Unintentional formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) is observed and investigated during the thermal desorption in an airflow of a sandy soil, doped artificially with either 1,2-dichlorobenzene (1,2-DiCBz) or hexachlorobenzene (HCBz) using a lab-scale experimental set-up. At all temperatures investigated (200, 250, 300, 350 and 400 °C), this thermal treatment creates significant amounts of PCDD, PCDF and polychlorinated biphenyls (PCB), starting from 1,2-DiCBz. The highest yield of PCDD/F formed from 1,2-DiCBz occurs at 250 °C, with a total (gas + residual soil) output of 117 and 166 pg/g PCDD and PCDF, respectively. Most output reports to the gas phase and the PCDD/F signature is significantly different for residue and gas phase. Also PCB are formed, at a scale of 224 ng/g (300 °C). Compared with 1,2-DiCBz, HCBz converts into PCDD/F even more actively at 350 and 400 °C: the total PCDD/F output created attains 967 pg/g PCDD and 465 pg/g PCDF at 350 °C. As a precursor, 1,2-DiCBz favours formation of PCDF, while PCDD predominates, when the HCBz contaminated soil is treated.

•PCDD/F isomer signature from 11 catalytic systems at 3 atmospheric conditions.•PCDD/F-formation pathway varies when catalysed by distinct catalysts.•CP-route congeners are supported more by metal chlorides than by oxides.•Oxygen affects isomers differently, depending on the catalytic system studied.A recent paper presented the results from de novo tests, involving 11 distinct catalytic systems (oxides and chlorides of Cd, Cr, Cu, Ni, and Zn, as well as a blank sample). Their PCDD and PCDF formation activity was shown. This paper further assesses their isomer signature, with special emphasis on those congeners associated with chlorophenol precursor routes, and on 2,3,7,8- and 1,9-substituted congeners. Each metal catalyst generates a significantly different signature, also affected by the presence or absence of oxygen in the reaction atmosphere. Oxide and chloride catalysts supply distinctive signatures, suggesting singly weighted pathways. Quite a large number of data was handled, so that throughout this analysis special attention was given to testing and developing an appropriate methodology, allowing appropriate correlation analysis and statistical data treatment. The large tables resulting relate to the 11 catalytic systems, studied at 3 levels of oxygen concentration, with 94 PCDD/F-congeners considered individually. They constitute an extensive reference data bank for confronting novel experimental data with this vast data set.

•Dry reforming of methanol was investigated for the first time.•A novel rotating gliding arc (RGA) reactor was used for this process.•Syngas production and high-efficiency CO2 conversion can be obtained in one step.•Reaction mechanisms of the plasma assisted process have been discussed.•This RGA plasma assisted process showed a significantly high efficiency.Herein, the CO2 reforming of methanol, or can be called dry reforming of methanol (DRM), was investigated for the first time using a rotating gliding arc plasma. The effect of input CH3OH concentration on the reaction performance of the DRM process has been investigated. Optical emission spectroscopy (OES) has been used to give insights into the formation of reactive species in the plasma chemical reactions. In addition, the possible reaction mechanisms of the plasma DRM process have been discussed. The plasma assisted DRM has been demonstrated to be a promising route for clean syngas production and high-efficiency CO2 conversion. This process provided a significantly higher efficiency for CO2 conversion compared to other plasma technologies, while maintaining a CO2 flow rate (or processing capacity) of one or several orders of magnitude higher.Download full-size image

This study combines a preliminary mechanochemical treatment and a subsequent thermal desorption for remediating soil, contaminated with polychlorinated biphenyls (PCBs). After 2 hours of grinding, assisted by addition of SiO2, the total concentration of PCBs and their TEQ-value decreased by 81.9% and 85.4%, respectively. The effect of thermal treatment at 400, 500 and 600 °C on the removal efficiency of PCBs from ground soil was then investigated. The residual amount of PCBs reduced with the rising temperature and dropped to 137 ng g−1 in the treated soil when the treatment temperature reached 600 °C, equivalent to a desorption efficiency of 99.85% and a removal efficiency of nearly 100%. The formation of polychlorinated dioxins and dibenzofurans (PCDD/Fs) was also monitored: PCDDs and PCDFs were generated, particularly at 400 °C, however their formation weakened at higher temperatures and hydrodechlorination dominated.

