Search Results (22)

Mitigating air pollutants such as SO_x and PM emitted from ships is an important task for marine environmental protection and improving air quality. To address this, exhaust gas after-treatment devices have been introduced, but treating pollutants like SO_x and PM individually poses challenges due to spatial constraints on ships. Consequently, a Total Gas Cleaning System (TGCS) capable of simultaneously reducing sulfur oxides and particulate matter has been developed. The TGCS combines a cyclone dust collector and a wet scrubber system. The cyclone dust collector is designed to maintain a certain distance from the bottom of the wet scrubber, allowing exhaust gases entering from the bottom to rise as sulfur oxides are adsorbed. Additionally, the exhaust gases descending through the space between the cyclone dust collector and the wet scrubber collide with the scrubbing solution before entering the bottom of the wet scrubber, facilitating the absorption of SO_x. In this study, the efficiency of the developed TGCS was evaluated, and the reduction effects based on design parameters were investigated. Furthermore, the impact of this device on ship engines was analyzed to assess its practical applicability. Experimental results showed that increasing the volume flow rate of the cleaning solution enhanced the PM reduction effect. Particularly, when the height of the Pall ring was 1000 mm and the volume flow rate was 35 L/min, the sulfur oxide reduction effect met the standards for Sulfur Emission Control Areas (SECA). Based on these findings, suggestions for effectively controlling atmospheric pollutants from ships were made, with the expectation of contributing to the development of systems combining various after-treatment devices. Full article

The efficacy of spray dry systems compared to wet flue gas desulphurisation (FGD) units depends on applying a highly reactive scrubbing reagent. This study assessed sodium-based compounds derived from natural sources and waste by-products as potential agents for treating sulphur dioxide (SO₂). Sodium carbonate (Na₂CO₃) and sodium bicarbonate (NaHCO₃) were acquired from mineral deposits, whereas the black ash waste (Na₂CO₃·NaHCO₃) was obtained from the pulp and paper sector. The sorbents introduced in slurry form were subject to SO₂ absorption conditions in a lab-scale spray dryer, including an inlet gas phase temperature of 120–180 °C, flue gas flow rate of 21–34 m³/h, and sodium to sulphur normalised stoichiometric ratio (Na:S) of 0.25–1. The comparative performance was evaluated using the metric of %SO₂ ($\%{\eta }_{DeS{O}_X}$) removal efficiency. The results showed that NaHCO₃ had the highest overall result, with a removal efficiency of 62% at saturation. Black ash was the second best-performing reagent, with a 56% removal efficiency, while Na₂CO₃ had the lowest efficiency (53%). The maximum degree of SO₂ reduction achieved using NaHCO₃ under specific operating parameters was at an NSR of 0.875 (69%), a reaction temperature of 120 °C (73%), and a gas inlet flow rate of 34 m³/h. In conclusion, the sodium reagents produced significant SO₂ neutralisation, exceeding 50% in their unprocessed state, which is within acceptable limits in small- to medium-sized coal-fired power plants considering retrofitting pollution control systems. Full article

Sinter flue gas produced by the iron-ore sinter process in steel plants is characterized by a large gas volume and complex components. Among the major air pollutants, preliminary emissions of volatile organic compounds (VOCs) and nitrogen oxides (NOx) exhibit an inevitable contribution to secondary aerosol and ozone formation. Herein, oxidation–absorption collaborative technology for in-plasma catalysis with sequential Na₂SO₃ wet scrubbing, aiming at co-elimination of NOx and VOCs from sinter flue gas, is proposed. Experimental parameters, including plasma discharge status, NO initial concentration, gas feed flux, Na₂SO₃ concentration, pH value, and absorption ions, were systematically investigated. The VOC and NOx removal performance of the integrated system was further investigated by taking simulated sinter flue gas as model pollutants. The results showed that the collaborative system has satisfactory performance for TVOC and NO removal rates for the effective oxidation of in-plasma catalysis and Na₂SO₃ absorption. The integration of plasma catalysis with Na₂SO₃ scrubbing could be an alternative technology for the co-elimination of sinter flue gas multi-compounds. Full article

