Decomposition of organochlorine compounds in flue gas from municipal solid waste incinerators using natural and activated acid clays

High-temperature particle control (HTPC) using a ceramic filter is a dust collection method without inefficient cooling and reheating of flue gas treatment; thus, its use is expected to improve the energy recovery efficiency of municipal solid waste incinerators (MSWIs). However, there are concerns regarding de novo synthesis and a decrease in the adsorptive removal efficiency of dioxins (DXNs) at approximately 300°C. In this study, the effect of natural and activated acid clays on the decomposition of monochlorobenzene (MCB), one of the organochlorine compounds in MSW flue gas, was investigated. From the results of MCB removal tests at 30–300°C, the clays were classified as adsorption, decomposition, and low removal types. More than half of the clays (four kinds of natural acid clays and two kinds of activated acid clays) were of the decomposition type. In addition, the presence of Cl atoms detached from MCB was confirmed by washing the clay used in the MCB removal test at 300°C. Activated acid clay was expected to have high dechlorination performance because of its proton-rich-composition, but only two clays were classed as decomposition type. Conversely, all the natural acid clays used in this work were of the decomposition type, which contained relatively higher di- and trivalent metal oxides such as Al₂O₃, Fe₂O₃, MgO, and CaO. These metal oxides might contribute to the catalytic dechlorination of MCB at 300°C. Therefore, natural and activated acid clays can be used as alternatives for activated carbon at 300°C to remove organochloride compounds such as DXNs. Their utilization is expected to mitigate the latent risks related to the adoption of HTPC, and also to contribute to the improvement of energy recovery efficiency of MSWI.

ImplicationsThe effect of natural and activated acid clays on MCB decomposition was investigated to evaluate their suitability as materials for the removal of organochlorine compounds, such as DXNs, from MSWI flue gas at approximately 300°C. More than half of the clays used in this study showed the decomposition characteristics of MCB. The presence of Cl atoms in the clay used in the MCB removal test at 300°C proved the occurrence of MCB decomposition. The results of this study suggest a novel flue gas treatment method to establish high-energy efficient MSWI systems.     

Partition and size distribution of heavy metals in the flue gas from municipal solid waste incinerators in Taiwan

This study investigates the partition of heavy metals in both solid and gas phases in the flue gas from municipal solid waste (MSW) incinerators. Six MSW incinerators in Taiwan were examined and heavy metals in the flue gas at the inlets and outlets of air pollution control devices (APCDs) were analyzed. Heavy metals including Hg, Pb, Cd, Zn, Cu and Cr were sampled by USEPA Method 29 and further analyzed using inductively coupled plasma-mass spectroscopy (ICP-MS) and cold vapor atomic absorption spectrometry (CVAAS). Experimental results revealed that the removal efficiencies of the APCDs for the heavy metals Pb, Cd, Zn, Cu and Cr greatly exceeded 90%, but that of Hg did not. Two groups of heavy metals upstream of APCDs were observed. Pb, Cd, Zn, Cu and Cr were present mainly in the solid phase with a solid to gas ratio (S/G) of over 12.3. However, in most cases, mercury appeared mainly in the gas phase with an S/G ratio from 0.15 to 1.04, because it has a low boiling point. Additionally, treatment with the APCDs increased the S/G ratio of mercury because gaseous mercury could be removed by injecting powdered activated carbon (PAC) into the flue gas. Moreover, the distribution of particle sizes in the solid phase was bimodal. Finer particles (d(p)2.5 microm) contained more Cr and Hg.     

Characterization of polychlorinated naphthalenes in stack gas emissions from waste incinerators

Nine typical waste incinerating plants were investigated for polychlorinated naphthalene (PCN) contents in their stack gas. The incinerators investigated include those used to incinerate municipal solid, aviation, medical, and hazardous wastes including those encountered in cement kilns. PCNs were qualified and quantified by isotope dilution high resolution gas chromatography–high resolution mass spectrometry techniques. An unexpectedly high concentration of PCNs (13,000 ng?Nm^?3) was found in the stack gas emitted from one waste incinerator. The PCN concentrations ranged from 97.6 to 874 ng?Nm^?3 in the other waste incinerators. The PCN profiles were dominated by lower chlorinated homologues, with mono- to tetra-CNs being the main homologues present. Furthermore, the relationships between PCNs and other unintentional persistent organic pollutants involving polychlorinated dibenzo-p-dioxins and dibenzofurans, polychlorinated biphenyls, hexachlorobenzene, and pentachlorobenzene were examined to ascertain the closeness or otherwise of their formation mechanisms. A good correlation was observed between ΣPCN (tetra- to octa-CN) and ΣPCDF (tetra- to octa-CDF) concentrations suggesting that a close relationship may exist between their formation mechanisms. The results would provide an improved understanding of PCN emissions from waste incinerators.     

