Development of ionic-liquid-impregnated activated carbon for sorptive removal of PFAS in drinking water treatment.

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.

Predicting apparent adsorption capacity of sediment-amended activated carbon for hydrophobic organic contaminants using machine learning.

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.

Environmental forensic approach towards unraveling contamination sources with receptor models: A case study in Nakdong River, South Korea.

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.

Thermal treatment of petroleum-contaminated marine sediment according to oxygen availability and temperature: Product quality as a potential plant-growth medium.

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.

Depth of double-lumen endobronchial tube: a comparison between real practice and clinical recommendations using height-based formulae.

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.

Novel ssDNA aptamer-based fluorescence sensor for perfluorooctanoic acid detection in water.

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.

Heavy metal adsorption capacity of powdered Chlorella vulgaris biosorbent: effect of chemical modification and growth media.

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.

Effects of treatment agents during acid washing and pH neutralization on the fertility of heavy metal-impacted dredged marine sediment as plant-growing soil.

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.

Exploring reductive degradation of fluorinated pharmaceuticals using Al2O3-supported Pt-group metallic catalysts: Catalytic reactivity, reaction pathways, and toxicity assessment.

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.

Applying steel slag leachate as a reagent substantially enhances pH reduction efficiency for humidification treatment.

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.

Unraveling the mystery of ultrafine bubbles: Establishment of thermodynamic equilibrium for sub-micron bubbles and its implications.

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 304-518 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.

Reduction of steel slag leachate pH via humidification using water and aqueous reagents.

A slag humidification process that aims to reduce the leachate pH of steel slag via carbonation was accomplished by simply wetting the slag and exposing it to the atmosphere for passive diffusion of atmospheric CO2. The optimization parameters of the process were studied. Results showed that by wetting the slag using various aqueous solutions (deionized water, NaCl solution and NaOH solution), such that its moisture content nearly reaches its water holding capacity, a significant reduction in leachate pH could be achieved. Pretreatment of the slag using 1 M NaOH and subsequent humidification using deionized water showed the best efficiency of 1.1 pH unit reduction among the tested conditions. Slag pretreatment could substantially enhance the carbonation degree on the slag surface, leading to conservation of the treatment effectiveness up to three times the leachate replenishment using deionized water. The benefit of the alkaline treatment to promote slag carbonation could also be achieved using a low to moderate (0.005-0.1 M) NaOH solutions for humidification without the pretreatment step. A 72.5% increase in the treatment efficiency could be achieved via a humidification treatment using 0.005 M NaOH solution compared to that using deionized water. This study shows the promise of humidification treatment as a low-cost, easily implemented, and environmentally friendly slag pH neutralization process that can be applied in the field for slag treatment prior to its use or disposal in the environment.

Effect of basic oxygen furnace slag addition on enhanced alkaline sludge fermentation and simultaneous phosphate removal.

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 1/10 g slag/L sludge, the reactor pH was maintained at 10 and the concentration of SCCs produced was the highest (i.e., 3510 mg COD L-1 from 14,000 mg VS L-1 of sludge mixture), followed by B/S ratios of 1/20, 1.50, 1/5, and 1/2.5 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.

Effect of using powdered biochar and surfactant on desorption and biodegradability of phenanthrene sorbed to biochar.

The present study aimed to investigate the relationship between the desorption and biodegradability of phenanthrene sorbed to biochars by employing two approaches that may change the desorption and biodegradability: the use of powdered biochars and nonionic surfactants. Biochars derived from two feedstocks (rice husk and sewage sludge; pyrolyzed at 500 °C but showing different aromaticity) were used. When the biochars were powdered to obtain particles <250 µm the mass fractions of the desorbed phenanthrene at ∼80 days (fdes) increased from 0.303 to 0.431 for sewage sludge biochars. On the other hand, fdes for rice husk biochars remained virtually unchanged (from 0.264 to 0.255). The mass fractions of the biodegraded phenanthrene (fbio) increased from 0.191 to 0.306 for rice husk biochars and from 0.077 to 0.168 for sewage sludge biochars. When a nonionic surfactant was added at the sub-critical micelle concentration (CMC), fbio increased by 4.7 times and 8.3 times for rice husk and sewage sludge biochars. For both types of biochars, fbio was larger than fdes when the surfactant was added. This study suggests that the addition of nonionic surfactants can be considered if the inhibition of microbial activity is of concern in soils and sediments treated by biochar.

Prediction of long-term heavy metal leaching from dredged marine sediment applied inland as a construction material.

