Preparation and characterization of activated carbons from tobacco stem by chemical activation

Activated carbons were prepared from tobacco stem by chemical activation using potassium hydroxide (KOH), potassium carbonate (K₂CO₃), and zinc chloride (ZnCl₂). The effects of the impregnation ratio (activating agent/precursor) and activating agents on the physical and chemical properties of activated carbons were investigated. The textual structure and surface properties of activated carbons were characterized by nitrogen (N₂) adsorption isotherm, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), x-ray photoelectron spectroscopy (XPS), and thermogravimetry (TG). ZnCl₂, acting as a superior activating agent compared to the others, produced much more porosity. The maximum specific surface area reached 1347 m²/g, obtained by ZnCl₂ activation with an impregnation ratio of 4.0. Moreover, ZnCl₂ activation yielded products with an excellent thermostability, attributed to different activation mechanisms. Various oxygen functions were detected on the activated carbon surface, and hydroxyl and ester groups were found to be in the majority.

Implications: Tobacco stem, the residue from cigarette manufacturing, is usually discarded as waste, leading to serious resource waste and environmental problems. This study provides an effective utilization available for this solid residue by using it as the starting material in the preparation of activated carbon with chemical activation. Activated carbons with high specific area and various surface functions have been prepared, and the effects of the amount and type of activating agents on the physical and chemical properties of activated carbon were investigated as well.     

Adsorption of mercury by activated carbon prepared from dried sewage sludge in simulated flue gas

Conversion of sewage sludge to activated carbon is attractive as an alternative method to ocean dumping for the disposal of sewage sludge. Injection of activated carbon upstream of particulate matter control devices has been suggested as a method to remove elemental mercury from flue gas. Activated carbon was prepared using various activation temperatures and times and was tested for their mercury adsorption efficiency using lab-scale systems. To understand the effect of the physical property of the activated carbon, its mercury adsorption efficiency was investigated as a function of its Brunauer–Emmett–Teller (BET) surface area. Two simulated flue gas conditions, (1) without hydrogen chloride (HCl) and (2) with 20 ppm HCl, were used to investigate the effect of flue gas composition on the mercury adsorption capacity of activated carbon. Despite very low BET surface area of the prepared sewage sludge activated carbons, their mercury adsorption efficiencies were comparable under both simulated flue gas conditions to those of pinewood and coal activated carbons. After injecting HCl into the simulated flue gas, all sewage sludge activated carbons demonstrated high adsorption efficiencies, that is, more than 87%, regardless of their BET surface area.

Implications: We tested activated carbons prepared from dried sewage sludge to investigate the effect of their physical properties on their mercury adsorption efficiency. Using two simulated flue gas conditions, we conducted mercury speciation for the outlet gas. We found that the sewage sludge activated carbon had mercury adsorption efficiency comparable to pinewood and coal activated carbons, and the presence of HCl minimized the effect of physical property of the activated carbon on its mercury adsorption efficiency.     

Adsorption properties of regenerative materials for removal of low concentration of toluene

A specific type of material, activated carbon fiber (ACF), was modified by SiO₂, and the final products ACF-x were obtained as ACF-12.5, ACF-20, ACF-40, and ACF-80 according to different dosages of tetraethoxysilane (TEOS). The modified material on the ACF surface had a significant and smooth cover layer with low content of silica from scanning electron microscope (SEM) image. The modified ACF-x showed the stronger hydrophobicity, thermal stability, and adsorption capacity, which had almost no effect in the presence of water vapor and no destruction in multiple cycles. ACF-20 was proven as the most efficient adsorbent in humid conditions. The dual-function system composed of the regenerative adsorbents and the combustion catalyst would be efficient in consecutive toluene adsorption/oxidation cycles, in which the combustion catalyst was prepared by the displacement reaction of H₂PtCl₆ with foam Ni. Therefore, the adsorption/catalytic oxidation could be a promising technique in the indoor air purification, especially in the case of very low volatile organic compound (VOC; toluene) concentration levels.

Implications: Exploring highly effective adsorptive materials with less expensive costs becomes an urgent issue in the indoor air protection. ACF-20 modified by SiO₂ with Pt/Ni catalysts shows stronger hydrophobicity, thermal stability, and adsorption capacity. This dual-function system composed of the regenerative materials and the combustion catalyst would be a promising technique in the indoor air purification, especially in the case of removal of very low concentration of toluene.     

