reaching stable conditions are relevant from a leaching behaviour and modelling point of view. These conditions are less important for the evaluation of environmental impact of MSWI bottom ash. Due to carbonation (calcite buffer formation) in MSWI bottom ash, it is not likely that these values will be reached under field exposure conditions. The percolation rate within the range now used does not appear to be very sensitive. The type of release mechanism (solubility, wash out, other) can be identified readily. Defining the relevant range of for a scenario based on an evaluation of material behaviour (mineralization, organic matter degradation) and external stresses is helpful in deciding which elements need to be addressed in quality control and for which elements improvement or additional controls may be needed. To create durable material improvements in ash quality it is essential to base treatment on understanding of the controlling mechanisms by using characterization data for evaluation of treatment. Therefore, it is important to relate changes to the input to the process, changes to the conversion process and changes after treatment to the basic characterization using at least time and dependent leaching data. Firstly to avoid solving one problem and creating a new one, and secondly, to ensure that a reduced leaching level is durable and not counteracted by exposure to external influences. By presenting quality control data in perspective to previous characterization data the power of decision based on a single data point increases drastically. This potential of this mode of data interpretation is grossly overlooked in current practice. For elements (e.g. metals) controlled by solubility, measures at the input side to reduce environmental impact are meaningless. Only when leachability of elements is correlated with total composition or availability, can measures at the input side of the installation be useful. Based on the assumption of complete transfer of inorganic elements from low ash content materials to the flue gas predictions of MSWI bottom ash composition and fly ash composition have been made. The agreement between the prediction and the measured composition data is quite good for Cu, Cd, Mo, Sb and As given the level of inherent variability in MSWI bottom ash composition. The Zn and Pb levels in bottom and fly ash are clearly underestimated. References. IAWG (International Ash Working Group; A.J.Chandler, T.T.Eighmy, J.Hartlen, O.Hjelmar, D.S.Kosson, S.E.Sawell, H.A.van der Sloot, J.Vehlow) Municipal Solid Waste Incinerator Residues. Studies in Environmental Science 67, Elsevier Science, Amsterdam, 974 pp. 2. Building Materials Decree. Staatsblad van het Koninkrijk der Nederlanden, 995, Ministere de l Environment. Circulaire Relative á la Valorisation de Mâchefers d Incineration de Residues Urbans en Techniques Routieres, DPPR/SEI/BPSEID/FC no 94- IV-, Paris, ECN-RX

11 4. Van der Hoek, E. and van der Sloot H.A., Korte testmethoden voor de beoordeling van de uitloging uit bouwmaterialen en afvalstoffen. KEMA 998. (in Dutch). 5. CEN TC 292 WG6. Characterization of waste. Leaching behaviour tests. Influence of under steady state conditions (in development, 998). 6. CEN TC 292 WG6. Characterization of waste. Leaching behaviour tests. Percolation simulation leaching test (in development, 998). 7. Methodology Document PrENV 2920, CEN TC 292 WG6, Van der Sloot, H.A., Developments in evaluating environmental impact from utilization of bulk inert wastes using laboratory leaching tests and field verification. Waste Management 6 (-3), 996, Hjelmar, O. Leachate from land disposal of coal fly ash. Waste Management & Research (990) 8, Dijkstra, J. J., van der Sloot, H.A. and Comans, R.N.J. Process identification and model development of contaminant transport in MSWI Bottom ash. Waste Management - special issue WASCON 2000 (in preparation).. Harmonization of leaching/extraction tests, 997. Studies in Environmental Science, Volume 70. Eds H.A. van der Sloot, L. Heasman, Ph Quevauviller, Elsevier Science, Amsterdam, 292 pp. 2. Technical work in support of the Network Harmonization of Leaching/Exctraction Tests. EU project SMT4-CT , Schreurs, J.P.G.M., van der Sloot, H.A. and Hendriks, Ch. F. Verification of laboratory-field leaching behaviour of coal fly ash and MSWI bottom ash as a roadbase material. Proceedings WASCON 997 Conference Putting Theory Into Practice, June 4-6, 997 Houthem, The Netherlands. 4. Meima, J. PhD Thesis: Leaching properties of MSWI bottom ash. RU Utrecht (997) Chptr Zevenbergen, C., Bradley, J.P., Wood T., Brown, R.S., van Reeuwijk, L.P., Schuiling, R.D.. Weathering as a process to control the release of toxic constituents from MSW bottom ash. In: Geology and Confinement of Toxic Waste, Proc. of the Int. Symp. Geoconfine '93, Montpellier, France, , Meima, J. A., van Zomeren, A. and Comans, R. N. J.. Complexation of Cu with Dissolved Organic Carbon in Municipal Solid Waste Incinerator Bottom Ash Leachates, ES&T, 999, 33, Johnson, C.A., Kersten, M., Ziegler, F. and Moor, H.C.. Leaching behaviour and solubility controlling phases of heavy metals in MSWI ash. Waste Management 6, 996, Baranger, Ph., Azaroual, M., Lanini, S., Piantone, P. and Freyssinet, Ph. Modelling the weathering of a bottom ash heap. Waste Stabilization & Environment Conference, Eds. J. Mehu, G. Keck and A. Navarro, Lyon, April , ECN-RX

