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Oxygen blown high-temperature gasification constitutes an opportunity for chemical recycling of plastic wastes. This article summarizes the results from comparative tests of combustion and gasification of two complex plastic wastes: a plastic reject (PR) from processing recycled paper and an automotive shredder residue (ASR). Calculated gasification efficiencies corresponded to about 80% and 60%, respectively. Gasification resulted in lower yields of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) compared to direct combustion. A two-stage process, including gasification followed by syngas combustion, reduced the emissions of HCl and PCDD/F in the flue gas to <1.4% and <0.2%, respectively, compared to the levels from direct combustion of the PR feedstock. Most of the PCDD/F (>99%) was captured along with particulate matter (soot) during gasification. The contribution to the toxic concentration of PCDD/F was mainly from the PCDF congeners. Fly ash particulate matter from ASR combustion contained a significant proportion of zinc, which thus constitutes a great potential for use in zinc recycling., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Studies show that nanoscale zero-valent iron (nZVI) particles enhance the formation of chlorinated compounds such as polychlorinated dioxins and furans (PCDD/Fs) during thermal processes. However, it is unclear whether nZVI acts as a catalyst for the formation of these compounds or contains impurities, such as PCDD/Fs, within its structure. We analyzed the presence of PCDD/Fs in nZVI particles synthesized through various production methods to elucidate this uncertainty. None of the 2,3,7,8-substituted congeners were found in the commercially-produced nZVI, but they were present in the laboratory-synthesized nZVI produced through the borohydride method, particularly in particles synthesized from iron (III) chloride rather than from iron sulfate. Total PCDD/F WHO-TEQ concentrations of up to 35 pg/g were observed in nZVI particles, with hepta- and octa-chlorinated congeners being the most abundant. The reagents used in the borohydride method were also analyzed, and our findings suggest that FeCl 3 effectively contains PCDD/Fs at concentrations that could explain the concentrations observed in the nZVI product. Both FeCl 3 and nZVI showed a similar PCDD/F patterns with slight differences. These results suggest that PCDD/Fs might transfer from FeCl 3 to nZVI during the production method, and thus, care should be taken when employing certain nZVI for environmental remediation., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The emissions of polybrominated diphenyl ethers (PBDEs), polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) and their chlorinated analogues (PCDD/Fs) during the thermal treatment of a high impact polystyrene (HIPS) TV casing were investigated. The halogenated compounds were analyzed in the original material and in the gases emitted during its treatment at temperatures between 50 °C and 250 °C. DecaBDE was the primary PBDE in the TV casing, which also contained high levels of PBDFs (ppm range). At the lower treatment temperatures, non-modified PBDEs evaporated from the samples. Conversely, at 200 °C or above, debromination reactions led to the formation of additional tri- through nonaBDE. The formation of new PBDD/Fs was also detected in the gas phase when the plastic was heated to 200 °C or 250 °C, with higher yields of furans than dioxins. This appreciably increased the toxic equivalent (TEQ) levels of the gas phase relative to those seen in the untreated sample. In all cases, the levels and TEQ contributions from PCDD/Fs were negligible compared to those for brominated analogues., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

This case study investigated PCDF and PCDD emissions from a 65 MW waste-to-energy plant to identify why an air pollution control system remodeling to accommodate increased production resulted in increased TEQ concentrations. Pre- and post-filter gases were collected simultaneously in four sample sets with varying filter temperatures and with/without activated carbon injection. Samples were analyzed to determine total PCDF and PCDD concentrations, as well as homologue profiles, and concentrations of individual congeners (some remained co-eluted). The total post filter PCDD concentrations where found to increase while the concentrations of PCDF and 2,3,7,8-substituted congeners declined. An investigation of the individual congener concentrations revealed that the increase of PCDD concentrations were due to a few congeners, suggesting a single formation route. The study also concludes that vital information about the formation could be obtained by not restricting the analysis to just the 2,3,7,8-substituted congeners., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The use of waste wood as an energy carrier has increased during the last decade. However, the higher levels of alkali metals and chlorine in waste wood compared to virgin biomass can promote the formation of deposits and organic pollutants. Here, the effect of fuel composition and the inhibitory effects of ammonium sulfate, (NH4)2SO4, on the concentrations of persistent organic pollutants (POPs) in the flue gas of a lab-scale combustor was investigated. Ammonium sulfate is often used as a corrosion-preventing additive and may also inhibit formation of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). In addition to PCDDs and PCDFs, polychlorinated naphthalenes (PCN) and biphenyls (PCB) were also analyzed. It was found that the flue gas composition changed dramatically when (NH4)2SO4 was added: CO, SO2, and NH3 levels increased, while those of HCl decreased to almost zero. However, the additive's effects on POP formation were less pronounced. When (NH4)2SO4 was added to give an S:Cl ratio of 3, only the PCDF concentration was reduced, indicating that this ratio was not sufficient to achieve a general reduction in POP emissions. Conversely, at an S:Cl ratio of 6, significant reductions in the WHO-TEQ value and the PCDD and PCDF contents of the flue gas were observed. The effect on the PCDF concentration was especially pronounced. PCN formation seemed to be promoted by the elevated CO concentrations caused by adding (NH4)2SO4., (Copyright © 2013. Published by Elsevier Ltd.)

