Influence of flue gas SO2 on the toxicity of heavy metals in municipal solid waste incinerator fly ash after accelerated carbonation stabilization

The influence of CO₂ content and SO₂ presence on the leaching toxicity of heavy metals in municipal solid waste incinerator (MSWI) fly ash was studied by examining the carbonation reaction of MSWI fly ash with different combinations of simulated incineration flue gases. Compared with raw ash, the leaching solution pH of carbonated ash decreased by almost 1 unit and the leaching concentrations of heavy metals were generally lower, with that of Pb decreasing from 19.45 mg/L (raw ash) to 4.08 mg/L (1# carbonated ash). The presence of SO₂ in the incineration flue gas increased the leaching concentrations of heavy metals from the fly ash to different extents after the carbonation stabilization reaction. The pH of the leaching solution was the main factor influencing the leaching concentrations of heavy metals. The increase in buffer capacity with the pH of carbonated ash caused an increase in heavy metal stability after the carbonation reaction. Accelerated carbonation stabilization of MSWI fly ash could reduce its long-term leaching concentrations (toxicity) of Cu, Pb, Se, and Zn. The leaching concentrations of heavy metals from carbonated ash also likely had better long-term stability than those from raw ash. The presence of SO₂ in the incineration flue gas increased the proportion of exchangeable state species of heavy metals; slightly increased the long-term leaching toxicity of Cu, Pb, Se, and Zn; and reduced the long-term stability of these metals in the fly ash after the carbonation reaction.     

Extraction of metals from municipal solid waste incinerator fly ash by hydrothermal process

This work examined the extraction properties of metallic elements from municipal incinerator fly ash under hydrothermal conditions. The ash was firstly pre-washed by distilled water, then subjected to hydrothermal treatments. The pre-washing process was effective for Na, K, Ca extraction with extraction percentages of 67%, 76% and 48%, respectively. The optimum contact time was 30 min for the pre-washing process. Five types of acids were tested for the extraction experiments and hydrochloric acid was found to be most effective for metal extraction from the ash. Compared to room condition, hydrothermal treatment accelerated the dissolution of the ash, thus promoted the reaction of acid with hazardous metals such as Cr, Cd, Pb, and furthermore, the consumption speed of acid was slowed down under hydrothermal condition. The acid simultaneously reacted with all the metal in the ash under hydrothermal condition but preferentially reacted with Ca at room condition. The optimum hydrothermal treatment temperature, time and liquid/solid ratio were 150 degrees C, 5h and 10:1 (ml:g), respectively.     

Utilization of municipal solid waste incineration (MSWI) fly ash in blended cement Part 1: Processing and characterization of MSWI fly ash

This paper is the first of a series of two articles dealing with the processes applied to MSWI fly ash with a view to reusing it safely in cement-based materials. Part 1 presents two stabilization processes and Part 2 deals with the use of the two treated fly ashes (TFA) in mortars. Two types of binder were used: an Ordinary Portland Cement (OPC) containing more than 95% clinker (CEM I 52.5R) and a binary blend cement composed of 70% ground granulated blast furnace slag and 30% clinker (CEM III-B 42.5N). In this first part, two stabilization processes are presented: the conventional process, called "A", based on the washing, phosphation and calcination of the ash, and a modified process, called "B", intended to eliminate metallic aluminum and sulfate contained in the ash. The physical, chemical and mineralogical characteristics of the two TFA were comparable. The main differences observed were those expected, i.e. TFA-B was free of metallic aluminum and sulfate. The mineralogical characterization of the two TFAs highlighted the presence of large amounts of a calcium aluminosilicate phase taking two forms, a crystalline form (gehlenite) and an amorphous form. Hydration studies on pastes containing mixed TFA and calcium hydroxide showed that this phase reacted with calcium hydroxide to form calcium aluminate hydrates. This formation of hydrates was accompanied by a hardening of the pastes. These results are very encouraging for the reuse of such TFA in cement-based materials because they can be considered as pozzolanic additions and could advantageously replace a part of the cement in cement-based materials. Finally, leaching tests were carried out to evaluate the environmental impact of the two TFAs. The elements which were less efficiently stabilized by process A were zinc, cadmium and antimony but, when the results of the leaching tests were compared with the thresholds of the European landfill directive, TFA-A could nevertheless be accepted at landfills for non-hazardous waste. The modifications of the process led to a significant reduction in the stabilization of chromium, selenium and antimony.     

