Leaching Dynamics Studies of Municipal Solid Waste Incinerator Ash

Abstract

An assessment of the short- and long-term hazards from municipal solid waste incinerator (MSWI) ash is made through the elemental analysis of 40 to 50 elements in the ash and leachates produced by several leaching procedures. The ash was analyzed using neutron activation analysis (NAA) and x-ray fluorescence (XRF). The leachates were analyzed using NAA and inductively-coupled plasma atomic emission spectroscopy (ICP). The leaching dynamics of an ash monofill were modelled with a series of extractions using simulated acid rain. An initial spike of the metals Ag, Ba, Be, Cr, Cu, Mo, Pb, Sr, and Zn in the leachates appears to be the greatest hazard posed by MSWI ash monofills. The elements As, Cd, Cu, Hg, Pb, S, and Zn were identified as potential long term hazards utilizing a sequential extraction procedure which approximates the total amount of the elements available over the lifetime of the monofill.

The pH of the resulting leachate is the single greatest factor governing the concentration of metals in solution, more important than the concentration of the element in the ash. These results are applied to an assessment of the suitability of the Toxicity Characteristic Leaching Procedure (TCLP) in measuring leaching potential of an MSWI ash monofill.     

Effects of the Basicity on the Comelting Conditions of Municipal Solid Waste Incinerator Fly Ash and Sewage Sludge Ash

Abstract

In this study, the effects of the basicity on the pouring point of the municipal solid waste incinerator fly ash-sewage sludge ash mixture is investigated. Four kinds of sewage sludge ash, which were collected from several primary and secondary sewage treatment plants and were produced by different processes and sludge conditioning alternatives, were used as modifiers. The results indicate that the pouring point of the mixture increased with increasing basicity, within the range of 0.65–1.90. The pouring point is affected by the contents of the mixtures (CaO, SiO₂, Al₂O₃, and the flux). It is suggested that an increase in the CaO content tends to raise the pouring point, whereas an increase in the SiO₂ and/or the Al₂O₃ contents cause as adverse reaction. The prediction equation, obtained by multilinear regression (significant level is 0.05), is as follows: pouring temperature =1189.6 + 4.19CaO-0.96 SiO₂-4.33 Al₂O₃ (R² = 0.91). In general, the pouring point decreased when the basicity was <1. The pouring point apparently increased when the basicity was>1.2. The regression squares for the different basicities were between 0.84 and 0.91. From these relationships, we note that a basicity index of 5 gave the best R² (0.91). From the results of this study, it can be concluded that the modification of the basicity of the fly ash by the addition of sewage sludge ash to lower the pouring point is feasible and leads to a more energy-efficient melting process. In addition, these synthetic slags have a good pozzolanic reactive activity.     

Generation of PCDD/F in Fly Ash from Municipal Solid Waste Incinerators

Abstract

Fly ash from municipal solid waste incinerators (MSWIs) has been characterized in terms of polychlorinated dibenzyl-p-dioxin and polychlorinated dibenzofuran (PCDD/F) content. Increasing values of PCDD/Fs have been found to correlate with decreasing temperatures of sampling points in flue gas treatment lines of the plants, confirming other researchers’ findings about temperature as the major controlling parameter for the PCDD/F formation. Measured PCDD/F ratios show that de novo synthesis is the dominant formation mechanism. The increasing trends of particulate-bound PCDD/Fs can be explained not only through the dominant de novo synthesis process but also considering the adsorption of gaseous PCDD/Fs on fly ash deposits, even outside the typical de novo synthesis temperature ranges. The effective role of a post-combustor unit, imposed by Italian law to destroy PCDD/Fs, also needs to be carefully reconsidered.     

