Ozone catalytic oxidation of toluene over triple perovskite-type catalysts modified with KMnO4

A unique triple perovskite-type catalyst was successfully synthesized using the simple sol-gel approach, and surface acid modification was added to improve the ozone catalytic oxidation (OZCO) process ability to remove toluene more effectively. Our study indicates that La3MnCuNiO9 catalyst treated with KMnO4 shows the best toluene oxidation activity. At 250 °C, the rates of conversion and mineralization were 100% and 83%, respectively, under thermal catalytic system when C7H8 concentration = 500 ppm. During the OZCO system ([C7H8] = 20 ppm, O3/C7H8=8; room temperature), for 6 h, the conversion rate remained at 100%. The high ratios of Mn4+/(Mn4++Mn3+), Cu2+, and abundant surface oxygen species, high specific surface area, and pore volume lead to remarkable catalytic performance of this catalyst. Meanwhile, the catalyst contributes to superior stability and water resistance. The catalytic mechanism of La3MnCuNiO9 after KMnO4 treatment in the context of OZCO was further discussed. Overall, after KMnO4 treatment, the La3MnCuNiO9 catalyst reveals extraordinary catalytic activity and excellent stability combination of this catalyst with ozone exhibits high toluene removal efficiency in the OZCO system and has a good potential for industrial applications.

Ozone catalytic oxidation of low-concentration formaldehyde over ternary Mn-Ce-Ni oxide catalysts modified with FeOx

Manganese oxide-based catalysts have attracted extensive attention due to their relatively low cost and remarkable performance for removing VOCs. In this research, we used the Pechini method to synthesize manganese-cerium-nickel ternary oxide catalysts (MCN) and evaluated the effectiveness of catalytic destruction of formaldehyde (HCHO) and ozone at room temperature. FeO_x prepared by the impregnation method was applied to modify the catalyst. After FeO_x treatment, the catalyst represented the best performance on both HCHO destruction and ozone decomposition under dry conditions and exhibited excellent water vapor resistance. The as-prepared catalysts were next characterized via H₂-temperature programmed reduction (H₂-TPR), temperature programmed desorption of O₂ (O₂-TPD), and X-ray photoelectron spectroscopy (XPS), and the results demonstrated that addition of FeO_x increased Mn³⁺ and Ce³⁺ concentrations, oxygen vacancies and surface lattice oxygen species, facilitated adsorption, and redox properties. Based on the results of in situ diffuse reflectance infrared Fourier transform spectrometry (DRIFTS), possible mechanisms of ozone catalytic oxidation of HCHO were proposed. Overall, the ternary mixed-oxide catalyst developed in this study holds great promise for HCHO and ozone decomposition in the indoor environment.

Modifying α-Al2O3 with cerium, zirconium, and sulfate for catalytic removal of C4F8

Modification of α-Al₂O₃ (A) with cerium (C), zirconium (Z), and sulfate (S) for effective C₄F₈ removal is evaluated at temperatures ≤ 650 °C. Catalytic hydrolysis of C₄F₈ is conducted to compare the performance of catalysts prepared (namely, A, AC, AZ, AS, ACS, and AZS). The interplay between rare earth element, acid amount, and surface area is further investigated. An investigation was carried out by characterization of catalysts by using XRD, BET, and NH₃-TPD. XRD pattern of the modified α-Al₂O₃ catalyst shows that the average grain size is 37 nm. BET analysis indicates that the surface area increases with the addition of Ce and Zr, while NH₃-TPD analysis shows the improvement of acid sites after the addition of Ce, Zr, and SO₄^2-. The experimental results indicate that C₄F₈ conversion over A catalyst reaches 14.81% at 550 °C with the addition of 38% H₂O_(g). Under the same operating condition, C₄F₈ conversion efficiencies achieved with AC and AZ catalysts increase to 42.03% and 50.1%, respectively. Furthermore, the efficiencies over AS, ACS, and AZS catalysts increase to 49.85%, 86.94%, and 87.18%, respectively. Stability tests show that the performances of the catalysts for C₄F₈ conversion are with the order of AZS > ACS > AZ > AC > AS > A at 650 °C during 24 h. The activation energy of the AZS catalyst in catalytic hydrolysis of C₄F₈ is 60.49 kJ/mol. The products of C₄F₈ conversion mainly include CO₂, CO, and COF₂ and small amounts of CHF₃ and C₂F₄. This study has confirmed that the AZS catalyst shows the best activity, acidity, and stability on C₄F₈ removal.

Characteristics of polycyclic aromatic hydrocarbons in ambient air of a tropical mega-area, Ho Chi Minh City, Vietnam: concentration, distribution, gas/particle partitioning, potential sources and cancer risk assessment

This is the first investigation on overall characteristics of 25 polycyclic aromatic hydrocarbons (PAHs) (15 PAHs regulated by US-EPA (excluding naphthalene) and 16 PAHs recommended by the European Union) in ambient air of Ho Chi Minh City, Vietnam. Their levels, congener profiles, gas/particle partitioning, potential sources of atmospheric PAHs (gas and particulate phases), and lung cancer risks in the dry and rainy seasons were examined. The ∑25 PAH concentration in the dry and rainy seasons ranged from 8.79 to 33.2 ng m^-3 and 26.0 to 60.0 ng m^-3, respectively. Phenanthrene and Indeno[123-cd]pyrene were major contributors to gaseous and particulate PAHs, respectively, while benzo[c]fluorene was dominant component of the total BaP-TEQ. The ∑16 EU-PAH concentration contributed to 13 ± 2.7% of the total ∑ 25 PAH concentration; however, they composed over 99% of the total ∑ 25 PAH toxic concentration. Adsorption mainly governed the phase partitioning of PAHs because the slope of correlation between logK_p and logP⁰_L was steeper than - 1. Vehicular emission was the primary source of PAHs in two seasons; however, PAHs in the dry season were also originated from biomass burning. Assessment of lung cancer risk showed that children possibly exposed to potential lung cancer risk via inhalation.

Characteristics of PM and PAHs emitted from a coal-fired boiler and the efficiencies of its air pollution control devices

Sampling and analysis of filterable particulate matter (FPM), FPM_2.5, condensable particulate matter (CPM), polycyclic aromatic hydrocarbons (PAHs), sulfur oxides (SO_x), and nitrogen oxides (NO_x) emitted from a coal-fired boiler equipped with selective catalytic reduction (SCR)+ electrostatic precipitator (ESP) + wet flue gas desulfurization (WFGD) + wet electrostatic precipitator (WESP) as air pollution control devices (APCDs) are conducted. The results show that NO_x concentration emitted from the coal-fired boiler is 56 ± 2.17 ppm (with the NO_x removal efficiency of 47.2%), which does not meet the best available control technology (BACT) emission standard (≤ 30 ppm). On the other hand, the WFGD adopted has a good removal efficiency for SO_x and HCl. Both SO_x and HCl emission concentrations are < 1 ppm, and removal efficiencies are > 99%. The FPM and FPM_2.5 emitted from the coal-fired boiler are 0.9 ± 0.06 mg/Nm³ and < 0.09 ± 0.006 mg/Nm³, respectively. The overall removal efficiency of FPM achieved with ESP+WFGD+WESP+MGGH is 99.98%. However, high concentration of CPM (37.4 ± 6.3 mg/Nm³) is measured, which is significantly higher than FPM and FPM_2.5. The concentrations of 27 PAHs at the WESP inlet and stack are measured as 667 ng/Nm³ and 547 ng/Nm³, respectively while the removal efficiencies of gas- and solid-phase PAHs are 9% and 58%, respectively. The results show that APCDs adopted are not effective in removing PAHs (only 18%), and gas-phase PAHs contribute the most in the total PAH emission. In addition, the benzo(a)pyrene equivalent (BaP_eq) concentration emitted from the stack is 28.8 ng-BaP_eq/Nm³, and most of it is contributed by 4-6 ring PAHs with high toxic equivalent factors (TEFs). Furthermore, the emission factors of air pollutant emitted from coal-fired boilers equipped with different combinations of APCDs are compiled and compared. The results show that except for CPM and NO_x, the emission factors of air pollutant calculated for this coal-fired boiler are lower if compared with other studies.Implications: Primary particles discharged from coal-fired processes include filterable particulate matter (FPM) and condensable particulate matter (CPM). PM_2.5 emissions would be greatly underestimated if CPM is ignored. Polycyclic aromatic hydrocarbons (PAHs) are semi-volatile organic compounds (SVOCs) formed by two or more fused benzene rings. PAHs have attracted much public attention because of toxicity and carcinogenicity. This study selects one coal-fired boiler with the best available control technology (BACT) to simultaneously measure the concentrations of PM, PAHs, and gaseous pollutants at the inlet and outlet of air pollution control devices (APCDs) to understand the efficacy of APCDs adopted and pollutant emission intensity.