This paper reports on a novel method to remove Hg⁰ in the wet scrubbing process using defect-rich colloidal copper sulfides for reducing mercury emissions from non-ferrous smelting flue gas. Unexpectedly, it migrated the negative effect of SO₂ on mercury removal performance, while also enhancing Hg⁰ adsorption. Colloidal copper sulfides demonstrated the superior Hg⁰ adsorption rate of 306.9 μg·g⁻¹·min⁻¹ under 6% SO₂ + 6% O₂ atmosphere with a removal efficiency of 99.1%, and the highest-ever Hg⁰ adsorption capacity of 736.5 mg·g⁻¹, which was 277% higher than all other reported metal sulfides. The Cu and S sites transformation results reveal that SO₂ could transform the tri-coordinate S sites into S₂²⁻ on copper sulfides surfaces, while O₂ regenerated Cu²⁺ via the oxidation of Cu⁺. The S₂²⁻ and Cu²⁺ sites enhanced Hg⁰ oxidation, and the Hg²⁺ could strongly bind with tri-coordinate S sites. This study provides an effective strategy to achieve large-capability adsorption of Hg⁰ from non-ferrous smelting flue gas. Full article

Secondary problems, such as the occurrence of side reactions and the accumulation of by-products, are a major challenge in the application of wet denitrification technology through urea solution. We revealed the formation mechanism of urea nitrate and clarified the main and side reaction paths and key intermediates of denitrification. Urea nitrate would be separated from urea absorption solution only when the concentration product of [urea], [H⁺] and [NO₃⁻] was greater than 0.87~1.22 mol³/L³. The effects of the urea concentration (5–20%) and reaction temperature (30–70 °C) on the denitrification efficiency could be ignored. Improving the oxidation degree of the flue gas promoted the removal of nitrogen oxides. The alkaline condition was beneficial to the dissolution process, while the acidic condition was beneficial to the reaction process. As a whole, the alkaline condition was the preferred process parameter. The research results could guide the optimization of process conditions in theory, improve the operation efficiency of the denitrification reactor and avoid the occurrence of side reactions. Full article

Sulfur and nitrogen oxides (SO_X/NO_X) are the primary air toxic gas pollutants emitted during fuel combustion, causing health and environmental concerns. Therefore, their emission in flue gases is strictly regulated. The existing technologies used to decrease SO_X/NO_X content are flue gas desulfurization, which necessitates high capital and operating costs, and selective catalytic reduction, which, in addition to these costs, requires expensive catalysts and high operating temperatures (350–400 °C). New wet scrubbing processes use O₃ or H₂O₂ oxidants to produce (NH₄)₂SO₄ and NH₄NO₃ fertilizers upon ammonia injection. However, these oxidants are expensive, corrosive, and hazardous. SiO₂/Co(OH)₂ nanocomposites are presented here as potential catalysts for SO_X/NO_X oxidation in wet scrubber reactors to scrub these toxic gases using atmospheric oxygen as the oxidant at relatively low temperatures of 60–90 °C. Several silica-cobalt-oxide-based nanocomposites were synthesized as potential catalysts at different concentrations and temperatures. The nanocomposite catalysts were characterized and exhibited excellent catalytic properties for SO_X/NO_X oxidation using atmospheric oxygen as the oxidant, replacing the problematic H₂O₂/O₃. We thus propose SiO₂-supported Co(OH)₂ nanoparticles (NPs) as excellent catalysts for the simultaneous scrubbing of polluting SO_X/NO_X gases in flue gases using atmospheric O₂ as the oxidation reagent at a relatively low-temperature range. Full article

Infrastructure developments in recent decades have led to increasing demand for high-performance paints for construction and decorative purposes. Emulsion paint is water-based paint that is commonly used for coating the internal and external surfaces of a building. The quality and performance of this emulsion paint are highly dependent on its constituent components, such as binders, pigment, solvents, and additives. Emulsion paints initially used conventional formaldehyde-based binders and were, for some reason, prohibited from being used in paints due to health and environmental issues. The development of bio-based paints with natural rubber latex (NRL) has the potential to be developed as an emulsion paint binder. The results showed that NRL grafting of styrene monomer or MMA showed much better resistance to wet scrub and abrasion than PVAc at a monomer concentration of 20%, for styrene, and 30%, for MMA, with washability values reaching each of 11 and 12 cycles at 4% binder concentration. The NgSt20-4 and NgMMA30-4 binders’ abilities to overcome wet scrub and abrasion increased with increasing paint binder concentrations, reaching 22 and 23 cycles at 10% binder concentration. Overall, the combination of NRL grafted with MMA monomer and 30% PVAc showed better performance and could compete with commercial binders such as PVAc. Adding methyl methacrylate monomer increases the adhesion and cohesion properties of the binder and increases the binder’s resistance to scrubbing and wet abrasion. However, the combination of NRL grafted MMA and 30% PVAc showed the same effectiveness as NRL grafted MMA without PVAc, with more economical production costs. Full article