Dehalogenation Potential of Municipal Waste Incineration Fly Ash

BACKGROUND, AIMS AND SCOPE: In the first part of this paper the main principles which control the dehalogenation of polychlorinated aromatic compounds on municipal waste incineration fly ash (MWI-FA) have been discussed and the model fly ash of similar dehalogenation activity has been proposed. Even if both systems show comparable dehalogenation properties, the main question concerning the postulated identical reaction mechanism in both cases is left unanswered. The other very important point is to what extent is this dechlorination mechanism thermodynamically controlled. The same problem is often discussed in the literature also for the de novo synthetic reactions. From the data it is clear that metallic copper plays a decisive role in the mechanism of the dehalogenation reaction. Although the results reported in the first part strongly support the idea that copper acts in this dechlorination as the reaction component, in contrast to its generally accepted catalytic behaviour, we believed that additional support for this conclusion can be obtained with the help of a thermodynamic interpretation of the mechanism of the reaction. RESULTS AND DISCUSSION: The pathways of hexachlorobenzene dechlorination on MWI-FA and model fly ash were studied in a closed system at 260-300 degrees C under nitrogen atmosphere. These pathways were the same for both systems, with the following prevailing sequences: hexachlorobenzene --> pentachlorobenzene --> 1,2,3,5-tetrachlorobenzene --> 1,3,5-trichlorobenzene --> 1,3-dichlorobenzene. Thermodynamic calculations were carried out by using the method of minimization total Gibbs energy of the whole system. In the calculations, the following reaction components were taken into account: all gaseous chlorinated benzenes, benzene, hydrogen chloride, a gaseous trimer Cu3Cl3, and also Cu2O and CuCl2 as solid components. The effect of the reaction temperature and the amount of copper and water vapour were considered as well. The effect of reaction temperature was determined from the data calculated for the 500 to 750 K temperature region. The effect of the initial composition was determined for the molar amounts of copper = 0.01-3 moles and water vapour = 0.2 to 3 moles per mole of chlorobenzene isomer CONCLUSIONS: The results of hexachlorobenzene dechlorination by MWI-FA and model fly ash under comparable reaction conditions allow us to conclude that both dechlorinations proceed via the same dechlorination pathways, which can be taken as an evidence of the identical dehalogenation mechanism for both systems. The relative percentual distribution of the dehalogenated products depends on the temperature, but not on the initial amount of water vapour or copper metal. On the other hand, the initial amount of copper substantially affects the conversion of the dehalogenation as well as the molar ratio of Cu3Cl3 to HCl in the equilibrium mixture. Comparison of the experimental with thermodynamic results supports the idea that dehalogenation reactions are thermodynamically controlled. RECOMMENDATIONS AND OUTLOOK: Thermodynamic analysis of the dehalogenation reactions may prove useful for a wide range of pollutants. The calculations concerning polychlorinated biphenyls and phenols are under study.     

Control of Mercury Emissions from a Municipal Solid Waste Incinerator in Japan

Abstract

The control of Hg emissions from a municipal solid waste incinerator (MSWI) is very important, because more than 78% of municipal solid waste (MSW) is incinerated. The Hg content of coal used in utility boilers is relatively low in Japan. In this study, recent trends in the Hg content of MSW in Japan and activated carbon (AC) injection as a control technology of Hg emission from an MSWI are discussed. The effect of AC injection on Hg removal from flue gas in an MSWI was investigated by pilot-scale experiments using a bag filter (BF). The injection of AC increases the Hg reduction ratio by 20–30% compared with cases without AC injection. The Hg reduction ratio increases as the flue gas temperature decreases. The Hg reduction ratio is closely related to the inlet Hg concentration and was expressed with a Langmuir-type adsorption isotherm.     

Greenhouse Gas Dynamics of Municipal Solid Waste Alternatives

ABSTRACT

Previous greenhouse gas studies comparing landfilling with combustion of municipal solid waste (MSW) are limited to examinations of the emissions weighted by their relative radiative activity. This paper adds another dimension by analyzing the atmospheric response to these emissions. The heart of the analysis is a time-dependent model using a perturbation analysis of the IS92a results of the Intergovernmental Panel on Climate Change (IPCC). Using as inputs the emissions from the two technologies, the model calculates atmospheric concentration histories. Scenarios for a landfill and a combustor envision each accepting 1000 Mg refuse/day for a 30-year operating period followed by a 70-year postclosure period. The baseline scenario examines the basic greenhouse impact of each technology. The other scenario adds active gas collection at the landfill and energy offset credits for avoided power plant carbon emissions. For both scenarios, CH₄ and trace gases from the landfill persist in the atmosphere, and they are relatively potent at forcing IR heating. The combination of these features place the landfill much higher than previously expected on the greenhouse impact scale. For the baseline scenario, the time-integrated radiative forcing from landfilling is 115 times that of combustion, and this ratio is 45 for the second scenario.     