Biomass combustion originating both from human activities and behaviour and from natural causes, has caused considerable concern as a result of the numerous pollutants emitted into the atmosphere, including polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and polychlorinated biphenyls, or in brief dioxins. The contribution of dioxins emissions from biomass combustion becomes more and more important, especially since evident guided emissions—principally from waste incineration and metallurgy—have been curtailed drastically. Different types of biofuels feature different chemical components, including cellulose, lignin, and proteins, and accompanying organic and inorganic compositions, thus showing different characteristics of dioxins generation. Combustion modes, either flaming or smouldering combustion, also show considerable influence on the amounts of dioxins emitted from the system and they may host distinct processes for forming dioxins. Lean in chlorine and catalytic copper, native biomass materials usually produce low emission factors. However, various contaminants are inevitably mixed into biofuels during combustion and significantly promote the dioxins generation. Emission factor data from a wide range of biomass burning sources are collated in the present review, suggesting that dioxins emissions are substantially influenced by the facilities used, their operating conditions and combustion processes, fuel composition, accidental addition of contaminants, etc. Their roles in biomass combustion and dioxins formation pathways, however, remain difficult to quantify, resulting in emission factor values stretching over several orders of magnitude and complicating the efforts to build a comprehensive global estimation of dioxins emissions from biomass burning.

•A novel reactor featuring a rotating gliding arc is used for biogas reforming.•Ni/γ-Al2O3 catalysts with different Ni loadings are prepared and characterized.•Plasma-catalytic reforming of biogas for syngas production is carried out.•A high conversion of CH4 and a moderate selectivity of syngas are achieved using plasma-catalysis.The combination of plasma and heterogeneous catalysis has been considered as an attractive and promising process for the synthesis of fuels and chemicals. In this work, plasma-catalytic reforming of biogas is carried out over Ni/γ-Al2O3 catalysts with different Ni loadings (6 wt.%, 8 wt.% and 10 wt.% Ni) in a novel rotating gliding arc (RGA) plasma reactor. In the plasma reforming of biogas without a catalyst, the CH4 conversion can reach up to 52.6% at a CH4/CO2 molar ratio of 3:7 and a total flow rate of 6 L/min. The combination of the RGA with the Ni/γ-Al2O3 catalysts enhances the performance of the plasma biogas reforming: increasing Ni loading enhances the conversion of CH4 and the maximum CH4 conversion of 58.5% is achieved when placing the 10 wt.% Ni/γ-Al2O3 catalyst in the downstream of the RGA reactor. The presence of the 10 wt.% Ni/γ-Al2O3 catalyst in the RGA reactor also increases the H2 yield by 17.6% compared to the reaction in the absence of a catalyst. A comparison of biogas reforming using different plasma technologies shows that the RGA plasma provides a higher conversion, significantly enhanced processing capacity and reduced energy cost for biogas conversion and syngas production. In addition, compared to biogas reforming using other non-thermal plasmas (e.g. dielectric barrier discharge), the RGA reforming process produces much cleaner gas products in which syngas is the major one.Download high-res image (117KB)Download full-size image

•A completed startup-shutdown procedure has been investigated.•The PCDD/F concentrations increase visibly during startup-shutdown procedure.•De novo synthesis is the major pathway of PCDD/F formation in present study.•Memory effect occurs in BF at the end of startup procedure.•PCDD/Fs in flue gases are dominated in solid phase at BF inlet.Compared with municipal solid waste incineration, studies on the PCDD/F emissions of hazardous waste incineration (HWI) under transient conditions are rather few. This study investigates the PCDD/F emission level, congener profile and removal efficiency recorded during startup and shutdown by collecting flue gas samples at the bag filter inlet and outlet and at the stack. The PCDD/F concentration measured in the stack gas during startup and shutdown were 0.56–4.16 ng I-TEQ Nm−3 and 1.09–3.36 ng I-TEQ Nm−3, respectively, far exceeding the present codes in China. The total amount of PCDD/F emissions, resulting from three shutdown-startup cycles of this HWI-unit is almost equal to that generated during one year under normal operating conditions. Upstream the filter, the PCDD/F in the flue gas is mainly in the particle phase; however, after being filtered PCDD/F prevails in the gas phase. The PCDD/F fraction in the gas phase even exceeds 98% after passing through the alkaline scrubber. Especially higher chlorinated PCDD/F accumulate on inner walls of filters and ducts during these startup periods and could be released again during normal operation, significantly increasing PCDD/F emissions.

