Co-processing of the MSWI flue gas in a lab-scale coal-fired drop-tube furnace.

Coal-fired power plants are characterized by high combustion temperature and well-equipped air pollution control devices. The trace organic pollutants in the municipal solid waste incineration (MSWI) flue gas would be completely destroyed if the MSWI flue gas was injected into the high temperature area of a coal-fired boiler. In this study, the emission characteristics of common gas pollutants, heavy metals, and dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in both flue gas and bottom ash when the MSWI flue gas was injected into a lab-scale coal-fired drop-tube furnace were investigated. After co-processing, the concentrations of NOx, SO2, CO, and all heavy metals in the flue gas emitted from the coal-fired drop-tube furnace did not change a lot. However, the concentration of HCl in the flue gas from drop-tube furnace increased after coupling the MSWI flue gas. Moreover, the I-TEQ values of the PCDD/Fs in the flue gas and bottom ash after coupling the MSWI flue gas were 0.037 ng I-TEQ/Nm3 and 0.63 ng I-TEQ/g, respectively. The main formation pathways of PCDD/Fs in the flue gas of drop-tube furnace were suggested to be de novo synthesis and precursor synthesis. Furthermore, the effects of oxygen content and temperature on the formation of PCDD/Fs were also studied. The reduction efficiencies of the total amount of PCDD/Fs in the flue gas from the co-processing system were more than 60%, and even reached 90%. Therefore, co-processing of the MSWI flue gas in coal-fired power plants might be an environmentally friendly technology.

The impact of hydrochloric acid on the catalytic destruction behavior of 1,2-dichlorbenzene and PCDD/Fs in the presence of VWTi catalysts.

Catalytic oxidation is regarded an effective technique to control the emissions of chlorinated benzenes (CBzs) and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from waste incinerators. Among the numerous factors affecting the degradation efficiency of CBzs and PCDD/Fs, limited attention has been paid to the impact of hydrochloric acid (HCl) present in the flue gas. This study investigates how HCl affects the catalytic degradation of 1,2-dichlorbenzene (1,2-DCBz) at different reaction times and temperature regimes. The results showed that the removal efficiency of 1,2-DCBz, which was achieved by the V2O5/WO3-TiO2 (VWTi) catalyst, decreased the largest by 10% in the presence of HCl. Furthermore, it was found that the increasing concentration of water vapor hindered the degradation efficiency of 1,2-DCBz. No relationship between the process temperature and the destruction efficiency of PCDD/Fs was observed in the presence of HCl. Potential increasing of the removal efficiency of 1,2-DCBz was confirmed by adding different amount of activated carbon (AC) in the presence of HCl.

Comparative analyses of catalytic degradation of PCDD/Fs in the laboratory vs. industrial conditions.

This study investigates the efficiencies and mechanisms of the catalytic degradation of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) first, in simulated laboratory conditions and then, in a commercial municipal solid waste incineration (MSWI) plant. Five commercially available V2O5-WO3/TiO2 (VWTi) catalysts were tested. The degradation efficiency of PCDD/Fs in the simulated flue gas ranged 22.8-91.7% and was generally higher than that in the MSWI flue gas of 8.0-85.4%. The degradation efficiency of PCDD/Fs in the real flue gas of the MSWI plant was largely hindered by the complex composition of the flue gas, which could not be completely reproduced in the simulated laboratory conditions. Furthermore, the degradation of the higher chlorinated PCDD/Fs was easier compared to the lower chlorinated ones in the presence of the VWTi catalysts, which was primarily driven by the tendency of the higher chlorinated PCDD/Fs to be adsorbed on the surface of the catalyst and further destructed due to their lower vapor pressure. In addition, powdered catalysts should be preferred over the honeycomb shaped ones as they exposed higher PCDD/Fs degradation efficiencies under equal reaction conditions. The chemical composition and a range of the relevant to the study properties of the catalysts, such as surface area, crystallinity, oxidation ability, and surface acidity, were analyzed. The study ultimately supports the identification of the preferred characteristics of the VWTi catalysts for the most efficient degradation of toxic PCDD/Fs and elucidates the corresponding deactivation reasons of the catalysts.

Low temperature destruction of PCDD/Fs by catalysis coupled with activated carbon.

