RESUMEN
This study presents a promising approach that enhances the sludge fermentation by using basic oxygen furnace (BOF) slag as an alkaline source for the first time. BOF slag added to the reactors could maintain a stable alkaline condition due to continuous release of Ca(OH)2 from slag. The reactor pH could be adjusted to a target value by the choice of the BOF slag dose. Concentrations of soluble chemical oxygen demand (sCOD) and short-chain carboxylates (SCCs) were substantially increased in the presence of BOF slag. At a BOF slag mass to sludge volume ratio of 1/10â¯g slag/L sludge, the reactor pH was maintained at 10 and the concentration of SCCs produced was the highest (i.e., 3510â¯mg COD L-1 from 14,000â¯mg VS L-1 of sludge mixture), followed by B/S ratios of 1/20, 1.50, 1/5, and 1/2.5â¯g slag L-1 sludge with reactor pH of 9.4, 8.9, 10.5, and 11, respectively. Our data suggest that the pH value that best facilitates the degradation of sludge into SCCs and inhibit the conversion of SCCs into biogas is around 10. Interestingly, compositions of the accumulated SCCs varied greatly depending on the BOF slag dose. BOF slag showed phosphorus removal ability due to enhanced precipitation of Ca-PO43--P complexes, which significantly lowered PO43- concentration of the reactor effluent.
Asunto(s)
Oxígeno , Fosfatos , Fermentación , Fósforo , Aguas del AlcantarilladoRESUMEN
This work presents the results of an international interlaboratory comparison on ex situ passive sampling in sediments. The main objectives were to map the state of the science in passively sampling sediments, identify sources of variability, provide recommendations and practical guidance for standardized passive sampling, and advance the use of passive sampling in regulatory decision making by increasing confidence in the use of the technique. The study was performed by a consortium of 11 laboratories and included experiments with 14 passive sampling formats on 3 sediments for 25 target chemicals (PAHs and PCBs). The resulting overall interlaboratory variability was large (a factor of â¼10), but standardization of methods halved this variability. The remaining variability was primarily due to factors not related to passive sampling itself, i.e., sediment heterogeneity and analytical chemistry. Excluding the latter source of variability, by performing all analyses in one laboratory, showed that passive sampling results can have a high precision and a very low intermethod variability (Asunto(s)
Sedimentos Geológicos
, Contaminantes Químicos del Agua
, Monitoreo del Ambiente
, Compuestos Orgánicos
, Medición de Riesgo
RESUMEN
The effectiveness of activated carbon (AC) treatment to sequester hydrophobic organic contaminants in sediments under stagnant contact was comprehensively studied for the first time. Two years of column experiments were conducted to simulate field conditions with two study sediments contaminated with petroleum and polychlorinated biphenyls, respectively, and variations in AC-sediment contact times, initial AC mixing regimes and distribution, AC particle sizes, and pore-water flow. The benefit of AC treatment was gradually enhanced with time toward the end point of the treatment, where sorption equilibrium is established between sediment and AC. After two years of stagnant contact, the contaminant uptake in polyethylene passive samplers embedded in the columns was reduced by 95-99% for polycyclic aromatic hydrocarbons and 93-97% for polychlorinated biphenyls with 5 and 4 wt % AC dose, respectively, when AC was initially applied by mechanical mixing. These results verify that AC treatment can effectively control the availability of hydrophobic organic contaminants under stagnant conditions within a reasonable time frame following an initial distribution of AC into the sediment. The effectiveness of AC treatment was strongly dependent on AC particle size and AC distribution, while the effect of AC initial mixing regimes and pore-water flow was not pronounced.