Aiming at NO_x (NO 90%, NO₂ 10%) and SO₂ in simulated vessel emissions, denitration and desulfurization were studied through ozone oxidation combined with seawater as absorbent. Specifically, the different influencing factors of denitration and desulfurization were analyzed. The results indicated that the oxidation efficiency of NO can reach over 90% when the molar ratio of O₃/NO is 1.2. Ozone oxidation and seawater washing in the same unit can decrease the temperature of ozone oxidation of NO, avoid high temperature ozone decomposition, and enhance the oxidation efficiency of NO. When NO inlet initial concentration is lower than 800 ppm, the NO_x removal efficiency can be improved by increasing NO inlet concentration, and when NO inlet initial concentration is greater than 800 ppm, increasing the concentration of NO would decrease the NO_x removal efficiency. Increasing the inlet concentration of SO₂ has minor effect on desulfurization, but slightly reduces the absorption efficiency of NO_x due to the competition of SO₂ and NO_x in the absorption solution. Besides, final products (${\mathrm{NO}}_2^{-}$, ${\mathrm{NO}}_3^{-}$, ${\mathrm{SO}}_3^{2-}$, and ${\mathrm{SO}}_4^{2-}$) were analyzed by the ion chromatography. Full article

Permafrost formation and degradation creates a highly patchy mosaic of boreal peatland ecosystems in Alaska driven by climate, fire, and ecological changes. To assess the biophysical factors affecting permafrost dynamics, we monitored permafrost and ecological conditions in central Alaska from 2005 to 2021 by measuring weather, land cover, topography, thaw depths, hydrology, soil properties, soil thermal regimes, and vegetation cover between burned (1990 fire) and unburned terrain. Climate data show large variations among years with occasional, extremely warm–wet summers and cold–snowless winters that affect permafrost stability. Microtopography and thaw depth surveys revealed both permafrost degradation and aggradation. Thaw depths were deeper in post-fire scrub compared to unburned black spruce and increased moderately during the last year, but analysis of historical imagery (1954–2019) revealed no increase in thermokarst rates due to fire. Recent permafrost formation was observed in older bogs due to an extremely cold–snowless winter in 2007. Soil sampling found peat extended to depths of 1.5–2.8 m with basal radiocarbon dates of ~5–7 ka bp, newly accumulating post-thermokarst peat, and evidence of repeated episodes of permafrost formation and degradation. Soil surface temperatures in post-fire scrub bogs were ~1 °C warmer than in undisturbed black spruce bogs, and thermokarst bogs and lakes were 3–5 °C warmer than black spruce bogs. Vegetation showed modest change after fire and large transformations after thermokarst. We conclude that extreme seasonal weather, ecological succession, fire, and a legacy of earlier geomorphic processes all affect the repeated formation and degradation of permafrost, and thus create a highly patchy mosaic of ecotypes resulting from widely varying ecological trajectories within boreal peatland ecosystems. Full article

The purpose of this research was to evaluate the impact of selected pigments on the performance of waterborne emulsion paint. Each pigment was incorporated into the paint at 5% w/w. Density and viscosity measurements as well as the rub-out test were used to test the wet state properties of the colored paint. Wet-scrub, adhesion-to-substrate, water-uptake, vapor-permeability, UV-aging, and other tests were conducted to evaluate effects of the pigments on the dried paint. Bohemian green earth pigment was found to have the most positive effect, as it improved the water resistance of the paint without changing its rheological properties. Therefore, this pigment was selected for further studies, in which the pigment was included as part of the paint formula rather than as a post-additive. The results were satisfactory, confirming the compatibility of the pigment with the formula. However, a slight change in the rheological profile of the paint was observed during tests on a rotational rheometer. This research shows the need for intensive quality control measures while testing alternative formulations, to both enable early detection of negative effects and identify possible improvements. Full article