Computer Simulation of a Municipal Solid Waste Combustor

A mathematical model has been developed to study the thermal and chemical processes occurring In a municipal solid waste mass combustor. Treating the solids feed as a mixture of pseudo-components, the model determines the Interrelationships between the solids feed rate, grate travel rate and length, amounts and distributions of primary and secondary air, extent of solids burn out, and the bed and flame temperatures. The model Incorporates the kinetics of pyrolysis of solids and simulates heat and mass transfer within the bed.

The temperature and mass flow profiles generated show that much of the grate Is taken up by the heatup and burnout zones. The heatup zone can be reduced by distributing the primary air to maintain minimal air flow In that region, thereby permitting rapid heatup. Increasing the solids feed rate and adjusting the air flow distributions can reduce the length of the burnout zone. The computer program, available on both PCs and mainframe, can be used for different MSW Incinerator dimensions and feed parameters to Investigate the effects of the control variables and optimize the desired output characteristics, e.g., maximize solids throughput.     

A Life-Cycle Inventory Model of Municipal Solid Waste Combustion

ABSTRACT

Evaluation of alternate strategies for municipal solid waste (MSW) management requires models to calculate environmental emissions as a function of both waste quantity and composition. A methodology to calculate waste component-specific emissions associated with MSW combustion is presented here. The methodology considers emissions at a combustion facility as well as those avoided at an electrical energy facility because of energy recovered from waste combustion. Emission factors, in units of kg pollutant per metric ton MSW entering the combustion facility, are calculated for CO₂-biomass, CO₂-fossil, SO_x , HCl, NO_x , dioxins/furans, PM, CO, and 11 metals. Water emissions associated with electrical energy offsets are also considered. Reductions in environmental emissions for a 500-metric-ton-per-day combustion facility that recovers energy are calculated.     

Comparison of Aerobic and Anaerobic Biotreatment of Municipal Solid Waste

Abstract

To increase the operating lifetime of landfills and to lower leachate treatment costs, an increasing number of municipal solid waste (MSW) landfills are being managed as either aerobic or anaerobic bioreactors. Landfill gas composition, respiration rates, and subsidence were measured for 400 days in 200-L tanks filled with fresh waste materials to compare the relative effectiveness of the two treatments. Tanks were prepared to provide the following conditions: (1) air injection and leachate recirculation (aerobic), (2) leachate recirculation (anaerobic), and (3) no treatment (anaerobic). Respiration tests on the aerobic wet tank showed a steady decrease in oxygen consumption rates from 1.3 mol/day at 20 days to 0.1 mol/day at 400 days. Aerobic wet tanks produced, on average, 6 mol of carbon dioxide (CO₂)/kg of MSW as compared with anaerobic wet tanks, which produced 2.2 mol methane/kg of MSW and 2.0 mol CO₂/kg methane. Over the test period, the aerobic tanks settled on average 35%, anaerobic tanks settled 21.7%, and the no-treatment tank settled 7.5%, equivalent to overall mass loss in the corresponding reactors. Aerobic tanks reduced stabilization time and produced negligible odor compared with anaerobic tanks, possibly because of the 2 orders of magnitude lower leachate ammonia levels in the aerobic tank. Both treatment regimes provide the opportunity for disposal and remediation of liquid waste.     