Asunto(s)
Carbón Orgánico/química , Sedimentos Geológicos/química , Bifenilos Policlorados/química , Hidrocarburos Policíclicos Aromáticos/química , Interacciones Hidrofóbicas e Hidrofílicas , Tamaño de la Partícula , Petróleo/análisis , Contaminación por Petróleo/prevención & control , Bifenilos Policlorados/análisis , Hidrocarburos Policíclicos Aromáticos/análisis , Polietileno/análisisRESUMEN
The validity of a hydrophobic organic contaminant mass transfer model to predict the effectiveness of in situ activated carbon (AC) treatment under stagnant sediment-AC contact is studied for different contaminants and sediments. The modeling results and data from a previous 24-month column experiment of uptake in polyethylene samplers are within a factor of 2 for parent- and alkylated-polycyclic aromatic hydrocarbons in petroleum-impacted sediment and factors of 3-10 for polychlorinated biphenyls. The model successfully reproduces the relative effects of AC-sediment contact time, contaminant properties, AC particle size, AC mixing regime, AC distribution, and hydraulic conditions observed in the sediment column experiments. The model tracks contaminant concentrations in different sediment compartments over time, which provides useful information on the contaminant sequestration by the added AC. Long-term projection of the effectiveness of AC amendment using the model shows that the effects of AC particle size and particle-scale heterogeneity in AC distribution are pronounced within a year or so. However, the effect of those factors becomes less significant after a much longer contact period (on the order of a decade or two), resulting in substantial reduction in pore-water concentrations, for example, greater than 99% for benz[a]anthracene, under various scenarios.
Asunto(s)
Carbón Orgánico/química , Sedimentos Geológicos/química , Modelos Teóricos , Bifenilos Policlorados/química , Hidrocarburos Policíclicos Aromáticos/química , Interacciones Hidrofóbicas e Hidrofílicas , Cinética , Peso Molecular , Tamaño de la Partícula , Petróleo , Bifenilos Policlorados/análisisRESUMEN
In-situ stabilization of hydrophobic organic compounds (HOCs) using activated carbon (AC) is a promising sediment remediation approach. However, predicting HOC adsorption capacity of sediment-amended AC remains a challenge because a prediction model is currently unavailable. Thus, the objective of this study was to develop machine learning models that could predict the apparent adsorption capacity of sediment-amended AC (KAC,apparent) for HOCs. These models were trained using 186 sets of experimental data obtained from the literature. The best-performing model among those employing various model frameworks, machine learning algorithms, and combination of candidate input features excellently predicted logKAC,apparent with a coefficient of determination of 0.94 on the test dataset. Its prediction results and experimental data for KAC,apparent agreed within 0.5 log units with few exceptions. Analysis of feature importance for the machine learning model revealed that KAC,apparent was strongly correlated with the hydrophobicity of HOCs and the particle size of AC, which agreed well with the current knowledge obtained from experimental and mechanistic assessments. On the other hand, correlation of KAC,apparent to sediment characteristics, duration of AC-sediment contact, and AC dose identified in the model disagreed with relevant arguments made in the literature, calling for further assessment in this subject. This study highlights the promising capability of machine learning in predicting adsorption capacity of AC in complex systems. It offers unique insights into the influence of model parameters on KAC,apparent.
Asunto(s)
Carbón Orgánico , Sedimentos Geológicos , Carbón Orgánico/química , Adsorción , Sedimentos Geológicos/química , Compuestos Orgánicos/química , Interacciones Hidrofóbicas e HidrofílicasRESUMEN
Per- and polyfluoroalkyl substances (PFASs) are emerging contaminants detected ubiquitously and have negative impacts on human health and ecosystem; thus, developing in-situ sensing technique is important to ensure safety. Herein, we report a novel colorimetric-based sensor with perfluoroalkyl receptor attached to citrate coated gold nanoparticles (Citrate-Au NPs) that can detect several PFASs including perfluorocarboxylates with different chain lengths (PFHxA, PFOA, PFNA, PFDA), perfluorooctanoic sulfonate (PFOS), and perfluorooctanoic phosphonate (PFOPA). The sensor detects PFASs utilizing fluorous interaction between PFASs and the perfluoroalkyl receptor of Citrate-Au NPs in a solution at a fixed salt concentration, inducing changes in nanoparticle dispersity and the solution color. The rate of spectrum shift was linearly dependent on PFASs concentrations. Citrate-Au NPs with size between 29 - 109 nm were synthesized by adjusting citrate/Au molar ratios, and 78 nm showed the best sensitivity to PFOA concentration (with level of detection of 4.96 µM). Citrate-Au NPs only interacted with PFASs with perfluoroalkyl length > 4 and not with non-fluorinated alkyl compound (nonanoic acid). The performance of Citrate-Au NP based sensor was strongly dependent on the chain length of the perfluoroalkyl group and the head functional group; higher sensitivity was observed with longer chain over shorter chain, and with sulfonate functional group over carboxylate and phosphonate. The sensor was tested using real water samples (i.e., tap water, filtered river water), and it was found that the sensor is capable of detecting PFASs in these conditions if calibrated with the corresponding water matrix. While further optimization is needed, this study demonstrated new capability of Citrate-Au NPs based sensor for detection of PFASs in water.
