Desorption Of Contaminants Research Articles

Investigation of biotransformation, sorption, and desorption of multiple chemical contaminants in pilot-scale drinking water biofilters

The evolving demands of drinking water treatment necessitate processes capable of removing a diverse suite of contaminants. Biofiltration can employ biotransformation and sorption to remove various classes of chemicals from water. Here, pilot-scale virgin anthracite-sand and previously used biological activated carbon (BAC)-sand dual media filters were operated for ∼250 days to assess removals of 0.4 mg/L ammonia as nitrogen, 50–140 μg/L manganese, and ∼100 ng/L each of trace organic compounds (TOrCs) spiked into pre-ozonated Colorado River water. Anthracite achieved complete nitrification within 200 days and started removing ibuprofen at 85 days. Limited manganese (10%) removal occurred. In contrast, BAC completely nitrified ammonia within 113 days, removed all manganese at 43 days, and exhibited steady state removal of most TOrCs by 140 days. However, during the first 140 days, removal of caffeine, DEET, gemfibrozil, naproxen, and trimethoprim decreased, suggesting a shift from sorption to biotransformation. Acetaminophen and sulfamethoxazole were removed at consistent levels, with complete removal of acetaminophen achieved throughout the study; ibuprofen removal increased with time. When subjected to elevated (1 μg/L) concentrations of TOrCs, BAC removed larger masses of chemicals; with a subsequent decrease and ultimate cease in the TOrCs spike, caffeine, DEET, gemfibrozil, and trimethoprim notably desorbed. By the end of operation, anthracite and BAC exhibited equivalent quantities of biomass measured as adenosine triphosphate, but BAC harbored greater microbial diversity (examined with 16S rRNA sequencing). Improved insight was gained regarding concurrent biotransformation, sorption, and desorption of multiple organic and inorganic contaminants in pilot-scale drinking water biofilters.

Evolution of Structural and Optical Properties of ZnO Nanorods Grown on Vacuum Annealed Seed Crystallites.

In this study, the ambient condition for the as-coated seed layer (SL) annealing at 350 °C is varied from air or nitrogen to vacuum to examine the evolution of structural and optical properties of ZnO nanorods (NRs). The NR crystals of high surface density (~240 rods/μm2) and aspect ratio (~20.3) show greatly enhanced (002) degree of orientation and crystalline quality, when grown on the SLs annealed in vacuum, compared to those annealed in air or nitrogen ambient. This is due to the vacuum-annealed SL crystals of a highly preferred orientation toward (002) and large grain sizes. X-ray photoelectron spectroscopy also reveals that the highest O/Zn atomic ratio of 0.89 is obtained in the case of vacuum-annealed SL crystals, which is due to the effective desorption of hydroxyl groups and other contaminants adsorbed on the surface formed during aqueous solution-based growth process. Near band edge emission (ultra violet range of 360–400 nm) of the vacuum-annealed SLs is also enhanced by 44% and 33% as compared to those annealed in air and nitrogen ambient, respectively, in photoluminescence with significant suppression of visible light emission associated with deep level transition. Due to this improvement of SL optical crystalline quality, the NR crystals grown on the vacuum-annealed SLs produce ~3 times higher ultra violet emission intensity than the other samples. In summary, it is shown that the ZnO NRs preferentially grow along the wurtzite c-axis direction, thereby producing the high crystalline quality of nanostructures when they grow on the vacuum-annealed SLs of high crystalline quality with minimized impurities and excellent preferred orientation. The ZnO nanostructures of high crystalline quality achieved in this study can be utilized for a wide range of potential device applications such as laser diodes, light-emitting diodes, piezoelectric transducers and generators, gas sensors, and ultraviolet detectors.

PORE WATER CONTRIBUTION TO IN-SITU SAMPLING OF POLYCYCLIC AROMATIC HYDROCARBONS IN SEDIMENT USING LOW DENSITY POLYETHYLENE

Passive sampling with low-density polyethylene (LDPE) was assessed to study the way it accumulates contaminants in sediment. Strips of LDPE were deployed in river sediment for a period of two months to evaluate their polycyclic aromatic hydrocarbon (PAH) accumulation following two modes: LDPE buried in sediment and exposed to pore water flow and contaminants desorbed from particles were compared to LDPE strips in the same sediment but in a confined space. The results present an obvious difference of accumulation between the two modes of exposure. LDPE exposed to pore water accumulated PAH depending on their hydrophobicity whereas LDPE only exposed to contaminant desorption from confined particles did not accumulate nor desorb PAH significantly. This observation shows that LDPE only takes up PAH present in pore water and not the PAH bound to sediment particles. Accumulation in LDPE is not the result of forced desorption from particles. The present study also found that LDPE sampling cannot estimate adsorbed molecules in confined sediment nor in turbid water. LDPE is an efficient tool for investigating pore water, the fate of micropollutants in sediment, the effect of bioturbation and bioirrigation on micropollutants and the effect of micropollutants on bioturbation activity.