PCDD/F in waste water discharges from flue gas scrubbers of waste incinerators and coal operated power plants

Scrubber water samples from different combustion plants and gypsum samples as obtained in the flue gas washing with lime water were analyzed for PCDD/F. Three of the investigated nine scrubber water samples showed PCDD/F contents between 0,4 and 11,5 ng I-TEq/1 where as in the 17 gypsum samples examined only in a few cases very low levels of HpCDD and OCDD could be detected.     

Characterization of municipal solid waste incineration and flue gas emission under anoxic environment in Tibet Plateau

Environmental Science and Pollution Research - Waste incineration is a process of full combustion reaction between waste and oxygen at high temperature. It is a new problem whether the special...     

小型焚烧设施烟气中二噁英类的排放和控制

对中国典型的小型焚烧设施现状和二噁英类排放进行了初步调查研究,未经处理的小型垃圾焚烧设施烟气中二噁英类毒性当量(TEQ)大于6 ng/m3,小型火化机烟气中二噁英类TEQ大于5 ng/m3.设计并检验了布袋除尘器和活性炭滤布的二噁英类去除效果.仅使用布袋除尘器二噁英类去除率不高,布袋除尘器和活性炭滤布联用可以有效去除飞灰和气相中的二噁英类,去除率达到90%左右,可达到《生活垃圾焚烧污染控制标准》(GB 18485-2001)二噁英类排放标准.     

Effects of water washing on removing organic residues in bottom ashes of municipal solid waste incinerators

Due to their potential toxicity and odourous nature, the residual organics in municipal solid waste incinerators are recently gaining attention as an important issue of resources recovery apart from their complex mixture of organic counterpart. Studies of the organic fractions in municipal solid waste incinerator residues have been limited. In this study, extended solid-phase extraction of the water-washed bottom ash and liquid-phase extraction of the washing water were carried out with regard to bottom ash samples from three mass-burning incinerators in Taipei County (Taiwan) during four consecutive seasons of year 2008-2009. Supercritical fluid extraction and Soxtec extraction techniques along with GC-MS were successfully used to characterize the residual organics in weathered and washed bottom ashes. Supercritical fluid extraction provided the quantification of aliphatics and aromatic compounds such as hexanoic acid and benzaldehyde, respectively. Soxtec extraction was useful for qualitative analysis of aromatic and aliphatic groups in the ashes and many of which were odourous and toxic compounds. By mixing one unit weight (g) bottom ash with two unit volume (mL) water for 15 min, total organic carbon in the bottom ash was greatly reduced (e.g., from 4.1 to 1.8 wt.%). Among the removed were foul odour-causing compounds such as pyridine and quinoline derivatives, while some aromatic compounds such as 4-hydroxybenzaldehyde and low-molecular-weight aliphatics such as hexanoic acid remained. The results here suggest that washing with water can be an effective pre-treatment step for removing odour-causing and environmental concerned organics.     

A sulfur-resistant CuS-modified active coke for mercury removal from municipal solid waste incineration flue gas

Environmental Science and Pollution Research - Adsorption is a typical method for air pollutant removal from flue gas. A CuS-modified active coke (CuS/AC) sorbent was developed to improve the...     

Generation of PCDD/F in fly ash from municipal solid waste incinerators

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.     

The utilization of catalyst sorbent in scrubbing acid gases from incineration flue gas