Comparative study on the removal efficiency of hydrogen sulfide (H2S) using three different packings

To improve the removal efficiency on hydrogen sulfide (H₂S), a biofilter was developed and was made of polyvinyl chloride (PVC) pipes. The effects of three different packings (i.e., packing A, packing B, and packing C), containing different proportions of activated carbon, sawdust, wormcast, perlite, and pig manure compost, based on different biofilter parameters on H₂S removal efficiency, were investigated. With the extension of running time, the H₂S removal rate of packing A reached up to 90.12%, that of packing B reached a peak at 92.96%, and that of packing C was highest at 87.21%. The contribution rate of each packing at the bottom of the device was significantly greater (p < 0.01) than that of other parts, and those of the top of the devices were all greater than those of the middle of the devices. The H₂S removal rate increased with greater filler layer height. The removal rate of group B increased first with humidity, and then declined, with the optimal humidity level for the removal of H₂S 50–65% in this study. With the prolongation of the run, the pH of packing A was reduced from 7.1 to 5.91, while the pH of packing B and C remained within the range of 6.53–7.10. An increase was found in the number of bacteria and fungi over time. The count of bacteria in packing B and C and following a decreasing order was bottom > middle > top, whereas that for fungi was the opposite. In conclusion, it is thought that packing B (comprising wormcast + sawdust + activated carbon) is more efficient in the removal of H₂S than the other packings and may thus be utilized in biofilters. These results hope to provide useful information for future related research on the removal efficiency of H₂S using packings.

Implications: Wormcasts use as biological filter packing to remove H₂S is limited and needs yet to be explored. A comparative study on the removal efficiency of H₂S using three packings showed the packings that included wormcast were more efficient than others, and showed the combined features of physical absorption and biological removal with long sustainability and good efficiency, although these were largely influenced by environmental factors and nutrient content for the microorganisms. In summary, wormcast could be utilized in biological filters in the future in related research beacuse of its good efficiency and low cost.     

Application of magnetically modified sewage sludge ash (SSA) in ionic dye adsorption

Incineration is a traditional method of treating sewage sludge and the disposal of derived ash is a problem of secondary waste treatment. In this study, sewage sludge ash (SSA) was coated with ferrite through a ferrite process and then used as an adsorbent for ionic dyes (methylene blue [MB] and Procion Red MX-5B [PR]). The modified SSA possessed surface potential that provided electrostatic attraction toward MB and PR. Adsorbent FA10 (named on the basis of being produced from 10 g of SSA in the ferrite process) was used for the adsorption of MB. Ideal pH for adsorption was 9.0 and maximum adsorption capacity based on Langmuir isotherm equation was 22.03 mg/g. Adsorbent FA2.5 (named on the basis of being produced from 2.5 g of SSA in the ferrite process) was used for PR adsorption. Ideal pH for adsorption was 3.0 and the maximum adsorption capacity (calculated as above) was 28.82 mg/g. Kinetic results reveal that both MB and PR adsorption fit the pseudo-second-order kinetic model better than the pseudo-first-order model. The values of activation energy calculated from rate constants were 61.71 and 9.07 kJ/mol for MB and PR, respectively.

Implications:

Magnetic modified adsorbent could be synthesized from sewage sludge ash (SSA). In this study, the adsorption ability of SSA toward ionic dye (methylene blue [MB] and Procion Red MX-5B [PR]) was enhanced by ferrite process. The synthesized Fe₃O₄ can act as an active site and provide electrostatic attraction toward cationic dye and anionic dye at different pH. The application of magnetic modified adsorbent in wastewater treatment can not only recycle the SSA, but also make SSA become an environmentally friendly material.     

Production of granular activated carbon from food-processing wastes (walnut shells and jujube seeds) and its adsorptive properties

Commercial activated carbon is a highly effective absorbent that can be used to remove micropollutants from water. As a result, the demand for activated carbon is increasing. In this study, we investigated the optimum manufacturing conditions for producing activated carbon from ligneous wastes generated from food processing. Jujube seeds and walnut shells were selected as raw materials. Carbonization and steam activation were performed in a fixed-bed laboratory electric furnace. To obtain the highest iodine number, the optimum conditions for producing activated carbon from jujube seeds and walnut shells were 2 hr and 1.5 hr (carbonization at 700°C) followed by 1 hr and 0.5 hr (activation at 1000°C), respectively. The surface area and iodine number of activated carbon made from jujube seeds and walnut shells were 1,477 and 1,184 m²/g and 1,450 and 1,200 mg/g, respectively. A pore-distribution analysis revealed that most pores had a pore diameter within or around 30–40 Å, and adsorption capacity for surfactants was about 2 times larger than the commercial activated carbon, indicating that waste-based activated carbon can be used as alternative.