The combination of mechanochemical method and thermal desorption for remediating polychlorinated biphenyls (PCBs) in contaminated soil was tested in this study. The effects of grinding time and heating time on PCB removal efficiency were investigated. The contaminated soil, mixed with CaO powder at a weight ratio of 1:1, was first ground using a planetary ball mill. After 4 h of grinding, the total PCB concentration and its toxic equivalence quantity (TEQ) decreased by 74.6 and 75.8%, respectively. Then, after being heated at 500 °C for 60 min, the residual PCBs in mechanochemical + thermal treated soil decreased to 247 ng/g, resulting in a removal efficiency of 99.95%. The removal effect can be promoted by longer grinding time and heating time; however, increased energy consumption was inevitable. The combination of grinding time and heating time should be optimized in a practical remediation process.

Thermal treatment of polychlorinated biphenyls (PCB) contaminated soil was shown in earlier work to generate polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF). In this study, the PCDD/F were studied arising during the remediation of p,p′-DDT contaminated soil by thermal desorption. Three kinds of soil (sandy, clayey and lateritic soil) were tested to investigate the effect of soil texture on PCDD/F formation. Those soils were artificially polluted with p,p′-DDT, obtaining a concentration level of 100 mg/kg. Thermal desorption experiments were conducted for 10 min at 300 °C in an air atmosphere. The total concentration of PCDD/F generated for three soils were 331, 803 and 865 ng/kg, respectively, and TeCDD and TeCDF were dominant among all PCDD/F congeners. After thermal desorption, the total amount of PCDD/F generated both in soil and in off-gas correlated positively with the amount of DDT added to soil. In addition, a possible pathway of the formation of PCDD/F was presented.

•A rotating gliding arc assisted pyrolysis system was proposed in waste oil conversion.•Dynamic arc behavior and numerical calculation was investigated to characterize arc.•Gas products distribution and solid carbon evolution was investigated in waste oil aerosol conversion.The aerosol gliding arc discharge-assisted pyrolysis was firstly proposed to convert the waste rapeseed oil. The arc motions in pure argon gas and oil mixture discharge were compared at different total flow rate. Calculated by FLUENT software, the average flow velocity distribution along the axis direction was obtained, ranging from 8 m/s at the arc initiated gap to 0.5 m/s at the exit. The distribution of gaseous products was investigated under the effect of applied voltage and pyrolysis temperature, which indicated 74% of waste oil was converted into gaseous products at applied voltage of 10 kV and pyrolysis temperature of 800 °C, respectively. Selectivity of gaseous products (CO, H2 and C2 hydrocarbons) exhibited different sensitivity to variation of operating conditions. Optical images were captured to record the evolution of deposited carbon on copper substrate under different temperatures, while the Raman spectroscopy implied that well-organized graphitized structure was formed at rotating gliding arc regime as well as the copper surface.

Coal-fired power plants are known to release a large quantity of polycyclic aromatic hydrocarbons (PAHs) and particulate matter. Some power plants have been upgraded with flue gas purification equipment to achieve ultralow emission. A coal-fired unit with ultralow emission was selected to investigate the influence of gas purification equipment on the PAH distribution in flue gas. The total concentration of the 16 PAHs at the inlet of the wet flue gas desulfurization (WFGD) system was 6.340 μg/m3, and naphthalene (Nap) was shown to be the major PAH compound. The total concentration of the 16 PAHs at the outlet of the wet electrostatic precipitator (WESP) was 0.870 μg/m3, and the 5-ring and 6-ring PAHs were the major PAH compounds. The WFGD system could partially reduce the concentration of PAHs in the flue gas. The WESP eliminated most of the Nap and a portion of the gas-phase PAHs, whereas the concentrations of some 5-ring and 6-ring PAHs in the particulate phase increased as the flue gas passed through the WESP. Under ultralow-emission conditions, the total toxic equivalent value of PAHs in flue gas at the outlet of WESP was 0.293 μg/m3.