生活垃圾焚烧烟气排放中二噁英对人体健康的风险评价

随着垃圾焚烧的广泛应用,由此产生的二次污染问题也日益显现出来,特别是二嗯英污染已引起世界的关注。这也是垃圾焚烧设施在环评阶段遭到周围公众反对的原因之一。文中介绍了二嗯英的危害、垃圾焚烧烟气中的二嗯英来源以及二嗯英的相关标准。以某垃圾焚烧发电厂为例,对垃圾焚烧烟气中的二嗯英类物质对人体健康的风险进行了评价,并提出了如何最大限度地减少垃圾焚烧处理过程中的二唔英排放量。     

城市生活垃圾管理生命周期分析研究

概述了生命周期评价方法、内容及框架,并将其引入城市生活垃圾管理系统中,对城市生活垃圾管理进行了生命周期可行性分析,提出了开展城市生活垃圾生命周期管理的具体实施措施。     

Stabilization/Solidification of Salt from a Waste Incinerator

ABSTRACT

A laboratory procedure was developed and verified for stabilizing salt produced by an industrial waste incinerator. This procedure is based on salt stabilization by means of an asphalt binder. Conductivity values and relevant anion contents in leachates of stabilized waste with an asphalt coating were near zero. The pH value of these leachates equaled the pH value of the water used, so that the stabilized waste salt represented inert material, posing no environmental hazard. An unusually significant reduction in the volume of processed salt occurred during stabilization. After compacting under 10.4 MPa pressure, the volume of test specimens was almost 55% smaller than the initial salt volume. In practice, this would mean more than a doubling of landfill waste capacity. Volume reduction was successfully explained by means of a mathematical model.     

Characterization of the effluents from a Municipal Solid Waste incinerator plant and of their environmental impact

An easy approach for the evaluation of the environmental impact of a Municipal Solid Waste (MSW) incinerator plant is described. In order to perform this study, selected chemical pollutants were monitored both in the plant emissions and in the waste to be burnt. The composition of waste was also determined. A mathematical model was worked out for the estimation of the ground deposition fluxes. A first validation of the model for the case studied was drawn by comparing the simulation values with data obtained on real soil samples.     

Partitioning Gas Tracer Tests for Measurement of Water in Municipal Solid Waste

Abstract

A key component in the operation of almost all bioreactor landfills is the addition of water to maintain optimal moisture conditions. To determine how much water is needed and where to add it, in situ methods are required to measure water within solid waste. Existing technologies often result in measurements of unknown accuracy, because of the variability of solid waste materials and time-dependent changes in packing density, both of which influence most measurement methods. To overcome these problems, a new technology recently developed by hydrologists for measuring water in the vadose zone—the partitioning gas tracer test—was tested. In this technology, the transport behavior of two gas tracers within solid waste is used to measure the fraction of the void space filled with water. One tracer is conservative and does not react with solids or liquids, while a second tracer partitions into the water and is separated from the conservative tracer during transport. This technology was tested in four different solid waste packings and was capable of determining the volumetric water content to within 48% of actual values, with most measurement errors less than 15%. This technology and the factors that affect its applicability to landfills are discussed in this paper.     

Filtration Properties of Fly Ash from Fluidized Bed Combustion

Some of the features of the fluidized-bed combustion (FBC) process have a direct bearing on the particulate properties that most strongly influence filtering pressure drop. A laboratory program was conducted to experimentally determine the relative pressure drop characteristics of ashes from the TVA-EPRI 20-MW bubbling bed, atmospheric pressure FBC (AFBC) pilot plant and six pulverized-coal combustion (PC) units. The combined influences of measured particle and dust cake properties on filtering pressure drop were estimated with existing filtration theories. These theories predict a higher pressure drop for a dust cake produced with the AFBC ash than for one consisting of any of the PC ashes. Laboratory measurements were made of the flow resistance of idealized, simulated dust cakes to confirm these predictions. Field operating data from the fabric filters collecting some of the tested ashes were available to validate the laboratory results. The laboratory and field data show relatively good agreement. The AFBC ash must be treated as a special case for fabric filters, and careful selection of cleaning method and fabric must be made to minimize the inherently high pressure drop characteristics of this ash.     

