Stina Jansson

Formation and chlorination of polychlorinated naphthalenes (PCNs) in the post-combustion zone during MSW combustion

Non- to octa-chlorinated naphthalenes (PCNs) were analyzed in flue gas samples collected simultaneously at three different temperatures (450 degrees C, 300 degrees C and 200 degrees C, respectively) in the post-combustion zone during waste combustion experiments using a laboratory-scale fluidized-bed reactor. PCN homologue profiles in all samples were dominated by the lower chlorinated homologues (mono- to triCN), with successive reductions in abundance with each additional degree of chlorination. The isomer distribution patterns reflected ortho-directionality behavior of the first chlorine substituent, and the beta-positions, i.e. the 2,3,6,7-substitution sites, seemed to be favored for chlorination. Injection of naphthalene into the post-combustion zone resulted in increased PCN levels at 200 degrees C, demonstrating the occurrence of chlorination reactions in the post-combustion zone. However, the increases were restricted to the least-chlorinated homologue (monoCN), probably because there was insufficient residence time for further chlorination. In addition, an episode of poor combustion (manifested by high CO levels) was accompanied by extensive formation of 1,8-diCN, 1,2,3- and 1,2,8-triCN; congeners with substitution patterns that are not thermodynamically favorable. These are believed to be products of PAH breakdown reactions and/or chlorophenol condensation. Overall, PCN formation is likely to occur via more than one pathway, including chlorination of naphthalene that is already present, de novo synthesis from PAHs and, possibly, chlorophenol condensation.

Atmospheric deposition, retention, and stream export of dioxins and PCBs in a pristine boreal catchment

The mass-balance between diffuse atmospheric deposition of organic pollutants, amount of pollutants retained by the terrestrial environment, and levels of pollutants released to surface stream waters was studied in a pristine northern boreal catchment. This was done by comparing the input of atmospheric deposition of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) and PCBs with the amounts exported to surface waters. Two types of deposition samplers were used, equipped with a glass fibre thimble and an Amberlite sampler respectively. The measured fluxes showed clear seasonality, with most of the input and export occurring during winter and spring flood, respectively. The mass balance calculations indicates that the boreal landscape is an effective sink for PCDD/Fs and PCBs, as 96.0-99.9 % of received bulk deposition was retained, suggesting that organic pollutants will continue to impact stream water in the region for an extended period of time.

Reduction of PCDD, PCDF and PCB during co-combustion of biomass with waste products from pulp and paper industry.

The use of waste wood as an energy carrier has increased during the last decade. However, elevated levels of alkali metals and chlorine in waste wood compared to virgin biomass can cause increased deposit formation and higher concentrations of organic pollutants. In this study, we investigated the effect of the ChlorOut technique on concentrations of organic pollutants. Ammonium sulfate was injected into the combustion system to inhibit formation of KCl (which causes deposits) and persistent organic pollutants, namely polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and biphenyls (PCBs). The results showed that concentrations of the toxic congeners of PCDD, PCDF and PCB decreased in the presence of ammonium sulfate.

Post-combustion formation of PCDD, PCDF, PCBz, and PCPh in a laboratory-scale reactor: influence of dibenzo-p-dioxin injection.

Formation of polychlorinated dibenzo-p-dioxins (PCDD), dibenzofurans (PCDF), benzenes (PCBz), and phenols (PCPh) was studied during combustion of an artificial municipal solid waste (MSW) in a laboratory-scale fluidized-bed reactor with simultaneous collection of flue gas samples at three different temperatures in the post-combustion zone (450 degrees C, 300 degrees C, and 200 degrees C). PCDF, PCBz, and PCPh were predominantly formed at or above the first sampling point (450 degrees C) with a dominance of the lower chlorinated homologues. PCDDs, on the other hand, were dominated by the intermediately chlorinated homologues with concentrations peaking at 300 degrees C. The dominating PCPh congeners clearly displayed the ortho-para directionality, which is indicative of electrophilic aromatic substitution, as did the PCBz isomer distribution patterns to some extent. Comparison of the observed PCBz isomer distribution patterns to prior work may indicate coupling of aliphatic species in chlorobenzene formation. The PCDDs seemed to be largely influenced by chlorophenol condensation reactions and to some extent chlorination reactions, while the PCDFs displayed a chlorination-oriented pattern for the mono- to tri-chlorinated homologues and a PCPh condensation pattern for the higher chlorinated homologues. Injection of non-chlorinated dibenzo-p-dioxin at 650 degrees C resulted in increased formation of Tri-HxCDD and a decrease in the dibenzofuran levels. The affected PCDD and PCDF congeners were not products expected to form from chlorine substitution, but instead are well known chlorophenol condensation products.

Relationships between congener distribution patterns of PCDDs, PCDFs, PCNs, PCBs, PCBzs and PCPhs formed during flue gas cooling.

The congener patterns of mono- to octa-chlorinated dibenzo-p-dioxins (PC(1-8)DD), dibenzofurans (PC(1-8)DF), naphthalenes (PC(1-8)N), mono- to deca-chlorinated biphenyls (PC(1-10)B), di- to hexa-chlorinated benzenes (PC(2-6)Bz) and mono- to penta-chlorinated phenols (PC(1-5)Ph) in flue gas samples collected simultaneously at 450°C, 300°C and 200°C in the post-combustion zone during waste incineration in a laboratory-scale reactor in a previous study, were in this study evaluated using principal component analysis (PCA). To our knowledge this is the most comprehensive chemical and multivariate analysis to date of the thermal formation of dioxins. The PCA indicated that different formation pathways occur in the temperature regions 450-300°C and 300-200°C, and reflected a chlorination effect of PCDF and PCDD between 450°C and 200°C which could not be discerned or was less pronounced for the other compound groups. Toxic equivalents (TEQs) of PCDDs, PCDFs and PCBs, as well as total TEQ values (TEQ(Total)) were also calculated, and correlations between changes in levels of specific congeners and the TEQs were explored in the PCA. Levels of four HxCDF congeners and 1,2,3,4,8-, 1,2,3,7,8-PeCDF and 2,3,4,7,8-PeCDF showed the strongest correlations with TEQ(Total) (R(2)≥0.9). In addition, levels of 1,2,4-TriCBz correlated strongly with TEQ(Total) (R(2)>0.7), supporting previous reports that it may be a potential indicator of the TEQ.