Application of thermal desorption for measuring PAHs on PM2.5

PM_2.5 and polycyclic aromatic hydrocarbons (PAHs) emitted from various sources may cause respiratory disease and lung cancer. Additionally, PAHs deposited on PM_2.5 would aggravate the hazard to human health once inhaled. Therefore, it is essential to investigate the PAHs adsorbed on PM_2.5 in ambient air. However, analysis of PAHs on PM_2.5 is limited so far due to high detection limit of the analytical method and complex pretreatment procedures of the sample. In this study, thermal desorption (TD) is combined with GC-HRMS for direct analysis of PAHs on PM_2.5 collected by the filter without pretreatment. The results indicate that distribution of PAHs on the filter is uniform and each filter section is representative for direct analysis of PAHs on PM_2.5. The optimal thermal desorption temperature and purge time of analysis are found at 320°C and 60 s, respectively. Furthermore, the PAHs on PM_2.5 of ambient air in Taiwan including traffic area, industrial area, suburban area, and background site are investigated. The results indicate that the concentrations of PAHs on PM_2.5 in ambient air of Northern, Central, and Eastern Taiwan are in the range of 0.13-6.63 ng/m³, with an average concentration of 2.23 ng/m³. The PAH concentration measured in winter is significantly higher than that in summer, and the concentration of PAHs on PM_2.5 ranges from 0.071 to 0.280 ng/μg while the average concentration is 0.133 ng/μg. The technology optimized in this study can be applied for rapid and accurate measurement of PAHs present on fine particles.

Application of plasma catalysis system for C4F8 removal

Octafluorocyclobutane (C₄F₈) with a GWP₁₀₀ (global warming potential) of 10,000 times of CO₂ is listed as potent greenhouse gas. Therefore, development of effective control technologies for reducing C₄F₈ emissions has become an emerging issue to be addressed. In this study, decomposition of C₄F₈ was investigated via three systems including catalytic hydrolysis, non-thermal plasma, and plasma catalysis, respectively. Decomposition of C₄F₈ achieved with catalytic hydrolysis reaches the highest efficiency of 20.1%, being obtained with γ-Al₂O₃ as catalyst in the presence of 10% H₂O_(g) and operating temperature of 800 °C. For plasma-based system, the highest C₄F₈ conversion obtained with non-thermal plasma is 62% at a voltage of 23 kV. As for the plasma catalysis system, 100% C₄F₈ conversion efficiency can be achieved at an applied voltage of 22-23 kV. The effects of various parameters such as gas flow rate and C₄F₈ concentration on plasma-based system show that the plasma catalysis also has better resistivity for the high gas flow rate. The highest energy efficiency of 0.75 g/kWh is obtained for the gas flow rate of 500 mL/min, with the C₄F₈ conversion of 41%. The highest conversion 89% was achieved with the O₂ content of 0.5%. Addition of Ar improves the performance of plasma-based system. When Ar is controlled at 20%, C₄F₈ conversions obtained with plasma catalysis reach 100% at applied voltage of 22-23 kV even in the presence of 5% O₂. The main products of the C₄F₈ conversion include CO₂, NO_x, and COF₂ when O₂ is added into the system. As water vapor is added, HF is also formed. This study has confirmed that combined non-thermal plasma with catalyst system to convert C₄F₈ is indeed feasible and has good potential for further development.

Emissions of PAHs, PCDD/Fs, dl-PCBs, chlorophenols and chlorobenzenes from municipal waste incinerator cofiring industrial waste

Concentrations and distributions of PAHs and chlorinated aromatic compounds including PCDD/Fs, dl-PCBs, chlorophenols (CPs), and chlorobenzenes (CBz) in the municipal waste incinerator are investigated to characterize their formation and emission via intensive stack sampling. In addition, the toxicity of fly ash contribution by PCDD/Fs and dl-PCBs is evaluated in this study. The results reveal that concentrations of PCDD/Fs and dl-PCBs in flue gas are significantly lower than those of CPs, CBz, and PAHs. Additionally, the removal efficiencies of PAHs and chlorinated aromatic compounds achieved with existing air pollution control devices are evaluated, indicating that the removal efficiencies achieved with activated carbon injection + baghouse (95-99%) are higher than those with semi-dry scrubber (SDS). Besides, PCDD/Fs and PCBs TEQ concentrations in SDS and BH ashes are within 1.61-2.66 WHO-TEQ/g and 0.09-0.19 WHO-TEQ/g, respectively. Furthermore, the calculated mass flow rates suggest that the input rate of PCDD/Fs and dl-PCBs of SDS are 60.24 mg/h and 59.74 mg/h, respectively. The mass flow rates of PCDD/Fs and dl-PCBs after SDS in flue gas are 32.47 mg/h and 49.73 mg/h, respectively. However, the discharge rates of PCDD/Fs and dl-PCBs from SDS are 120.60 mg/h and 27.05 mg/h, respectively, indicating that PCDD/Fs are significantly formed within the SDS. PCDD/Fs formation is attributed to the operating temperature of SDS (240 ± 11.5 °C), which is within the temperature window for de novo synthesis. Thus, operating parameters of the APCDs should be optimized to reduce the formation of PAHs and chlorinated aromatic pollutants from MWI.

Characteristics of PCDD/Fs in PM2.5 from emission stacks and the nearby ambient air in Taiwan

This study aimed to find the characteristics of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in fine particulate matter from different stationary emission sources (coal-fired boiler, CFB; municipal waste incinerator, MWI; electric arc furnace, EAF) in Taiwan and the relationship between PM_2.5 and PM_2.5-bound PCDD/Fs with Taiwanese mortality risk. PM_2.5 was quantified using gravimetry and corresponding chemical analyses were done for PM_2.5-bound chemicals. Mortality risks of PM_2.5 exposure and PCDD/Fs exposure were calculated using Poisson regression. The highest concentration of PM_2.5 (0.53 ± 0.39 mg/Nm³) and PCDD/Fs (0.206 ± 0.107 ng I-TEQ/Nm³) was found in CFB and EAF, respectively. Higher proportions of PCDDs over PCDFs were observed in the flue gases of CFB and MWI whereas it was reversed in EAF. For ambient air, PCDD/F congeners around the stationary sources were dominated by PCDFs in vapor phase. Positive matrix factorization (PMF) analysis found that the sources of atmosphere PCDD/Fs were 14.6% from EAF (r = 0.81), 52.6% from CFB (r = 0.74), 18.0% from traffic (r = 0.85) and 14.8% from MWI (r = 0.76). For the dioxin congener distribution, PCDDs were dominant in flue gases of CFB and MWI, PCDFs were dominant in EAF. It may be attributed to the different formation mechanisms among wastes incineration, steel-making, and coal-burning processes.

Evaluation of the effectiveness of nonthermal plasma disinfection

As concern has increased regarding the interaction between efficiency and safety of disinfection, plasma becomes a viable alternative for disinfection in comparison with traditional methods. Dielectric barrier discharge (DBD) is applied to deactivate Bacillus subtilis and Escherichia coli , respectively, and disinfection efficiency is experimentally evaluated in this study. Tests are conducted with different working gases to investigate their effects on disinfection. Results show that Ar plasma diluted with 25% O₂ enhances the germicidal effects to5.9 and 6.9 (log reduction) for B. subtilis and E. coli, respectively, and OES results show that active Ar and O species play important roles to weaken cell wall of microbes and further disinfect E. coli and B. subtilis. Analysis of protein and total sugar release indicates that active species such as ozone, NO and Ar* produced by plasma result in hydrolysis of the cell. In the meantime, charged particles produced by plasma would affect the amount of sugar released, resulting in different germicidal effects. Overall, plasma can disinfect microorganisms mainly via the generation of oxidising agents including ozone, NO and UV with a comparatively short treatment period, which is typically less than 5 min.