•A rotating gliding arc (RGA) discharge reactor is developed for tar destruction.•The highest destruction efficiency could exceed 95% using toluene as tar surrogate.•The two major gaseous products are hydrogen and acetylene.•The liquid and solid byproducts are collected and determined.Non-thermal plasma is considered as an alternative treatment of tar present in the effluent from gasification processes. In this study, a novel rotating gliding arc (RGA) discharge reactor was developed for tar destruction. Toluene in nitrogen flow was used as a tar surrogate. The physical features of RGA discharge and its application to toluene destruction are investigated at different input concentrations and total gas flow rates. As a result, the highest destruction efficiency could exceed 95%, with a toluene concentration of 10 g/N m3 and a total flow rate of 0.24 N m3/h. The two major gaseous products are H2 and C2H2, with maximum selectivity of 39.35% and 27.0%, respectively. A higher input concentration slightly reduces this destruction efficiency but the energy efficiency further expanded, with a highest value of 16.61 g of toluene eliminated/kW h. In addition, the liquid and solid byproducts are collected downstream of the RGA reactor and determined qualitatively and semi-quantitatively. The amount and structure of these by-products is instructive for reaching a better comprehension of the chemical consequences of plasma treatment to the model compound and to the carrier gas nitrogen.

In this study, hydrogen production from water splitting in N2 using an atmospheric pressure rotating gliding arc plasma was investigated. The effect of input H2O concentration and total flow rate on the performance of the plasma water splitting process (e.g., H2 and O2 yield, H2 production rate, and energy yield of H2) was investigated. N2 showed a pronouncedly facilitating effect on the H2O splitting and H2 production process due to the reactions of the excited N2 species [e.g., electronically excited metastable N2(A)] with the H2O molecules. The maximum H2 production rate reached up to 41.3 μmols−1, which is much higher than that of other typical non-thermal plasmas (e.g., ~0.2 μmols−1 for a dielectric barrier discharge). Optical emission diagnostics has shown that in addition to the NO, N2, and N2+ that were observed in the pure N2 spectra, strong OH and NH emission lines also appeared in the H2O/N2 spectra. OH radical is considered as a key intermediate species that could contribute to the formation of H2, O2, and H2O2. The increase of the H2O concentration could lead to a continuous enhancement of the OH intensity. The rotational temperature of N2+ dropped drastically from 2875 ± 125 to 1725 ± 25 K with the addition of 1 % (mol/mol) H2O into the N2 plasma.

•A rotating gliding arc (RGA) reactor was used for waste rapeseed oil conversion.•Electrical characteristics and dynamic motions in oil discharge were investigated.•Product (gases, liquid, solid carbon) distribution was analyzed to postulate reaction pathways.Rotating gliding arc discharge was used to convert waste rapeseed oil into high value chemical products. Electrical parameters and arc dynamics under different operating conditions were investigated to obtain a visualized understanding of oil-electrochemical conversion in plasma. Gas selectivity and oil conversion exhibited that higher applied voltage promoted syngas production with better energy efficiency. Increasing the waste oil input and N2 flow rate facilitated the generation of total gas phase products, while decreasing the yields of syngas. Liquid products indicated similar composition distribution of alkyl chain structures, while alkanes, cycloalkanes, olefins, and aromatic hydrocarbons were favored under the effects of plasma. The texture and morphology of solid carbon on electrodes were dependent on the applied electrical power and indicated the existence of graphitic structures.

