Destruction and formation of polychlorinated dibenzo-p-dioxins and dibenzofurans during pretreatment and co-processing of municipal solid waste incineration fly ash in a cement kiln

Degradation and regeneration inhibition of PCDD/Fs in incineration fly ash by low-temperature thermal technology

Low-temperature thermal degradation of PCDD/Fs for incineration fly ash (IFA), as a novel and emerging technology approach, offers promising features of high degradation efficiency and low energy consumption, presenting enormous potential for application in IFA resource utilization processes. This review summarizes the concentrations, congener distributions, and heterogeneity characteristics of PCDD/Fs in IFA from municipal, medical, and hazardous waste incineration. A comparative analysis of five PCDD/Fs degradation technologies is conducted regarding their characteristics, industrial potential, and applicability. From the perspective of low-temperature degradation mechanisms, pathways to enhance PCDD/Fs degradation efficiency and inhibit their regeneration reactions are discussed in detail. Finally, the challenges to achieve low-temperature degradation of PCDD/Fs for IFA with high-efficiency are prospected. This review seeks to explore new opportunities for the detoxification and resource utilization of IFA by implementing more efficient and viable low-temperature degradation technologies.

Environmental impacts of cement kiln co-incineration sewage sludge biodried products in a scale-up trial

The biodrying technology as a pretreatment technology can overcome the limitations of cement kilns co-incineration sewage sludge (SS) on energy consumption. But the impact of SS biodried products on cement kilns and the route carbon reduction potential of biodrying + cement kilns have not been studied. In this study, SS biodrying and cement kiln co-incineration biodried product trials were conducted to highlight the matrix combustion characteristics, and the impact of biodried products on cement kilns (clinker capacity, coal consumption, and pollutant discharge). The carbon emissions of the four scenarios were assessed based on these results. The results showed that water removal rate reached 65.5 % after 11-day biodrying, and the wet-based lower heating value of the biodried product increased by 76.0 % compared with the initial matrix. Comprehensive combustibility index of the biodried product (0.745 × 10-7 %2℃-3min-2) was better than that of SS (0.433 × 10-7 %2℃-3min-2) although a portion of the organic matter was degraded. Cement kiln co-incineration of biodried products (150 t/d) resulted in per tonne of clinker saved 5.61 kg of coal due to the heat utilization efficiency of biodried products reached to 93.7 %. However, it led to an increase in the emission concentrations of NOX and SO2. Assessment results indicated that the biodrying + cement kiln pathway reduced CO2 emissions by 385.7 kg/t SS. Biodried products have greater potential to reduce emissions as alternative fuels than as fertilizers. This study indicated the advantages of SS biodrying + cement kiln co-incineration route.

Physical properties, chemical composition, and toxicity leaching of incineration fly ash by multistage water washing

Incineration fly ash contains a large amount of chloride, which limits the scope of its resource utilization. Water washing effectively removes chlorides and soluble substances, increasing the ability to dispose of them. The properties of incineration fly ash after multi-level water washing have been studied, providing theoretical guidance for the safe disposal of water-washed ash at all levels. Taking a practical project as an example, this paper analyzed the impact of three-stage countercurrent water washing on the physicochemical properties and toxicity leaching of incineration fly ash with different washing grades by XRD, BET, XRF, SEM, and ICP-MS. The results showed that with the improvement of washing grade, the removal rate of chloride ions was more than 86.96%. However, due to the removal of soluble substances, dioxins enriched from 98 ng-TEQ/kg of raw ash to 359 ng-TEQ/kg of tertiary washed incineration fly ash. Cr, Cu, and Zn also increased from 40.35 mg/L, 356.55 mg/L, and 3290.58 mg/L of raw ash to 136.30 mg/L, 685.75 mg/L, and 5157.88 mg/L, respectively. Pozzolanic activity had increased from 40.56% of the raw ash to 74.12% of the tertiary-washed incineration fly ash. There was no risk of excessive heavy metal leaching, and the dioxin content was lower than the raw ash in the primary washed incineration fly ash. After multi-stage water washing, incineration fly ash accumulated heavy metals, so more attention must be paid to the issue of heavy metal content in the safe disposal process.