In order to enhance the oxidation and adsorption capacity of catalyst, two kinds of activated carbon (AC) are mechanically mixed with V2O5-WO3/TiO2 catalyst respectively. In this study, the mixtures (M-1: catalyst mixing with AC based on lignite; M-2: the one on coconut shell) are investigated to destroy high concentration (9.8 ng I-TEQ Nm(-3)) PCDD/Fs at low temperature (160 °C). Adding AC into the catalyst obviously increases removal efficiency (RE) and destruction efficiency (DE). However, M-2 presents higher RE value and lower DE value compared with M-1 at the same conditions as the stronger adsorption capacity of AC based on coconut shell. For the M-2 mixture, RE values are decreasing while DE values show an opposite trend with the ratios of catalyst to AC increasing. Oxygen plays a positive role on the destruction of PCDD/Fs by accelerating the conversion of V(4+)Ox and V(5+)Ox. Adjusting oxygen content from 0 to 20 % could increase the DE value from 27.4 to 82.2 % for the M-1 and from 15.8 to 68.9 % for the M-2. In the presence of ozone, a dark brown flock will be generated when the ratio of AC and catalyst is 4:1 due to the reaction between AC and ozone, which results in the lower RE and DE values. The RE and DE values reach the maximum of 96.3 %, 90.6 % in this paper, respectively, when the ratio of AC and catalyst is 1:1 with ozone. Finally, the regenerating of mixture is investigated. Most of dioxin residues in the mixture are desorbed and oxidized by catalysis at 200 °C in the presence of oxygen.

Catalytic decomposition of gaseous 1,2-dichlorobenzene over CuOx/TiO2 and CuOx/TiO2-CNTs catalysts: Mechanism and PCDD/Fs formation.

Gaseous 1,2-dichlorobenzene (1,2-DCBz) was catalytically decomposed in a fixed-bed catalytic reactor using composite copper-based titanium oxide (CuOx/TiO2) catalysts with different copper ratios. Carbon nanotubes (CNTs) were introduced to produce novel CuOx/TiO2-CNTs catalysts by the sol-gel method. The catalytic performances of CuOx/TiO2 and CuOx/TiO2-CNTs on 1,2-DCBz oxidative destruction under different temperatures (150-350 °C) were experimentally examined and the correlation between catalyst structure and catalytic activity was characterized and the role of oxygen in catalytic reaction was discussed. Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) generation during 1,2-DCBz catalytic oxidation by CuOx/TiO2-CNTs composite catalyst was also examined. Results indicate that the 1,2-DCBz destruction/removal efficiencies of CuOx (4 wt%)/TiO2 catalyst at 150 °C and 350 °C with a GHSV of 3400 h(-1) are 59% and 94% respectively and low-temperature (150 °C) catalytic activity of CuOx/TiO2 on 1,2-DCBz oxidation can be improved from 59 to 77% when CNTs are introduced. Furthermore, oxygen either in catalyst or from reaction atmosphere is indispensible in reaction. The former is offered to activate and oxidize the 1,2-DCBz adsorbed on catalyst, thus can be generally consumed during reaction and the oxygen content in catalyst is observed lost from 39.9 to 35.0 wt% after reacting under inert atmosphere; the latter may replenish the vacancy in catalyst created by the consumed oxygen thus extends the catalyst life and raises the destruction/removal efficiency. The introduction of CNTs also increases the Cu(2+)/Cu(+) ratio, chemisorbed oxygen concentration and surface lattice oxygen binding energy which are closely related with catalytic activity. PCDD/Fs is confirmed to be formed when 1,2-DCBz catalytically oxidized by CuOx/TiO2-CNTs composite catalyst with sufficient oxygen (21%), proper temperature (350 °C) and high concentration of 1,2-DCBz feed (120 ppm).

High temperature suppression of dioxins.

Combined Sulphur-Nitrogen inhibitors, such as sewage sludge decomposition gases (SDG), thiourea and amidosulphonic acid have been observed to suppress the de novo synthesis of dioxins effectively. In this study, the inhibition of PCDD/Fs formation from model fly ash was investigated at unusually high temperatures (650 °C and 850 °C), well above the usual range of de novo tests (250-400 °C). At 650 °C it was found that SDG evolving from dried sewage sludge could suppress the formation of 2,3,7,8-substituted PCDD/Fs with high efficiency (90%), both in weight units and in I-TEQ units. Additionally, at 850 °C, three kinds of sulphur-amine or sulphur-ammonium compounds were tested to inhibit dioxins formation during laboratory-scale tests, simulating municipal solid waste incineration. The suppression efficiencies of PCDD/Fs formed through homogeneous gas phase reactions were all above 85% when 3 wt. % of thiourea (98.7%), aminosulphonic acid (96.0%) or ammonium thiosulphate (87.3%) was added. Differences in the ratio of PCDFs/PCDDs, in weight average chlorination level and in the congener distribution of the 17 toxic PCDD/Fs indicated that the three inhibitors tested followed distinct suppression pathways, possibly in relation to their different functional groups of nitrogen. Furthermore, thiourea reduced the (weight) average chlorinated level. In addition, the thermal decomposition of TUA was studied by means of thermogravimetry-fourier transform infrared spectroscopy (TG-FTIR) and the presence of SO2, SO3, NH3 and nitriles (N≡C bonds) was shown in the decomposition gases; these gaseous inhibitors might be the primary dioxins suppressants.