Emission characteristics of dl-PCNs, PCDD/Fs, and dl-PCBs from secondary copper metallurgical plants: Control technology and policy

This study investigated the characteristics of dl-PCNs, PCDD/Fs and dl-PCBs emitted from two typical secondary copper metallurgical plants processing copper sludge equipped with different sets of air pollution control devices (APCDs). Results indicated that the emission factors of dl-PCNs and PCDD/Fs of plant A are 0.00775 and 1.09 μg TEQ/ton, respectively, which are remarkably lower than those of plant B (3.12, 181 and 25.5 μg TEQ/ton for dl-PCNs, PCDD/Fs and dl-PCBs, respectively). Dl-PCNs contributed 0.7-2.7% of total TEQ for flue gases and up to 2.6% of TEQ for ash samples. The TEQ concentration of dl-PCNs in fly ash individually exceeds the regulated level of 1 ng TEQ/g regulated by Taiwan EPA, indicating that emission and discharge of dl-PCNs should be regulated. The combination of semidry scrubber and activated carbon injection (ACI) + baghouse (BH) is effective for simultaneous removals of dl-PCNs and PCDD/Fs in plant A; while the combination of cyclone, secondary combustion chamber, ACI + BH and wet scrubber (WS) is not optimal for removing dl-PCNs, PCDD/Fs and dl-PCBs. Memory effect occurring within BH and WS is responsible for low removal efficiencies of these POPs in plant B. This study suggests appropriate APCDs for simultaneous removal of three POP groups and recommends the inclusion of dl-PCNs in emission standard.

Reduction of polychlorinated naphthalenes (PCNs) emission from municipal waste incinerators in Taiwan: Recommendation on control technology

Emission factor and removal efficacy of PCNs are evaluated via the flue gas sampling of two MWIs equipped with different air pollution control devices (APCDs) in Taiwan. MWI-A is equipped with ESP, wet scrubber (WS) and selective catalytic reduction (SCR), while cyclone (CY), semi-dry absorber (SDA), activated carbon injection (ACI) and baghouse (BH) are employed in MWI-B. The average concentrations of PCNs measured at stacks of MWI-A and MWI-B are 2.1 ng Nm^-3 (0.218 pg TEQ Nm^-3) and 23.2 ng Nm^-3 (0.425 pg TEQ Nm^-3), respectively. The emission factors of PCNs calculated from feeding rates of waste and stack sampling results range from 6.7 to 6.95 μg t^-1 (0.790-1.45 ng TEQ t^-1). PCNs are formed in ESP via chlorination, while SCR and SDA + ACI + BH are effective in removing PCNs with the overall efficacies of 97.6% and 94.3%, respectively. PCN removal efficiencies achieved with SCR and SDA + ACI + BH increase as chlorination level increases. Specifically, around 72% and 82% of Mono-CN are removed by SCR and SDA + ACI + BH, respectively. The removal efficacies of other homologues achieved with SCR are consistently high (96-100%). Dominances of Mono-to Tri-CNs in scrubbing liquid collected from WS and higher removal efficacies of these homologues achieved with WS + ESP compared with ESP alone indicate that WS can capture low chlorinated PCNs to some extent. The results suggest that CY + SDA + ACI + BH should be equipped in MWI for effective removal of PCNs, while ESP, WS and SCR should be utilized with precaution to eliminate PCNs formation and enhance the PCNs removal efficiency.

Characterization of PCN emission and removal from secondary copper metallurgical processes

This study investigates the characteristics of PCN emission and removal from two secondary copper metallurgical processes (plants A and B) equipped with different air pollution control devices (APCDs). Different operating conditions and feeding materials result in varying emission factors of PCNs from two plants. The average PCN concentration emitted from plant B (7597 ng Nm^-3) is significantly higher than that emitted from plant A (32.5 ng Nm^-3) and those reported in China (5.8-2845 ng Nm^-3). Similar trend is found for fly ash samples collected from two plants. Low chlorinated homologues (Mono-to Tri-CNs) are the major contributors to total PCNs measured in flue gas, fly ash and slag samples. Combination of semi-dry absorber, activated carbon injection and baghouse is effective for PCN removal in plant A, with the overall removal efficiency of 98%. The overall removal efficiency of PCNs achieved with APCDs equipped in plant B is 90%, however, increases of some homologues as the flue gases passing through baghouse and wet scrubber are found, suggesting the occurrence of memory effect within baghouse and wet scrubber.

Efficacy of the novel continuous sampling system for PCDD/Fs and unintentional persistent organic pollutants

Long-term sampling is essential for monitoring the air pollutants emitted from stack since it can monitor the pollutants emission continuously including the stages of start-up, shutdown and normal operation. However, commercial continuous sampling equipment such as AMESA faces the challenges of high weight and complicated sampling procedures. This study has developed a long-term and automatic sampling system (National Central University continuous stack sampling system, NCU-CS³), and compared the efficiency with manual sampling train (MST). The results indicate that relative standard deviation (RSD) of PCDD/Fs concentrations measured between NCU-CS³ and MST is <20%, demonstrating that the difference between NCU-CS³ and MST in measuring PCDD/Fs is insignificant. Besides, the effects of adsorbent temperature, adsorbent amount and type of adsorbent on breakthroughs of PAHs and unintentional-persistent organic pollutants (UPOPs) such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), chlorinated phenols (CPs), chlorinated benzenes (CBs) and polychlorinated naphthalenes (PCNs) are evaluated. The results indicate that the breakthrough of pollutants increases with increasing temperature of XAD-2 and decreases with increasing XAD-2 amount. Moreover, XAD-4 is used as alternative adsorbent to test the breakthrough and the results indicate that the breakthroughs of UPOPs of XAD-4 as adsorbent are lower than that with XAD-2 due to higher specific surface area of XAD-4. Furthermore, the residual of PCDD/Fs with NCU-CS³ as the sampling train is relatively low (1.5-3.8%), which meets the regulation of EN 1948-5 (10%).

Oral Rehabilitation of Patients Sustaining Orofacial Injuries: The UPenn Initiative

Tissue injuries in the oral and maxillofacial structures secondary to trauma, warfare, ablative cancer, and benign tumor surgery result in significant losses of speech, masticatory and swallowing functions, aesthetic deformities, and overall psychological stressors and compromise. Optimal oral rehabilitation remains a formidable challenge and an unmet clinical need due to the influence of multiple factors related to the physiologic limitations of tissue repair, the lack of site and function-specific donor tissues and constructs, and an integrated team of multidisciplinary professionals. The advancements in stem cell biology, biomaterial science, and tissue engineering technologies, particularly the 3-dimensional bioprinting technology, together with digital imaging and computer-aided design and manufacturing technologies, have paved the path for personalized/precision regenerative medicine. At the University of Pennsylvania, we have launched the initiative to integrate multidisciplinary health professionals and translational/clinical scientists in medicine, dentistry, stem cell biology, tissue engineering, and regenerative medicine to develop a comprehensive, patient-centered approach for precision and personalized reconstruction, as well as oral rehabilitation of patients sustaining orofacial tissue injuries and defects, especially oral cancer patients.

Characterization of PCDD/Fs and dl-PCBs emission from combustion of PCB-containing oil in a fluidized-bed incinerator

Emissions of PCDD/Fs and dl-PCBs from the combustion of PCB-containing oil in a hazardous waste incinerator are characterized. Flue gas samples are simultaneously taken at three points, including the outlet of ultrasonic wet scrubber, the outlet of heat exchanger and stack. In addition, solid matter samples including incinerator bottom ash, wet scrubber sludge, heat exchanger ash and baghouse ash are also collected. The results indicate that TEQ concentration (PCDD/Fs + dl-PCBs) measured in stack from the combustion of PCB-containing oil is 0.51 ng WHO-TEQ/Nm³. For the solid matter, PCDD/F and dl-PCB concentrations of baghouse ash and wet scrubber sludge are significantly higher than those measured in bottom and heat exchanger ashes. The total removal efficiencies of PCDD/Fs + dl-PCBs achieved with bag filtration (BF) + activated carbon injection (ACI) reaches 65.0%. The emission factors of PCDD/Fs and dl-PCBs from incinerating PCB-containing oil are 1.05 and 0.08 ng WHO-TEQ/L, respectively. The overall PCDD/Fs and dl-PCBs destruction efficiencies achieved with fluidized-bed incinerator reach 99.87% and 99.9998%, respectively, which demonstrates that incineration is an effective engineering practice for treating PCB-containing oil. Moreover, this is the first study suggesting the ratios of PCB-114/(PCB-126+ PCB-114) and PCB-157/(PCB-169+ PCB-157) as indicators to distinguish the emission source of dl-PCB from combustion process and technical mixture evaporation in diagnostic ratio analysis.