12 9. Born, J.P.: Quantities and qualities of MSWI residues in the Netherlands. In: Environmental aspects of Construction with waste materials. Eds. J.J.J.M. Goumans, H.A. van der Sloot, Th.G. Aalbers, Elsevier Science Publishers, Amsterdam, 994, Kosson, D.S. and van der Sloot, H.A. Integration of Testing Protocols for Evaluation of Contaminant Release from Monolithic and Granular Wastes. In: Waste Materials In Construction - Putting Theory into Practice. Studies in Environmental Science 7. Eds. J.J.J.M. Goumans, G.J. Senden, H.A. van der Sloot. Elsevier Science Publishers, Amsterdam, 997, Vehlow, J. Thermische Behandlungsverfahren für Hausmüll im Vergleich. Beitrag zur Schulungsreihe: Restabfallgehandlung in der Steiermark. 3. April 998, Graz. Forschungszentrum Karlsruhe, Institut für Technische Chemie, Bereich Thermische Abfallbehandlung, Karlsruhe, Vehlow, J.. Mitverbrennen von Rest-Abfällen aus dem Siedlungs- und Sonderabfallbereich - eine Frage der Zulassung oder der Verfahrenstechnik. Seminar 02 im Rahmen der UTECH BERLIN 96. Fortbildungszentrum Gesundheits- und Umweltschutz Berlin e.v. (FGU Berlin), 26. Februar 996, pp Sawell, S.E., Chandler, A.J., Rigo, H.G., Hetherington, S.A. and Fraser, J.. The Waste Analysis, Sampling, Testing and Evaluation Program: Effect of Lead and Cadmium spiking of MSW on the characteristics of MSWI Residues. Proceedings Municipal Waste Combustion. VIP 32. Air & Waste Management Association Pittsburg, Pennsylvania, , Steketee, J. Onderzoek naar de relatie tussen samenstelling van afvalcomponenten en de uitloging van AVI residuen. Tauw Milieu. R D03/jjs Van de Beek, A.I.M., Cornelissen, A.A.J. and Aalbers, Th.G. Fysisch en Chemisch Onderzoek aan Huishoudelijk Agval.. Publ. RIVM, Rap , Versluijs, C.W., Anthonissen, I.H. and Valentijn, E.A. Mammoet 85: Integrale evaluatie van deelonderzoeken. RIVM report Bilthoven Hjelmar. O., Chap. 4.4 Incineration: Residues. In Christensen, T.H. (Ed.): Waste Technology, Teknisk Forlag, Copenhagen, 998, pp (in Danish). 28. CEN TC 292 Characterization of waste - Working Group 6 - Working documents ECN-RX

13 Table.Overview of principles and methods for treatment of MSWI residues (after [20]). Treatment principle Examples of processes and unit operations Bottom ash Fly ash Acid gas cleaning residues (with or without fly ash) Separation Washing and extraction, e.g. at various values Chemical precipitation Crystallization/evaporation Ion exchange Density and particle size based separation Distillation Elektrolysis Elektrokinetic separation Magnetic separation Eddy current separation a a a a a/b a/b b b a/b a/b b b b b c c Stabilization and/or solidification Addition of hydraulic binders Addition of pore-filling additives Chemical stabilization a a/b a a/c a a a/c b Thermal treatment Sintering Melting/vitrification a a/c a/c a/c c c a: Part of existing and proven treatment technology b: Have shown promising results, may be expected to be included in future treatment systems c: Currently under investigation or have been investigated and not found technically and/or economically feasible Table 2. Comparison of calculated composition for bottom ash (BA) and fly ash (FA) with average composition of Dutch MSWI bottom ash and fly ash (all data in mg/kg). Cd Cu Mo Pb Sb Zn As Cr Cr* Bottom Calculated BA 7, , , ash from input Average BA 4,0 2200, ,6 7 Netherlands Fly ash Calculated FA from input Average FA Netherlands * Cr based on adjusted values for the organic fraction. ECN-RX

14 000 Leached at L/S=0 (mg/kg) MSWI Fly ash MSWI Bottom ash Vitrified MSWI Fly ash RDF ash Own RDF ash C l: 50,000 mg/kg MSWI Fly ash C l: 8,000 mg/kg MSWI Bottom ash Cl:,500 mg/kg Vitrified MSWI Fly ash C l: 50 mg/kg Figure. Leaching behaviour of Cd from MSWI residues (bottom ash, fly ash[]) in comparison with Refuse derived Fuel (RDF) ash [] and vitrified MSWI fly ash []). All leaching test were carried out at L/S = 0 (mg/kg). Data illustrate role of increasing Cl - concentration on Cd leachability from MSWI and related residues. 4 ECN-RX