RESUMEN
Continuous growth in fluoroarene production has led to environmental pollution and health concerns owing to their persistence, which is attributed to the stable C-F bond in their structures. Herein, we investigated fluoroarene decomposition via hydrodefluorination using a rhodium-based catalyst, focusing on the effects of the chemical structure and functional group on the defluorination yield. Most compounds, except (pentafluoroethyl)benzene, exhibited full or partial reduction with pseudo-first-order rate constants in the range of 0.002-0.396 min-1 and defluorination yields of 0%-100%. Fluoroarenes with hydroxyl, methyl, and carboxylate groups were selected to elucidate how hydrocarbon and oxygen-containing functional groups influence the reaction rate and defluorination. Inhibition of the reaction rate and defluorination yield based on functional groups increased in the order of hydroxyl < methyl < carboxylate, which was identical to the order of the electron-withdrawing effect. Fluoroarenes with polyfluoro groups were also assessed; polyfluoro groups demonstrated a different influence on catalyst activity than non-fluorine functional groups because of fluorine atoms in the substituents undergoing defluorination. The reaction kinetics of (difluoromethyl)fluorobenzenes and their intermediates suggested that hydrogenation and defluorination occurred during degradation. Finally, the effects of the type and position of functional groups on the reaction rate and defluorination yield were investigated via multivariable linear regression analysis. Notably, the electron-withdrawing nature of functional groups appeared to have a greater impact on the defluorination yield of fluoroarenes than the calculated C-F bond dissociation energy.
Asunto(s)
Rodio , Catálisis , Rodio/química , Cinética , Halogenación , Oxidación-Reducción , Fluorobencenos/química , Hidrocarburos Fluorados/químicaRESUMEN
Adsorption of per- and poly-fluoroalkyl substances (PFAS) on activated carbon (AC) is considerably hindered by the surface water constituents, degrading the ability of the AC adsorption process to remove PFAS in drinking water treatment. Herein, we developed ionic-liquid-impregnated AC (IL/AC) as an alternative to AC for PFAS sorption and demonstrated its performance with real surface water for the first time. Ionic liquids (ILs) of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (IL(C2)) and 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (IL(C6)) were selected from among 272 different ILs using the conductor-like screening model for realistic solvents (COSMO-RS) simulation. Impregnation of the ILs in AC was verified using various analytical techniques. Although the synthesized IL/ACs were less effective than pristine AC in treating PFAS in deionized water, their performances were less impacted by the surface water constituents, resulting in comparable or sometimes better performances than pristine AC for treating PFAS in surface water. The removal efficiencies of 10 wt% IL(C6)/AC for six PFAS were 1.40-1.96 times higher than those of pristine AC in a surface water sample containing 2.6 mg/L dissolved organic carbon and millimolar-level divalent cation concentration. PFAS partitioning from the surface water to ILs was not hindered by dissolved organic matter and was enhanced by the divalent cations, indicating the advantages of IL/ACs for treating significant amounts of PFAS in water. The synthesized IL/ACs were effective at treating coexisting pharmaceutical and personal-care products in surface water, showcasing their versatility for treating a broad range of water micropollutants.
Asunto(s)
Agua Potable , Fluorocarburos , Líquidos Iónicos , Carbón Orgánico , Simulación por ComputadorRESUMEN
We report polyethylene (PE)-water partitioning coefficients (K(PE)) for 17 parent-polycyclic aromatic hydrocarbons (PAHs), 22 alkylated-PAHs, 3 perdeuterated parent-PAHs, and 100 polychlorinated biphenyl (PCB) congeners or coeluting congener groups. The K(PE) values for compounds in the same homologue group are within 0.2 log units for alkylated-PAHs but span up to an order of magnitude for PCBs, due to the greater contribution of the position of the substituents (i.e., chlorines for PCBs and alkyl groups for alkylated-PAHs) to the molecular structure. The K(PE) values in deionized water for parent- and alkylated-PAHs show a good correlation with a regression model employing the number of aromatic carbons (C(AR)) and aliphatic carbons (C(AL)) in each compound: log K(PE) = -0.241 + 0.313 C(AR) + 0.461 C(AL). The regression model is useful for the assessment of freely dissolved aqueous concentrations of alkylated-PAHs, which comprise a significant fraction of the total in petroleum-derived PAHs and in some pyrogenic PAH mixtures. For PCBs, experimentally determined octanol-water partitioning coefficients are the best predictor of the K(PE) values among the molecular parameters studied. The effect of salinity up to 20 or 30 parts per thousand is found to be relatively insignificant on K(PE) values for PAHs or PCBs, respectively.