Plasma catalytic oxidation of toluene over double perovskite-type oxide via packed-bed DBD

Various perovskite-type catalysts including La₂CoMnO₆, LaCoO₃, and LaMnO₃ are first evaluated for the activities toward C₇H₈ removal. Experimental results indicate that double-type La₂CoMnO₆ shows better activity if compared with single perovskites due to high lattice oxygen content and good reducibility. Subsequently, perovskite catalysts are combined with plasma (NTP) to form in-plasma catalysis (IPC) and post-plasma catalysis (PPC) systems. The results indicate that IPC systems have better higher performance than that of NTP-alone and PPC. Especially, high C₇H₈ conversion (100%) and mineralization efficiency (96.8%) can be achieved with the applied voltage of 18 kV and temperature of 120 °C when La₂CoMnO₆ is integrated with NTP to form IPC system. Also, it owns the highest energy efficiency (0.14 g/kWh). It is concluded that IPC performance for C₇H₈ removal is closely related with the properties of catalyst surface. In addition, the kinetics of IPC systems are investigated by a simplified model, and the result indicates that IPC with La₂CoMnO₆ as catalyst has a higher overall energy constant. This study reveals that double-type La₂CoMnO₆ is of higher activity than single perovskites for C₇H₈ removal, and demonstrates that double-type La₂CoMnO₆ is of high potential to form plasma catalysis system for VOCs removal.

Characterization of polybrominated diphenyl ethers (PBDEs) in various aqueous samples in Taiwan

In this study, 20 groundwater samples and 7 surface water samples were collected and analyzed by HRGC-HRMS to evaluate the levels, congener distributions, and dissolved/solid partitioning of polybrominated diphenyl ethers (PBDEs) in water matrix as well as the removal efficiency of a typical water treatment plant (WTP). The results indicated that the level of PBDEs concentrations ranging from 18.51 to 4212 pg/L and 30.24 to 1021 pg/L were found in groundwater and surface water, respectively. BDE-209 predominated and contributed over 90% of total PBDEs concentrations for all samples analyzed. In addition, the dissolved/solid distribution indicated that 60-80% of PBDEs were measured in solid phase. 97% of total PBDEs was removed in a WTP. Positive matrix factorization (PMF) analysis was conducted for groundwater samples and the results indicated that 3% and 41% of PBDEs were attributed to octa and deca-BDEs commercial mixtures, respectively, while 56% resulted from anaerobic microorganism debromination process. Understanding the PBDEs occurrences, distribution and debromination process as well as their removal efficiency of water treatment plant could provide valuable information on the fate of those compounds in environment.

Storage and reduction of NOx by combining Sr-based perovskite catalyst with nonthermal plasma

A novel NO_x storage and reduction (NSR) system is developed for NO_x removal by integrating Sr-based perovskite catalyst with nonthermal plasma (NTP)-assisted process. In this hybrid system, Sr-based perovskite catalyst is applied for NO_x adsorption in the lean-burn condition while NTP is used as a desorption-reduction step to convert NO_x into N₂ under rich-burn condition. Innovative Sr-based perovskites including SrKMnCoO₄/BaO/Al₂O₃ (SKMCBA), SrKMnCeO₄/BaO/Al₂O₃ (SKMCeBA), and SrKCoNiO₄/BaO/Al₂O₃ (SKCNBA) are successfully prepared by impregnation method. Results indicate that SKMCBA possesses the highest NO_x trapped (214 μmole NO_x/g_catalyst) at 400 °C among 3 Sr-based perovskites investigated. High performance of SKMCBA for NO_x adsorption is mainly attributed to the addition of Mn and Co which own good oxidation ability. Further, SKMCBA is combined with NTP-assisted process for NO_x reduction. Result indicates that NO_x conversion achieved with NTP-assisted process reaches 83% with the applied voltage of 18 kV and frequency of 10 kHz in the absence of reducing agent. Additionally, various reducing agents including hydrogen (H₂), carbon monoxide (CO), and propene (C₃H₆) are introduced, individually, into the NTP reduction process, and the results indicate that performance of NSR with NTP can be effectively enhanced. Especially, 100% NO_x conversion is achieved with H₂-NTP. This study demonstrates that reduction of NO_x via NTP-assisted process is promising.

Effect of reducing agent on catalytic hydrodechlorination of aqueous-phase OCDD/F

Removal/destruction of aqueous-phase octachlorodibenzo-p-dioxin (OCDD) and octachlorodibenzofuran (OCDF) via hydrodechlorination process (HDC) is experimentally evaluated over palladium/activated carbon (Pd/AC) catalyst. Pd catalyst is mainly used as active component for effectiveness in removing dioxin from wastewater. Studies on the removal of PCDD/Fs accomplished with HDC reaction in aqueous phase are limited and the influencing factors have not been clarified. In this study, high-concentration OCDD/F are selected as targets, and the effects of solvent and operating temperature on dechlorination efficiency are investigated via experimental tests. The results indicate that the highest hydrodechlorination efficiency is achieved with isopropanol as solvent. The OCDD/F removal efficiency achieved with the solution of 80% isopropanol is higher than that of 50% isopropanol, whereas the destruction efficiency of OCDD/F reveals the opposite trend. Generally, the removal and destruction efficiencies of PCDFs are higher than those of PCDDs. In addition, the activation energies of OCDD and OCDF are calculated with the Arrhenius equation as 24.8 and 23.1 kJ/mol, respectively. Stability tests are conducted with three cycles. Overall, the results indicate that a high performance (≥99%) can be achieved by combining hydrodechlorination with Pd/AC at a temperature range of 303-353 K, demonstrating that Pd/AC has good potential for removing PCDD/Fs from wastewater.

Atmospheric concentrations and gas-particle partitioning of PCDD/Fs and dioxin-like PCBs around Hochiminh city

Atmospheric PCDD/Fs and dl-PCBs samples were collected in Hochiminh city, Vietnam to address the effect of meteorological parameters, especially rainfall, on the occurrence and gas/particle partitioning of these persistent organic pollutants. The results indicate that PCDD/Fs and dl-PCBs concentrations in industrial site are higher than those measured in commercial and rural sites during both rainy and dry seasons. In terms of mass concentration, ambient PCDD/F levels measured in dry season are significantly higher than those measured in rainy season while dl-PCB levels do not vary significantly between rainy and dry seasons. The difference could be attributed to different gas/particle partitioning characteristics between PCDD/Fs and dl-PCBs. PCDD/Fs are found to be mainly distributed in particle phase while dl- PCBs are predominantly distributed in gas phase in both rainy and dry seasons. Additionally, Junge-Pankow and Harner-Bidleman models are applied to better understand the gas/particle partitioning of these pollutants in atmosphere. As a results, both PCDD/Fs and dl-PCBs are under non-equilibrium gas/particle partitioning condition, and PCDD/Fs tend to reach equilibrium easier in rainy season while there are no clear trend for dl-PCBs. Harner-Bidleman model performs better in evaluating the gas/particle partitioning of PCDD/Fs while Junge-Pankow model results in better prediction for dl-PCBs.

Removal of VOCs from gas streams with double perovskite-type catalysts

Double perovskite-type catalysts including La₂CoMnO₆ and La₂CuMnO₆ are first evaluated for the effectiveness in removing volatile organic compounds (VOCs), and single perovskites (LaCoO₃, LaMnO₃, and LaCuO₃) are also tested for comparison. All perovskites are tested with the gas hourly space velocity (GHSV) of 30,000hr^-1, and the temperature range of 100-600°C for C₇H₈ removal. Experimental results indicate that double perovskites have better activity if compared with single perovskites. Especially, toluene (C₇H₈) can be completely oxidized to CO₂ at 300°C as La₂CoMnO₆ is applied. Characterization of catalysts indicates that double perovskites own unique surface properties and are of higher amounts of lattice oxygen, leading to higher activity. Additionally, apparent activation energy of 68kJ/mol is calculated using Mars-van Krevelen model for C₇H₈ oxidation with La₂CoMnO₆ as catalyst. For durability test, both La₂CoMnO₆ and La₂CuMnO₆ maintain high C₇H₈ removal efficiencies of 100% and 98%, respectively, at 300°C and 30,000hr^-1, and they also show good resistance to CO₂ (5%) and H₂O_(g) (5%) of the gas streams tested. For various VOCs including isopropyl alcohol (C₃H₈O), ethanal (C₂H₄O), and ethylene (C₂H₄) tested, as high as 100% efficiency could be achieved with double perovskite-type catalysts operated at 300-350°C, indicating that double perovskites are promising catalysts for VOCs removal.

Catalytic oxidation of trichloroethylene from gas streams by perovskite-type catalysts

Three perovskite-type catalysts including LaMnO₃, La_0.8Ce_0.2MnO₃, and La_0.8Ce_0.2 Mn_0.8Ni_0.2O₃ are prepared using citric acid sol-gel method and evaluated as catalyst for the oxidation of trichloroethylene (TCE) in air with temperature ranging from 100 to 600 °C. The physicochemical properties of three perovskite-type catalysts were characterized by SEM, EDS, XRD, BET, and XPS to investigate the relationship with catalytic activities. The results show that the removal efficiency of TCE achieved with La_0.8Ce_0.2Mn_0.8Ni_0.2O₃ (the best one) reaches 100% at 400 °C and the mineralization efficiency reaches 100% at 600 °C. The enhanced activity can be attributed to the addition of Ce and Ni which increases the surface areas, active oxygen species, and the redox ability of the Mn⁴⁺/Mn³⁺ ratio on the catalyst surface. As La_0.8Ce_0.2Mn_0.8Ni_0.2O₃ is applied for TCE oxidation, the main intermediate chlorinated byproduct detected is tetrachloroethylene (C₂Cl₄) which is generated by the reaction of TCE and chlorine (Cl₂). The activation energy for the TCE oxidation with La_0.8Ce_0.2Mn_0.8Ni_0.2O₃ catalyst is 51 kJ/mol using kinetic models of power-law type.