Review of thermal treatments for the degradation of dioxins in municipal solid waste incineration fly ash: Proposing a suitable method for large-scale processing

Dioxin degradation is considered essential for the environmentally sound management of municipal solid waste incineration fly ash (MSWIFA). Among the many degradation techniques, thermal treatment has shown good prospects owing to its high efficiency and wide range of applications. Thermal treatment is divided into high-temperature thermal, microwave thermal, hydrothermal, and low-temperature thermal treatments. High-temperature sintering and melting not only have dioxin degradation rates higher than 95 % but also remove volatile heavy metals, although energy consumption is high. High-temperature industrial co-processing effectively solves the problem of energy consumption, but with a low fly ash (FA) mixture, and the process is limited by location. Microwave thermal treatment and hydrothermal treatment are still in the experimental stage and cannot be used for large-scale processing. The dioxin degradation rate of low-temperature thermal treatment can also be stabilized at higher than 95 %. Compared to other methods, low-temperature thermal treatment is less costly and energy consumption with no restriction on location. This review comprehensively compares the current status of the above-mentioned thermal treatment methods and their ability to dispose of MSWIFA, especially the potential for large-scale processing. Then, the respective characteristics, challenges, and application prospects of different thermal treatment methods were discussed. Finally, based on the goal of low carbon and emission reduction, three possible approaches for improvement were proposed to address the challenges of large-scale processing of low-temperature thermal treatment, namely, adding a catalyst, changing the FA fraction, or supplementing with blockers, providing a reasonable development direction for the degradation of dioxins in MSWIFA.

Chlorine and heavy metals removal from municipal solid waste incineration fly ash by electric field enhanced oxalic acid washing

Electric field enhanced oxalic acid (H₂C₂O₄) washing was conducted to examine the simultaneously removal efficiency of heavy metals (HMs) and chlorine, especially insoluble chlorine from municipal solid waste incineration fly ash (MSW FA). Results show that chlorine and HMs can be effectively removed with a total chlorine, As, Ni and Zn removal rate of 99.10%, 79.08%, 75.42% and 71.43%, when the electrode exchange frequencies is 40 Hz, current density is 50 mA/cm², H₂C₂O₄ adding amount is 0.5 mol/L and the reaction time is 4 h. Insoluble chlorine removal efficiency is up to 95.32%, much higher than reported studies. And the chlorine content in the residue is lower than 0.14%. Meanwhile, HMs removal efficiency is remarkable, 41.62%-67.51% higher than that of water washing. The high-efficient removal effect is caused by the constantly changing direction of electrons hitting the fly ash surface, which provides more escape channels for internal chlorine and HMs. These results proved that electric field enhanced oxalic acid washing could be a promising method for removing contaminants from MSWI fly ash.

Chemical characteristics of bottom ash from biomedical waste incinerators in Ghana

Biomedical waste (BMW) incineration is the most used alternative disposal method in developing countries, such as Ghana. The improper disposal of incinerator-generated bottom ash (BA) is a significant concern due to the hazardous nature of waste. A study was conducted at Tema Hospital (TGH) and Asuogyaman Hospital (VRAH) incinerator sites. The BA samples were sent to the Council for Scientific and Industrial Research, Institute of Industrial Research, Ghana. The BA samples were weighed with fisher analytical balance, ground, and sieved with standard grade meshes of 120, 100, and 80 to determine the BA particle size distribution. The chemical composition and heavy metals were analysed using X-ray fluorescence spectrometry (XRF) and atomic absorption spectroscopy (AAS) techniques. The results indicated the chemical composition of the analysed BA samples was CaCO₃ (49.90%), CaO (27.96%) and MgCO₃ (6.02%) for TGH and CaCO₃ (48.30%), CaO (27.07%), and SiO₂ (6.10%) for VRAH, respectively. The mean concentration (M) (kg m^-3) and standard deviation (SD) for TGH in the BA were 7.082 ± 0.478 (Ti), 4.657 ± 0.127 (Zn) and 4.271 ± 1.263 (Fe), while that of VRAH consisted of 10.469 ± 1.588 (Ti), 7.896 ± 2.154 (Fe) and 4.389 ± 0.371 (Zn). Therefore, the heavy metals' mean concentration at the BA is above the WHO permissible limits of soil, i.e., 0.056 kg m^-3 (Ti), 0.085 kg m^-3 (Pb), 0.100 kg m^-3 (Cr) and 0.036 kg m^-3 (Cu). Furthermore, the heavy metal mean concentrations of TGH and VRAH present in the BA analysed samples were ranked in descending order: Ti > Zn > Fe and Ti > Fe > Zn, respectively. It is therefore recommended that BA must be properly disposed of because of the hazardous nature of heavy metals present in the analysed samples, which are able to cause environmental and public health issues.