Catalyst sorbents based on alumina-supported CuO, CeO2, and CuO-CeO2 were applied to a dry scrubber to clean up the SO2/HCl/NO simultaneously from pilot-scale fluidized-bed incineration flue gas. In the presence of organic compounds, CO and the submicron particles SO2 and HCI removed by the fresh catalyst sorbents and NO reduced to N2 by NH3 under the catalysis of fresh and spent desulfurization/dechloridization (DeSO2/DeHCl) catalyst sorbents (copper compounds, Cu, CuO, and CuSO4) were evaluated in this paper. The fresh and spent catalyst sorbents were characterized by the Brunner-Emmett-Teller method (BET), X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), inductively coupled plasma-mass spectrometry (ICP-MS), and the elemental analyzer (EA). The study showed that the performances of CuO, CeO2, and CuO-CeO2/gamma-Al2O3 were better than that of Ca(OH)2. The removal efficiency of SO2 and HCl was 80-95% in the dry scrubber system. Under NH3/NO = 1, NO could not be reduced to N2 because it was difficult to control the ratio of air/fuel in the flue gas. For estimating the feasibility of regenerating the spent catalyst sorbents, BET and EA analyses were used. They indicated that the pore structures were nearly maintained and a small amount of carbon accumulated on their surface.     

垃圾焚烧飞灰中不同粒径的毒性特性

对广州市某垃圾焚烧发电厂的焚烧飞灰进行粒径分级毒性分析研究。主要研究了粒径在35～1 000μm范围内的飞灰的腐蚀性和短期浸出毒性,包括Cr、Cd、Mg、Pb、Mn、Fe、Cu、Zn、Ni、Co等重金属,SO24-,Cl-,NO3--N和NO2--N,同时也研究了飞灰的物质组成和矿物特性。研究结果表明,所有粒径飞灰的浸出液pH值在12.3～12.5之间,属于有腐蚀性的危险废物,重金属Mg、Pb、Zn的浸出浓度最高,分别为168.78、53.94和86.40 mg/L。飞灰浸出液和含量最高分别达到8.87g/L和1.38 g/L,同时浸出液中测出一定量的硝态氮和亚硝态氮,证明飞灰吸附了垃圾焚烧过程中产生的氮氧化物气体。另外,研究得出飞灰的基本组成元素为Ca、Si、Cl、K、Na、S、Al、Mg和Fe,而重金属则以Zn、Pb、Mn、Cu、Cr等为主。矿物相主要为含硅和钙的化合物及NaCl和KCl等氯化物。     

A new approach for biological online testing of stack gas condensate from municipal waste incinerators

A biological testing system for the monitoring of stack gas condensates of municipal waste incinerators has been developed using Euglena gracilis as a test organism. The motility, velocity and cellular form of the organisms were the endpoints, calculated by an image analysis system. All endpoints showed statistically significant changes in a short time when organisms were exposed to samples collected during combustion situations with increased pollutant concentrations. The velocity of the organisms proved to be the most appropriate endpoint. A semi-continuous system with E. gracilis for monitoring stack gas condensate is proposed, which could result in an online system for testing stack gas condensates in the future.     

Surface emission of landfill gas from solid waste landfill

The surface emission of landfill gas (LFG) was studied to estimate the amount of LFG efflux from solid waste landfills using an air flux chamber. LFG efflux increased as atmospheric temperature increased during the day, and the same pattern for the surface emission was observed for the change of seasons. LFG efflux rate decreased from summer through winter. The average LFG efflux rates of winter, spring and summer were 0.1584, 0.3013 and 0.8597 m³ m⁻² h⁻¹ respectively. The total amount of surface emission was calculated based on the seasonal LFG efflux rate and the landfill surface area. From the estimates of LFG generation, it is expected that about 30% of the generated LFG may be released through the surface without extraction process. As forced extraction with a blower proceeded, the extraction well pressure decreased from 1100 to –100 mm H₂O, and the LFG surface efflux decreased markedly above 80%. Thus, the utilization of LFG by forced extraction would be the good solution for global warming and air pollution by LFG.     

Health risk assessment of dioxin emissions from municipal waste incinerators: the Neerlandquarter (Wilrijk, Belgium)

Two municipal waste incinerators in the vicinity of a residential area close to the city of Antwerp caused concern to local habitants. Risk assessment was performed combining chemical, toxicological measurements and model calculations. As the first step in risk assessment an inventory was made of historic emissions from both incinerators with emphasis on dioxins. The operational atmospheric transport and deposition model for priority substances (OPS) was used to calculate the deposition of dioxins in the vicinity of incinerators. The observed soil contamination pattern did not correspond to the calculated deposition pattern, indicating that other sources may contribute at least partly to the local PCDD/PCDF contamination of the area. Dioxin exposure of people in the Neerlandquarter as a function of the food consumption behavior was calculated using a mathematical model (VLIER-HUMAAN) combined with transfer factors. According to the results of these calculations, just residing in the impact area does not result in a meaningful risk. Only if locally produced food was consumed (milk, meat and vegetables), exposure in the Neerlandquarter was enhanced compared to the average dioxin exposure estimated for the Flemish population. Exposure in 1997 was below the exposure in 1980. As a consequence of different eating habits and lower bodyweight, children are subjected to significantly higher exposure than adults. Adverse health outcomes from dioxin exposure in the past cannot be excluded. There was no evidence for enhanced exposure to genotoxicants based on a comparison of chromosomal damage to blood cells of children from the study area to those from a control group.     

