Evaluation of PCDD/Fs emission from fluidized bed incinerators co-firing MSW with coal in China

The levels and homologue profile of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from stack gas of three typical fluidized bed incinerators co-firing municipal solid waste (MSW) with Chinese coal were measured. The PCDD/Fs emission was in the range of 0.0054-0.1961 ng I-TEQ/N m(3). Comparison of PCDD/Fs detection results by HRGC/HRMS and HRGC/LRMS suggested that it was feasible to detect fly ash with high PCDD/Fs concentration by HRGC/LRMS. Several factors on PCDD/Fs emission were discussed. The primary reason for the lower PCDD/Fs emission was the inhibition mechanism of relatively high sulfur in feeding coal on PCDD/Fs formation. The emission results also showed that there was no directly correlation between PCDD/Fs levels and CO, O(2) and HCl concentration in flue gas. It was estimated that about 0.1034 g I-TEQ was annually emitted to atmosphere from the tested three MSW incinerators (total daily treatment capacity is 800 tonnes MSW).     

Treatment of hazardous sorbents generated from the adsorption of heavy metals during incineration

The emission of heavy metals during waste incineration can be effectively reduced through the practice of employing non-toxic sorbents. These sorbents can react with toxic metals at high temperatures and create metal binding between them by various physical and chemical mechanisms. After the adsorption process, the used sorbents, which contain heavy metals, need to be desorbed to reduce their potential environmental hazards or provide reusable sorbents for economical aspect. The sorbent's adsorption efficiency is affected by different operating conditions and waste elemental compositions during incineration, which, in turn, affect their desorption characteristics. However, the effects of operating condition and waste elemental composition on the stability of heavy metals in the sorbents and the desorption efficiencies have been little studied. This study investigates the desorption characteristics of heavy metals (Cr, Pb, Cu, and Cd) from the hazardous sorbents with different extracting reagents (H(2)O, HCl, EDTA, and Na(2)S(2)O(5)). The hazardous sorbents were generated under different adsorption time and various input waste elemental compositions during incineration process.     

Properties of MSW fly ash-calcium sulfoaluminate cement matrix and stabilization/solidification on heavy metals

In this paper, investigations were undertaken to formulate the properties of fly ash-calcium sulfoaluminate (CSA) cement matrix by blending MSW fly ash with CSA cement. The compressive strength, pore structure, hydration phases, and leaching behavior of Zn and Pb doped MSW fly ash-CSA cement matrices were determined by XRD, MIP, DSC, FTIR, EDX, TCLP leaching test and other experiments. The results showed that the addition of MSW fly ash to form fly ash-CSA cement matrix reduced the compressive strengths of matrices and made the pore distribution of matrices coarser, compared to that of pure CSA cement matrix. However, fly ash-CSA cement matrix could effectively immobilize high concentration of heavy metal such as lead and zinc with much lesser leaching of TCLP. Besides ettringite AFt, Friedel phase was a new hydration phase formed in the matrix. The formation of these hydration phases was responsible for huge reservoir of heavy metal stabilization by chemical fixing. Therefore, it could be postulated that MSW fly ash-CSA cement matrix was a potential new constituent of S/S matrix for high concentration of heavy metals such as Zn and Pb ions.     

Extraction of heavy metals from MSW incinerator fly ashes by chelating agents

An extraction process has been studied on a laboratory scale for the pretreatment of municipal solid waste (MSW) incinerator fly ash to remobilize Cr, Cu, Pb, and Zn. Five different types of fly ashes were treated with HCl, nitrilotriacetic acid (NTA), ethylendiaminetetraacetate (EDTA), or diethylenetriaminepentaacetate (DTPA) in a batch process in the pH range 2.5-10. The extraction of heavy metals by HCl was dependent on pH, increasing with increasing acid concentration. The efficiency of the chelating agents was independent of pH. By the treatment with 3.0% EDTA or DTPA, 20-50% of Cr, 60-95% of Cu, 60-100% of Pb, and 50-100% of Zn were extracted in the pH range 3-9. NTA was also effective in extracting Cr, Cu, and Zn. The maximum extraction of Cr, Cu, Pb, and Zn was obtained at 0.3-1.0% concentration of the chelating agents. NTA was effective in extracting Pb at a concentration as low as 0.1%. Extraction behavior of other elements during the treatment was also studied. The leaching test on the residues after the treatment with chelating agents showed that the fly ashes were successfully detoxified to meet the guideline for landfilling.     