Asunto(s)
Bifenilos Policlorados/química , Hidrocarburos Policíclicos Aromáticos/química , Polietileno/química , Contaminantes Químicos del Agua/química , Agua/química , Alquilación , Análisis de RegresiónRESUMEN
We present a first comprehensive set of experiments that demonstrate the performance of activated carbon (AC) to reduce the availability of polycyclic aromatic hydrocarbons (PAHs) including alkylated-PAHs in petroleum-impacted sediments. The uptake in polyethylene samplers for total PAHs in a well-mixed sediment slurry was reduced up to 99% and 98% for petroleum-impacted sediments with oil contents of 1% and 2%, respectively, by treatment with 5% AC. The AC showed similar efficiency for parent-PAHs and a suite of alkylated-PAHs, which predominate over parent-PAHs in petroleum-impacted sediments. A mass transfer model was used to simulate the AC performance in a slurry phase with site-specific mass transfer parameters determined in this study. Comparison between the experimental data and simulation results suggested that dissolved organic matter and/or oil phase may have attenuated the AC performance by a factor of 5-6 for 75-300 µm AC with 5% dose at one month. The attenuation in AC performance became negligible with increase in AC-sediment slurry contact time to 12 months and with decrease in AC particle size. The results show the potential for AC amendment to sequester PAHs in petroleum-impacted sediments and the effect of contact time and AC particle size on the efficiency of the treatment.
Asunto(s)
Carbón Orgánico/química , Contaminantes Ambientales/aislamiento & purificación , Sedimentos Geológicos/análisis , Petróleo/análisis , Hidrocarburos Policíclicos Aromáticos/aislamiento & purificación , Simulación por Computador , Restauración y Remediación Ambiental/métodos , Modelos QuímicosRESUMEN
The sustainable management of dredged sediment from contaminated sites needs to consider the end-use of the treated sediment. In this regard, modifying conventional sediment treatment techniques to generate a product that is suitable for a range of terrestrial uses is necessary. In the present study, we evaluated the product quality of treated sediment as a potential plant-growth medium following the thermal treatment of marine sediment contaminated by petroleum. The contaminated sediment was subject to thermal treatment at temperatures of 300, 400, or 500 °C, and no, low, or moderate oxygen availability, and the resulting treated sediment was analyzed in terms of its bulk properties, spectroscopic properties, organic contaminants, water-soluble salts and organic matter, and the leachability and extractability of heavy metals. All operational combinations for the treatment process reduced the total petroleum hydrocarbon content of the sediment from 4922 mg kg-1 to lower than 50 mg kg-1. The thermal treatment process stabilized the heavy metals in the sediment, reducing the zinc and copper concentration by up to 58.9% and 89.6%, respectively, in the leachate from the toxicity characteristic leaching procedure. The hydrophilic organic and/or sulfate salt byproducts of the treatment were phytotoxic, but these can easily be removed by washing the sediment with water. By combining the sediment analysis results with experimental data from barley germination and early-growth tests, the end product was found to be of higher quality when higher temperatures and lower oxygen availability were employed in the treatment process. These findings demonstrate that it is possible to retain the natural organic resources of the original sediment by optimizing the thermal treatment, thus ensuring a suitably high product quality for use as a plant-growth medium.