Biomonitoring of PCDD/Fs in populations living near portuguese solid waste incinerators: levels in human milk

In the context of two Environmental Health Surveillance Programs, launched in response to public and scientific concern in relation to waste incinerators located near Lisbon and in Madeira Island, two human biomonitoring projects have been started in Portugal, focussed in dioxins and dioxin-like compounds in human milk. Results from the undertaken studies have already provided data on the extent and pattern of dioxin body burden of both studied groups as well as a preliminary temporal trend of dioxin levels for the population residing near Lisbon incinerator. The present paper investigates difference between exposed and non-exposed subjects under study and, from a preventive perspective, possible covariates of the dioxin levels in human milk. Emissions from both incinerators appear to be well controlled as there is no increase of human body burden of dioxins as measured in human milk of individuals living near these facilities. Concerning other determinants of dioxin levels, results suggest confirmation of previously found significant age-dependent trend towards higher levels of dioxins in aged subjects. On the contrary, association between mother's levels of dioxins and parity lost significance. Apart from the issue of incineration, the general conclusion for the general population is that living in Lisbon as compared to Madeira results in higher milk dioxin levels and possible health risks. The profile of the single congeners for PCDD/Fs in human milk from Madeira and Lisbon shows similar contributions for 12378-PCDD, 23478-PCDF, 123678-HCDD and 2378-TCDD, that account altogether for about 84% of the total identified dioxin body burden in the studied groups.     

Evaluation of the leachability of polychlorinated dibenzo-p-dioxins and dibenzofurans in raw and solidified air pollution control residues from municipal waste incinerators

Leachability of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from raw and solidified air pollution control (APC) residues with selected solvents, including acetic acid, simulated acid rain, humic acid, linear alkylbenzene sulfonate (LAS) and n-hexane was investigated. High-chlorinated PCDD/F congeners were observed in all leachates of raw APC residue samples, with the largest total leaching concentration (61.60 ngm(-3); 0.30 ngI-TEQm(-3)) from treatment with humic acid. Low-chlorinated congeners were mainly leached with LAS and n-hexane. Solidification and stabilization (S/S) processes with cement and sulfur-containing chelating agent decreased the leachability of PCDD/Fs by up to 98% with humic acid and LAS as solvents. However, S/S processes enhanced the leachability of both high- and low-chlorinated PCDD/F congeners with n-hexane as the solvent, which largely increased the toxic equivalent quantity of leachates. These results suggest that conventional S/S processes may effectively restrain the release of PCDD/Fs when APC residues are leached with rain water or natural organic compounds (e.g., humic acid), but may have a deteriorated effect when APC residues are leached with nonpolar organic solvents (e.g., n-hexane) coexisting in the landfill sites.     

Dechlorination and destruction of PCDDs/PCDFs in fly ashes from municipal solid waste incinerators by low temperature thermal treatment

Dechlorination and destruction characteristics of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/PCDFs) in fly ashes from commercial-scale municipal solid waste incinerators by low temperature thermal treatment using a laboratory-scale heating system were investigated. Experiments were carried out in reducing atmosphere at temperatures of 300 degrees C, 450 degrees C and 600 degrees C respectively, for the treatment time of 1h and 3h. Concentrations of PCDDs/PCDFs in raw fly ashes ranged from 35.5 to 107.3 microg kg(-1) (1.5-3.4 microg TEQ kg(-1)) and treated fly ashes ranged from 0.34 to 45.3 microg kg(-1) (0.012-1.63 microg TEQ kg(-1)). Concentrations of PCDDs/PCDFs in fly ashes treated at the different temperatures and times were observed to decrease with increase of treatment temperature and time by dechlorination or destruction. The distribution of octa- and hepta-chlorinated congeners were decreased and tetra-, penta- and hexa-chlorinated congeners were increased at 300 degrees C and 450 degrees C, but the distribution of octa- and hepta-chlorinated congeners were increased and tetra-, penta- and hexa-chlorinated congeners were again decreased at 600 degrees C. Total destruction efficiencies of PCDDs/PCDFs in fly ashes showed above 95% at the treatment temperature of 450 degrees C for 3h. However, removal efficiency of each congener in fly ashes varied, especially, 2,3,7,8-TeCDD and 1,2,3,7,8-PeCDD in fly ash A increased. And the dechlorination and destruction characteristics of PCDDs/PCDFs in fly ash A and B was different due to difference in contents of Ca-compounds and metal oxides such as CuO and PbO in fly ashes.     