Control of Fly Ash from Conventional Coal-Fired Utility Boilers

This paper presents a detailed review and critical evaluation of current technologies as applied to fine particulate emissions from coal-fired utility boilers. Quantitative assessments of the capabilities of both conventional and novel air pollution control devices to meet three different performance standards—the present New Source Performance Standard (NSPS) of 0.03 Ib particulate/MBtu heat input, and standards of 0.05 and 0.1 Ib particulate/MBtu are included. Each of the three conventional devices (electrostatic precipitator, fabric filter baghouse, and wet scrubber) is compared and rated with respect to eight different performance categories. This information can be used to determine the relative effectiveness and attractiveness of these three control devices. Novel devices are compared and rated in the same manner, the conclusions from which may provide the research administrator with a guide for the selection of those novel devices which offer the best potential for commercialization.

The major conclusions of the investigation are: (1) The use of conventional scrubbers for fine particulate control on coal-fired utility boilers may no longer be feasible at the new NSPS of 0.03 Ib/MBtu. (2) At the old NSPS (0.1 Ib/MBtu) conventional electrostatic precipitators and baghouses were often competitive. For the new stricter standard, however, the baghouse generally is the more attractive alternative. (3) Novel devices appear to offer almost no hope for this particular application (at a commercial level) between now and 1985 and only little hope before 1990.     

Airborne Emissions of Mercury from Municipal Solid Waste. I: New Measurements from Six Operating Landfills in Florida

Abstract

Mercury-bearing material enters municipal landfills from a wide array of sources, including fluorescent lights, batteries, electrical switches, thermometers, and general waste; however, the fate of mercury (Hg) in landfills has not been widely studied. Using automated flux chambers and downwind atmospheric sampling, we quantified the primary pathways of Hg vapor releases to the atmosphere at six municipal landfill operations in Florida. These pathways included landfill gas (LFG) releases from active vent systems, passive emissions from landfill surface covers, and emissions from daily activities at each working face (WF). We spiked the WF at two sites with known Hg sources; these were readily detected downwind, and were used to test our emission modeling approaches. Gaseous elemental mercury (Hg⁰) was released to the atmosphere at readily detectable rates from all sources measured; rates ranged from ～1–10 ng m^?2 hr^?1 over aged landfill cover, from ～8–20 mg/hr from LFG flares (LFG included Hg⁰ at μg/m³ concentrations), and from ～200–400 mg/hr at the WF. These fluxes exceed our earlier published estimates. Attempts to identify specific Hg sources in excavated and sorted waste indicated few readily identifiable sources; because of effective mixing and diffusion of Hg⁰, the entire waste mass acts as a source. We estimate that atmospheric Hg releases from municipal landfill operations in the state of Florida are on the order of 10–50 kg/yr, substantially larger than our original estimates, but still a small fraction of current overall anthropogenic losses.     

Airborne Emissions of Mercury from Municipal Solid Waste. II: Potential Losses of Airborne Mercury before Landfill

Abstract

Waste distribution and compaction at the working face of municipal waste landfills releases mercury vapor (Hg⁰) to the atmosphere, as does the flaring of landfill gas. Waste storage and processing before its addition to the landfill also has the potential to release Hg⁰ to the air if it is initially present or formed by chemical reduction of Hg^II to Hg⁰ within collected waste. We measured the release of Hg vapor to the atmosphere during dumpster and transfer station activities and waste storage before landfilling at a municipal landfill operation in central Florida. We also quantified the potential contribution of specific Hg-bearing wastes, including mercury (Hg) thermometers and fluorescent bulbs, and searched for primary Hg sources in sorted wastes at three different landfills. Surprisingly large fluxes were estimated for Hg losses at transfer facilities (～100 mg/hr) and from dumpsters in the field (～30 mg/hr for 1,000 dumpsters), suggesting that Hg emissions occurring before landfilling may constitute a significant fraction of the total emission from the disposal/landfill cycle and a need for more measurements on these sources. Reducing conditions of landfill burial were obviously not needed to generate strong Hg⁰ signals, indicating that much of the Hg was already present in a metallic (Hg⁰) form. Attempts to identify specific Hg sources in excavated and sorted waste indicated few readily identifiable sources; because of effective mixing and diffusion of Hg⁰, the entire waste mass acts as a source. Broken fluorescent bulbs and thermometers in dumpsters emitted Hg⁰ at 10 to >100 μg/hr and continued to act as near constant sources for several days.