Review on characteristics of PAHs in atmosphere, anthropogenic sources and control technologies

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds composed of multiple aromatic rings. PAHs are ubiquitous atmospheric pollutants which are well-recognized as carcinogenic, teratogenic and genotoxic compounds. PAHs are released from incomplete combustion or pyrolysis of materials containing carbon and hydrogen, such as coal, oil, wood and petroleum products. Understanding the characteristics of PAHs in atmosphere, source profiles and technologies available for controlling PAHs emission is essential to reduce the impacts of PAHs. This paper offers an overview on concentration and distribution of atmospheric PAHs, emission factors and distribution of PAHs in different sources, and available control technologies. Characteristics of atmospheric PAHs vary with meteorological conditions and emission sources, while characteristics of PAHs emission depend on burned material and combustion condition. Combination of some technologies may be necessary for effective removal of both low-ring and high-ring PAHs.

Adsorption of mesitylene via mesoporous adsorbents

Mesitylene (or 1,3,5-trimethylbenzene) is a volatile organic compound emitted from various industrial processes, e.g., spray coating. Its emissions have become a critical issue because mesitylene is toxic and cannot be removed using traditional adsorbents, e.g., zeolite (H-ZSM-5; the diameter of mesitylene molecules is greater than the pore size of H-ZSM-5). Hence, an adsorbent with a large pore size, MCM-41, is used in this study to investigate its adsorption capacity for mesitylene and compare with that of H-ZSM-5. Experimental results reveal that MCM-41 without Al₂O₃ exhibits a good adsorption capacity (184 mg/g) for the gas stream containing 100 ppm of mesitylene at a relative humidity of 10%. The adsorption kinetics is well described by the Freundlich isotherm. Furthermore, experimental results reveal that MCM-41 is effective for the adsorption of low concentrations (10 ppm) of mesitylene. In addition, adsorption-desorption tests revealed that the sample MCM-41-AS is stable to sustain the adsorption capacity after 10 adsorption-desorption cycles. After 10 adsorption-desorption cycles, MCM-41-AS retains 92.4% of its initial adsorption capacity (170 vs. 184 mg/g). Finally, MCM-41 and H-ZSM-5 in series are effective for the simultaneous removal of mesitylene and toluene in the gas stream.

IMPLICATIONS

This study aims to improve the performance of adsorbent for mesitylene, which is typically applied in the spray-coating industry. The zeolite MCM-41-AS is selected as a candidate for the investigation. Experimental results reveal that MCM-41-AS exhibits a good adsorption capacity for mesitylene and that it can be integrated with H-ZSM-5-25 for the simultaneous adsorption of mesitylene and toluene.

Characterization of PCDD/Fs and dioxin-like PCBs emitted from two woodchip boilers in Taiwan

This study investigates the formation and removal of PCDD/Fs and dl-PCBs in two woodchips boilers during different operating periods. Results indicate that combustion condition affects PCDD/F and dl-PCB formation within the woodchip combustion process. PCDD/F and dl-PCB concentrations during the start-up period are much higher than those measured during normal operation and shut-down periods due to unstable combustion. PCDD/F and dl-PCB concentrations at APCDs inlet of Plant A are significantly higher than that of Plant B due to the lower combustion temperature (500-850 °C) compared with Plant B (850-925 °C). Major PCDD/F congeners at APCDs inlet of both plants during normal operation are O₈CDD, 1,2,3,4,6,7,8-H₇CDD and 1,2,3,4,6,7,8-H₇CDF, while major dl-PCBs are TeCB-77, PeCB-118 and PeCB-126. The removal efficiencies of PCDD/F and PCBs achieved with the APCDs of Plant A are 95.6% and 88.6%, respectively, while those of Plant B are 99.3% and 94.9%. Possibly, the AC concentration of Plant A exceeds the optimal AC concentration and, PCDD/Fs and dl-PCBs might be formed because the AC injected can supply additional reaction area and carbon source. Also, this may be due to different operating temperatures of APCDs, which affects removal efficiency of PCDD/F and dl-PCB congeners. The emission factors (PCDD/Fs + dl-PCBs) of Plants A and B are calculated as 17.86 and 1.25 μg I-TEQ/ton, respectively. Concentrations of PCDD/Fs in the BF ash of Plants A and B during normal operation are measured as 98.57 and 38.06 ng I-TEQ/g, which are significantly higher than the standard limit (1.0 ng I-TEQ/g) promulgated by Taiwan EPA.

Desorption of isopropyl alcohol from adsorbent with non-thermal plasma

Effective desorption of isopropyl alcohol (IPA) from adsorbents with non-thermal plasma is developed. In this system, IPA is effectively adsorbed with activated carbon while dielectric barrier discharge is applied to replace the conventional thermal desorption process to achieve good desorption efficiency, making the treatment equipment smaller in size. Various adsorbents including molecular sieves and activated carbon are evaluated for IPA adsorption capacity. The results indicate that BAC has the highest IPA adsorption capacity (280.31 mg IPA/g) under the operating conditions of room temperature, IPA of 400 ppm, and residence time of 0.283 s among 5 adsorbents tested. For the plasma desorption process, the IPA selectivity of 89% is achieved with BAC as N₂ is used as desorbing gas. In addition, as air or O₂ is used as desorbing gas, the IPA desorption concentration is reduced, because air and O₂ plasmas generate active species to oxidize IPA to form acetone, CO₂, and even CO. Furthermore, the results of the durability test indicate that the amount of IPA desorbed increases with increasing desorption times and plasma desorption process has a higher energy efficiency if compared with thermal desorption. Overall, this study indicates that non-thermal plasma is a viable process for removing VOCs to regenerate adsorbent.

Combined fast selective reduction using Mn-based catalysts and nonthermal plasma for NOx removal

In this study, the concept of fast SCR for NO reduction with NH₃ as reducing agent is realized via the combination of nonthermal plasma (NTP) with Mn-based catalyst. Experimental results indicate that 10% wt. Mn-Ce-Ni/TiO₂ possesses better physical and chemical properties of surface, resulting in higher NO removal efficiency if compared with 10% wt. Mn-Ce/TiO₂ and 10% wt. Mn-Ce-Cu/TiO₂. Mn-Ce-Ni/TiO₂ of 10% wt. achieves 100% NO_x conversion at 150 °C, while 10% wt. Mn-Ce/TiO₂ and 10% wt. Mn-Ce-Cu/TiO₂ need to be operated at a temperature above 200 °C for 100% NO_x conversion. However, NO conversion achieved with 10% wt. Mn-Ce-Ni/TiO₂ is significantly reduced as H₂O_(g) and SO₂ are introduced into the SCR system simultaneously. Further, two-stage system (SCR with DBD) is compared with the catalyst-alone for NO_x conversion and N₂ selectivity. The results indicate that 100% NO_x conversion can be achieved with two-stage system at 100 °C, while N₂ selectivity reaches 80%. Importantly, NO_x conversion achieved with two-stage system could maintain >95% in the presence of C₂H₄, CO, SO₂, and H₂O_(g), indicating that two-stage system has better tolerance for complicated gas composition. Overall, this study demonstrates that combining NTP with Mn-based catalyst is effective in reducing NO_x emission at a low temperature (≤200 °C) and has good potential for industrial application.

Catalytic removal of phenol from gas streams by perovskite-type catalysts

Three perovskite-type catalysts prepared by citric acid method are applied to remove phenol from gas streams with the total flow rate of 300mL/min, corresponding to a GHSV of 10,000/hr. LaMnO₃ catalyst is first prepared and further partially substituted with Sr and Cu to prepare La_0.8Sr_0.2MnO₃ and La_0.8Sr_0.2Mn_0.8Cu_0.2O₃, and catalytic activities and fundamental characteristics of these three catalysts are compared. The results show that phenol removal efficiency achieved with La_0.8Sr_0.2Mn_0.8Cu_0.2O₃ reaches 100% with the operating temperature of 200°C and the rate of mineralization at 300°C is up to 100%, while the phenol removal efficiencies achieved with La_0.8Sr_0.2MnO₃ and LaMnO₃ are up to 100% with the operating temperature of 300°C and 400°C, respectively. X-ray photoelectron spectroscopy (XPS) analysis shows that the addition of Sr and Cu increases the lattice oxygen of La_0.8Sr_0.2Mn_0.8Cu_0.2O₃, and further increases mobility or availability of lattice oxygen. The results indicate that La_0.8Sr_0.2Mn_0.8Cu_0.2O₃ has the best activity for phenol removal among three catalysts prepared and the catalytic activity of phenol oxidation is enhanced by the introduction of Sr and Cu into LaMnO₃. Apparent activation energy of 48kJ/mol is calculated by Mars-Van Krevelen Model for phenol oxidation with La_0.8Sr_0.2Mn_0.8Cu_0.2O₃ as catalyst.