Characteristics of heavy metals on particles with different sizes from municipal solid waste incineration

Information on the concentration and size distribution of particles in the flue gas streams is essential for selecting and designing particle removal systems. Two municipal solid waste incinerators (MWIs) were selected for conducting flue gas sampling to determine the particulate distribution and heavy metals concentration on particles with different sizes by US EPA Method 5 sampling train and a cascade impactor. In addition, the characteristics of heavy metals contained on particles were investigated via isokinetic sampling of flue gas stream of air pollution control devices (APCDs). The experimental results indicated that average particulate matter (PM) concentrations at APCDs inlet were 2288.2+/-825.9 and 3069.2+/-810. 0mg/Nm(3), while the concentrations of PM at stack were 1.51+/-0.20 and 14.81+/-4.52mg/Nm(3) in MWI-A and MWI-B, respectively. The differential mass size distribution of PM and differential elemental size distribution of Zn, Pb, and Cu in front of APCDs were of bimodal forms. Results indicate that Zn>Pb>Cu in order of mass concentration in each stage. The fine particles represent approximately 70% and the coarse particles account for the rest 30% of total particulate matters collected on eight stages for both incinerators. Zn, Pb and Cu on fine particles account for approximately 80% and those on the coarse particles are less than 20% of the total heavy metals collected on eight stages of the cascade impactor for both incinerators.     

The influence of heavy metals on partitioning of PAHs during incineration

The presence of heavy metals (Cr, Cd, Pb and Zn) in feedstock increases the partitioning of polycyclic aromatic hydrocarbons (PAHs) in the solid as well as in the gaseous phases, which has been reported in our previous study. However, the partitioning of PAHs in air-pollution control equipment (APCE) has not been investigated thus far. Hence, the present work was conducted to study the partitioning of PAHs in APCE and the effect of heavy metals on PAHs formation by varying the target heavy metals in the feedstock.A fluidized bed incineration system which includes a primary combustion chamber (sand bed), a secondary combustion chamber (freeboard), and an APCE (cyclone and scrubber) was utilized in this study. The feedstock that contained various heavy metals was fed into the incinerator, and then the PAHs in the cyclone and scrubber were analyzed to determine the effect of heavy metals on PAHs partitioning. The results indicate that the presence of Pb and Zn in feedstock facilitates the formation of PAHs.     

Effect of improving flue gas cleaning on characteristics and immobilisation of APC residues from MSW incineration

The flue gas cleaning system of a MSW incinerator with a capacity of 350 kt/year was changed to improve the HCl elimination efficiency. Instead of the semi-wet operating spray reactor and subsequent baghouse, a two-step wet flue gas cleaning was added behind the baghouse. Elemental composition, X-ray powder diffraction patterns and TGA measurements showed that the resulting APC residue was totally different from the former residue. As a consequence, leaching characteristics of both residues also differed and another treatment was required prior to disposal. For the former residue, mainly leaching of Pb (>100 mg/l), necessitated treatment prior to landfilling. The lower alkalinity of the new residue resulted in a leachate pH of 9.7 and a Pb concentration of 0.8 mg/l. The leachate pH of the former residue was 12.4. The leaching of Pb and Zn increased above 100 mg/l when immobilising the new residue with cement. Better results were obtained when immobilising with micro silica. The high CaCl2 x 2H2O content of the new residue brought along clogging of the bag filter system. Adding 1.4% of CaO (or 1.9% of Ca(OH)2) to the residue already improved these inconveniences but again significantly changed the leaching behaviour of the residue.     