Implications:Wastes discharged from agricultural and food industries results in a serious environmental problem. A method is proposed to convert food-processing wastes such as jujube seeds and walnut shells into high-grade granular activated carbon. Especially, the performance of jujube seeds as activated carbon is worthy of close attention. There is little research about the application of jujube seeds. Also, when compared to two commercial carbons (Samchully and Calgon samples), the results show that it is possible to produce high-quality carbon, particularly from jujube seed, using a one-stage, 1,000°C, steam pyrolysis. The preparation of activated carbon from food-processing wastes could increase economic return and reduce pollution.     

Public health and components of particulate matter: The changing assessment of black carbon

In 2012, the WHO classified diesel emissions as carcinogenic, and its European branch suggested creating a public health standard for airborne black carbon (BC). In 2011, EU researchers found that life expectancy could be extended four to nine times by reducing a unit of BC, vs reducing a unit of PM_2.5. Only recently could such determinations be made. Steady improvements in research methodologies now enable such judgments.

In this Critical Review, we survey epidemiological and toxicological literature regarding carbonaceous combustion emissions, as research methodologies improved over time. Initially, we focus on studies of BC, diesel, and traffic emissions in the Western countries (where daily urban BC emissions are mainly from diesels). We examine effects of other carbonaceous emissions, e.g., residential burning of biomass and coal without controls, mainly in developing countries.

Throughout the 1990s, air pollution epidemiology studies rarely included species not routinely monitored. As additional PM_2.5. chemical species, including carbonaceous species, became more widely available after 1999, they were gradually included in epidemiological studies. Pollutant species concentrations which more accurately reflected subject exposure also improved models.

Natural “interventions” - reductions in emissions concurrent with fuel changes or increased combustion efficiency; introduction of ventilation in highway tunnels; implementation of electronic toll payment systems – demonstrated health benefits of reducing specific carbon emissions. Toxicology studies provided plausible biological mechanisms by which different PM species, e.g., carbonaceous species, may cause harm, aiding interpretation of epidemiological studies.

Our review finds that BC from various sources appears to be causally involved in all-cause, lung cancer, and cardiovascular mortality, morbidity, and perhaps adverse birth and nervous system effects. We recommend that the U.S. EPA rubric for judging possible causality of PM_2.5. mass concentrations, be used to assess which PM_2.5. species are most harmful to public health.

Implications: Black carbon (BC) and correlated co-emissions appear causally related with all-cause, cardiovascular, and lung cancer mortality, and perhaps with adverse birth outcomes and central nervous system effects. Such findings are recent, since widespread monitoring for BC is also recent. Helpful epidemiological advances (using many health relevant PM_2.5 species in models; using better measurements of subject exposure) have also occurred. “Natural intervention” studies also demonstrate harm from partly combusted carbonaceous emissions. Toxicology studies consistently find biological mechanisms explaining how such emissions can cause these adverse outcomes. A consistent mechanism for judging causality for different PM_2.5 species is suggested.

A list of acronyms will be found at the end of the article.     

Gas reforming and tar decomposition performance of nickel oxide (NiO)/SBA-15 catalyst in gasification of woody biomass

In the gasification of biomass, it is necessary to limit the amount of by-product tar and increase the yields of hydrogen (H₂) and carbon monoxide (CO) (syngas). Therefore, we conducted gasification and reforming experiments on woody biomass using an electric tubular furnace, to evaluate the gas reforming and tar decomposition performance of a NiO/SBA-15 catalyst. As a result, we found that this catalyst is effective for H₂ production. It is believed that the increase in H₂ volume due to the catalyst occurs through a steam reforming reaction involving hydrocarbons, including methane (CH₄), and the water-gas shift reaction. With respect to the influence of the gasifying agent on the reforming effect of the catalyst, the amount of generated carbon dioxide (CO₂) and hydrogen (H₂) increases because the shift reaction is promoted by supplying steam. On the other hand, it was inferred that the shift reaction rarely occurred because it approaches equilibrium by supplying O₂. Furthermore, it is suggested that light aromatic hydrocarbons are decomposed by the catalyst.

Implications: The mesoporous silica catalyst NiO/SBA-15 was highly effective for H₂ production and decomposition of light aromatic compounds in the gasification of woody biomass. In the catalyst reaction, supplying steam promoted H₂ production. From thermodynamic analysis and discussion, it was also inferred that supplying O₂ might prevent the water gas shift reaction. The results are useful for designing a process needed for rich H₂ production and gas refining process for further use of syngas.     