•A DC rotating gliding arc (RGA) reactor was developed for methanol decomposition.•The effect of carrier gas on plasma methanol conversion process was investigated.•The maximum CH3OH conversion of 92.4% and the H2 selectivity of 53.1% were achieved.•Formation of reactive species was detected in the plasma CH3OH conversion process.•RGA CH3OH conversion shows higher energy efficiency compared to other cold plasmas.A direct current rotating gliding arc (RGA) reactor co-driven by a magnetic field and tangential flow has been developed for the non-oxidative decomposition of methanol into hydrogen and other valuable products. The influence of input CH3OH concentration and carrier gas (N2 and Ar) on the reaction performance of the plasma process has been investigated in terms of the conversion of CH3OH, product selectivity, and energy efficiency of the process. The maximum CH3OH conversion of 92.4% and hydrogen selectivity of 53.1% are achieved in the plasma methanol conversion using N2 as a carrier gas. Optical emission diagnostics has shown the formation of a variety of reactive species (e.g., H, OH, CH, CN, N2 and C2) in the plasma decomposition of methanol. The vibrationally and electronically excited species (e.g., N2 (A3Σu+) and Ar*) could be critical in the conversion of CH3OH, leading to a higher CH3OH conversion in the CH3OH/N2 RGA due to the presence of more reaction pathways. Compared to other non-thermal plasmas, the RGA plasma shows a much better process performance, offering a promising and flexible route for hydrogen production.

Porous carbon-based materials are commonly used to remove various organic and inorganic pollutants from gaseous and liquid effluents and products. In this study, the adsorption of dioxins on both activated carbons and multi-walled carbon nanotube was internally compared, via series of bench scale experiments. A laboratory-scale dioxin generator was applied to generate PCDD/Fs with constant concentration (8.3 ng I-TEQ/Nm3). The results confirm that high-chlorinated congeners are more easily adsorbed on both activated carbons and carbon nanotubes than low-chlorinated congeners. Carbon nanotubes also achieved higher adsorption efficiency than activated carbons even though they have smaller BET-surface. Carbon nanotubes reached the total removal efficiency over 86.8 % to be compared with removal efficiencies of only 70.0 and 54.2 % for the two other activated carbons tested. In addition, because of different adsorption mechanisms, the removal efficiencies of carbon nanotubes dropped more slowly with time than was the case for activated carbons. It could be attributed to the abundant mesopores distributed in the surface of carbon nanotubes. They enhanced the pore filled process of dioxin molecules during adsorption. In addition, strong interactions between the two benzene rings of dioxin molecules and the hexagonal arrays of carbon atoms in the surface make carbon nanotubes have bigger adsorption capacity.

In this study, eight fly ash samples and three bottom ash samples from different areas are collected for analysis of their physicochemical properties and emission content of dioxin precursors and metals. Their surface characteristics, their effects on dioxin precursors, and important aspects of the compositions of residual ash (fly ash and bottom ash) are investigated. Poly-chlorobenzenes (PCBzs) in the fly ash of a fluidized bed incinerator (FBI) are 7.35 to 357.94 µg/kg, and in that of a fire grate incinerator (FGI) are 6.74 to 96.52 µg/kg. The concentrations in bottom ash are the same (i.e., 2.23 to 2.99 µg/kg) regardless of the furnace type. The concentrations of polycyclic aromatic hydrocarbons (PAHs) in FGI fly ash samples (0.293 to 1.783 mg/kg) are less than these in samples from FBIs (1.820 to 38.012 mg/kg). Low boiling point PAHs (mainly 2- and 3-ringed PAHs) and high boiling point PCBzs (mainly HxCB and PeCBz) are the major constituents of residual ash. Different distributions of PCBzs and PAHs are mainly dictated by the incineration characteristics of FBI and FGI. Al and Fe, as non-toxic “light metals” are the major constituents of the residual ash, and Ni and Zn as non-toxic heavy metals play important roles in the total heavy metal. Cu, Pb, and Cr are the three major toxic heavy metals. The correlation of the metals and the dioxin precursors is discussed and distinguished.探索中国生活垃圾焚烧残灰中重金属、 氯苯、 多环芳烃等有毒成分的排放特性、 排放水平及相互之间的关联特性, 并认识其产生、 排放与焚烧炉型、 焚烧条件的关联, 以探索控制其危害的有效方法。1. 对中国几个典型的生活垃圾焚烧炉现场采样, 获得多个飞灰和底渣的样品; 2. 通过多种不同的检测手段和方法, 分别检测残灰的基本物理化学特性、 氯苯、 多环芳烃和主要金属元素的浓度; 3. 结合焚烧炉型和焚烧特性等条件, 分析各有毒成分的排放特性和相互之间的关联特性。1. 氯苯、 多环芳烃和重金属受焚烧因素影响, 在残灰中的排放特性各不相同, 流化床焚烧炉能消除焚烧和原始垃圾的扰动, 能控制氯苯在残灰中的排放, 但多环芳烃排放控制不如炉排焚烧炉; 2. 残灰中主要的有机有毒成分为高氯代氯苯和 2 至 4 环等少环类多环芳烃; 3. 氯苯和多环芳烃在残灰中的含量可能因为不同的产生机理而表现出一定的负关联特点; 4. 残灰中的金属主要为铝和铁等轻金属, 浓度远高于重金属元素, 而无毒重金属 (主要为Mn、 Ni、 As 和 Zn) 浓度高于有毒重金属元素 (Cu、 Pb 和 Cr), 且不同金属表现出不同的对氯苯和多环芳烃的催化促进或抑制作用。