Dioxins from medical waste incineration: Normal operation and transient conditions.

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are key pollutants in waste incineration. At present, incinerator managers and official supervisors focus only on emissions evolving during steady-state operation. Yet, these emissions may considerably be raised during periods of poor combustion, plant shutdown, and especially when starting-up from cold. Until now there were no data on transient emissions from medical (or hospital) waste incineration (MWI). However, MWI is reputed to engender higher emissions than those from municipal solid waste incineration (MSWI). The emission levels in this study recorded for shutdown and start-up, however, were significantly higher: 483 ± 184 ng Nm(-3) (1.47 ± 0.17 ng I-TEQ Nm(-3)) for shutdown and 735 ng Nm(-3) (7.73 ng I-TEQ Nm(-3)) for start-up conditions, respectively. Thus, the average (I-TEQ) concentration during shutdown is 2.6 (3.8) times higher than the average concentration during normal operation, and the average (I-TEQ) concentration during start-up is 4.0 (almost 20) times higher. So monitoring should cover the entire incineration cycle, including start-up, operation and shutdown, rather than optimised operation only. This suggestion is important for medical waste incinerators, as these facilities frequently start up and shut down, because of their small size, or of lacking waste supply. Forthcoming operation should shift towards much longer operating cycles, i.e., a single weekly start-up and shutdown.

Distribution of PCDD/Fs in the fly ash and atmospheric air of two typical hazardous waste incinerators in eastern China.

Distribution of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) in the fly ash and atmospheric air of one medical waste incinerator (MWI) and one industrial hazardous waste incinerator (IHWI) plants were characterized. The PCDD/F concentrations of the stack gas (fly ash) produced from MWI and IHWI were 17.7 and 0.7 ng international toxic equivalent (I-TEQ)/Nm(3) (4.1 and 2.5 ng I-TEQ/g), respectively. For workplace air, the total concentrations of PCDD/Fs were 11.32 and 0.28 pg I-TEQ/Nm(3) (819.5 and 15.3 pg/Nm(3)). We assumed that the large differences of PCDD/F concentrations in workplace air were due to the differences in chlorine content of the waste, combustion conditions, and other contamination sources. With respect to the homologue profiles, the concentrations of PCDFs decreased with the increase of the substituted chlorine number for each site. Among all of the PCDD/F congeners, 2,3,4,7,8-PeCDF was the most important contributor to the I-TEQ value accounting for ca. 43 % of two sites. The gas/particle partition of PCDD/Fs in the atmosphere of the workplace in the MWI was also investigated, indicating that PCDD/Fs were more associated in the particle phase, especially for the higher chlorinated ones. Moreover, the ratio of the I-TEQ values in particle and gas phase of workplace air was 11.0. At last, the relationship between the distribution of PCDD/Fs in the workplace air and that from stack gas and fly ash was also analyzed and discussed. The high correlation coefficient might be a sign for diffuse gas emissions at transient periods of fumes escaping from the incinerator.

PCDD/Fs' suppression by sulfur-amine/ammonium compounds.

Three distinct -S and -NH2 or NH4(+) containing compounds, including ammonium thiosulfate, aminosulfonic acid and thiourea, were studied as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) inhibitors. All these three -S and -N containing compounds tested show strong suppression of PCDD/Fs formation, especially for thiourea which has not been studied before. With a (S+N)/Cl molar ratio of only 0.47, thiourea could inhibit 97.3% of PCDD/Fs and even 99.8% of I-TEQ. At an unusually high de novo test temperature (650 °C), the PCDD/Fs' formation was still very low but also the inhibition capacity of thiourea was weak, with an efficiency of 59% for PCDD/Fs when with a (S+N)/Cl molar ratio of 1.40. The results also revealed that the inhibition capability of the combined -S/-NH2 or -S/NH4(+) suppressant was strongly influenced by both the nature of the functional group of nitrogen and the value of the molar ratio (S+N)/Cl. The amine functional group -NH2 tends to be more efficient than ammonium NH4(+) and within a certain range a higher (S+N)/Cl value leads to a higher inhibition efficiency. Moreover, the emission of gases was continuously monitored: the Gasmet results revealed that SO2, HCN and NH3 were the most important decomposition products of thiourea. Thiourea is non-toxic, environment-friendly and can be sprayed into the post-combustion zone in form of powder or aqueous solution. The cost of thiourea at least can be partially compensated by its high inhibition efficiency. Therefore, the application of thiourea in a full-scale incinerator system is promising and encouraging.