Comparison on surface properties and desulfurization of MnO2 and pyrolusite blended activated carbon by steam activation

In this study, MnO₂ and pyrolusite were used as the catalysts to prepare modified activated carbon, that is, AC-Mn and AC-P, respectively, from coals by blending method and steam activation. The Brunauer–Emmett–Teller (BET) results indicated that the AC-P had higher surface areas and micropore volumes than the AC-Mn with the same blending ratio. The relative contents of basic functional groups (i.e., C = O, π-π*) on AC-P were slightly lower than those on AC-Mn, while both contained the same main metal species, namely, MnO. The desulfurization results showed that with 3 wt% of blending ratio, AC-Mn3 and AC-P3 had higher sulfur capacities at 220 and 205 mg/g, respectively, which were much higher than for the blank one (149.6 mg/g). Moreover, the AC-P had relatively higher sulfur capacity than the AC-Mn with the same contents of Mn, which might be attributed to the existence of other metals in pyrolusite. After the desulfurization process, MnO were gradually transferred into MnSO₄, and the relative contents of basic functional groups decreased evidently for both AC-Mn3 and AC-P3. The results demonstrated that pyrolusite could be one good alternative to MnO₂ to prepare modified activated carbon for desulfurization.

Implications: MnO₂ and pyrolusite were used as the additives to prepare modified activated carbon from coals by a blending method and by steam activation, that is, AC-Mn and AC-P, respectively. The AC-P had higher surface areas and micropore volumes than the AC-Mn with the same blending ratio. The AC-Mn and AC-P had higher sulfur capacities than a blank one. Moreover, the AC-P had relatively higher sulfur capacity than the AC-Mn with the same contents of Mn. The results demonstrated that pyrolusite could be one good alternative to MnO₂ to prepare modified activated carbon for desulfurizatio.     

Development of a chemical kinetic model for a biosolids fluidized-bed gasifier and the effects of operating parameters on syngas quality

In an effort to decrease the land disposal of sewage sludge biosolids and to recover energy, gasification has become a viable option for the treatment of waste biosolids. The process of gasification involves the drying and devolatilization and partial oxidation of biosolids, followed closely by the reduction of the organic gases and char in a single vessel. The products of gasification include a gaseous fuel composed largely of N₂, H₂O, CO₂, CO, H₂, CH₄, and tars, as well as ash and unburned solid carbon. A mathematical model was developed using published devolatilization, oxidation, and reduction reactions, and calibrated using data from three different experimental studies of laboratory-scale fluidized-bed sewage sludge gasifiers reported in the literature. The model predicts syngas production rate, composition, and temperature as functions of the biosolids composition and feed rate, the air input rate, and gasifier bottom temperature. Several data sets from the three independent literature sources were reserved for model validation, with a focus placed on five species of interest (CO, CO₂, H₂, CH₄, and C₆H₆). The syngas composition predictions from the model compared well with experimental results from the literature. A sensitivity analysis on the most important operating parameters of a gasifier (bed temperature and equivalence ratio) was performed as well, with the results of the analysis offering insight into the operations of a biosolids gasifier.

Implications:

As gasification becomes a more prominent waste disposal option, understanding the effects of feedstock composition and gasifier parameters on the production of syngas (rate and quality) becomes increasingly important. A model has been developed for the gasification of dried sewage sludge that will allow for prediction of changes in syngas quality (and energy recovery from the waste), and should be helpful in assessing the benefits of new gasification projects.     

Preparation and reactivation of magnetic biochar by molten salt method: Relevant performance for chlorine-containing pesticides abatement

Molten salt has been regarded as a versatile and environmental-friendly method for the material preparation and waste destruction. In this work, molten FeCl3 was utilized for the generation of magnetic biochar (MBC) derived from simultaneous activation and magnetization of biomass. The sample characterization indicated that MBC had a rough surface with BET surface area of 404 m2/g and total pore volume of 0.35cm3/g. Highly dispersed Fe3O4 and nitrogen could be deposited on the surface, leading to an excellent magnetization property. The MBC exhibited a great 2,4-Dichlorophenol (2.4-DCP) and atrazine removal performance in solution with the maximum adsorption capacity achieved 298.12 mg/g and 102.17 mg/g. Kinetics results demonstrated that MBC adsorption met the Pseudo-first-order model better. Molten NaOH-Na2CO3 was provided for the re-activation of exhausted MBC. 2,4-DCP was firstly desorbed from the MBC and subsequently destructed by the active species in the melt medium. Chlorine can be captured in the molten alkaline medium from the XRD pattern of residues.The MBC could be easily recovered with a yield of 98.2% and fixed carbon content of 61.0% after the molten salt regeneration process. With no 2,4-DCP detected, 65.5% and 31.69% of initial Cl was found in washing water and residues with the molten NaOH-Na2CO3, respectively. After 4 cycles of regeneration and adsorption, 60.55%-72.22% of initial adsorption capacity can be kept. This preparation and regeneration method can be an effective way to reduce the risk of secondary pollution of chlorinated organic compounds during adsorbent regeneration.