PCDD/Fs and dl-PCBs concentrations in water samples of Taiwan

Polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and coplanar polychlorinated biphenyls (dioxin-like PCBs) have received much public concern worldwide due to their persistence and toxicity. The presence of these compounds in environmental matrices, especially in water bodies, enhances the risk of human exposure to these toxic pollutants. In this study, seventeen 2,3,7,8 chlorinated PCDD/Fs and twelve dl-PCBs were measured in 11 groundwater samples collected throughout Taiwan and 2 surface water samples collected in northern Taiwan. PCDD/F and PCB concentrations in two surface water samples are relatively low, with the average concentrations of 0.038 and 0.001 pg WHO-TEQ/L (7.474 and 1.862 pg L^-1), respectively. As for groundwater samples, PCDD/F concentrations measured range from 0.005 to 3.963 pg WHO-TEQ/L, while dl-PCB concentrations range from 2.5 × 10^-5 to 0.189 pg WHO-TEQ/L. Total WHO-TEQ concentrations range from 0.005 to 3.963 pg WHO-TEQ/L, reflecting serious contamination of PCDD/Fs and PCBs in groundwater at some sampling sites. In term of total PCDD/Fs, PCDDs constitute a significant fraction (77.3%), and OCDD is most abundant, followed by HpCDD/Fs and HxCDD/Fs. PCB 118 is dominant among 12 dl-PCBs measured, followed by PCB 105 and PCB 77. Solid-phase PCDD/Fs generally predominate in water samples and PCDFs are of slightly lower distribution in solid phase in comparison with PCDDs, while PCBs are mainly distributed in dissolved phase. Results of principal component analysis (PCA) indicate that use of PCP and Na-PCP, thermal processes and PCBs-containing products might be the major sources of PCDD/Fs and PCBs in water samples measured.

PAH emissions from coal combustion and waste incineration

The characteristics of PAHs that are emitted by a municipal waste incinerator (MWI) and coal-fired power plant are examined via intensive sampling. Results of flue gas sampling reveal the potential for PAH formation within the selective catalytic reduction (SCR) system of a coal-fired power plant. In the large-scale MWI, the removal efficiency of PAHs achieved with the pilot-scaled catalytic filter (CF) exceeds that achieved by activated carbon injection with a bag filter (ACI+BF) owing to the effective destruction of gas-phase contaminants by a catalyst. A significantly lower PAH concentration (1640ng/g) was measured in fly ash from a CF module than from an ACI+BF system (5650ng/g). Replacing the ACI+BF system with CF technology would significantly reduce the discharge factor (including emission and fly ash) of PAHs from 251.6 to 77.8mg/ton-waste. The emission factors of PAHs that are obtained using ACI+BF and the CF system in the MWI are 8.05 and 7.13mg/ton, respectively. However, the emission factor of MWI is significantly higher than that of coal-fired power plant (1.56mg/ton). From the perspective of total environmental management to reduce PAH emissions, replacing the original ACI+BF process with a CF system is expected to reduce environmental impact thereof.

Combining nonthermal plasma with perovskite-like catalyst for NOx storage and reduction

A new NOx storage and reduction (NSR) system is developed for NOx removal by combining perovskite-like catalyst with nonthermal plasma technology. In this hybrid system, catalyst is mainly used for oxidizing NO to NO2 and storing them, while nonthermal plasma is applied as a desorption-reduction step for converting NOx into N2. An innovative catalyst with a high NOx storage capacity and good reduction performance is developed by successive impregnation. The catalysts prepared with various metal oxides were investigated for NOx storage capacity (NSC) and NOx conversion. Characterization of the catalysts prepared reveals that addition of cobalt (Co) and potassium (K) considerably increases the performance for NSC. Results also show that SrKMn0.8Co0.2O4 supported on BaO/Al2O3 has good NSC (209 μmol/gcatalyst) for the gas stream containing 500 ppm NO and 5 % O2 with N2 as carrier gas. For plasma reduction process, NOx conversion achieved with SrKMn0.8Co0.2O4/BaO/Al2O3 reaches 81 % with the applied voltage of 12 kV and frequency of 6 kHz in the absence of reducing agents. The results indicate that performance of plasma reduction process (81 %) is better than that of thermal reduction (64 %). Additionally, mixed gases including 1 % CO, 1 % H2 and 1 % CH4, and 2 % H2O(g) are simultaneously introduced into the system to investigate the effect on NSR with plasma system and results indicate that performance of NSR with plasma can be enhanced. Overall, the hybrid system is promising to be applied for removing NOx from gas streams. Graphical abstract ᅟ.

Catalytic decomposition of gaseous PCDD/Fs over V2O5/TiO2-CNTs catalyst: Effect of NO and NH3 addition

There is a strong need for a control technology that simultaneously achieving the abatement of PCDD/Fs (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans) and nitrogen oxides (NOx) emissions in waste incineration industry. TiO2 and carbon nanotubes (CNTs) were used as composite carriers to support vanadium oxide as an innovative catalyst to simultaneously control PCDD/Fs and NO emissions. The removal efficiencies (RE) of PCDD/Fs by V2O5/TiO2-CNTs catalyst under a space velocity (SV) of 20,000 h(-1) reaches 99.9% at 150 °C and adsorption is supposed to be the main mechanism at this temperature. The influence of NONH3 reaction on PCDD/Fs catalytic reaction is investigated. The kinetics analysis exhibits that the addition of NO and NH3 reduces the activation energies for OCDD (octachlorodibenzo-p-dioxin) and OCDF (octachlorodibenzofuran) decomposition to 3.6 kJ/mol and 5.4 kJ/mol respectively.

Enhancement of nitric oxide decomposition efficiency achieved with lanthanum-based perovskite-type catalyst

Direct decompositions of nitric oxide (NO) by La0.7Ce0.3SrNiO4, La0.4Ba0.4Ce0.2SrNiO4, and Pr0.4Ba0.4Ce0.2SrNiO4 are experimentally investigated, and the catalysts are tested with different operating parameters to evaluate their activities. Experimental results indicate that the physical and chemical properties of La0.7Ce0.3SrNiO4 are significantly improved by doping with Ba and partial substitution with Pr. NO decomposition efficiencies achieved with La0.4Ba0.4Ce0.2SrNiO4 and Pr0.4Ba0.4Ce0.2SrNiO4 are 32% and 68%, respectively, at 400 °C with He as carrier gas. As the temperature is increased to 600 °C, NO decomposition efficiencies achieved with La0.4Ba0.4Ce0.2SrNiO4 and Pr0.4Ba0.4Ce0.2SrNiO4, respectively, reach 100% with the inlet NO concentration of 1000 ppm while the space velocity is fixed at 8000 hr(-1). Effects of O2, H2O(g), and CO2 contents and space velocity on NO decomposition are also explored. The results indicate that NO decomposition efficiencies achieved with La0.4Ba0.4Ce0.2SrNiO4 and Pr0.4Ba0.4Ce0.2SrNiO4, respectively, are slightly reduced as space velocity is increased from 8000 to 20,000 hr(-1) at 500 °C. In addition, the activities of both catalysts (La0.4Ba0.4Ce0.2SrNiO4 and Pr0.4Ba0.4Ce0.2SrNiO4) for NO decomposition are slightly reduced in the presence of 5% O2, 5% CO2, or 5% H2O(g). For durability test, with the space velocity of 8000 hr(-1) and operating temperature of 600 °C, high N2 yield is maintained throughout the durability test of 60 hr, revealing the long-term stability of Pr0.4Ba0.4Ce0.2SrNiO4 for NO decomposition. Overall, Pr0.4Ba0.4Ce0.2SrNiO4 shows good catalytic activity for NO decomposition.