Fate of heavy metals during municipal solid waste incineration in Shanghai

The transfer behavior of heavy metals during municipal solid waste (MSW) incineration was investigated based on 2-year field measurements in two large-scale incinerators in Shanghai. Great temporal and spatial diversification was observed. Most of Hg and Cd were evaporated and then removed by air pollution control (APC) system through condensation and adsorption processes, thus being enriched in the fine APC residues particles. Cr, Cu, and Ni were transferred into the APC residues mainly by entrainment, and distributed uniformly in the two residues flows, as well as in the ash particles with different sizes. Pb and Zn in the APC residues were from both entrainment and evaporation, resulting in the higher concentrations (two to four times) compared with the bottom ash. Arsenic was transported into the flue gas mainly by evaporation, however, its transfer coefficient was lower. Though the heavy metals contents in the APC residues were higher than that in bottom ash, more than 80% of As, Cr, Cu, and Ni, 74-94% of Zn, as well as 46-79% of Pb remained in the bottom ash, due to its high mass ratio (85-93%) in the residues. While 47-73% of Cd and 60-100% of Hg were transferred into the APC residues, respectively.     

Comparative analysis of PCDD/Fs in soil around waste incineration plants in China using CALUX bioassay and HRGC/HRMS

In this study, the contamination of soil by PCDD/Fs and other dioxin-like chemicals in the vicinity of Municipal Solid Waste Incinerators (MSWIs) and Hazardous Waste Incinerators (HWIs) is estimated by the XDS-CALUX bioassay. The resulting CALUX-TEQ value is compared with the WHO-TEQ value obtained from HRGC/HRMS analysis, in order to validate the CALUX bioassay as suitable screening method for PCDD/Fs determination of soil samples. The results show that the CALUX-TEQ and the WHO-TEQ values are significantly correlated (R = 0.87). The WHO-TEQ and CALUX-TEQ of soil samples collected from four waste incineration plants in China were in the range from 1.72 to 31.4 pg-TEQ/g and 1.71 to 44.2 pg-TEQ/g respectively, with a mean value of 6.09 pg-TEQ/g and 11.0 pg-TEQ/g. Considering the homologue patterns, a principal component analysis (PCA) and a hierarchical cluster analysis (HCA) of the PCDD/Fs in the soil samples, the emissions of MSWIs and HWIs were probably not the only source of PCDD/Fs.     

Degradation of PCDD/Fs by mechanochemical treatment of fly ash from medical waste incineration

The potential of mechanochemical treatment (MC) to degrade PCDD/Fs contained in fly ash was tested via grounding with and without calcium oxide (CaO) under atmospheric pressure. Three types of fly ash collected from medical waste incineration were compared, originating either from rotary kiln fluidized bed multi-stage incinerator using activated carbon spray (FA1, FA2), or a simple stoker incinerator without activated carbon spray (FA3). In test I: CaO to FA1 mixed at ratio of 6-60% was milled at rotational speed of 350 rpm; in test II: FA2 and FA3 without CaO were milled at rotational speed of 400 rpm. The duration of the tests was 2h. The results from the present study indicate that (1) under two test conditions of with and without CaO, PCDD/Fs contained in real fly ash both can be degraded by mechanochemical treatment, (2) under condition of blending with CaO, the degradation efficiency of PCDD/Fs increased with increasing ratio of CaO, (3) the degradation efficiency of PCDD/Fs may increase with rotational speed increasing and (4) the destruction and dechlorination are major mechanism for PCDD/Fs degradation. These results show that mechanochemical treatment is a high potential technology for PCDD/Fs degradation in fly ash.     

Stabilization of heavy metals in municipal solid waste incineration ash using mixed ferrous/ferric sulfate solution

The purpose of this study is to test the effectiveness of mixing FeSO4 and Fe2(SO4)(3) solutions with municipal solid waste incineration (MSWI) ash at room temperature to prevent heavy metals in treated ash from being dissolved. After conducting toxicity characteristic leaching procedure (TCLP) tests nine times, the accumulation of extracted lead from treated scrubber ash was lower than regulated limits by the sixth test. X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive spectrometer (SEM/EDS) studies of the ash revealed that the mixed solution reacted with the scrubber ash to form Ca4Fe9O17, which coated the surface of ash particles.     