Implications: Molten salt (MS) is a salt or multiple salts with a low melting point, and has been applied in many sectors and is regarded as a crucial role in terms of energy, environmental, and resource sustainability. In our paper, magnetic biochar was prepared by one-step activation and magnetization of fir dust using molten FeCl₃?6H₂O. Meanwhile, a regeneration method using molten alkaline salt was provided. Magnetic biochar generated in our study performed well in the 2,4-dichlorophenol and atrazine adsorption. After four cycles of regeneration and adsorption, 72.2% of initial 2,4-DCP adsorption capacity can be kept.     

Reduced combustion mechanism for C1–C4 hydrocarbons and its application in computational fluid dynamics flare modeling

Emissions from flares constitute unburned hydrocarbons, carbon monoxide (CO), soot, and other partially burned and altered hydrocarbons along with carbon dioxide (CO₂) and water. Soot or visible smoke is of particular concern for flare operators/regulatory agencies. The goal of the study is to develop a computational fluid dynamics (CFD) model capable of predicting flare combustion efficiency (CE) and soot emission. Since detailed combustion mechanisms are too complicated for (CFD) application, a 50-species reduced mechanism, LU 3.0.1, was developed. LU 3.0.1 is capable of handling C₄ hydrocarbons and soot precursor species (C₂H₂, C₂H₄, C₆H₆). The new reduced mechanism LU 3.0.1 was first validated against experimental performance indicators: laminar flame speed, adiabatic flame temperature, and ignition delay. Further, CFD simulations using LU 3.0.1 were run to predict soot emission and CE of air-assisted flare tests conducted in 2010 in Tulsa, Oklahoma, using ANSYS Fluent software. Results of non-premixed probability density function (PDF) model and eddy dissipation concept (EDC) model are discussed. It is also noteworthy that when used in conjunction with the EDC turbulence-chemistry model, LU 3.0.1 can reasonably predict volatile organic compound (VOC) emissions as well.

Implications: A reduced combustion mechanism containing 50 C₁–C₄ species and soot precursors has been developed and validated against experimental data. The combustion mechanism is then employed in the computational fluid dynamics (CFD) of modeling of soot emission and combustion efficiency (CE) of controlled flares for which experimental soot and CE data are available. The validated CFD modeling tools are useful for oil, gas, and chemical industries to comply with U.S. Environmental Protection Agency’s (EPA) mandate to achieve smokeless flaring with a high CE.     

Distribution of mercury in the combustion products from coal-fired power plants in Guizhou,southwest China

Method 30B and the Ontario Hydro Method (OHM) were used to sample the mercury in the flue gas discharged from the seven power plants in Guizhou Province, southwest China. In order to investigate the mercury migration and transformation during coal combustion and pollution control process, the contents of mercury in coal samples, bottom ash, fly ash, and gypsum were measured. The mercury in the flue gas released into the atmosphere mainly existed in the form of Hg°. The precipitator shows a superior ability to remove Hg^p (particulate mercury) from flue gas. The removal efficiency of Hg²⁺ by wet flue gas desulfurization (WFGD) was significantly higher than that for the other two forms of mercury. The synergistic removal efficiency of mercury by the air pollution control devices (APCDs) installed in the studied power plants is 66.69–97.56%. The Hg mass balance for the tested seven coal-fired power plants varied from 72.87% to 109.67% during the sampling time. After flue gas flowing through APCDs, most of the mercury in coal was enriched in fly ash and gypsum, with only a small portion released into the atmosphere with the flue gas. The maximum discharge source of Hg for power plants was fly ash and gypsum instead of Hg emitted with flue gas through the chimney into the atmosphere. With the continuous upgrading of APCDs, more and more mercury will be enriched in fly ash and gypsum. Extra attention should be paid to the re-release of mercury from the reutilization of by-products from APCDs.