The effects of fuel composition and ammonium sulfate addition on PCDD, PCDF, PCN and PCB concentrations during the combustion of biomass and paper production residuals

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 additives 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.

Assessment of chemical and material contamination in waste wood fuels - A case study ranging over nine years

The increased demand for waste wood (WW) as fuel in Swedish co-combustion facilities during the last years has increased the import of this material. Each country has different laws governing the use of chemicals and therefore the composition of the fuel will likely change when combining WW from different origins. To cope with this, enhanced knowledge is needed on WW composition and the performance of pre-treatment techniques for reduction of its contaminants. In this study, the chemical and physical characteristics of 500 WW samples collected at a co-combustion facility in Sweden between 2004 and 2013 were investigated to determine the variation of contaminant content over time. Multivariate data analysis was used for the interpretation of the data. The concentrations of all the studied contaminants varied widely between sampling occasions, demonstrating the highly variable composition of WW fuels. The efficiency of sieving as a pre-treatment measure to reduce the levels of contaminants was not sufficient, revealing that sieving should be used in combination with other pre-treatment methods. The results from this case study provide knowledge on waste wood composition that may benefit its management. This knowledge can be applied for selection of the most suitable pre-treatments to obtain high quality sustainable WW fuels.

Persistent Organic Pollutants in Streamwater: Influence of Hydrological Conditions and Landscape Type

Concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), and hexachlorobenzene (HCB) in streamwater were measured in a remote catchment in northern Sweden and downstream to the Baltic Sea. Sampling took place at seven sites during two years and under different hydrological conditions: during the snow-free, snow-covered, and spring-flood seasons. Concentrations varied substantially between seasons and were up to 20 times higher during the spring flood compared to the preceding snow-covered period. The increase in concentrations with runoff was due to higher levels of particle-associated contaminants, while the dissolved concentrations remained stable. Particulate-contaminant concentrations were positively correlated primarily to suspended particulate matter (SPM) at sites in areas with a high land-cover fraction of sorted sediment. When upstream sampling locations were compared, a mire-dominated stream had higher concentrations and a lower retention of atmospherically deposited contaminants than a forest stream of the same catchment size. Contaminant concentrations (normalized to volume) did not increase consistently downstream despite the presence of several point sources. However, when normalized to the amount of SPM, concentrations were on average >20 times higher at the outlet in the Baltic Sea compared to the outlet from the remote catchment without point sources.

PCDDs, PCDFs and PCNs in products of microwave-assisted pyrolysis of woody biomass – Distribution among solid, liquid and gaseous phases and effects of material composition

Microwave-assisted pyrolysis (MAP) of lignocellulosic biomass is a technique that could potentially be used to produce and upgrade renewable energy carriers. However, there is no available information about the formation of dioxins and other organic pollutants in MAP treatment of woody biomass. In this study, MAP experiments were conducted in lab-scale using virgin softwood, bark, and impregnated wood as feedstocks. The non-condensable gas, liquid (fractionated into aqueous and oil phases), and char fractions generated during pyrolysis were collected and analysed for polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and naphthalenes (PCNs). The concentrations of PCDDs, PCDFs and PCNs in the pyrolysis products ranged from 0.52 to 43.7 ng kg(-1). All investigated compound groups were most abundant in the oil fraction, accounting for up to 68% (w/w) of the total concentrations. The highest PCDD, PCDF and PCN concentrations were found from the pyrolysis of bark, which has relatively high contents of chlorine and mineral matter, followed by impregnated wood, which contains organic and metal-based preservatives. The homologue profiles of all three compound groups were dominated by the less chlorinated homologues. The homologue abundance decreased as the degree of chlorination increased. This trend was observed for all three feedstocks.

Effects of regional differences in waste composition on the thermal formation of polychlorinated aromatics during incineration.

Two artificial wastes (A and B) whose contents reflect regional differences in municipal solid waste composition, were used to investigate the thermal formation of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs), and naphthalenes (PCNs) during incineration. Flue gas samples were simultaneously collected at three ports in the post-combustion zone corresponding to flue gas temperatures of 400, 300, and 200 °C. The combustion of Waste B, which had a higher chlorine and metal content than Waste A, produced greater levels of highly-chlorinated homologues, as demonstrated by a higher degree of chlorination. The total concentrations of PCDDs, PCDFs, PCBs, and PCNs formed in the combustion of both wastes increased as temperature decreased along the convector. There were no significant differences in total concentrations between Waste A and Waste B combustion at specific temperatures, with exception of PCDFs at 400 °C. Orthogonal Projections to Latent Structures Discriminant Analysis (OPLS-DA) modeling, used to evaluate the data for all compound groups, suggest that during flue gas quenching at temperatures of 400 °C low-chlorinated homologues are preferentially formed in the presence of copper, which is known to be a very active catalyst for this process. At 300 and 200 °C, the formation of highly-chlorinated homologues is favored.