Resource utilization of municipal solid waste incineration fly ash - cement and alkali-activated cementitious materials: A review

The increase in municipal solid waste (MSW) production has led to an increase in MSW incineration fly ash (MSWIFA) production. MSWIFA contains toxic and harmful substances such as heavy metals and dioxins, which can cause harm to the environment if not treated properly. Only a few MSWIFAs will be landfilled directly, and the rest will need to be treated by other methods. The treatment of MSWIFA can be divided into three types: separation, stabilization/solidification (S/S), and thermal treatment, which are either not fully developed or too costly. Resource utilization is a sustainable means of treating MSWIFA. MSWIFA is used in the production of cement and alkali-activated cementitious materials as a means of resource utilization with significant advantages. This can alleviate the consumption of nature and reduce greenhouse gas emissions in conventional cement production. Compared with MSWIFA cement, MSWIFA alkali-activated cementitious material can be achieved with almost no consumption of natural resources, which is worthy of further research to realize the large-scale application of MSWIFA. At the end of the paper, the perspective of separation of dioxins from MSWIFA, co-processing of MSWI ash, and production of "MSWIFA green materials" is presented.

Synergistic effect of polyvinyl chloride and coal ash on thermal separation of heavy metals from MSWI fly ash through molten salt process

Municipal solid waste incineration fly ash (FA) contains high contents of salts and high concentrations of heavy metals, which makes FA disposal extremely difficult. However, heavy metal elements could potentially be separated from FA during thermal treatment process to make it possible to be recycled. This work aims to study the volatilization of heavy metals in FA treated by molten salt method. The influence of polyvinyl chloride (PVC) and coal ash (CA) on volatilization of heavy metals was investigated. Within the scope of this study, the highest heavy metal removal rate can be under the condition: the calcium chloride/sodium chloride weight ratio 1:1, the FA/molten salt weight ratio 1:10, treatment temperature 1000°C for 2 hours in reducing atmosphere. The volatilization rates of lead, zinc, copper, chromium and manganese were 86.20, 67.53, 65.24, 50.07 and 39.45%, respectively. On the basis of molten salt treatment, adding PVC could promote the volatilization of heavy metals. The volatilization rate of lead was 96.71%, and the volatilization rates of chromium and manganese were higher than 60% when the content of PVC was 5 wt%. When adding 10 wt% CA and 1 wt% polyvinyl chloride, the volatilization rate of lead could reach 100%. The experiments and thermodynamic calculations showed that silicon dioxide and aluminium oxide in CA and hydrochloric acid decomposed from PVC could promote the chlorination and volatilization of heavy metals. The volatilized heavy metal chlorides provided the possibility of recovery and utilization of heavy metals in FA.

Disposal technology and new progress for dioxins and heavy metals in fly ash from municipal solid waste incineration: A critical review

Incineration has gradually become the most effective way to deal with MSW due to its obvious volume reduction and weight reduction effects. However, since heavy metals and organic pollutants carried by municipal solid waste incinerator fly ash (MSWI FA) pose a serious threat to the ecological environment and human health, they need to be handled carefully. In this study, the current status of MSWI FA disposal was first reviewed, and the harmless and resourceful disposal technologies of heavy metals and organic pollutants in MSWI FA are summarized as well. A summary of the advantages and disadvantages of each technology, including sintering, melting/vitrification, hydrothermal treatment, mechanochemistry, solidification/stabilization of MSWI FA, is compared. Finally, the research work that needs to be strengthened in the future (such as codisposal of multiple wastes, long-term stability research of disposal products, etc.) was proposed. Through comprehensive analysis, some reasonable and feasible suggestions were provided for the effective and safe disposal of MSWI FA in the future.