•A rotating gliding arc (RGA) reactor was used for dry methane reforming (DMR).•Spectroscopic characteristics in the CH4/CO2 discharge were investigated.•Co-generation of syngas and carbon nanomaterials containing graphene sheets in RGA.Dry methane reforming (DMR) via rotating gliding arc (RGA) discharge, co-driven by a magnetic field and tangential flow, was investigated in this study. Optical emission spectroscopy (OES) was used to characterize the major active species (energetic electrons, radicals, ions, atoms and excited molecules) in the DMR chemical process. The influence of the operational conditions (applied voltage and CH4/CO2 ratio) on the basic spectroscopic parameters (electron excitation temperature, electron density and rotational temperature) was determined by spectroscopic methods. The rotational and electron excitation temperatures were approximately 1100–1200 K and 1.1–1.7 eV, respectively, indicating the non-thermal equilibrium characteristics of the RGA discharge. The electron density was approximately 5–20 × 1021 m−3 by fitting the line shape of Hα at 656 nm. The conversions of the reactants (CH4 and CO2) and the selectivities of the products (H2, CO and C2 hydrocarbon) were analyzed using a gas chromatograph (GC) under different energy inputs or feed gas proportions. The structure and morphology of carbon black produced during the chemical process was characterized by high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy, indicating the properties of electrical conductivity and high absorption capacity that can be useful for potential application.

•A developed rotating gliding arc (RGA) reactor was used for methane reforming.•The RGA plasma was shown to occur as a warm plasma.•CN, C2, and CH radicals form in the RGA CH4 + N2 plasma according to the spectra.•The maximum CH4 conversion rate could be up to 91.8% in the RGA N2 plasma.Hydrogen production from methane decomposition via an atmospheric pressure rotating gliding arc (RGA) discharge reactor co-driven by a magnetic field and tangential flow is investigated. The motion and V–I characteristics of the RGA are studied with a high-speed camera and oscilloscope. Optical emission spectroscopy (OES) is used to characterize RGA plasmas in N2 and CH4 + N2, and the RGA plasma is shown to occur as a warm plasma. For the CH4 + N2 plasma, CN, C2, and CH spectral lines are observed. The vibrational and rotational temperatures are 0.56–0.86 eV and 1325–1986 K, respectively. The effects of load resistance, the CH4/N2 ratio, and the feed flow rate on the performance of methane decomposition are investigated. The maximum CH4 conversion rate and H2 selectivity are 91.8% and 80.7% when the CH4/N2 ratio is 0.1 and 0.05, respectively, at a flow rate of 6 L/min. The possible reaction mechanisms of the methane decomposition process are discussed. This study is expected to establish a basis for the further industrial applications of H2 production.