Asunto(s)
Metales Pesados , Petróleo , Temperatura , Sedimentos Geológicos/química , Metales Pesados/análisis , Agua/análisisRESUMEN
BACKGROUND: The depth of double-lumen endobronchial tube (DLT) is reportedly known tobe directly proportional to height and several height-based recommendations have beensuggested. This retrospective study was designed to find out the difference between calculated depths using height-based formulae and realistic depths in clinical practice of DLTplacement by analyzing pooled data from patients intubated with left-sided DLT. METHODS: The electronic medical records of adults, intubated with DLT from February 2018to December 2020, were reviewed. Data retrieved included age, sex, height, weight, andsize and depth of DLT. The finally documented DLT depth (depth final, DF) was comparedwith the calculated depths, and the relationship between height and DF was also evaluated.A questionnaire on endobronchial intubation method was sent to anesthesiologists. RESULTS: A total of 503 out of 575 electronic records of consecutive patients were analyzed.Although the relationship between height and DF was shown to have significant correlation(Spearman's rho = 0.63, P < 0.001), DF was shown to be significantly greater than calculated depths (P < 0.001). Despite 57.1% of anesthesiologists have knowledge of clinical recommendations to anticipate size and depth of DLT, no one routinely utilizes those recommendations. CONCLUSIONS: Anesthesiologists tend to place DLTs in a deeper position than expected whendepths are calculated using height-based recommendations. Although such discrepanciesmay not be clinically meaningful, efforts are needed to standardize the methods of endobronchial intubation to prevent potential complications associated with malposition.
RESUMEN
The upstream of Nakdong River is contaminated by heavy metals such as Cd, Cu, Zn, As, and Pb. Although the origin of the contamination is unequivocal, it is suspected that the heavy metals have been leached from several mine tailings and a refinery. Here, receptor models, absolute principal component score (APCS) and positive matrix factorization (PMF), were used to identify the contamination sources. Source markers representing each source (factor) were investigated using correlation analysis for five major contaminants (Cd, Zn, As, Pb, and Cu) and identified as following: Cd and Zn for the refinery (factor 1), As for mine tailings (factor 2). The categorization of sources into two factors was statistically validated via the cumulative proportion and APCS-based KMO test score with the values >90 % and > 0.7 (p < 0.001), respectively. High R2 values of linear regressions between the predicted data from receptor models and observed data indicate the reliability of the model prediction; moreover, the predicted initial concentrations of contaminants were validated using a sediment sample collected from near the refinery (chi-test: p > 0.200). Concentration distribution and source contribution using GIS revealed the heavy metal contaminated zones affected by the precipitation.
Asunto(s)
Metales Pesados , Contaminantes del Suelo , Monitoreo del Ambiente , Ríos , Cadmio/análisis , Plomo/análisis , Reproducibilidad de los Resultados , Contaminantes del Suelo/análisis , Metales Pesados/análisis , República de Corea , China , Medición de RiesgoRESUMEN
Activated carbon (AC) amendments to sediments were tested for nontoxic, secondary effects on survival, weight change, and energetic biomarkers of the deposit feeder Neanthes arenaceodentata. The tests employed silica sand, reference sediments, and contaminated sediments. Survival was not affected by the sediment type, the AC dose (20% versus 5%), or the AC particle size. Without additional food supply, exposure to untreated and AC-amended sediments resulted in similar reduction of weight and lipid content, with no difference between ingestible and noningestible AC. Overall, whether with or without AC, the organisms showed signs of starvation, as the organisms would most likely rely on organic surface deposits for their diet in the environments from which the sediments were collected. When additional food was supplied, the organisms grew significantly and maintained higher lipid and glycogen contents. However, when feeding on fish food, organisms grew less in AC amendments with slightly lower lipid and glycogen contents relative to organisms exposed to untreated sediment. Batch tests show that AC did not sorb sediment-associated nitrogen but sorbed nitrogen from fish food. Despite some effects of AC on these deposit feeders, absolute effects of AC amendments on growth and energy reserves were not significant.