Long-term monitoring and modeling of polychlorinated dibenzo-p-dioxins and dibenzofurans from municipal solid waste incinerators and surrounding area in northern Taiwan

Municipal solid waste incinerators (MSWIs) have long been the major contributors of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) to ambient air in Taiwan. After stringent MSWI emission standards were introduced in 2001, the long-term continuous monitoring of flue gas and ambient air quality became necessary to ensure the effectiveness of the related control strategies. Three MSWIs and the surrounding ambient air were investigated in the current study for PCDD/F characteristics during 2006 to 2011. The average concentrations in the flue gas ranged from 0.008?~?0.0488 ng I-TEQ/Nm³, which is much less than the emission standard in Taiwan (0.1 ng I-TEQ/Nm³) (I-TEQ is the abbreviation of International Toxic Equivalent). This led to extremely low levels in the ambient air, 0.0255 pg I-TEQ/Nm³, much less than the levels seen in most urban areas around the world. Additionally, the results obtained using the Industrial Source Complex Short-Term Dispersion Model (ISCST3) indicate that the PCDD/F contributions from the three MSWIs to the ambient air were only in the range from 0.164?~?0.723 %. Principal component analysis (PCA) showed that the PCDD/Fs in the air samples had very similar characteristics to those from mobile sources. The results thus show that stringent regulations have been an effective control strategy, especially for urban areas, such as Taipei City.     

Investigation of 1,4-dioxane originating from incineration residues produced by incineration of municipal solid waste

As a groundwater contaminant, 1,4-dioxane is of considerable concern because of its toxicity, refractory nature to degradation, and rapid migration within an aquifer. Although landfill leachate has been reported to contain significant levels of 1,4-dioxane, the origin of 1,4-dioxane in leachate has not been clarified until now. In this study, the origins of 1,4-dioxane in landfill leachate were investigated at 38 landfill sites and three incineration plants in Japan. Extremely high levels of 1,4-dioxane 89 and 340 microg l(-1), were detected in leachate from two of the landfill sites sampled. Assessments of leachate and measurement of 1,4-dioxane in incineration residues revealed the most likely source of 1,4-dioxane in the leachate to be the fly ash produced by municipal solid waste incinerators. Effective removal of 1,4-dioxane in leachate from fly ash was achieved using heating dechlorination systems. Rapid leaching of 1,4-dioxane observed from fly ash in a sequential batch extraction indicated that the incorporation of a waste washing process could also be effective for the removal of 1,4-dioxane in fly ash.     

Characterisation and fingerprinting of PCBs in flue gas and ash from waste incineration and in technical mixtures

Congener patterns of mono- to deca-chlorinated biphenyls (PC1-10B) were evaluated in (a) waste incineration flue gases collected in the post-combustion zone of a laboratory-scale fluidized-bed reactor, (b) ashes from two different MSW incineration plants, and (c) published data of eight Aroclor formulations. The congener patterns of the flue gases, ashes, and Aroclor mixtures clearly differed from each other, likely reflecting differences in formation pathways. The flue gas congener patterns were largely dominated by the least chlorinated congeners, whereas the ashes displayed more evenly distributed patterns. The most abundant congeners indicated a preference for 3,3',4,4'-oriented substitution, which may be related to de novo-type formation involving perylene. Principal component analysis confirmed that congener patterns differed among the three matrices and also distinguished flue gases collected at 200 °C from those collected at 300 °C and 450 °C. This distinction could be partly explained by the degree of chlorination, although the substitution status of the ortho-position, and substitution in the 3,3',4,4'-positions also seemed to be influential. Injecting biphenyl into the post-combustion zone of the reactor did not alter the patterns, indicating that availability of the backbone structure is not a limiting factor for PCB formation.