Analysis and discussion on formation and control of dioxins generated from municipal solid waste incineration process

Dioxins are a kind of persistent organic pollutants (POPs) with extremely toxic. Municipal solid waste incineration (MSWI) process has become one of the most dominant discharge sources of dioxins. A comprehensive discussion about dioxin formation mechanisms was reviewed in this paper, and the mechanisms of high-temperature gas-phase reaction and "de novo" synthesis were systematically illustrated in the form of diagrams. What's more, the effects of various influencing factors on the formation of PCDD/Fs were briefly analyzed in the form of a table. We believed that temperature, catalyst, chlorine source, carbon source, oxygen concentration and moisture were necessary factors for PCDD/Fs formation. Control technologies of dioxins in MSWI process were summarized subsequently from three stages: pre-combustion, in-combustion and post-combustion, and a device for synergistic removal of dioxins based on multi-field force coupling and technical routes for controlling dioxin emissions were proposed, so as to provide mechanisms and methods for effectively reducing the emission concentration of dioxins. An introduction was also conducted of dioxin control technologies in municipal solid waste incineration fly ash (MSWI-FA) in this paper, and their mechanisms, advantages, disadvantages and technical maturity were illustrated in the form of diagrams, which can provide theory and reference for in-depth research of follow-up scholars and industrial application of dioxin control technologies. Finally, current research hotspots, challenges and future research directions were proposed.Implications: In this paper, the main research contents and achievements are as follows: With the emphasis placed on the formation mechanism of dioxins and effects of various influencing factors on the formation of PCDD/Fs. The control technology of dioxins in MSWI process is summarized subsequently from three stages: pre-combustion, in-combustion and post-combustion.A device for synergistic removal of dioxins based on multi-field force coupling and technical routes for controlling dioxin emissions are proposed.A systematic review is conducted of the research progress on control technologies of dioxins in MSWI fly ash in the most recent years.The mechanisms, advantages, disadvantages and technical maturity of PCDD/Fs degradation technologies in MSWI fly ash are illustrated in the form of diagrams.Current research hotspots, challenges and future research directions are proposed.

Removal of harmful components from MSWI fly ash as a pretreatment approach to enhance waste recycling

Municipal solid waste incineration (MSWI) fly ash contains many harmful components that may limit its potential for recycling. An effective pretreatment is therefore required before any recycling can be implemented. In this study, the effects of four pretreatment methods (water washing, CO₂-aided washing, CO₃^2--aided washing, and CO₂ and CO₃^2--aided washing) on the extraction behavior of chloride, sulfate, and heavy metals were evaluated. Water washing was found to be effective for the extraction of all easily and moderately soluble Cl-bearing salts, achieving Cl extraction ratios of 88%, 90%, and 96% for ash from Chongqing (CQ), Qingdao (QD), and Tianjin (TJ), respectively. Injection of CO₂ during washing facilitated decomposition of the hardly soluble Cl-bearing salts, increasing the Cl extraction efficiency by 6% for CQ ash and 9% for QD ash. However, for the TJ ash that contained few insoluble Cl-bearing minerals, CO₂ injection decreased the Cl extraction rate. The addition of CO₃^2- had a negative influence on Cl extraction for all ashes, but it slightly promoted sulfate extraction. Despite the high Cl removal rate, only 23-37% of the sulfate and 0.1-12% of heavy metals were removed. Overall, water-based pretreatment, especially CO₂-aided washing, significantly altered the physical, chemical, and mineralogical characteristics of the fly ash, making it more suitable for recycling. Consequently, the blending ratio of the fly ash for cement clinker manufacture increased from 0.2 to 0.3% in the raw ash to 3.5-5.5% in the treated ash, enabling the extensive use of ash materials.