In this study, thermal desorption was combined with the addition of nano zerovalent iron (nZVI) to remediate polychlorinated biphenyl (PCB)-contaminated soil collected from a storage point for PCB-contaminated capacitors and transformers. The thermal desorption test conditions were varied from 300 to 600 °C, both with blank soil and with 100 mg of nZVI added. Next, the effect of the amount of nZVI added (0, 20, 40, 100, 200 mg) was investigated by thermal treatment at 400 °C. The test results show that thermal desorption eliminates most of the PCB load and that the presence of nZVI clearly enhances thermal desorption. After thermal treatment at 400 °C, a removal efficiency of 94.2 % was reached, with the use of 200 mg of nZVI. At 600 °C, the PCB removal efficiency after 1 h attained 98.35 % with 100 mg of nZVI and 97.40 % without nZVI. The presence of nZVI effectively decreased both the sum and the WHO-TEQ value of the 12 dl-PCBs.

The huge amount of medical waste (MW) has caused a tough challenge to environmental protection in China because of its serious infectious potential. At present, incineration is the most common technology for MW disposal. Unfortunately, the medical waste incinerator (MWI) is considered one of the major sources of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). This study was conducted to investigate the generation and the components of MW; the fingerprint of PCDD/Fs in MWI; and PCDD/F, polychlorinated biphenyl (PCB) and hexachlorobenzene concentrations in residue ash. The estimated annual production of MW was estimated to be 0.97 million tons in China in 2008; in addition, plastic and rubber accounted for 24.5% of MW contents. PCDD/F emissions from MWI could be divided into two main groups according their fingerprints, and the ratio of PCDFs/PCDDs was mostly over 1.5, with a mean value of 3.43. The toxic equivalent of PCDD/Fs was over 30 times that of the value of PCBs in the residue ash, and PCDD/F contents in fly ash accounted for approximately 67% of the total output of PCDD/Fs, which was in line with the UNEP default emission factors for MWI (class 3, 63.7%).

The emission and contact drying kinetics of the paper mill sludge (PMS) were studied through experiments carried out in a paddle dryer. To get a better understanding of its drying mechanism, a penetration model developed by Tsotsas and Schlünder (1986) was used to simulate the drying kinetics of the PMS. The result indicated that this kinetics could be divided into three phases: pasty, lumpy and granular phases, and could be successfully simulated by the penetration model as the related sludge parameters were integrated into the model. The emission rate curves of the volatile compounds (VCs) were interrelated to the drying rate curve of the PMS, especially for volatile fatty acids (VFAs) and ammonia in this study.

Nitrogen containing compounds such as ammonia, urea and amines can effectively inhibit the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Sewage sludge accumulates both sulfur and nitrogen during wastewater treatment so it could be used to reduce PCDD/Fs formation. Indeed, it is observed in this study that the gas evolving from the sludge drying process can significantly suppress chlorobenzene (CBz) and PCDD/Fs formation from fly ash collected from a hospital waste incinerator. For instance, the reduction of hexachlorobenzene (HxCBz) and PCDD/Fs amount was 92.1% and 78.7%, respectively, when the drying gas evolving from 2 g sludge flew through 2 g fly ash. These tests were conducted in the frame of projects devoted to hospital waste incineration. The disposal technology for hospital waste (HW), developed in this institute, features rotary kiln pyrolysis combined with post-combustion followed by flue gas cleaning. Hence, some preliminary tests were devoted to investigate dioxins suppression by co-pyrolysis and co-combustion of polyvinyl chloride (PVC) and sludge in lab scale. More experimental research will be conducted to appropriately assess these effects of sludge on PCDD/Fs emissions during co-pyrolysis/combustion of HW and sludge.Highlights► The gas evolved from sludge drying process and dry sludge is used to control dioxins emission for its high nitrogen content. ► The evolved gas shows a significant inhibition in dioxins formation from fly ash. ► The co-pyrolysis/combustion of PVC and dry sludge doesn’t carry out suppression of PCDD/Fs emission. ► Two-stage incineration (pyrolysis and combustion) is more favorable for dioxins control than direct combustion.