IMPLICATIONS

Nitrous oxide (NO) not only causes adverse environmental effects such as acid rain, photochemical smog, and deterioration of visibility and water quality, but also harms human lungs and respiratory system. Pervoskite-type catalysts, including La0.7Ce0.3SrNiO4, La0.4Ba0.4Ce0.2SrNiO4, and Pr0.4Ba0.4Ce0.2SrNiO4, are applied for direct NO decomposition. The results show that NO decomposition can be enhanced as La0.7Ce0.3SrNiO4 is substituted with Ba and/or Pr. At 600 °C, NO decomposition efficiencies achieved with La0.4Ba0.4Ce0.2SrNiO4 and Pr0.4Ba0.4Ce0.2SrNiO4 reach 100%, demonstrating high activity and good potential for direct NO decomposition. Effects of O2, H2O(g), and CO2 contents on catalytic activities are also evaluated and discussed.

Catalytic destruction vs. adsorption in controlling dioxin emission

This study investigates the removal efficiencies of PCDD/Fs achieved with a catalytic filter (CF) and with activated carbon injection followed by bag filter (ACI+BF) as applied in an industrial waste incinerator (IWI) and a hazardous waste incinerator (HWI), respectively. Catalytic filtration has been successfully applied to remove PCDD/Fs from gas streams. Comparing the CF to the ACI+BF system, it appears that the PCDD/F removal efficiency achieved with a CF is higher than that of an ACI+BF system. The PCDD/F emissions from both incinerators are well controlled to meet the regulatory limit of 0.1 ng I-TEQ/Nm(3). Additionally, the PCDD/F concentration in BF ash is higher than the regulation limit of Taiwan (1.0 ng I-TEQ/g). In contrast, the PCDD/F concentration in CF ash is only 0.274 ng I-TEQ/g. The difference is attributed to the fact that the ACI+BF system just transfers PCDD/Fs from gas phase to solid phase and further increases the PCDD/F concentration in fly ash, while CF technology effectively destroys the gas-phase PCDD/Fs. Therefore, the disposal of the fly ash discharged from CF would be less expensive compared with the fly ash discharged from the ACI+BF system. In this study, the PCDD/F emission factors of both incinerators are also established.

Adsorption-desorption characteristics of methyl ethyl ketone with modified activated carbon and inhibition of 2,3-butanediol production

Activated carbon (AC) is seldom applied for recovering ketone-based volatile organic compounds because of safety concerns. Adsorption of methyl ethyl ketone (MEK) with AC is a highly exothermic reaction that potentially causes fires in AC beds. Moreover, 2,3-butanediol (BDO) is produced in the desorbed solvent, causing yellowing and odor of the recovered solvent. This study applied a continuous adsorption-desorption apparatus for evaluating the operating capacities and BDO concentration in recovered MEK containing modified and original ACs. AC-1 (TAKETA- G2X) was used as the target for modification. The experimental results indicate that using MgO as the modifier increases the ignition point by 12°C and that applying KNO3 as the modifier reduces the AC ignition point by 28°C (compared with AC-1). The BDO concentration of the desorbed MEK solvent can be reduced by increasing the loading of the modifying agent (Ethanolamine) (Im-1: 3.1 wt%; Im-5: 6.2 wt%). Moreover, applying the AC pretreated with nitrogen (Im-6) as adsorbent significantly reduces the BDO concentration (from 0.123 wt% to 0.073 wt%). Because desorption and purging procedures were performed in N2 atmospheres, the BDO concentrations of the desorbed MEK solvents were relatively low and ranged from 0.032 wt% to 0.043 wt%. When the MEK concentration was reduced to 2000 ppm, lower BDO concentrations (0.012-0.022 wt%) were measured in the recovered MEK solvent. The way to modify activated carbon and a better desorbing sequence to effectively inhibit the oxidation of MEK to BDO are developed. The results obtained indicate that the BDO concentration in the desorbed solvent was lower than the original MEK solvent (0.023 wt%). Different approaches can be applied simultaneously to achieve high inhibition effects; however, carbon adsorption performance may be negatively affected.

IMPLICATIONS

The study is motivated to improve the quality of recovered solvent and reduce fire hazards, particularly when AC is applied for adsorbing a ketone-based solvent (e.g., MEK). The experimental results indicate that the BDO concentration in the recovered solvent can be reduced and the ignition point of AC can be increased by modifying the AC with an appropriate agent.

Adsorption and destruction of PCDD/Fs using surface-functionalized activated carbons

Activated carbon adsorbs polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) from gas streams but can simultaneously generate PCDD/Fs via de novo synthesis, increasing an already serious disposal problem for the spent sorbent. To increase activated carbon's PCDD/F sorption capacity and lifetime while reducing the impact of hazardous waste, it is beneficial to develop carbon-based sorbents that simultaneously destroy PCDD/Fs while adsorbing the toxic chemicals from gas streams. In this work, hydrogen-treated and surface-functionalized (i.e., oxygen, bromine, nitrogen, and sulfur) activated carbons are tested in a bench-scale reactor as adsorbents for PCDD/Fs. All tested carbons adsorb PCDD/F efficiently, with international toxic equivalent removal efficiencies exceeding 99% and mass removal efficiencies exceeding 98% for all but one tested material. Hydrogen-treated materials caused negligible destruction and possible generation of PCDD/Fs, with total mass balances between 100% and 107%. All tested surface-functionalized carbons, regardless of functionality, destroyed PCDD/Fs, with total mass balances between 73% and 96%. Free radicals on the carbon surface provided by different functional groups may contribute to PCDD/F destruction, as has been hypothesized in the literature. Surface-functionalized materials preferentially destroyed higher-order (more chlorine) congeners, supporting a dechlorination mechanism as opposed to oxidation. Carbons impregnated with sulfur are particularly effective at destroying PCDD/Fs, with destruction efficiency improving with increasing sulfur content to as high as 27%. This is relevant because sulfur-treated carbons are used for mercury adsorption, increasing the possibility of multi-pollutant control.

Characteristics of PCDD/F emissions from secondary copper smelting industry

Characteristics and mechanisms of PCDD/F formation with different feed materials in secondary copper smelting industry are investigated. The results indicate that PCDD/Fs are significantly formed even with the reaction time less than 0.1s, especially when the material containing high residues (Cu3) is fed. High copper content (65±2%) in the feed material enhances PCDD/F formation rate. Memory effect and de novo synthesis are two important mechanisms leading to PCDD/F formation. PCDD/F concentrations at the cyclone's inlet are between 2.92 and 12.4ng-TEQNm(-3) and increase with increasing residue content in the feed material. Two regions are identified for high potential of PCDD/F formation including the brass melt surface of the induction furnace and piping before the induced draft fan of the inlet hood. PCDD/Fs in flue gas are effectively removed with a cyclone and bag filter at low operating temperatures (<60°C) to meet the emission limit of 1.0ng-TEQNm(-3). 1,2,3,4,6,7,8-HpCDF has the largest mass fraction of PCDD/Fs and can serve as a fingerprint for emissions from secondary copper smelting processes. The total emission factor of PCDD/Fs from flue gas, residual and fly ash in the secondary copper smelting process investigated is 22.01μg-TEQtonne(-1).

Removal of formaldehyde over Mn(x)Ce(1)-(x)O(2) catalysts: thermal catalytic oxidation versus ozone catalytic oxidation

Mn(x)Ce(1)-(x)O(2) (x: 0.3-0.9) prepared by Pechini method was used as a catalyst for the thermal catalytic oxidation of formaldehyde (HCHO). At x=0.3 and 0.5, most of the manganese was incorporated in the fluorite structure of CeO(2) to form a solid solution. The catalytic activity was best at x=0.5, at which the temperature of 100% removal rate is the lowest (270°C). The temperature for 100% removal of HCHO oxidation is reduced by approximately 40°C by loading 5wt.% CuO(x) into Mn(0.5)Ce(0.5)O(2). With ozone catalytic oxidation, HCHO (61 ppm) in gas stream was completely oxidized by adding 506 ppm O₃over Mn(0.5)Ce(0.5)O(2) catalyst with a GHSV (gas hourly space velocity) of 10,000 hr⁻¹ at 25°C. The effect of the molar ratio of O(3) to HCHO was also investigated. As O(3)/HCHO ratio was increased from 3 to 8, the removal efficiency of HCHO was increased from 83.3% to 100%. With O(3)/HCHO ratio of 8, the mineralization efficiency of HCHO to CO(2) was 86.1%. At 25°C, the p-type oxide semiconductor (Mn(0.5)Ce(0.5)O(2)) exhibited an excellent ozone decomposition efficiency of 99.2%, which significantly exceeded that of n-type oxide semiconductors such as TiO(2), which had a low ozone decomposition efficiency (9.81%). At a GHSV of 10,000 hr⁻¹, [O(3)]/[HCHO]=3 and temperature of 25°C, a high HCHO removal efficiency (≥ 81.2%) was maintained throughout the durability test of 80 hr, indicating the long-term stability of the catalyst for HCHO removal.