Dioxin emission and distribution from cement kiln co-processing of hazardous solid waste

Cement kiln collaborative disposal technology can not only dispose of hazardous waste but also provide energy for the cement industry. However, the addition of hazardous waste may promote the formation of dioxins in cement kilns. In this study, typical hazardous solid wastes, such as solidified fly ash, electroplating sludge, and industrial residue, were co-processed in a cement kiln with different feeding positions and different feeding amounts. The concentrations of dioxins in the flue gas, clinker, and precalciner furnace slag were investigated. The effect of adding mixed hazardous solid waste on the formation of dioxin was also studied. The results showed that the concentration of dioxin in the flue gas without added hazardous waste was 1.57 ng/m³, and the concentration varied from 1.03 to 6.49 ng/m³ after the addition of hazardous waste. In addition, the concentration of dioxin in the flue gas and solid samples increased substantially when the co-processing ratio doubled. The large amount of Cu in solidified fly ash promoted the formation of dioxins, while the higher S content in the electroplating sludge suppressed the formation of dioxins. Compared with the addition of single hazardous waste, the concentration of dioxin in precalciner furnace slag increases by about 300%. Furthermore, the distributions of isomers in the clinker and precalciner furnace slag were similar. 1,2,3,4,6,7,8-HpCDD and OCDD accounted for a large proportion of the mass concentration, and the contribution rate ranged from 48.7 to 82.0%. Most importantly, correlation analysis showed that the concentration of dioxin was closely related to the copper content, hazardous waste types and additive proportion, with correlation coefficients of 0.79, 0.83, and 0.89, respectively. This study provides a basis for exploring the high environmental benefits of disposing of hazardous solid waste by co-processing in cement kilns.

Treatment of municipal solid waste incineration fly ash: State-of-the-art technologies and future perspectives

Municipal solid waste incineration (MSWI) fly ash is considered as a hazardous waste that requires specific treatment before disposal. The principal treatments encompass thermal treatment, stabilization/solidification, and resource recovery. To maximize environmental, social, and economic benefits, the development of low-carbon and sustainable treatment technologies for MSWI fly ash has attracted extensive interests in recent years. This paper critically reviewed the state-of-the-art treatment technologies and novel resource utilization approaches for the MSWI fly ash. Innovative technologies and future perspectives of MSWI fly ash management were highlighted. Moreover, the latest understanding of immobilization mechanisms and the use of advanced characterization technologies were elaborated to foster future design of treatment technologies and the actualization of sustainable management for MSWI fly ash.

Field-scale study of co-processing dichlorodiphenyltrichloroethane-contaminated soil in a cement kiln

Persistent organic pollutants in soil are not readily degraded in the short term. The utilization of co-processing solid waste in cement kilns has received increasing attention in recent years. Co-processing may be a good way of disposing of dichlorodiphenyltrichloroethane-contaminated soil (CS). The feasibility of co-processing CS pretreated to desorb dichlorodiphenyltrichloroethane, was assessed by performing an industrial-scale trial, focusing on the risks posed by emissions to the environment. Samples of the input and output in cement kiln were collected for determining clinker quality, production operation, pollutant emissions, cement kiln system destruction efficiency, and distribution profiles of persistent organic pollutants unintentionally produced from kiln. The destruction efficiency and destruction removal efficiency both were > 99.99% in cement kiln system at the appropriate CS feeding rate. Emissions of stack gases produced by cement kilns co-processing CS were within the reasonable range set in China. Dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), and polychlorinated biphenyls (PCBs) concentrations and distribution profiles in flue gases and particulate samples from two tests showed PCBs mainly formed at the same sites as PCDD/Fs, indicating they are may formed in a similar way in cement kiln. A comparison with the processing parameters in the clinker, cement kiln dust, and flue gas under baseline and co-processing conditions, manifested that co-processing had no effect on the operation or cement quality of the cement kiln. Thus co-processing CS at a rate of 20 t/h with pretreatment process, is an environmentally sound and highly efficient treatment for CS.