Polychlorinated biphenyls removal from weathered municipal solid waste incineration fly ash by collector-assisted column flotation

Polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) are highly toxic micropollutants emitted from municipal solid waste incineration (MSWI), in particular, concentrated in the unburned carbon (UC) of MSWI fly ash. Because of concerns over their adverse health effects, a number of countries have classified MSWI fly ash as hazardous material and required further treatment before its final disposal in landfills. The technologies for removing the toxic chlorinated micropollutants in the MSWI fly ash have been studied, however, until now no mature technique has been obtained in this purpose. In this research, we used a technique of collector-assisted column flotation to remove PCBs-enriched UC from MSWI fly ash. We found that 36.9% PCBs could be removed from fresh MSWI fly ash with 61.7% UC removal efficiency, whereas only 21.7% PCBs could be removed from weathered MSWI fly ash with a low UC removal efficiency of 33.7%. By adding a mixture of two kinds of surfactants: sorbitan mono-oleate and polyoxyethylene (20) sorbitan mono-oleate to the weathered fly ash slurry as the collector assistant, 39.3% PCBs was removed at the hydrophile–lipophile balance (HLB) value of 13.5, while the UC removal efficiency increased to 49.0%. The results showed that the collector assistant could enhance PCBs and UC removal efficiencies during the column flotation process, and the mechanism has been discussed in detail. Higher PCBs and UC removal efficiencies could be expected by further optimizing the conditions of collector-assisted column flotation.     

Stabilization/solidification of a municipal solid waste incineration residue using fly ash-based geopolymers

The stabilization/solidification (S/S) of a municipal solid waste incineration (MSWI) fly ash containing hazardous metals such as Pb, Cd, Cr, Zn or Ba by means of geopolymerization technology is described in this paper. Different reagents such as sodium hydroxide, potassium hydroxide, sodium silicate, potassium silicate, kaolin, metakaolin and ground blast furnace slag have been used. Mixtures of MSWI waste with these kinds of geopolymeric materials and class F coal fly ash used as silica and alumina source have been processed to study the potential of geopolymers as waste immobilizing agents. To this end, the effects of curing conditions and composition have been tested. S/S solids are submitted to compressive strength and leaching tests to assess the results obtained and to evaluate the efficiency of the treatment. Compressive strength values in the range 1-9 MPa were easily obtained at 7 and 28 days. Concentrations of the metals leached from S/S products were strongly pH dependent, showing that the leachate pH was the most important variable for the immobilization of metals. Comparison of fly ash-based geopolymer systems with classical Portland cement stabilization methods has also been accomplished.     

Vitrification of fly ash from municipal solid waste incinerator

Fly ash from municipal solid wastes (MSW) incinerators in Korea contains a large amount of toxic materials and requires pertinent treatments. However, since fly ash in Korea has a high chlorine concentration, it is difficult to apply cementation and chemical treatment techniques. In this study, we report the vitrification of fly ash along with the properties of the glasses and leaching characteristics of heavy metal ions.Fly ash can be vitrified by melting at 1500 degrees C for 30 min with the addition of >5 wt.% of SiO2. Glasses showed Vickers hardness of 4000-5000 MPa, bending strength of 60-90 MPa and indentation fracture toughness of approximately 0.9 MPa m(1/2). Glasses also showed the excellent resistance against leaching of heavy metal ions with Cd2+ <0.04 ppm, Cr3+ <0.02 ppm, Cu2+ <0.04 ppm and Pb2+ <0.2 ppm. These results indicate that the vitrification technique is effective for the stabilization and recycling of toxic incinerator fly ash.     