Implications: Method 30B and the Ontario Hydro Method (OHM) were used to test the mercury concentration in the flue gas discharged from seven power plants in Guizhou Province, China. The concentrations of mercury in coal samples, bottom ash, fly ash, and gypsum were also measured. By comparison of the mercury content of different products, we found that the maximum discharge source of Hg for power plants was fly ash and gypsum, instead of Hg emitted with flue gas through the chimney into the atmosphere. With the continuous upgrading of APCDs, more and more mercury will be enriched in fly ash and gypsum. Extra attention should be paid to the re-release of mercury from the reutilization of by-products from APCDs.     

Evaluation of thermal optical analysis method of elemental carbon for marine fuel exhaust

The awareness of black carbon (BC) as the second largest anthropogenic contributor in global warming and an ice melting enhancer has increased. Due to prospected increase in shipping especially in the Arctic reliability of BC emissions and their invented amounts from ships is gaining more attention. The International Maritime Organization (IMO) is actively working toward estimation of quantities and effects of BC especially in the Arctic. IMO has launched work toward constituting a definition for BC and agreeing appropriate methods for its determination from shipping emission sources. In our study we evaluated the suitability of elemental carbon (EC) analysis by a thermal-optical transmittance (TOT) method to marine exhausts and possible measures to overcome the analysis interferences related to the chemically complex emissions. The measures included drying with CaSO_4, evaporation at 40–180ºC, H₂O treatment, and variation of the sampling method (in-stack and diluted) and its parameters (e.g., dilution ratio, Dr). A reevaluation of the nominal organic carbon (OC)/EC split point was made. Measurement of residual carbon after solvent extraction (TC-C_SOF) was used as a reference, and later also filter smoke number (FSN) measurement, which is dealt with in a forthcoming paper by the authors. Exhaust sources used for collecting the particle sample were mainly four-stroke marine engines operated with variable loads and marine fuels ranging from light to heavy fuel oils (LFO and HFO) with a sulfur content range of <0.1–2.4% S. The results were found to be dependent on many factors, namely, sampling, preparation and analysis method, and fuel quality. It was found that the condensed H₂SO₄ + H₂O on the particulate matter (PM) filter had an effect on the measured EC content, and also promoted the formation of pyrolytic carbon (PyC) from OC, affecting the accuracy of EC determination. Thus, uncertainty remained regarding the EC results from HFO fuels.

Implications: The work supports one part of the decision making in black carbon (BC) determination methodology. If regulations regarding BC emissions from marine engines will be implemented in the future, a well-defined and at best unequivocal method of BC determination is required for coherent and comparable emission inventories and estimating BC effects. As the aerosol from marine emission sources may be very heterogeneous and low in BC, special attention to the effects of sampling conditions and sample pretreatments on the validity of the results was paid in developing the thermal-optical analysis methodology (TOT).     

Capture of CO2 on γ-Al2O3 materials prepared by solution-combustion and ball-milling processes

A series of porous γ-Al₂O₃ materials was prepared by solution-combustion and ball-milling processes. The as-prepared powders were physicochemically characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and N₂ physisorption measurements and their performances in CO₂ adsorption at different pressures (0.5 to 1.5 MPa) and temperatures (40 to 60ºC) were investigated. It was found that γ-Al₂O₃ synthesized by the solution-combustion process and ball milled at 10 hr exhibited the best CO₂ adsorption performance at 60ºC and 1.5 MPa, achieving a maximum of 1.94 mmol/g compared to the four studied materials, as a result of their interesting microstructure and surface properties (i.e., nanocrystallinity, specific surface area, narrow pore size distribution, and large total pore volume). Our study shows that the γ-Al₂O₃ prepared by solution combustion followed by ball milling presents a fairly good potential adsorbent for efficient CO₂ capture.

Implications: In this work, γ-Al₂O₃ materials were successfully obtained by solution combustion and modified via ball milling. These improved materials were systematically investigated as solid adsorbents of accessible surface areas, large pore volumes, and narrow pore size distribution for the CO₂ capture. These studied solid adsorbents can provide an additional contribution and effort to develop an efficient CO₂ capture method as means of alleviating the serious global warning problem.     