Co-disposal of municipal solid waste incineration fly ash and bottom slag: A novel method of low temperature melting treatment

Conventional melting for disposing municipal solid waste incineration (MSWI) fly ash or bottom slag needed high temperature and consumed high energy. High calcium content in fly ash and high silicon content in bottom slag brought them high melting point, respectively. Based on the analysis of chemical composition and phase diagram, suitable contents, namely 30%-40% CaO, 45%-60% SiO₂ and 10%-15% Al₂O₃, were proposed to obtain a lower-melting-point mixture system. When the mass ratio of fly ash to bottom slag was 1:5, lowest melting point can be obtained. It was 1,190 ℃, lower than that of fly ash (1,448 ℃) and bottom slag (1,310 ℃). The toxicity characteristic leaching procedure of slags obtained from low melting treatment met the leaching toxicity of Chinese standard GB 5085.3-2007, and the slags containing about 25 wt% CaO, 10 wt% Al₂O₃ and 45 wt% SiO₂ can be used for preparing CaO-Al₂O₃-SiO₂ glass ceramics. The co-process of fly ash and bottom slag realized the low temperature melting treatment with low energy consumption.

Potential of preparing cement clinker by adding the fluorine-containing sludge into raw meal

Fluorine-containing sludge from semiconductor industries were one kind of hazardous wastes, there was hardly effective treatment to realize its safe disposal and utilization. This paper evaluated the potential of preparing cement clinker by adding the sludge into raw meal by a series of experiments. The results revealed 2.0 % addition of the sludge markedly improved the burnability of the produced clinker, and promoted the formation of alite with more amounts and smaller size, but the 5.0 % addition of the sludge resulted in the abundant formation of interstitial phases to inhibit the formation of alite and belite. The better workability was gained with the addition of 2.0 %, and the optimal 28 d compressive strength was 50.76 MPa. The distribution of fluorine was higher in silicate phases, and it was mainly accumulated in the interfaces of silicate phases. Fluorine in the sludge was immobilized by calcium to form the binding forms of calcium fluoride in produced clinker and hydration products. The immobilization ratios of fluorine, copper, zinc and nickel were more than 99.5 %, and the addition of the sludge (≤5.0 %) into raw meal could not induce further environment hazards.

Comparative study on inorganic Cl removal of municipal solid waste fly ash using different types and concentrations of organic acids

In this study, different organic acids-such as citric, acetic, lactic, propionic, and butyric acid-were evaluated to ascertain the optimum leaching solvent for dechlorinating fly ash. Results suggest that the acid type, concentration, and interactions between both parameters contributed significantly to the variations in the efficiency of fly ash dechlorination. Simple main-effect analysis suggested that a higher acid concentration yields better dechlorination efficiency. However, improvements in dechlorination efficiency did not necessarily yield a low chlorine content leaching residue because in a specific acid concentration region, the increased acid concentration may also accelerate the mass reduction rate of the leaching residue. Experimental results also demonstrate that citric and acetic acid yield the highest dechlorination efficiency, followed by propionic and butyric acid. The least dechlorination efficiency of lactic acid could be attributed to the formation of precipitate (i.e. calcium lactate) which might cover the chlorides and reduce the contact area of intimal chlorides with the leaching solvent. Therefore, a specific concentration of organic matter fermentation broth rich in citric and acetic radicals may present itself as an ideal water substitute for fly ash dechlorination.

Co-disposal of incineration fly ash and sewage sludge via hydrothermal treatment combined with pyrolysis: Cl removal and PCDD/F detoxification

In this study, the incineration fly ash (IFA) of municipal solid waste (MSW) and municipal sewage sludge (MSS) was synergistically subjected to hydrothermal treatment coupled with pyrolysis (HTP). The regulation of Cl removal and the destruction and detoxification of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) were investigated. The results demonstrated that during hydrothermal treatment (HTT), the Cl removal rate increased with temperature, most of the soluble chlorides were removed, and the acid dissolution of Cl in the hydro-residue was significantly reduced. At hydrothermal temperatures exceeding 180 °C, the variation in the Cl removal rate decreased. Although a certain quantity of PCDD/Fs dissolved in the hydrothermal liquid, the total destruction rate achieved by HTT remained more than 90%. The detoxification rate did not exceed 60% owing to the formation of low-chlorinated PCDD/Fs. Subsequent pyrolysis of the hydro-residue further improved the Cl removal rate, which increased with pyrolysis temperature; the Cl content of pyro-char was reduced to 1.8% and that of the leached acid was less than 0.5 mg/g at 800 °C. In addition, PCDD/Fs in tar and pyrolysis gas were not detected under optimal conditions; the PCDD/F concentration of pyro-char was reduced to 0.17 ng I-TEQ/kg. The destruction and detoxification efficiencies of PCDD/Fs reached 98.49% and 92.50%, respectively. Thus, the method of HTP was conducive to the co-disposal of IFA and MSS.