The direct use of natural rubber latex (NRL) as a binder for emulsion paints did not produce emulsion paints with good opacity, washability resistance, and regulated touch drying time, even when mixed with polyvinyl acetate (PVAc). This study aimed to study the properties of opacity (hiding power), washability resistance, and set drying touch time of emulsion paint with a binder added from a mixture of modified natural rubber latex (NRL) and PVAc. NRL modifications included UV photodepolymerization with TiO₂ catalyst and grafting copolymerization of methyl methacrylate and styrene (NRL-g-(MMA-co-St)). NRL was mixed with PVAC at ratios of 0/100; 15/85; 25/75; 35/65; 50/50; 100/0% w/w before being used as a binder for emulsion paint. Emulsion paint samples had different binder contents, namely 2, 4, 6, and 8% w/w. Tests on paint samples included opacity using a UV-Vis spectrophotometer (EASYSPEC safas Monaco), washability using the Digital BGD 526 Wet Abrasion Scrub Tester, and drying time set using the ASTM STP500 procedure. The results showed that the opacity (hiding power), washability resistance, and set drying touch time met the emulsion paint standards for all binder levels, except the 100% w/w modified NRL composition. The higher level of NRL in the binder causes these properties to decrease and become unstable. The best opacity (hidden power), washing resistance, and drying touch time were obtained on modified NRL with a concentration of 15% w/w. The binder content in the paint was around 4% w/w, with an opacity of about 1.78% abs, washing resistance of 12 times, and the set drying touch time to 80 min. Full article

Nitrogen and sulpher oxides (NO_x, SO_x) have become a global issue in recent years due to the fastest industrialization and urbanization. Numerous techniques are used to treat the harmful exhaust emissions, including dry, traditional wet and hybrid wet-scrubbing techniques. However, several difficulties, including high-energy requirement, limited scrubbing-liquid regeneration, formation of secondary pollutants and low efficiency, limit their industrial utilization. Regardless, the hybrid wet-scrubbing technology is gaining popularity due to low-costs, less-energy consumption and high-efficiency removal of air pollutants. The removal/reduction of NO_x and SO_x from the atmosphere has been the subject of several reviews in recent years. The goal of this review article is to help scientists grasp the fundamental ideas and requirements before using it commercially. This review paper emphasizes the use of green and electron-rich donors, new breakthroughs, reducing GHG emissions, and improved NO_x and SO_x removal catalytic systems, including selective/non-catalytic reduction (SCR/SNCR) and other techniques (functionalization by magnetic nanoparticles; NP, etc.,). It also explains that various wet-scrubbing techniques, synthesis of solid iron-oxide such as magnetic (Fe₃O₄) NP are receiving more interest from researchers due to the wide range of its application in numerous fields. In addition, EDTA coating on Fe₃O₄ NP is widely used due to its high stability over a wide pH range and solid catalytic systems. As a result, the Fe₃O₄@EDTA-Fe catalyst is projected to be an optimal catalyst in terms of stability, synergistic efficiency, and reusability. Finally, this review paper discusses the current of a heterogeneous catalytic system for environmental remedies and sustainable approaches. Full article

A dielectric barrier discharge (DBD) reactor combined with a wet scrubbing tower was used to carry out an experimental study on desulfurization and denitrification. The effects of the packing type, packing height, spray density, mass fraction of the NaOH solution, discharge power in the DBD reactor, and simulated flue gas flow rate on the desulfurization and denitrification efficiency were analyzed, along with the influence weight of each factor, using orthogonal testing. The experimental results showed that SO₂ was easily absorbed by the scrubbing solution, while the desulfurization efficiency remained at a high level (97–100%) during the experiment. The denitration efficiency was between 12 and 96% under various operating conditions. Denitration is the key problem in this system. The influence weights of the DBD power, simulated flue gas flow rate, mass fraction of the NaOH solution, spray density, packing type, and packing height on the denitration efficiency were 56.96%, 18.02%, 11.52%, 5.02%, 4.33%, and 4.16%, respectively. This paper can provide guidance to optimize the desulfurization and denitrification efficiency of this DBD reactor combined with a wet scrubbing system. Full article