Bioremediation of PCDD/Fs-contaminated municipal solid waste incinerator fly ash by a potent microbial biocatalyst

Removal of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from fly ash poses a serious problem. In the study presented here, we used a microbial biocatalyst which is a mixture of 4 bacterial and 5 fungal dioxin-degrading strains. The ability of this biocatalyst to bioremediate PCDD/Fs from contaminated municipal solid waste incinerator (MSWI) fly ash was examined by solid-state fermentation under laboratory conditions. Treatment of MSWI fly ash with the microbial biocatalyst for 21 days resulted in a 68.7% reduction in total toxic PCDD/Fs. Further analyses revealed that the microbial biocatalyst also removed 66.8% of the 2,3,7,8-substituted congeners from the fly ash. During the treatment period, the presence of the individual strains composing the microbial biocatalyst was monitored by the amplification of strain-specific DNA sequences followed by denaturing gradient gel electrophoresis (DGGE). This analysis showed that all of the bacterial and fungal strains composing this dioxin-degrading microbial mixture maintained under the dioxin treatment conditions. These results demonstrate that this microbial biocatalyst could potentially be used in the bioremediation of PCDD/Fs from contaminated fly ash.     

Thermal treatment of the fly ash from municipal solid waste incinerator with rotary kiln

Reuse of the fly ash from the municipal solid waste incinerator (MSWI) is a policy of Taiwan EPA. However, the fly ash is often classified as a hazardous waste and cannot be reused directly because the concentrations of heavy metals exceed the TCLP regulations. The main objective of this study is to investigate the continuous sintering behavior of fly ash with a rotary kiln and seek a solution to reduce the concentrations of heavy metal to an acceptable value. The partitions of the heavy metals in the process are also considered. The results of TCLP showed that among the metals of Cr, Cd, Cu and Pb, only the concentrations of Pb in raw fly ash exceeded the regulation. At sintering temperatures of 700, 800 and 900 degrees C, the concentration of Pb decreased in sintering products, however, the concentration of Pb still exceeded the limitation at 700 and 800 degrees C. Additionally, the water-washing was used to pre-treat the fly ash before sintering process. The washing treatment effectively reduced the leaching concentrations of Pb to agree the regulations. Therefore, water-washing followed by a sintering treatment is an available process for detoxifying the fly ash of MSWI.     

关于水热技术处理垃圾焚烧飞灰的研究探讨

生活垃圾焚烧飞灰含有重金属和有毒有机物,对环境危害十分严重。水热法被认为是一种有效的无害化处理技术,能将飞灰改性,降低飞灰毒性,还可以合成沸石类物质,提高产物的应用价值。本文基于垃圾焚烧飞灰理化特性,对现有的水热处理技术进行了较为全面的总结。根据水热法的机理,系统地介绍了传统水热法、微波水热法、熔融预处理的微波水热法和超声波水热法,并通过对比分析指出各方法在处理效率、处理效果等方面存在的问题。此外,还简要介绍了水热处理后飞灰的主要应用领域。最后结合近几年水热技术的研究现状,提出了新型水热技术在工业化应用上存在的大型化的局限性以及未来发展方向。     

Approaches adopted to assess environmental impacts of PCDD/F emissions from a municipal solid waste incinerator

Different approaches were carried out in this work to assess environmental impacts of a municipal solid waste incinerator. A total of seven sites in the vicinity of the facility were chosen to collect air, banyan leaf and soil samples for analyses of PCDD/Fs by high-resolution gas chromatography/high-resolution mass spectrometry. Based on the PCDD/F concentrations of the three matrices determined at sites upwind, downwind and area of maximum ground concentration, it was found that the environmental impact of the MSWI was not obvious. PCDD/F concentration isopleths of the three environmental compartments coupled with wind rose of the region proved that the influence of the MSWI on the environment was also rather limited. It clarified emission sources by confirming that the PCDD/F concentrations originated mostly from the existing stationary emission sources in the vicinity. Through principal component and cluster analyses on congener profiles, the influence of metallurgical facilities and medical waste incinerators on the ambient air was assessed. Moreover, the modeling of ISCST3 demonstrated also that the contribution of the MSWI to ambient atmospheric PCDD/Fs was minimal. The approaches studied have led to identical conclusions, and thus are useful to cross-evaluate the environmental impact of an MSWI.     