Assessing the chromium mobility in ashes through SiO2-Al2O3-Fe2O3-CaO system: The role of composition

Given the millions of coal-fired power stations worldwide and the generalization of co-firing technologies in the near future, the aqueous extraction experiments were taken to study the effects of oxides on Cr mobility in ashes through SiO₂-Al₂O₃-Fe₂O₃-CaO system. The results identify that both the component and the species of Cr in samples are vital factors to govern the fate of Cr during combustion. Although Cr-oxide hardly reacts with Al₂O₃, SiO₂, and mixtures at 900 °C, the immobilization of Cr in Si-Al glass is ascribable to the heat-driven phase transformation of Cr-rich clay. The strong capture of Cr-oxide by CaO leads to the primary extraction of active Cr with the high toxicity and mobility; however, the opposite effect is found by Fe₂O₃. But the interactions of Al-/Si- oxides with others can trigger some changes in Cr mobility, wherein there is the lowest mobility of Cr in the case of Cr entering into the structures of Fe-rich SiO₂/Si-Al glass during combustion. Thus, without regard to the sample source, it is effective to reduce the environmental risk of Cr in ashes through raising SiO₂ and reducing M_CaO/M_Fe2O3 < 5/4 prior to combustion.

Selective Recovery of Copper(II) from Incineration Ash Produced from a Municipal Waste Incineration Facility Using a Flow-through Type Electrolysis Method

Recovery of copper was attempted from municipal waste incineration ashes using acid extraction and electrodeposition by a flow-through type electrolysis cell (FE). Efficient extraction of copper from the incineration ash was obtained using 0.5 mol L^-1 sulfuric acid, i.e., copper extraction rate: 78% from bottom ash and 88% from fly ash. The copper in the 10-fold diluted extractant injected into the FE was quantitatively adsorbed by applying -0.4 V and was quantitatively desorbed by eluting with nitric acid.

Pretreatment of municipal solid waste incineration fly ash and preparation of solid waste source sulphoaluminate cementitious material

Municipal solid waste incineration fly ash (MSWI-FA) is a kind of hazardous waste, and it is of great significance to treat it harmlessly and resourcefully. This study proposes the preparation of sulphoaluminate cementitious materials using water-washed MSWI-FA, flue-gas desulfurization gypsum, and aluminum ash. The changes in the composition and morphology of MSWI-FA before and after washing were investigated, and the effects of various washing conditions on the removal rate of chloride salt from MSWI-FA were analyzed. The effect of firing temperature on the mineral content of the sulphoaluminate cementitious material was also investigated. In addition, the strength and heavy metal leaching characteristics of the corresponding materials were tested. The results show that more than 90% of chloride salts were removed by water washing MSWI-FA two times. Using MSWI-FA as the main raw material, the sulphoaluminate cementitious material containing mostly calcium sulphoaluminate and dicalcium silicate could be prepared successfully at 1270 °C; the amount of MSWI-FA in the raw material can be as high as 35% (dry weight). Moreover, the sulphoaluminate cementitious material can effectively solidify heavy metals in the raw materials. The leaching concentrations of eight heavy metal ions, i.e., Cu, Zn, Cd, Pb, Cr, Ni, Ba, and As are far lower than the concentration limits set by national standards.