Arctic wetlands play a critical role in the global carbon cycle and are experiencing disproportionate impacts from climate change. Even though Alaska hosts 65% of U.S. wetlands, less than half of the wetlands in Alaska have been mapped by the U.S. Fish and Wildlife Service National Wetlands Inventory (NWI) or other high-resolution wetlands protocols. The availability of time series satellite data and the development of machine learning algorithms have enabled the characterization of Arctic wetland inundation dynamics and vegetation types with limited ground data input. In this study, we built a semi-automatic process to generate sub-pixel water fraction (SWF) maps across the Coastal Plain of the Arctic National Wildlife Refuge (ANWR) in Alaska using random forest regression and 139 Sentinel-2 images taken in ice-free seasons from 2016 to 2019. With this, we characterized the seasonal dynamics of wetland inundation and explored their potential usage in determining NWI water regimes. The highest levels of surface water expression were detected in June, resulting from seasonal active layer thaw and snowmelt. Inundation was most variable in riverbeds, lake and pond margins, and depressional wetlands, where water levels fluctuate substantially between dry and wet seasons. NWI water regimes that indicate frequent inundation, such as permanently flooded wetlands, had high SWF values (SWF ≥ 90%), while those with infrequent inundation, such as temporarily flooded wetlands, had low SWF values (SWF < 10%). Vegetation types were also classified through the synergistic use of a vegetation index, water regimes, synthetic-aperture radar (SAR) data, topographic data, and a random forest classifier. The random forest classification algorithms demonstrated good performance in classifying Arctic wetland vegetation types, with an overall accuracy of 0.87. Compared with NWI data produced in the 1980s, scrub-shrub wetlands appear to have increased from 91 to 258 km² over the last three decades, which is the largest percentage change (182%) among all vegetation types. However, additional field data are needed to confirm this shift in vegetation type. This study demonstrates the potential of using time series satellite data and machine learning algorithms in characterizing inundation dynamics and vegetation types of Arctic wetlands. This approach could aid in the creation and maintenance of wetland inventories, including the NWI, in Arctic regions and enable an improved understanding of long-term wetland dynamics. Full article

Currently, the availability of a wide variety of universal adhesives makes it difficult for clinicians to choose the correct system for specific bonding situations to dentin substrate. This study aimed to determine whether there are any alternative techniques or additional strategies available to enhance the bond strength of universal adhesives to dentin through a systematic review and meta-analysis. Two reviewers executed a literature search up to September 2020 in four electronic databases: PubMed, ISI Web of Science, Scopus, and EMBASE. Only in vitro studies that reported the dentin bond strength of universal adhesives using additional strategies were included. An analysis was carried out using Review Manager Software version 5.3.5 (The Nordic Cochrane Centre, The Cochrane Collaboration, Copenhagen, Denmark). The methodological quality of each in vitro study was assessed according to the parameters of a previous systematic. A total of 5671 potentially relevant studies were identified. After title and abstract examination, 74 studies remained in systematic review. From these, a total of 61 studies were included in the meta-analysis. The bond strength of universal adhesives to dentin was improved by the use of one of the following techniques: Previous application of matrix metalloproteinases (MMP) inhibitors (p < 0.001), prolonged application time (p = 0.007), scrubbing technique (p < 0.001), selective dentin etching (p < 0.001), non-atmospheric plasma (p = 0.01), ethanol-wet bonding (p < 0.01), prolonged blowing time (p = 0.02), multiple layer application (p = 0.005), prolonged curing time (p = 0.006), and hydrophobic layer coating (p < 0.001). On the other hand, the use of a shortened application time (p = 0.006), and dentin desensitizers (p = 0.01) impaired the bond strength of universal adhesives to dentin. Most of the analyses performed showed a high heterogenicity. The in vitro evidence suggests that the application of universal adhesives using some alternative techniques or additional strategies may be beneficial for improving their bonding performance to dentin. This research received no external funding. Considering that this systematic review was carried out only with in vitro studies, registration was not performed. Full article