Column leaching studies have been suggested as a reference for site-specific prediction of the long-term leaching characteristics of trace constituents in granular materials used as construction materials. In this study, the concept of the long-term leaching prediction using column studies is applied for dredged marine sediment impacted by heavy metals. The column studies show tailing of the liquid to solid ratio-dependent heavy metal leaching for sediment after heavy metal treatment by acid washing. A dual-mode first-order decay model, applied for the first time in this study for column leaching studies, is able to reproduce the leaching characteristics observed. A procedure for long-term leaching prediction using the dual-mode model is developed and applied to a virtual field scenario for which the sediment is beneficially used as a construction material. The prediction results show that by more accurately reproducing the column study results, the dual-mode model generally predicts greater long-term heavy metal loading to the underlying soil layer and longer duration of leaching than the single-mode model. The heavy metal leaching observed in the columns does not show any correlation with the sequential extraction procedure and toxicity characteristic leaching procedure (TCLP) results, suggesting that the column leaching test should be considered to be independent of such batch test procedures.

Anionic surfactant modification of activated carbon for enhancing adsorption of ammonium ion from aqueous solution.

This study investigates the effect of anionic surfactant modification on activated carbon (AC) to enhance the adsorption of ammonium ion in aqueous solution. Sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS) or sodium octanoate (SO) was used for the modification. At the initial aqueous concentration of 55 mg NH4-N/L and the adsorbent dose of 50 g/L, the SDS-modified AC showed the highest ammonium removal efficiency of 82% among the modified ACs studied. The hydrophobic group of SDS was strongly attached to AC showing almost negligible desorption after the modification. At the same time, the sulfate functional group of SDS provided ion exchange sites favorable for the ammonium ion adsorption. By maximizing SDS loading to the AC, ammonium removal efficiency can further be improved (5% increase). When Na+, K+ or Ca2+ coexisted in the ammonium solution at the concentration of 55 mg/L, the inhibition effect of these cations on ammonium removal efficiency was negligible (<5%). This study shows the potential of anionic surfactant-modified ACs as the excellent adsorbents for ammonium removal from water.

Advancing the Use of Passive Sampling in Risk Assessment and Management of Sediments Contaminated with Hydrophobic Organic Chemicals: Results of an International Ex Situ Passive Sampling Interlaboratory Comparison.

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 ∼10), 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 (

Effect of biochar particle size on hydrophobic organic compound sorption kinetics: Applicability of using representative size.

Particle size of biochar may strongly affect the kinetics of hydrophobic organic compound (HOC) sorption. However, challenges exist in characterizing the effect of biochar particle size on the sorption kinetics because of the wide size range of biochar. The present study suggests a novel method to determine a representative value that can be used to show the dependence of HOC sorption kinetics to biochar particle size on the basis of an intra-particle diffusion model. Biochars derived from three different feedstocks are ground and sieved to obtain three daughter products each having different size distributions. Phenanthrene sorption kinetics to the biochars are well described by the intra-particle diffusion model with significantly greater sorption rates observed for finer grained biochars. The time to reach 95% of equilibrium for phenanthrene sorption to biochar is reduced from 4.6-17.9days for the original biochars to <1-4.6days for the powdered biochars with <125µm in size. A moderate linear correlation is found between the inverse square of the representative biochar particle radius obtained using particle size distribution analysis and the apparent phenanthrene sorption rates determined by the sorption kinetics experiments and normalized to account for the variation of the sorption rate-determining factors other than the biochar particle radius. The results suggest that the representative biochar particle radius reasonably describes the dependence of HOC sorption rates on biochar particle size.

Assessment of hydrophobic organic contaminant availability in sediments after sorbent amendment and its complete removal.

Sorbents amended to sediments in situ for sequestration of hydrophobic organic contaminants (HOCs) may be swept away from the treated sites due to hydrodynamic forces applied to the sediment surface. The purpose of this study is to examine the possibility of recovery of HOC availability in sorbent-amended sediment after complete removal of the sorbent. Sediment contact with an easily separable model sorbent Tenax beads for 28 days in a slurry phase resulted in 74-98% reduction in polycyclic aromatic hydrocarbon and polychlorinated biphenyl availability compared to the untreated controls. HOC availability in the sorbent-treated sediment slightly increased by sorbent removal and after one month of mixing in a slurry phase because the slowly-desorbing HOC fraction was released and repartitioned back to the sediment, partially replenishing the rapidly-desorbing HOC fraction. However, HOC availability did not further increase during an extended mixing period of 12 months suggesting that the repartitioning process was not an infinite source. HOC availability after the 12-month post-treatment mixing for the sorbent-treated sediment was 53-97% lower than that of the untreated sediment because of the combined effect of HOC mass removal from sediment (with the sorbent) and incomplete recovery of available HOC fraction in the sorbent-treated sediment.