Inhibition of the de novo synthesis of PCDD/Fs on model fly ash by sludge drying gases.

Sludge drying gases (SDG), evolving from drying and mild thermal decomposition (<300°C) of raw sewage sludge contain NH3 and SO2 as well as other N- and S-compounds. All of these are potential PCDD/Fs suppressants. It is indeed observed that these SDG suppress 2,3,7,8-substitued PCDD/Fs formation on Model Fly Ash (MFA) with an efficiency up to 97.6% in wt. units and 96% in I-TEQ, respectively. This suppression is strong for (the bulk of) PCDD/Fs, adsorbed on the model fly ash; conversely, sludge drying gases enhance PCDD/Fs desorption from MFA. Moreover, TCDD/Fs are suppressed least, possibly following stepwise dechlorination of higher chlorinated PCDD/Fs. Characteristics, such as the type, origins and amount of sludge, its moisture-, nitrogen- and sulfur content and the nature of the thermal treatment applied are all expected to influence upon the suppression capabilities. In this study three types of dry sludge are tested and applied as suppressant in four different amounts or modes. The quality of the sludge drying gases is continuously monitored: the Gasmet results reveal that NH3 and SO2 are the most important components of SDG. The MFA reaction residue is scrutinized by Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS) analysis. A large number of particles attaching to the surface of model fly ash are observed by SEM. Moreover, EDS analysis reveals that part of the chlorine in MFA is carried away with the SDG and replaced by sulfur, so that eliminating chlorine may be part of the inhibition mechanism. However, further research is still needed to establish the optimum operating modes and to confirm the role of both inorganic and organic nitrogen and sulfur compounds in the suppression of PCDD/Fs formation on model fly ash.

Treating PCDD/Fs by combined catalysis and activated carbon adsorption.

V2O5-WO3/TiO2 catalysts are used to destroy dioxins present in the gas phase, yet both their removal efficiency (RE) and destruction efficiency (DE) decrease with rising initial concentration (IC). Therefore, activated carbons (AC-1: based on lignite; AC-2: based on coconut shell) were mixed with the catalyst to tackle these high IC gases. A gas phase dioxin-generating system was used to supply three different stable IC-values. When the highest IC is used (20.5 ng I-TEQ Nm(-3)) without AC, at 200°C, the RE and DE-value of PCDD/Fs reaches only 76% and 64%, respectively. At the same conditions, using a mix of catalyst and AC-2, these RE and DE-values rise to 90.1% and 82.0%, respectively. The mix catalyst/AC also shows better performance at low temperature (160 and 180°C). The AC characteristics influence upon the adsorption and degradation abilities of the mixtures.

[Study on vitrification of simulated medical wastes by thermal plasma].

The simulated medical wastes with different feed compositions were vitrified in a thermal plasma reactor, the core of which was a DC double anode plasma torch. The purpose of this study was directed towards the mobility characteristics of heavy metals contained during the vitrification process, the leaching behavior of heavy metals in the vitrified slag and the effectiveness of vitrification were investigated. Results indicated that the morphology of vitrified slag was amorphous state which showed the mostly glassy slag of SiO2 and the microstructure of slag was very compact. This thermal plasma could be effectively utilized for encapsulation of heavy metal in wastes, as the vitrification ratio was between 68.5% - 89.4%. Toxicity characteristic leaching procedure results showed that the slag had an excellent resistance against leaching of heavy metal ions. Except that the leaching concentration of Cd was lower than the detecting limit, those of Ni, Cr, Zn, Cu and Pb were much lower than that specified in relevant national standards. These results indicate that, with the proper feed compositions, the thermal plasma disposition is an alternative technology with a highly efficiency to dispose medical wastes.

[Study on the low temperature drying of components of municipal solid waste and its model analysis].