Deodorization of pig manure using lignin peroxidase with different electron acceptors

Odor pollution is a big environmental problem caused by large-scale livestock production in China, and developing a practical way to reduce these odors is pressing. In this study, a combination of 0.2–1.0 U/mL lignin peroxidase (LiP) and one of three peroxides (H₂O₂, CaO₂, 2Na₃CO₃·3H₂O₂) was examined for its efficiency in reducing the release of eight chemicals (propionic acid, isobutyric acid, isocaproic acid, isovaleric acid, phenol, p-cresol, indole, and skatole), NH₃, H₂S, and odor intensity from pig manure. The results showed an approximately 90% reduction in p-cresol, 40–60% reduction in odor intensity, 16.5–40% reduction in indolic compounds, and 25–40% reduction in volatile fatty acids. Being the electron acceptors of LiP, 2Na₃CO₃·3H₂O₂ and CaO₂ performed better than H₂O₂ in reducing the concentration of eight chemicals, NH_3, H₂S, and odor intensity from pig manure. The effect of deodorization can last for up to 72 hr.

Implications: In China, one of the major environmental problems caused by confined feeding is odor pollution, which brings a major threat to the sustainability, profitability, and growth of the livestock industry. To couple the LiP with the electron acceptors, a low–cost, simple, and feasible method for odor removal was established in this study. Based on the study results, a practical treatment method was provided for odor pollution and supply the farm operators a more flexible time to dispose treated manure.     

Limitations of the toxicity characteristic leaching procedure for providing a conservative estimate of landfilled municipal solid waste incineration ash leaching

Limitations of the toxicity characteristic leaching procedure (TCLP) for simulating pollutant leaching from wastes disposed of in full-scale landfills are well understood in the waste management profession; the TCLP solution has a lower pH and greater organic acid content than typical landfill leachate. The TCLP serves its intended regulatory objective, however, as long as a conservative estimate of leaching is provided. Here, we examine TCLP’s ability to represent worst-case leaching conditions for monofilled municipal solid waste incineration (MSWI) ash. A critical examination of TCLP’s applicability to MSWI ash is especially relevant, as ash management at MSWI facilities often centers on passing TCLP, regardless of environmental risk posed by the ash or its recyclability. Multiple batch leaching tests were conducted on different MSWI ash streams: mixed ash, fly ash, and different size fractions of bottom ash. Batch-test results were compared with leachate simulating MSWI ash monofills. The TCLP did not consistently provide the most conservative estimate of leaching, supporting the need to consider alternative methodologies in future regulatory development.

Implications: This paper analyzes the existing hazardous waste regulatory testing requirement for municipal solid waste incinerator (MSWI) ash management to evaluate whether the TCLP serves its intended purpose in providing the most conservative estimate of landfilled MSWI ash. The results will serve as guidance and motivation for policy makers and the regulatory community to reevaluate the TCLP’s application for characterizing MSWI ash leaching in certain disposal scenarios and could promote consideration of alternative testing procedures based upon results of this study. This study serves to promote representative and accurate quantification of leaching risk from MSWI ash.     

Understanding selected trace elements behavior in a coal-fired power plant in Malaysia for assessment of abatement technologies

The Proposed New Environmental Quality (Clean Air) Regulation 201X (Draft), which replaces the Malaysia Environmental Quality (Clean Air) 1978, specifies limits to additional pollutants from power generation using fossil fuel. The new pollutants include Hg, HCl, and HF with limits of 0.03, 100, and 15 mg/N-m³ at 6% O₂, respectively. These pollutants are normally present in very small concentrations (known as trace elements [TEs]), and hence are often neglected in environmental air quality monitoring in Malaysia. Following the enactment of the new regulation, it is now imperative to understand the TEs behavior and to assess the capability of the existing abatement technologies to comply with the new emission limits. This paper presents the comparison of TEs behavior of the most volatile (Hg, Cl, F) and less volatile (As, Be, Cd, Cr, Ni, Se, Pb) elements in subbituminous and bituminous coal and coal combustion products (CCP) (i.e., fly ash and bottom ash) from separate firing of subbituminous and bituminous coal in a coal-fired power plant in Malaysia. The effect of air pollution control devices configuration in removal of TEs was also investigated to evaluate the effectiveness of abatement technologies used in the plant. This study showed that subbituminous and bituminous coals and their CCPs have different TEs behavior. It is speculated that ash content could be a factor for such diverse behavior. In addition, the type of coal and the concentrations of TEs in feed coal were to some extent influenced by the emission of TEs in flue gas. The electrostatic precipitator (ESP) and seawater flue gas desulfurization (FGD) used in the studied coal-fired power plant were found effective in removing TEs in particulate and vapor form, respectively, as well as complying with the new specified emission limits.