Comparisons of levels of polychlorinated dibenzo-p-dioxins/dibenzofurans in the surrounding environment and workplace of two municipal solid waste incinerators

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the surrounding environment (outdoor) and workplace air of two municipal solid waste incinerators (MSWIs, T and M) were characterized and compared. T and M represented two typical municipal solid waste incinerators in the north of Taiwan, which have different processes for controlling the PCDD/F emissions. The results of this study are summarized as follows. (1) The total PCDD/F and the total PCDD/F WHO-TEQ concentrations in the workplace air were 5-13 and 5-15 times higher than those in the outdoor air, respectively. Obviously, it is worthwhile to explore more on health risk assessment for exposure of PCDD/Fs emitted from MSWIs, particularly in the workplace air. (2) Mean total PCDD/F I-TEQ concentrations in the outdoor air ranged between 0.0216 and 0.155 pg I-TEQ/Nm(3) and averaged 0.0783 pg I-TEQ/Nm(3) (0.0828 pg WHO-TEQ/Nm(3)) during two seasons for two MSWIs, which were 6.5-fold higher than that of a remote site (0.0119 pg I-TEQ/Nm(3) or 0.0132 pg WHO-TEQ/Nm(3)) in Taiwan. However, the above outdoor air concentration levels in the MSWIs were still much lower than the air quality limitation of PCDD/Fs (0.6 pg I-TEQ/Nm(3)) in Japan []. (3) PCDFs were the primary toxicity distributors for PCDD/Fs in the outdoor air, since the ratios of PCDDs/PCDFs (I-TEQ) at all sampling sites ranged from 0.180 to 0.492 and were less than unity. (4) The OCDD, OCDF, 1,2,3,4,6,7,8-HpCDD and 1,2,3,4,6,7,8-HpCDF were the four dominant species in both workplace and outdoor air near MSWIs. (5) By spraying water on and wetting both the fly and bottom ashes, the mean total PCDD/F I-TEQ concentration in the workplace air was reduced 86.9% in the T MSWI. The above results indicate an appropriate improving action did inhibit the fugitive emission of PCDD/Fs and reduce the health risk of workers during work handling ashes in MSWIs.     

Dose-mortality assessment on municipal solid waste incinerator (MSWI) ash

This study provides a novel attempt to put forward, in general toxicological terms, quantitative series of toxicity of various ashes of municipal solid waste incinerator (MSWI) for reusability in various applications. Previous study disclosed that growth inhibition of Escherichia coli DH5alpha occurred at concentrations above 0.156, 0.625 and 0.0195 gL(-1) for bottom ash (BA), cyclone ash (CA), scrubber ash (SA), respectively, suggesting the toxicity series of SA>BA>CA. However, the severity of such a toxicity series was not clearly revealed, thus whether ashes were still feasible for reuse in further applications was still remained uncertain. Compared to NaNO3, CrCl2 and CdCl2, the existing toxicities of ashes were apparently significant even these ashes were all satisfied by the TCLP guidelines for EPA regulations. Dose-response analysis based upon loss of cell viability (e.g., EC50) stated a toxicity series of SA>CrCl2>BA>CdCl2>CA>NaNO3. The ranking of Hill slope B in BA>SA>CA>NaNO3>CrCl2>CdCl2 clearly suggested the smallest tolerance (e.g., ranges from EC20 to EC50) for ashes very likely due to synergistic toxicity of multiple species present in ashes. The findings showed that toxicity attenuation of ashes should be the first-ranking task prior to practical reuse and recycle in applications.     