The drying behaviors of four typical municipal solid waste (MSW) components (including waste paper, textile, pericarp and wood) were studied under low temperature. Effects of temperature on drying characteristic, thin layer drying models, effective moisture diffusion coefficient and activation energy were investigated in this paper. Experimental results showed that with increasing temperature, the drying rate increased, but the added value reduced gradually. Four mathematical models were used to simulate drying curves of MSW components. Modified Page model was found to give better predictions when moisture content was more than 25%. Based on the Fick's second law, the effective moisture diffusion coefficient for waste paper, textile, pericarp and wood were 8.24 x 10(-8)-23.67 x 10(-8), 7.73 x 10(-8)-12.56 x 10(-8), 3.57 x 10(-8)-14.18 x 10(-8) and 6.51 x 10(-8)-23.84 x 10(-8)m2 x s(-1). The activation energy determined through Arrhenius equation were 25.26, 10.75, 32.16 and 29.49 kJ x mol(-1), respectively. Carried on the similar dry experiments to practical MSW, It was found that Modified Page model was also suitable for simulating the drying process of practical MSW, its effective moisture diffusion coefficient and activation energy were 6.78 x 10(-8)-18.65 x 10(-8)m2 x s(-1) and 22.36 kJ x mol(-1), respectively.

Dioxins and their fingerprint in size-classified fly ash fractions from municipal solid waste incinerators in China--mechanical grate and fluidized bed units.

The distribution of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs), in brief dioxins, has seldom been addressed systematically in fly ash from municipal solid waste incinerators (MSWIs). This study shows the amount and fingerprint of PCDD/Fs in fly ash from four different Chinese MSWIs, that is, three mechanical grate units and one circulating fluidized bed unit. In these fly ash samples, dioxins-related parameters (international toxic equivalent quantity, total amount of PCDD/Fs, individual isomer classes, and 17 toxic 2,3,7,8-substituted congeners) all tend to increase with decreasing particle size for mechanical grate incinerators, yet only for the finest fraction for fluidized bed units. Moreover, the fluidized bed incinerator seems superior to grate incineration in controlling dioxins, yet a comparison is hampered by internal differences in the sample, for example, the fluidized bed fly ash has much lower carbon and chlorine contents. In addition, the presence of sulfur from mixing coal as supplemental fuel to the MSW may poison the catalytic steps in dioxins formation and thus suppress the formation of dioxins. With more residual carbon and chlorine in the fly ash, it is easier to form dioxins during cooling. Nevertheless, there is no apparent relation between Fe, Cu, and Zn contents and that of dioxins in fly ash.

Health risk assessment of PCDD/F emissions from municipal solid waste incinerators (MSWIs) in China.

The objectives of this study were to determine the environmental impacts of polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran (PCDD/Fs) emitted from two typical municipal solid-waste incinerators (MSWIs), named M and L, in China. The main differences between the two MSWIs relate to incineration technologies, treatment capacities, emission standards and meteorological conditions. The distribution of PCDD/Fs in the surrounding ambient air and soils of the MWSIs were monitored and compared. In addition, air dispersion models and health risk assessments were combined to determine the behaviour and transport of PCDD/Fs. The results indicated that higher PCDD/F emission levels resulted in higher concentrations in the surrounding environment. The average PCDD/F levels emitted from the M MSWI was about seven times higher than those emitted from the L MSWI and about 10 times and 2 times higher in air and soils, respectively. The simulation results were similar to the trend of the monitored results. Both the observed and the simulation results suggested that the atmospheric pollution by PCDD/F surrounding the M MSWI was relatively serious; the environmental impact of the L MSWI was not significant.

Baseline soil levels of PCDD/Fs established prior to the construction of municipal solid waste incinerators in China.

In order to determine the baseline contamination by polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in different areas in China, prior to the construction of municipal solid waste incinerators (MSWIs), a total of 32 representative soil samples was collected near 16 incinerators and analyzed for their PCDD/F concentrations. The PCDD/F baseline concentrations in the soil samples ranged from 0.32 to 11.4 ng I-TEQ kg(-1) (dry matter), with average and median value of 2.73 and 2.24 ng I-TEQ kg(-1) (dry matter), respectively, and a span between maximum and minimum recorded value of 36. The PCDD homologues predominated in 26 out of 32 soil samples, with the ratio (PCDDs)/(PCDFs) ranging from 1.1 to 164; however in the other 6 samples, PCDF homologues were larger, with the same ratio varying from 0.04 to 0.8. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used to examine PCDD/F amount and profile in these soil samples, and their possible associations with known emission sources: in this process 6 really distinct isomer fingerprints were identified. Background PCDD/F levels and profiles were comparable to those found in soils from China and other countries and indicate a rather low baseline PCDD/F contamination of soils. The present data provide the tools for future assessment of a possible impact of these MSWIs.