Direct N2O decomposition over La2NiO4-based perovskite-type oxides

Direct decomposition of N2O by perovskite-structure catalysts including La2NiO4, LaSrNiO4, and La0.7Ceo.3SrNiO4 was investigated. The catalysts were prepared by the Pechini method and characterized by x-ray diffraction (XRD), BETI scanning electron microscopy (SEM), and 02-TPD. Experimental results indicate that the properties of La2NiO4 are significantly improved by partially substituting La with Sr and Ce. N2O decomposition efficiencies achieved with LaSrNi04 and La0.7Ce0.3SrNiO4 are 44 and 36%, respectively, at 400 degrees C. As the temperature was increased to 600 degrees C, N2O decomposition efficiency achieved with LaSrNiO4 and La0.7Ce0.3SrNiO4 reached 100% at an inlet N2O concentration of 1000 ppm, while the space velocity was fixed at 8,000 hr(-1). In addition, effects of various parameters including oxygen, water vapor and space velocity were also explored. The results indicate that N2O decomposition efficiencies achieved with LaSrNiO4 and La0.7Ce0.3SrNiO4 are not significantly affected as space velocity is increased from 8,000 to 20,000 hr(-1), while La0.7Ce0.3SrNiO4 shows better tolerance for O2 and H2O(g). On the other hand, N2 yield with LaSrNiO4 as catalyst can be significantly improved by doping Ce. At a gas hour space velocity of 8000 hr(-1) and a temperature of 600 degrees C, high N2O decomposition efficiency and N2 yield were maintained throughout the durability test of 60 hr, indicating the long-term stability of La0.7Ce0.3SrNiO4 for N2O decomposition.

Pilot tests on the catalytic filtration of dioxins

Tests were conducted to study the removal efficiencies (REs) of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) from flue gas during a test program involving a pilot-scale catalytic filter (CF) module and a full-scale municipal solid waste incinerator (MSWI). The REs attained with the CF on a side stream and a conventional activated carbon (AC) injection and baghouse filtration system in the full-scale MSWI are evaluated via simultaneous sampling and analysis of both gas- and particle-phase PCDD/Fs. Flue gas without AC is supplied to the pilot-scale CF module for evaluating its RE capabilities. The REs achieved with the CF at 180 °C are 96.80 and 99.50%, respectively, for the gas phase and the particulate contained. The gas-phase PCDD/F RE rises significantly at 200 and 220 °C. The air/cloth (A/C) ratio defined as is the gas flow rate (m(3)/min) divided by the filtration area (m(2)) also affects the PCDD/F RE, especially in the gas phase. At 180 °C, a RE of gas-phase PCDD/Fs of 95.94% is attained with the CF at 0.8 m/min, yet it decreases at higher A/C ratios (1 and 1.2 m/min). A significantly lower toxic equivalency (TEQ) concentration (0.71 ng I-TEQ/g) was measured in the filter dust of the CF module compared to that collected by the AC adsorption system (4.18 ng I-TEQ/g), apparently because of the destruction of gas-phase PCDD/Fs by the catalyst.

Pyrolysis of MWI fly ash -- effect on dioxin-like congeners

Removal and destruction of dioxin-like congeners, including polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and biphenyls (PCBs), from fly ash were investigated at varying pyrolysis temperatures and reaction times and using calcium-based additives. Destruction efficiencies based on TEQ and mass both increase with rising treatment temperature. However, additional low chlorinated PCDD/Fs were formed significantly by dechlorination of high chlorinated PCDD/Fs, at pyrolysis temperatures of 250 and 300°C. Surprisingly, lower destruction efficiencies were realized in the presence of Ca-based additive, compared with those without additive, and TEQ values of fly ash into which CaO was introduced increased, compared with the raw ash, due to significant formation of low chlorinated PCDD/Fs (4-5 Cl). However, complex interactions among unburned carbon, sulfur and metals in the fly ash collected in this study make it difficult to pinpoint the exact causes. The results obtained in this study indicate that degradation and formation of dioxin-like congeners take place simultaneously in pyrolysis process, such as formation of low chlorinated PCDD/Fs via dechlorination of highly chlorinated PCDD/Fs.

Application of bimetallic iron (BioCAT slurry) for pentachlorophenol removal from sandy soil

Bimetallic iron nanoparticles have mostly been applied to the degradation of chlorinated compounds in the aqueous phase. In this study, the degradation of pentachlorophenol (PCP) spiked into sandy soil is considered as a first exploratory step for remediating PCP in real contaminated soil using a commercial preparation of bimetallic iron (Trade name BioCAT). After 21 days of treatment a PCP removal efficiency of 90% was achieved, along with 70% dechlorination efficiency, for a dosage of 600 mg BioCAT slurry/kg soil. Degradation of PCP by BioCAT follows first order kinetics in PCP. Stepwise dechlorination is the main pathway of PCP elimination from soil slurries contacted with BioCAT. Such dechlorination is confirmed by the appearance of intermediate products, as well as by release of chlorides. Additionally, the increasing pH value and the rapid decrease of the oxidation/reduction potential (ORP) also attest to the reductive dechlorination of PCP. The reaction products comprehend lower chlorinated phenols, including three TeCP isomers, four TrCP isomers, four DCP isomers, two MCP isomers and phenol. These findings indicate that BioCAT could be applied for field treatment of PCP-contaminated soil under ambient conditions.

PCDD/PCDF behavior in low-temperature pyrolysis of PCP-contaminated sandy soil

This study investigates the behavior of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) formation, dechlorination and destruction in PCP-contaminated sandy soil by low-temperature thermal treatment. Experimental tests were carried out in a nitrogen atmosphere in the temperature range of 200-400 °C with a treatment time of 30 min. 70% of PCP removal from the soil was achieved, resulting in 1436±230 ng/kg, the highest PCDD/F formation at 250 °C; however, the highest toxic concentration was measured around 4.20±0.62 ng TEQ/kg at 300 °C with 80% PCP removal from the soil. Further analysis has revealed that OCDD is the most dominant congener that is supposed to be formed from the pyrolysis of PCP, while OCDF is the second prevailing congener, possibly due to pyrolysis of 2,3,4,5-TeCP being a main byproduct of PCP pyrolysis. Detection of less chlorinated dioxins and furans over 300 °C indicates the dechlorination of highly chlorinated dioxins and furans, especially octachlorinated dibenzo-p-dioxin (OCDD) at 350 °C and 400 °C. Desorption from soil was supposed as a main mechanism for the distribution of PCDD/Fs in the gaseous phase, and not much difference in dioxins and furan levels was observed at 350 °C and 400 °C in the gaseous phase. Therefore, 350 °C is the most appropriate temperature to remove most PCP and PCDD/Fs from soil, as well as to meet PCDD/F emission standards (0.1 ng I-TEQ/Nm(3)).

Effect of dietary supplementation of Lactobacillus-fermented Artemisia princeps on growth performance, meat lipid peroxidation, and intestinal microflora in Hy-line Brown male chickens

The objective of this experiment was to investigate the effect of dietary supplementation of Lactobacillus-fermented Artemisia princeps (LFA) on growth performance, meat lipid peroxidation, and intestinal microflora in Hy-line Brown male chickens. A total of six hundred twenty-four 1-d-old Hy-Line Brown male chicks were randomly allotted to 3 dietary treatments with 4 replicated pens consisting of 52 chicks. The control diet was formulated to be adequate in energy and nutrients. Two additional diets were prepared by adding 2.5 or 5.0 g/kg of LFA to the control diet. The experimental diets were fed on an ad libitum basis to the birds during 7 wk. Body weight gain and feed intake were recorded at 2 and 7 wk. At the end of the experiment, 2 birds from each treatment were killed by cervical dislocation and the samples for ileal content, breast, and thigh meat were collected for the determination of meat lipid peroxidation and microbial population. Results indicated that increasing inclusion level of LFA in diets improved BW gain (linear and quadratic, P < 0.05) and tended to improve feed efficiency (linear and quadratic, P < 0.10) of birds during 0 to 7 wk. Feeding the diets containing increasing amounts of LFA to birds reduced (quadratic, P < 0.05) thiobarbituric acid-reactive substance (TBARS) values in breast and thigh meat during 15 d of storage. The concentrations of Lactobacillus spp. in the ileal content of birds increased (linear and quadratic, P < 0.05), but those of Salmonella spp. tended to be decreased (quadratic, P < 0.10) as inclusion level of LFA in diets increased. These results suggest that dietary LFA may be used as a functional ingredient to improve growth performance, meat lipid stability, and intestinal health of birds.