Leaching behavior of heavy metals from municipal solid wastes incineration (MSWI) fly ash used in concrete

The characteristics of municipal solid waste incineration (MSWI) fly ash, surface leaching toxicity and successive leaching concentration of heavy metals from MSWI fly ash-cement hardened pastes were studied. And, the relationships between leaching concentrations of heavy metals and leaching time were also discussed. Experimental results showed that immobilization effect of cement on MSWI fly ash is good. Even if MSWI fly ash-cement hardened pastes were damaged, the leaching toxicity is still in a safety range. In early leaching stage, the surface leaching rate is relatively a little high, up to 10(-5)-10(-4)cmd(-1) order of magnitude, in the later time of leaching, its rate rapidly declined, down to 10(-7). Most of leached heavy metals are produced at early ages. The leaching concentration of heavy metals and leaching time has strong positive relationships. In factual utilizing circumstances, heavy metals' leaching from MSWI fly ash-cement hardened pastes is a very slow and gradually diluting process. The leaching toxicity of heavy metals is far lower than that of the National Standard of China, and minimum harmful matters can be contained and released in the environment. Reusing of MSWI fly ash as partial replacement for cement in concrete mixes is potentially feasible.     

Characteristics and mobility of heavy metals in an MSW landfill: implications in risk assessment and reclamation

To assess the reclamation feasibility of a landfill, the characteristics, distribution, and mobility of heavy metals in the landfill were investigated. The refuse was characterized as containing high concentrations of heavy metals, a relatively high pH, and a high ratio of NH(4)-N to total nitrogen (TN). The results of heavy metal distribution showed that relatively high levels of heavy metals were accumulated in the landfill. Sequential extraction revealed that the relative amounts of heavy metals were different in the samples. Zn demonstrated the greatest mobility compared to other heavy metals, whereas Cd was well retained in the landfill. Leaching experiments indicated that the mobility of heavy metals in the landfill was generally low under normal neutral conditions. However, release of heavy metals can be increased greatly when medium conditions become more acidic and aerobic.     

Electrodialytic removal of heavy metals from municipal solid waste incineration fly ash using ammonium citrate as assisting agent

Electrodialytic remediation, an electrochemically assisted separation method, has previously shown potential for removal of heavy metals from municipal solid waste incineration (MSWI) fly ashes. In this work electrodialytic remediation of MSWI fly ash using ammonium citrate as assisting agent was studied, and the results were compared with traditional batch extraction experiments. The application of electric current was found to increase the heavy metal release significantly compared to batch extraction experiments at comparable conditions (same liquid-to-solid ratio, same assisting agent, and same extraction time). Up to 86% Cd, 20% Pb, 62% Zn, 81% Cu and 44% Cr was removed from 75 g of MSWI fly ash in electrodialytic remediation experiments using ammonium citrate as assisting agent. The time range for the experiments varied between 5 and 70 days.     

Effect of heavy metals on the biodegradation of dibenzofuran in liquid medium

The effect of heavy metals on the degradation of dibenzofuran by Sphingomonas wittichii RW1 was determined in liquid cultures. The results showed that 10mg/L cadmium, mercury and copper not only affected the growth of RW1 with dibenzofuran but also the ability of resting cells to degrade this compound. Growth and degradation were strongly inhibited by mercury, even at 1mg/L, while the inhibitory effect of cadmium and copper at the same concentration or at 5mg/L were negligible. In contrast, arsenic and lead did not affect degradation or growth, even at very high concentrations of 100mg/L. Subsequent analyses additionally revealed that concentrations of arsenic and lead remained unchanged following incubation, while those of cadmium, mercury and copper decreased significantly.     

Distribution of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/Fs) and dioxin-like polychlorinated biphenyls (dioxin-like PCBs) in the soil in a typical area of eastern China

The distribution and concentrations of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dioxin-like PCBs, also called co-PCBs) in a typical area of eastern China were evaluated by analysis of 21 soil and 6 sediment samples. The range of WHO-TEQ values for the PCDD/Fs and dioxin-like PCBs in 17 soil samples representing the background investigation in the study area was 0.017-5.04 pg g(-1) (dry weight, dw), with a mean value 0.967(+/-1.361)pg g(-1) and medium value 0.348 pg g(-1), which indicates that the levels of PCDD/Fs and dioxin-like PCBs over the major part of this district were low. However, the WHO-TEQ values (6.52-16.7 pg g(-1) dw) for PCDD/Fs and dioxin-like PCBs in soil samples to the leeward of a known contaminated disassembly industrial park were much higher than that of the background investigation, and the levels of sediment samples downstream of this area were in the range 2.25-34.6 pg g(-1) (dw). The levels of WHO-TEQ in soil and sediment samples decreased with an increase in distance from the researched pollution source. The principal component analysis demonstrated that the PCDD/Fs and dioxin-like PCBs in major part of contaminated sediment and soil samples derived from the correlative matrix. Yet the different distribution patterns of them in part of sediment samples strongly indicate that other potential sources may be exist, further researches should be done to get more information about the sources and the distributions of the PCDD/Fs and PCBs.     