Industrial disposal processes for treatment of polychlorinated dibenzo-p-dioxins and dibenzofurans in municipal solid waste incineration fly ash

Hazardous waste disposal is a serious environmental concern in China. Therefore, in this study, industrial trials were conducted in a low-temperature thermal degradation facility, a tunnel kiln, and a shaft kiln to effectively treat dioxins in municipal solid waste incineration (MSWI) fly ash. The results indicated that the low-temperature thermal degradation facility efficiently decomposed polychlorinated dibenzo-p-dioxins and dibenzofurans in the MSWI fly ash. Additionally, the concentrations of dioxins in the treated fly ash and exhaust gas were lower than the suggested standard limits and the degradation ratio of dioxins was ∼99%. Therefore, treated fly ash characterized by acceptable dioxin risks could be utilized for the production of non-fired building materials. The results from the tunnel kiln indicated complete decomposition of the dioxins in the firing and insulating sections. However, the addition of fly ash in the tunnel kiln increased the concentration of dioxins in the flue gas. This can be primarily attributed to the heterogeneous catalytic synthesis reaction in the low-temperature section of the tunnel kiln. The results from the shaft kiln indicated degradation of at least 22% of the dioxins in the ash. The dioxin concentration in the flue gas was lower than the national standard while that in the clinker was within a reasonable limit. Furthermore, the environmental risks were significantly reduced at fly ash addition ratios lower than 3%.

Unintentional persistent organic pollutants in cement kilns co-processing solid wastes

Co-processing solid waste in cement kilns has become increasingly widespread in recent years. Persistent organic pollutants (POPs) can be unintentionally produced and emitted from cement kilns, especially kilns in which solid waste is co-processed. Unintentionally produced POP formation and emission by cement kilns co-processing solid waste therefore need to be studied in detail to allow the potential risks posed by cement kiln co-processing techniques to be assessed. Many field studies and laboratory simulation experiments have been performed to investigate the formation and release of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). However, the formations, characteristics and emission factors of various emerging unintentionally produced POPs have not been comprehensively reviewed. Here, emissions of well-known unintentionally produced POPs (PCDD/Fs and polychlorinated biphenyls) and emerging unintentionally produced dioxin-like POPs (polybrominated dibenzo-p-dioxins and dibenzofurans, polychlorinated naphthalenes, and chlorinated and brominated polycyclic aromatic hydrocarbons) in cement kilns co-processing solid waste are reviewed, focusing on formations and influencing factors of those unintentional POPs. Data from field studies indicated that the main stages in which POPs are unintentionally produced in cement kilns co-processing solid waste are the cyclone preheater outlet, suspension preheater boiler, humidifier tower, and back-end bag filter. The raw material composition, chlorine and bromine contents, and temperature are the most important factors affecting POP formation. The homolog distributions and congener profiles of POPs formed unintentionally in cement kilns were compared, and it was found that larger amounts of less-chlorinated homologs than more-chlorinated homologs are emitted. Emission factors for various unintentionally produced POPs for cement kilns co-processing solid waste were summarized, and could be useful for compiling global emission inventories for pollutants covered by the Stockholm Convention. This comprehensive review improves our understanding of unintentional production and emissions of POPs by cement kilns co-processing solid waste.

Cigarette smoke or exhaust gas from waste incineration – where are more dioxins?

In Poland, incineration is a relatively new method of waste treatment. Modern installations for waste incineration have two functions: they reduce the quantity (volume) of the waste and are a source of electricity and/or heat. During all combustion processes including waste incineration, polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCD/Fs) (well known as dioxins) are formed. These compounds are considered to be extremely dangerous for living organisms including human beings. Dioxins are formed in any process of combustion of solid and liquid fuels in the presence of chlorine, oxygen and organic matter at appropriate temperatures. Combustion processes also occur during cigarette smoking, which is also a source of dioxin emissions. Although smoking has been classified as a less important source of dioxins in the environment, it directly affects our health. This work’s aim is to determine and compare the degree of harmfulness caused by the amount of inhaled dioxins: cigarette smoking or living near a waste incineration plant. Based on literature and experimental data, the concentration of dioxins in cigarette smoke and exhaust gases generated by municipal waste incineration plants as well as number of dioxins absorbed per day by the body will be presented.