15 Concentration (mg/l) Semi-dry-FF Dry-FF Boiler ash ESP ash Bottom ash Fly Ash BA W G6 Fly Ash Cd DTL Concentration (mg/l) Cr Bottom ash Dry-FF Boiler ash Fly Ash Fly Ash Semi-dry-FF Grat e sift ings BA BA BA W G Figure 2. Characteristic leaching behaviour of Cd and Cr from MSWI residues, in particular MSWI, bottom ash and MSWI fly ash [,,28]. Leaching experiments carried out at L/S =0 l/kg. The smooth lines reflect the generic leaching behaviour of bottom ash (two data clusters) and fly ash. BA= bottom ash. ECN-RX

16 Conce ntration (mg/l) Mo Dry-FF Bottom ash ESP ash Grate siftings 0.00 BA W G Conce ntration (mg/l) Bottom ash Semi-dry-FF Grate siftings Dry-FF Boiler ash ESP ash Fly Ash Fly Ash BA BA W G6 Zn Figure 3. Characteristic leaching behaviour of Mo and Zn from MSWI residues, in particular MSWI, bottom ash and MSWI fly ash [,,28]. Leaching experiments carried out at L/S =0 l/kg. The smooth lines reflect the generic leaching behaviour of bottom ash (two data clusters) and fly ash. 6 ECN-RX

17 Leached (mg/kg) 0 0. Mo stat 48 h stat 68 h Colum n, RT 2.7 h 0 Leached cumulative (mg/kg) 0. Mo Leached (mg/l) 0 0. Mo Colum n, RT 5.6 h 0.0 Colum n, RT= 40.5 h L/S L/S Leached (mg/kg) V Leached cumulative (mg/kg) Leached (mg/l) V Colum n, RT=2.7 h V L/S Colum n, RT=5.6 h Colum n, RT=40.5 h 0. 0 L/S Figure 4. Leaching of V and Mo from MSWI bottom ash in a dependence test (left) and in a percolation test (middle: cumulative release and right: eluate concentrations). Dotted line in middle graph points at solubility control [28]. ECN-RX

18 Figure 5. Leaching of V and Mo as a function of contact time in the dependence test ( static mode, L/S=0 l/kg) [28]. Leached (mg/kg) V Leached (mg/kg) Mo Time (hours) Time (hours) Amount of acid/base added (ml) B 0 A 8 A 6 A 4 A Time (Hours) Figure 6. Acid consumption in dependence test on MSWI bottom ash illustrating continuation of dissolution reactions at 6 and 4. A and B denote acid or base addition [28]. 8 ECN-RX

19 3 2 MSWI BA ANC/BNC (mol/kg) Figure 7. Acid Neutralization Capacity of MSWI bottom ash obtained from acid/base consumption in the dependence test [28]. 0 MSWI Bottom ash 0000 MSWI Bottom ash BMD Cat I 000 Leached (mg/kg) 0. Relevant domain Leached (mg/kg) 00 0 BMD Cat I 0.0 Cr 0. Zn Figure 8. Leaching behaviour of Cr and Zn from MSWI bottom ash as a function of as a means of evaluating long-term environmental impact and the role of external stresses on release [2]. Dotted line represents a hypothetical limit value based on BMD Cat I limit values in the Dutch Building Materials Decree [2]. The box reflects the relevant domain for a given application. All data obtained for L/S=0 l/kg. ECN-RX

20 0000 Mo 0000 Cu DOC complexation BMD Cat II Leached ug/l 00 BMD Cat II Leached ug/l 00 BMD Cat I BMD Cat I 0 0 Control through waste input Inorganic Cu Pb Zn 000 BMD Cat II Leached ug/l 00 0 BMD Cat I Leached ug/l BMD Cat I BMD Cat II Not critical due to rate of carbonation Figure 9. Compliance leaching test data for MSWI bottom ash from different Dutch MSW incinerators [9] in relation to characterization data ( stat solid line) for MSWI bottom ash as QC for application in road constructions. Extraction conditions were LS=20, 24 hrs, leachant demineralized water. Each symbol fill pattern represents a different facility. BMD Cat I and BMD Cat II [2] are limit values from the Building Materials Decree converted from mg/kg to microgram per litre at L/S=0. 20 ECN-RX

21 Figure 0 Relation between total Mo in Bottom ash and leached Mo from bottom ash at L/S=0 l/kg ( range 0.5 2; n= 64 [9]). Mo Leached at L/S=0 (mg/kg) 00 0 Log (Mo leached) = - 0, ,8968 * log (Total Mo) R=0, Total Mo (mg/kg) ECN-RX

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