地聚合物固化/稳定化重金属的影响因素及作用机制

地聚合物是指采用天然矿物或固体废弃物及人工硅铝化合物为原料,在碱性条件下通过矿物缩聚而形成的三维网状聚合胶凝材料。地聚合物独特的结构与性质使其在固化/稳定化重金属方面具有明显优势,近年来已成为国内外研究热点。针对地聚合物固化/稳定化重金属,重点阐述了影响地聚合物固化/稳定化重金属效果的重要因素,并综述了国内外研究者对地聚合物固化/稳定化重金属作用机制的研究成果。     

Effect of solids concentration on removal of heavy metals from mine tailings via bioleaching

Mining of mineral ore and disposal of resulting waste tailings pose a significant risk to the surrounding environment. The objective of this work is to demonstrate the feasibility to remove heavy metals from mine tailings with the use of bioleaching and meanwhile to investigate the effect of solids concentration on removal of heavy metals from mine tailings by indigenous sulfur-oxidizing bacteria and the transformation of heavy metal forms after the bioleaching process. This work showed the laboratory results of bioleaching experiments on Pb-Zn-Cu mine tailings. The results showed that 98.08% Zn, 96.44% Cu, and 43.52% Pb could be removed from mine tailings by the bioleaching experiment after 13 days at 1% (w/v) solids concentration and the rates of pH reduction, ORP rise and sulfate production were reduced with the increase of solids concentration, due to the buffering capacity of mine tailing solids. The results also indicated that solid concentration 1% was found to be best to bacterial activity and metal solubilization of the five solids concentration tested (1%, 2%, 5%, 8% and 10%) under the chosen experimental conditions. In addition, the bioleaching had a significant impact on changes in partitioning of heavy metals.     

Patterns and sources of PCDD/Fs and dioxin-like PCBs in surface sediments from the East River, China

The contamination status of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (DL-PCBs) was preliminarily investigated in surface sediments collected from the East River during April 2007. The contamination levels of PCDD/Fs and DL-PCBs ranged from 2.1 to 9.8 with mean concentration of 4.5 pg WHO₉₈-TEQ g⁻¹ and ranged from 0.042 to 0.45 with mean concentration of 0.19 pg WHO₉₈-TEQ g⁻¹, respectively. All sediments were characterized by the elevated levels of PCDDs, especially OCDD. Higher concentrations of PCDD/Fs were found in the sediments from Guangzhou and Dongguan. Source analysis revealed that PCDD/Fs in the sediments from Guangzhou were mainly from the secondary copper smelters and steel-making plants, and PCDD/Fs in the sediment from Dongguan were mainly from MSWIs. PCP and paper mills were unlikely to be the main sources.     

Effect of heavy metals and water content on the strength of magnesium phosphate cements

In this paper the mechanical properties of magnesium potassium phosphate cements used for the Stabilization/Solidification (S/S) of galvanic wastes were investigated. Surrogate wastes (metal nitrate dissolutions) were employed containing Cd, Cr(III), Cu, Ni, Pb or Zn at a concentration of 25 g dm⁻³ and different water-to-solid (W/S) ratios (0.3, 0.4, 0.5 and 0.6 dm³ kg⁻¹) have been employed. Cements were prepared by mixing hard burned magnesia of about 70% purity with potassium dihydrogen phosphate. Compressive strength and tensile strength of specimens were determined. In addition the volume of permeable voids was measured. It was found that when comparing pastes that the volume of permeable voids increases and mechanical strength decreases with the increase of water-to-solid ratio (W/S). Nevertheless pastes with the same material proportions containing different metals show different mechanical strength values. The hydration products were analyzed by XRD. With the increase of water content not previously reported hydration compound was detected: bobierrite.