Sequential extraction for evaluating the leaching behavior of selected elements in municipal solid waste incineration fly ash

A sequential extraction method has been applied for the determination of binding forms of trace elements in the municipal solid waste incineration (MSWI) fly ash and evaluating their leaching behavior in view of their potential environmental impact. The elemental determinations in the different leachates are performed by ICP-AES and ICP-MS, respectively. The morphology and mineralogical phases after extraction step were performed by scanning electron microscopy (SEM). Total of 20 elements in the samples are investigated. A reference material of city waste incineration fly ash (BCR No. 176) is also tested to examine the applicability as well as accuracy of the proposed method. The sum of most elements present in the individual fractions shows a good agreement with the total elemental concentrations. The extraction efficiencies are generally higher than 80% except for that of Cr and V. The extractable data of most elements give information about the binding forms of various elements in both incineration fly ashes. It was found that the elements such as Ca, K, Na, Pb, Zn, Cd, Cu and Sr have exhibited a remarkable mobility in fly ash. More than half of them would be dissolved or exchanged under a mild leaching condition. The toxic elements such as Pb, Cd, Zn and Cu have a great potential to be released into the environment under normal conditions.     

Fluidized bed incinerator for medical waste that generates no residual dioxin: a mini-review

The advantages of medical waste incineration include the sterilization of bacteria, stabilization of chemical activity, and reduction in waste volume. During the incineration of medical waste, dioxin is generated owing to the high chlorine content. Based on previous research, a conventional fluidized bed combustor with a minimum retrofit to dispose of medical waste without residual dioxins is presented in this study. Coal or pyrite was added to inhibit dioxin formation in the combustion chamber. Fly ash and activated carbon which had adsorbed dioxin were pelletized with adhesive material, and the pelletized fly ash was then recycled to the incinerator for burning. The pelletized fly ash with adhesive material was finally discharged as bottom ash. Bottom ash constitutes the net output of the entire incineration system. and its dioxin content can be neglected. An incineration system that does not produce dioxin residue was achieved; however, a better formula for the pelletized fly ash is still required.

Title page (short abstract)

1. The emission of dioxin from medical waste incinerators can’t be eliminated by disabling PVC as a raw material of medical devices.

2. Based on the knowledge shown in the previous literature, an integrated fluidized bed incineration system without dioxin residual installed in a large hospital is proposed in this study.

3. There are many ways to reduce dioxin formation during the incineration process; however, conventional methods can’t eliminate the existence of dioxin in fly ash.

4. Pelletized fly ash recycled to the incinerator for re-burning and discharged in the form of bottom ash which is considered dioxin free.

     

Understanding biotoxicity for reusability of municipal solid waste incinerator (MSWI) ash

This feasibility study using Escherichia coli DH5alpha as a reporter microorganism tended to disclose toxicity ranking of various ashes of municipal solid waste incinerator (MSWI) in comparison with typical toxic chemicals for reusability in further applications. Previous study indicated that growth inhibition to bacterial cells occurred at concentrations above 0.156, 0.625 and 0.0195g/L for bottom ash (BA), cyclone ash (CA), scrubber ash (SA), respectively, suggesting the toxicity ranking of SA>BA>CA. This follow-up study clearly stated that compared to cadmium(II) and chromium(II) SA seemed to be the most toxic species to DH5alpha. Large amounts of supplemented lime (CaO) were used for neutralization of acid gas in incinerator, SA was thus contained high-levels of sulfate, chloride and nitrate salts. Therefore, compared to other ashes a marked increase in toxicity was observed in SA. Regarding soluble cations and anions in ashes, nitrite ion seemed to stimulate instead of repress cell growth. In contrast, nitrate ion showed so-called "sufficient challenge" characteristics for growth enhancement and inhibition at low and high concentration, respectively. Low solubility of metallic ions (e.g., Pb(II) and Cu(II)) in ashes likely resulted in low mobility in the environment and low risk to humans. The findings showed that toxicity attenuation of SA will be inevitably required as SA is even more toxic than Cr(II) and Cd(II).     