This study investigated the degradation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in contaminated soil using low temperature treatment (200-280°C) both alone and in combination with nanosized zerovalent iron (nZVI) particles or CaO. Control soil samples and soil fortified with nZVI particles or CaO were treated at 200 and 250°C in sealed glass ampoules. Treatment of the ampouled samples at 250°C was more effective than treatment at 200°C and the reduction in PCDD/F concentration was greatest when soil was treated at 250°C with nZVI addition (indeed, treatment at 200°C in the absence of nZVI resulted in increases in total PCDD and PCDD/F concentrations). In larger-scale experiments based on the obtained results, using a rotary furnace, the greatest reduction in total PCDD/F concentration was achieved by treating soil at 280°C, and adding nZVI to the soil resulted in almost no detectable PCDD/F in the gas phase., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

In a laboratory-scale combustion reactor, flue-gas samples were collected at two temperatures in the post-combustion zone, 700°C and 400°C, using two different water-cooled sampling probes. The probes were the cooled probe described in the European Standard method EN-1948:1, referred to as the original probe, and a modified probe that contained a salt/ice mixture to assist the cooling, referred to as the sub-zero probe. To determine the efficiency of the cooling probes, internal temperature measurements were recorded at 5cm intervals inside the probes. Flue-gas samples were analyzed for polychlorinated dibenzo-p-dioxin and dibenzofurans (PCDD/Fs). Samples collected at 700°C using the original cooling probe showed higher concentrations of PCDD/Fs compared to samples collected using the sub-zero probe. No significant differences were observed between samples collected at 400°C. The results indicated that artifact formation of PCDD/Fs readily occurs during flue-gas sampling at high temperatures if the cooling within the probe is insufficient, as found for the original probe at 700°C. It was also shown that this problem could be alleviated by using probes with an enhanced cooling capacity, such as the sub-zero probe. Although this may not affect samples collected for regulatory purposes in exit gases, it is of great importance for research conducted in the high-temperature region of the post-combustion zone., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) content of three fly ash samples with different elemental compositions from different municipal waste incinerators were analyzed before and after thermal treatment at 300 °C or 500 °C. Gas phase emissions during the treatments were also collected and analyzed. Substantial reductions in the total PCCD/F content of the ashes were observed after treatment at 500 °C, seemingly due to degradation rather than dechlorination. Treatment at 300 °C resulted in an increase in the PCDD/F content of the three ashes. Initial concentration of PCDD/F in the untreated ashes did not reflect the outcome of the treatment at the different temperatures. In addition, the composition of the ash was found to influence the rate of decomposition and formation of PCDD and PCDF during thermal treatment; the results showed that Cu, Fe, Ca and S play important roles in these processes., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

We have estimated the concentration and distribution of the mono to octa-chlorinated congeners of polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) in fly ashes at various sampling points in a large-scale municipal solid waste incinerator at Umeå, Sweden, as they cooled from 700 to 170 degrees C. Differences between the ashes were observed, the PCDD homologue profile was found to vary with temperature. The total amount of PCDD and PCDF increased as the temperature decreased in the postcombustion zone. The increase was due to both adsorption to the fly ash and formation of PCDD and PCDF. Mono-to trichlorinated PCDD predominated at high temperatures, whereas hepta- and octachlorinated PCDD predominated at temperatures below 400 degrees C. PCDF predominated over PCDD in the whole temperature range. However,the changes in homologue profile for PCDFwere minor. The isomer distribution within the homologue groups was not changed asthetemperature decreased in the postcombustion zone.

A thermal degradation procedure for reducing the concentrations of mono- to octa-chlorinated PCDD/Fs, PCBs and hexa-chlorobenzenes (HCB) in filter ash from incinerated municipal solid waste (MSW) is described. Thermal treatment of filter ash samples at 500 degrees C for 60 min in a closed system providing low oxygen conditions resulted in 97% and 99% reductions in the total and I-TEQ concentrations of PCDD/Fs, to 6.8 microg kg(-1) ash and <0.05 microg I-TEQ kg(-1) ash, respectively. Increasing the thermal treatment time to 480 min, at the same temperature, yielded 99% reductions in both total and I-TEQ concentrations of the mono- to octa-chlorinated PCDD/Fs. Similar effects were observed for HCB and PCBs. The data from this study indicate that PCDD/Fs and other toxic organic compounds in ash from incinerated MSW, can be effectively degraded by this procedure, which combines relatively low-temperatures, short treatment times, and low oxygen conditions.

Due to their high concentrations of toxic organic compounds such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F), metals, and water-soluble salts, fly ashes are classified as hazardous waste in the European Union and are required to be deposited in controlled landfills. We have shown here that the tetra- to octachlorinated PCDD/F in fly ash can be degraded by thermal treatment. The temperature needed for total degradation of PCDD/F depends on the composition of the fly ash. Its concentrations of unburned carbon and alkaline compounds were found to be important in this respect. Experimental design was used to investigate the effects of varying the temperature, residence time, and atmosphere on the degradation of PCDD/F in three different types of fly ash. The results showed that the three ashes clearly showed different degradation potentials for PCDD/F during thermal treatment. The concentrations of unburned carbon, alkaline species such as CaO and Na2O, and metals such as copper and iron strongly influenced the degradation of PCDD/F. However, the different combinations of pH and amounts of native PCDD/F, unburned carbon, metals (Cu, Fe, Sn and Na), and sulfur in the ashes made it difficult or even impossible to conclude that any single parameter was responsible for the degradation of PCDD/F in these thermal treatment experiments. The decreases observed in all of the experiments are due to dechlorination and/or destruction of PCDD/F: depending on the temperature and ash composition, either of these processes may be the more important.