Implications:Coals used by power plants in Peninsular Malaysia come from the same supplier (Tenaga Nasional Berhad Fuel Services), which is a subsidiary of the Malaysia electricity provider (Tenaga Nasional Berhad). Therefore, this study on trace elements behavior in a coal-fired power plant in Malaysia could represent emission from other plants in Peninsular Malaysia. By adhering to the current coal specifications and installation of electrostatic precipitator (ESP) and flue gas desulfurization, the plants could comply with the limits specified in the Malaysian Department of Environment (DOE) Scheduled Waste Guideline for bottom ash and fly ash and the Proposed New Environmental Quality (Clean Air) Regulation 201X (Draft).     

Investigation of adsorption characteristics of four toxic gases (nitric oxide,nitrogen dioxide,sulfur dioxide,and hydrogen chloride) on the inner surface of nickel-coated manganese steel cylinders and aluminum cylinders

To develop standard toxic gas mixtures, it is essential to identify adsorption characteristics of each toxic gas on the inner surface of a gas cylinder. Thus, this study quantified adsorbed amounts of the four toxic gases (nitric oxide [NO], nitrogen dioxide [NO₂], sulfur dioxide [SO₂], and hydrogen chloride [HCl]) on the inner surface of aluminum cylinders and nickel-coated manganese steel cylinders. After eluting adsorbed gases on the inside of cylinders with ultrapure water, a quantitative analysis was performed on an ion chromatograph. To evaluate the reaction characteristics of the toxic gases with cylinder materials, quantitative analyses of nickel (Ni), iron (Fe), and aluminum (Al) were also performed by inductively coupled plasma optical emission spectrometry (ICP-OES). It was found that the amounts of NO, NO₂, and SO₂ adsorbed on the inner surface of aluminum cylinders were less than 1.0% at the level of 100 μmol/mol mixing ratio, whereas the signal for most heavy metal elements were below their respective detection limits. This study found that the amounts of HCl adsorbed on the inner surface of nickel-coated manganese steel cylinders were less than 5% at the level of 100 μmol/mol mixing ratio, whereas Ni (86 μmol) and Fe (28 μmol) were detected in the same cylinders. It was revealed that the adsorption mainly took place via the reaction of HCl with inner surface material of nickel-coated manganese steel cylinders. On the other hand, in the case of aluminum cylinders, the amounts of the adsorption were determined to be less than 1% at the level of HCl 100 μmol/mol mixing ratio, whereas most of Ni, Fe, and Al were detected at levels similar to their limits of detection. As a result, this study found that aluminum cylinders are more suitable for preparing HCl gas mixtures than nickel-coated manganese steel cylinders.

Implications: To develop a standard toxic gas mixture, it is essential to understand the adsorption characteristics of each toxic gas inside a gas cylinder. It was found that the amounts of NO, NO₂, and SO₂ adsorbed inside aluminum cylinders were less than 1.0% at the level of 100 μmol/mol mixing ratio. The amounts of HCl adsorbed inside nickel-coated manganese steel cylinders were less than 5% at the level of 100 μmol/mol mixing ratio, whereas those inside aluminum cylinders were less than 1%, indicating that aluminum cylinders are more suitable for preparing HCl gas mixtures.     

Effect of potassium hydroxide activation in the desulfurization process of activated carbon prepared by sewage sludge and corn straw

Series sludge straw–based activated carbons were prepared by sewage sludge and corn straw with potassium hydroxide (KOH) activation, and the desulfurization performance of activated carbons was studied. To obtain the best desulfurization performance, the optimum ratio between the raw materials and the activator was investigated. The results showed that when the mass ratio of sewage sludge, corn straw, and KOH was 3:7:2, the activated carbon obtained the best breakthrough and saturation sulfur sorption capacities, which were 12.38 and 5.74 times, respectively, those of samples prepared by the nonactivated raw materials. The appropriate KOH could improve the microporosity and alkaline groups, meanwhile reducing the lactone groups, which were all beneficial to desulfurization performance. The chemical adsorption process of desulfurization can be simplified to four main steps, and the main desulfurization products are elemental sulfur and sulfate.

Implications: Sewage sludge (SS) and corn straw (CS) both have great production and wide distribution and are readily available in China. Much attention has been paid on how to deal with them effectively. Based on the environment protection idea of waste treatment with waste and resource recycling, low-cost adsorbents were prepared by these processes. The proposed method can be expanded to the municipal solid waste recycling programs and renewable energy plan. Thus, proceeding with the study of preparing activated carbon by SS and straw as a carbon-based dry desulfurization agent could obtain huge social, economic, and environmental benefits.