The hydration properties of pastes containing municipal solid waste incinerator fly ash slag

This study investigated the hydration properties of Type I, Type III and Type V cements, mixed with municipal solid waste incinerator fly ash, to produce slag-blended cement pastes. The setting time of slag-blended cement pastes that contained 40% slag showed significantly retardation the setting time compared to those with a 10% or even a 20% slag replacement. The compressive strength of slag-blended cement paste samples containing 10 and 20% of slag, varied from 95 to 110% that developed by the plain cement pastes at later stages. An increased blend ratio, due to the filling of pores by C-S-H formed during pozzolanic reaction tended to become more pronounced with time. This resulting densification and enhanced later strength was caused by the shifting of the gel pores. It was found that the degree of hydration was slow in early stages, but it increased with increasing curing time. The results indicated that it is feasible to use MSWI fly ash slag to replace up to 20% of the material with three types of ordinary Portland cement.     

Biotoxicity evaluation of fly ash and bottom ash from different municipal solid waste incinerators

Different types of municipal solid waste incinerator (MSWI) fly and bottom ash were extracted by TCLP and PBET procedures. The biotoxicity of the leachate of fly ash and bottom ash was evaluated by Vibrio fischeri light inhibition test. The results indicate the following: (1) The optimal solid/liquid ratio was 1:100 for PBET extraction because it had the highest Pb and Cu extractable mass from MSWI fly ash. (2) The extractable metal mass from both fly ash and bottom ash by PBET procedure was significantly higher than that by TCLP procedure. (3) The metal concentrations of fly ash leachate from a fluidized bed incinerator was lower than that from mass-burning and mass-burning combined with rotary kiln incinerator. (4) The TCLP and PBET leachate from all MSWI fly ash samples showed biotoxicity. Even though bottom ash is regarded as a non-hazardous material, its TCLP and PBET leachate also showed biotoxicity. The pH significantly influenced the biotoxicity of leachate.     

Carbon dioxide sequestration in municipal solid waste incinerator (MSWI) bottom ash

During bottom ash weathering, carbonation under atmospheric conditions induces physico-chemical evolutions leading to the pacification of the material. Fresh bottom ash samples were subjected to an accelerated carbonation using pure CO2. The aim of this work was to quantify the volume of CO2 that could be sequestrated with a view to reduce greenhouse gas emissions and investigate the possibility of upgrading some specific properties of the material with accelerated carbonation. Carbonation was performed by putting 4mm-sieved samples in a CO2 chamber. The CO2 pressure and the humidity of the samples were varied to optimize the reaction parameters. Unsieved material was also tested. Calcite formation resulting from accelerated carbonation was investigated by thermogravimetry and differential scanning calorimetry (TG/DSC) and metal leaching tests were performed. The volume of sequestrated CO2 was on average 12.5L/kg dry matter (DM) for unsieved material and 24 L/kg DM for 4mm-sieved samples. An ash humidity of 15% appeared to give the best results. The reaction was drastically accelerated at high pressure but it did not increase the volume of sequestrated CO2. Accelerated carbonation, like the natural phenomenon, reduces the dangerous nature of the material. It decreases the pH from 11.8 to 8.2 and causes Pb, Cr and Cd leaching to decrease. This process could reduce incinerator CO2 emissions by 0.5-1%.     

Feasibility study of using brick made from municipal solid waste incinerator fly ash slag

This study deals with the effect of MSWI slag on fired clay bricks. Brick samples were heated to temperatures which varied from 800 to 1,000 degrees C for 6h, with a heating rate of 10 degrees C/min. The material properties of the resultant material then determined, including speciation variation, loss on ignition, shrinkage, bulk density, 24-h absorption rate and compressive strength. Toxicity Characteristic Leaching Procedure tests were also conducted. The results indicate that the heavy metal concentrations in the leachates met the current regulatory thresholds. Increasing the amount of MSWI slag resulted in a decrease in the water absorption rate and an increase in the compressive strength of the MSWI-slag bricks. The 24-h absorption rate and compressive strength of the MSWI-slag brick made from samples containing slag sintered at 1,000 degrees C all met the Chinese National Standard (CNS) building requirements for second-class brick. The addition of MSWI slag to the mixture reduced the degree of firing shrinkage. This indicates that MSWI slag is indeed suitable for the partial replacement of clay in bricks.