Inhibition of PCDD/F by adding sulphur compounds to the feed of a hazardous waste incinerator.

Sulphur compounds, including (NH(4))(2)SO(4) and pyrite, were tested as suppressants in a hazardous waste incineration facility. The test results suggested that adding sulphur compounds only slightly reduced PCDD/F stack emissions; this restricted effect was attributed to the release of fly ash in large amounts during the sulphur adding experiments, i.e., it was due to a malfunctioning of the baghouse filter. Nevertheless, for the combined flow of flue gas+fly ash a reduction of more than 50% was achieved for the total PCDD/F concentrations and the total toxic concentrations, and an even higher inhibition capability was observed for PCDD. Also, a simulation of the thermodynamic equilibrium conditions by sulphur dioxide was conducted in the domain of experimental interest. Deactivation of catalysts, which promote PCDD/F formation, was found to be the dominant inhibition mechanism in low temperature PCDD/F formation. SO(2) could also inhibit the formation of molecular Cl(2) via the Deacon reaction, but that was not the main reason for inhibition.

Thermal removal of PCDD/Fs from medical waste incineration fly ash--effect of temperature and nitrogen flow rate.

The fly ash used in this study was collected from a bag filter in a medical waste rotary kiln incineration system, using lime and activated carbon injection followed by their collection as mixed fly ash. Experiments were conducted on fly ash in a quartz tube, heated in a laboratory-scale horizontal tube furnace, in order to study the effect of temperature and nitrogen flow rate on the removal of PCDD/Fs. Results indicated that in this study PCDD/Fs in the fly ash mostly were removed and desorbed very little into the flue gas under thermal treatment especially when the heating temperature was higher than 350 °C, and dechlorination and destruction reactions took important part in the removal of PCDD/Fs. However, in terms of flow rate, when flow rate was higher than 4 cm s(-1), destruction efficiency of PCDD/Fs decreased dramatically and the main contributors were P(5)CDF, H(6)CDF and H(7)CDF desorbed to flue gas, the PCDD/Fs in the fly ash decreased with enhanced flow rate.

Photocatalytic decomposition on nano-TiO2: destruction of chloroaromatic compounds.

Photocatalysis is applied increasingly in addressing and solving environmental and energy-related problems. Especially the TiO2-derived catalysts attract attention because of their catalytic efficiency, wide range of applications, ease in use, and low cost (it costs about 150 Yuan a kilogram in China). This review first describes the principles of photocatalytic destruction by semiconductors and then focuses on degradation rates and reaction mechanisms in a variety of photocatalytic uses of modified TiO(2). Finally, these concepts are illustrated by selected examples relating to the photocatalytic degradation of organic persistent pollutants, such as polychlorinated benzenes (PCBz), biphenyls (PCB) and dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). And some approaches towards industrial application are analyzed.

Levels of PCDD/Fs in soil in the vicinity of a medical waste incinerator in China: the temporal variation during 2007-2009.

In 2004, it is estimated that 1.18 kg I-TEQ of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) emitted from medical waste incinerators (MWIs) in China, accounting for 11.5% of the total PCDD/Fs emissions. So it is essential to assess the environmental impact of MWIs. A new MWI of China was started operation in May 2007, and implemented an advanced technology in the combustion and air pollution control system by the BAT/BEP guideline in August 2008. From 2007 to 2009, levels of PCDD/Fs were determined in soil collected in the vicinity of this MWI. The blank survey (2007) was conducted before the start-up operation of this plant. After the operation, soil samples were collected again at the same sampling sites as the blank survey. The average concentration of PCDD/Fs in soil increased from 1.13 pg I-TEQ g(-1) to 2.29 pg I-TEQ g(-1) after 1 year operation of the MWI (2007-2008), and a marked decrease (0.50 pg I-TEQ g(-1)) was observed during 2008-2009. In addition, the current level (2009) was still higher than the blank value (2007). The composited analysis of the experimental results indicated levels of PCDD/Fs were still comparative lower and a limited neighbourhood of the MWI was slightly affected by the emission from this incinerator, meanwhile other un-known PCDD/Fs sources and potential influenced factors could not be neglected in this investigated region.