Asunto(s)
Carbón Orgánico/toxicidad , Restauración y Remediación Ambiental , Conducta Alimentaria/efectos de los fármacos , Sedimentos Geológicos/química , Poliquetos/efectos de los fármacos , Poliquetos/fisiología , Adsorción/efectos de los fármacos , Animales , Bioensayo , Biomarcadores/metabolismo , Peso Corporal/efectos de los fármacos , Metabolismo Energético/efectos de los fármacos , Glucógeno/metabolismo , Metabolismo de los Lípidos/efectos de los fármacos , Proteínas/metabolismo , Análisis de SupervivenciaRESUMEN
Per- and polyfluoroalkyl substances (PFAS) are widely detected environmental contaminants, and there is a great need for development of sensor technologies for rapid and continuous monitoring of PFAS. In this study, we have developed fluorescence based aptasensor that can possibly monitor perfluorooctanoic acid (PFOA) in water with limit of detection (LOD) of 0.17 µM. This is first to report the successful isolation of PFAS binding ssDNA aptamers. The obtained aptamer selectively binds PFOA with dissociation constant (KD) of 5.5 µM. Specific aptamer binding sites to PFOA were identified and the length of the fluorinated carbons was a key binding factor rather than the functional group. The aptamer binding to structurally similar PFAS compounds (i.e., perfluorocarboxylic acids and perfluorosulfonic acids with 4-8 carbon chains) was also investigated; the aptamer KD values were 6.5 and 3.3 µM for perfluoroheptanoic acid and perfluorohexanesulfonic acid, respectively, while other analogs did not bind to the aptamer. The presence of major inorganic ions and dissolved organic matter had negligible influences on the aptamer performance (<14% at a 10 mM concentration), and the aptamer performance was also robust in real wastewater effluent conditions, with a KD of 7.4 µM for PFOA. Fluorescence-based aptasensor developed in this study is adequate in monitoring PFOA levels in water contaminated with the accident spills and heavy usage of fire-fighting foams near the industrial sites and military bases. More importantly, the study opens up new capability of aptasensors to efficiently monitor the trace amount of various PFAS compounds and other fluorinated alternatives in natural and engineered water environments.
Asunto(s)
Ácidos Alcanesulfónicos , Fluorocarburos , Contaminantes Químicos del Agua , Caprilatos , Materia Orgánica Disuelta , Fluorescencia , Fluorocarburos/análisis , Agua , Contaminantes Químicos del Agua/análisisRESUMEN
This study investigates the effect of chemical modification and growth medium on the surface characteristics and heavy metal adsorption capacities of Chlorella vulgaris biosorbents, which are prepared in a powder form for the ease of their transport and application. NaOH treatment partially lyses surface cells on cell aggregates, producing rough microscale structures on the biosorbent surface, which enhances the specific surface area by 19-fold and the heavy metal adsorption capacity by factors of 2.4-4.1. Autotrophic C. vulgaris incubation using nitrogen- and phosphorus-rich medium is even a more effective strategy for enhancing the adsorption capacity, showing factors of 1.6-9.4 increase compared to the use of a minimal medium. High phosphorus content of cell residues on the biosorbent surface obtained by luxury phosphorus uptake is responsible for the substantial enhancement. This study suggests a potential of utilizing nitrogen- and phosphorus-rich waste streams to produce a highly efficient microalgal biosorbent for heavy metal adsorption.
Asunto(s)
Chlorella vulgaris , Metales Pesados , Contaminantes Químicos del Agua , Adsorción , Cinética , Polvos , Contaminantes Químicos del Agua/análisisRESUMEN
The present study was aimed at investigating the effects of different acids and pH neutralizers applied to dredged marine sediment for the treatment of heavy metals, and the resulting influence on the sediment quality as a plant growth medium. The inspection of barley germination in the dredged marine sediment revealed that residual salts are critical plant stressors whose adverse effects exceed those exhibited by high-level heavy metals and petroleum hydrocarbons present in the sediment. Acid washing and pH neutralization reduced not only the heavy metal contents but also the sediment salinity (by factors of 6.1-9.5), resulting in 100% germination of barley. For acid-washed and calcium-oxide-neutralized sediment, the barley growth was comparable to that observed in untreated and water washed sediment despite factors of 5.2-8.0 greater sediment salinity in the former. This result represents the protective effect of residual calcium against sodium and chloride toxicity. Water washing of acid-washed and pH-neutralized sediments further enhanced barley growth owing to the reduction in osmotic pressure. This study showed the effect of different sediment-washing reagents on the product quality. It also indicated the significance of balancing the enhancement of product quality and economic cost of further treatment requirements.
Asunto(s)
Metales Pesados , Contaminantes del Suelo , Fertilidad , Sedimentos Geológicos , Concentración de Iones de Hidrógeno , Metales Pesados/análisis , SueloRESUMEN
HYPOTHESIS: We test the validity of the Young-Laplace equation and Henry's law for sub-micron bubble suspensions, which has long been a questionable issue. Application of the two theories allows characterization of bubble diameter and gas molecule partitioning between gaseous and dissolved phases using two easily measurable variables: total gas content (CT) and bubble volume concentration (BVC). EXPERIMENTS: We measure CT and BVC for sub-micron bubble suspensions generated from three pure gases, which allows calculation of bubble diameter for each suspension using the Young-Laplace equation and Henry's law. Uncertainties involved in the experimental measurements are assessed. Bubble size for each suspension is also directly measured using a dynamic light scattering (DLS) technique for comparison. FINDINGS: Applying the two theories we calculate that the bubble diameters are in the range of 304-518â¯nm, which correspond very well with the DLS-measured diameters. Sensitivity analyses demonstrate that the correspondence of the calculated and DLS-measured bubble diameters should take place only if the two theories are valid. The gas molecule partitioning analysis shows that >96% of gas molecules in the suspension exist as dissolved phase, which suggests the significance of the dissolved phase for applications of the bubble suspensions.
RESUMEN
Recently, an increasing number of pharmaceutical compounds has become fluorinated. Owing to their pharmacological efficacy, the use of these fluorinated pharmaceuticals continues to grow, and they constitute 20% of the drugs on the current market. However, only a few studies have investigated the fate and transformation of these emerging contaminants in natural and engineered aquatic environments. In the present study, the H2-based reductive transformation of three fluorinated pharmaceutical compounds (levofloxacin, sitagliptin, and fluoxetine) were investigated using alumina-supported monometallic and bimetallic catalysts of the Pt-group noble metals (i.e., Ru, Rh, Pd, and Pt) under ambient temperature and pressure conditions. Degradation of all three compounds was observed with catalytic reactivity ranging from 4.0 × 10-3 to 2.14 × 102 L/(min·gcat), in which fluoxetine generally showed the highest reactivity, followed by sitagliptin and levofloxacin. The fluorination yields and transformation products were characterized for each fluorinated compound and three different degradation mechanisms were elucidated: 1) hydrodefluorination of C-F bond to CH bond, 2) hydrogenation of aromatic ring, and 3) reductive cleavage of CO bond from phenyl ether. Toxicity assessment using Aliivibrio fischeri showed there were no significant changes in toxicity over levofloxacin and sitagliptin degradation, suggesting the formation of no highly toxic by-products during catalytic reduction. For fluoxetine, an increased toxicity was observed during its degradation while ECOSAR-predicted toxicity values of all identified intermediates were lower than that of fluoxetine, suggesting the formation of unidentified secondary by-products that contribute to the overall toxicity. The study showed that catalytic reduction is a promising remediation process for treating and defluorinating the fluorinated pharmaceutical compounds.
Asunto(s)
Halogenación , Preparaciones Farmacéuticas , Óxido de Aluminio , Catálisis , HidrogenaciónRESUMEN
A cost-effective, easy-to-implement, and sustainable approach is needed to mitigate the production of alkaline leachate from steel slags that are reused or disposed in the environment. To address this issue, a humidification treatment process, which is operated by wetting a stack of steel slag using aqueous reagents and letting atmospheric CO2 to be passively diffused into the slag pores to induce slag carbonation reaction, was previously developed. In this study, we demonstrate that the leachate of raw steel slag can be recycled and used as a humidification reagent to substantially enhance the treatment efficiency as well as to enable operating the process with neither synthetic chemical consumption nor wastewater discharge. In a 24-h study, a 0.61-unit reduction in slag pH is achieved using a raw slag leachate as a reagent, which is substantially greater than a 0.28-unit reduction using deionized water. The net amount of CaCO3 produced during an extended humidification duration of 4 weeks is increased by 2.7-fold when the leachate is used instead of deionized water. A series of systematically designed experiments demonstrates that the pH (11.0) and ionic strength (0.0048) are the two major characteristics of the raw slag leachate that contribute to the enhanced efficiency of humidification treatment. With further demonstration at larger scales in follow-up studies, the novel humidification process that utilizes the leachate generated on-site as a reagent is expected to be a feasible alternative for alkali waste treatment prior to its reuse or disposal.