Ecotoxicity assessment of particulate matter emitted from heavy-duty diesel-powered vehicles: influence of leaching conditions

Concerns regarding the environmental impact of diesel exhaust particulate matter (DPM) have increased in recent years. Following emission to the atmosphere, these fine materials can sorb many contaminants at their surface, which can subsequently be released, for instance, due to physicochemical environmental changes. The desorption of contaminants from particulate matter will increase the environmental pollution and can promote ecotoxicological effects. In this context, the objective of this study was to assess the aquatic ecotoxicity profile of extracts of DPM obtained at two different pH values. Thus, after collecting particulate matter from the diesel exhaust of heavy engines, extracts were obtained with pure water (at pH 2.00 and 5.00) and with a mixture of three organic solvents (dichloromethane, n-hexane, and acetone). To assess the environmental impact of DPM, the exhaust extracts were used in a battery of aquatic bioassays including key organisms of the food chain: bacteria (Aliivibrio fischeri), algae (Scenedesmus subspicatus), daphnids (Daphnia magna), and fishes (Danio rerio). The aqueous leachate at natural pH (2.0) and solvent extracts were extremely ecotoxic, while the aqueous leachate at pH=5.0 showed the lowest ecotoxicity. The global ranking of sensitivity for the biotests tested was daphnids > algae > bacteria > fishes. Thus, the use of this bioassay battery could improve our understanding of the impact of DPM on aquatic environments, which is dependent on the pH of the leaching process.

Evaluation of surfactant performance in in situ foam flushing for remediation of dichlorodiphenyltrichloroethane-contaminated soil

The aim of this study was to select the appropriate surfactant for the remediation of dichlorodiphenyltrichloroethane-contaminated soil using an in situ foam-flushing technique. The research investigated the performance of the nonionic surfactants polyethylene glycol octyl phenyl ether, polysorbate, and polyoxyethylene lauryl ether, as well as the anionic surfactant sodium dodecyl sulfate, in foam static characteristics, solubility enhancement of dichlorodiphenyltrichloroethane, adsorption loss onto soil, and dichlorodiphenyltrichloroethane desorption from contaminated soil using a foam-flushing approach. Considering the above four criteria, the overall performance suggested polyethylene glycol octyl phenyl ether should be selected for the remediation of dichlorodiphenyltrichloroethane-contaminated soil due to its better foamability and stability, relatively high solubilization ability for dichlorodiphenyltrichloroethane, and greatest contaminant desorption efficiency from soil via foam flushing. Results of the dichlorodiphenyltrichloroethane desorption experiments showed that desorption efficiency of dichlorodiphenyltrichloroethane by different surfactants was largely influenced by foam static characteristics and solubility enhancement of dichlorodiphenyltrichloroethane rather than adsorption loss onto soil, which indicated that foam static characteristics and solubilization ability of surfactants were two key criteria for selection of high-performance foam surfactant.

Desorption of Nitroaromatic Compounds From Explosive-contaminated Soil by Washing

ABSTRACTThe soil contaminated by explosive production wastewater was treated by washing using water as solvent. The effect of contact time and temperature, water/soil ratio and washing steps on desorption efficiency was investigated. Six kinetic models—parabolic diffusion model, zero-order equation, pseudo-first-order equation, pseudo-second-order equation, power function equation and Elovich equation—were used to study the desorption kinetics of nitroaromatic compounds from contaminated soil to water. The eluent of contaminated soil before and after washing was characterized by UV–vis analysis. The results showed that the removal rate was fast at the initial stage and then slowed down after 60 min. The desorption of contaminants from soil to water is endothermic. Washing with small quantities of water in high frequency is preferred when water volume is limited. The pseudo-second-order model can be used to describe the desorption process. Soil washing can remove most of the contaminants from the contaminated soil.

Quantitative detection of powdered activated carbon in wastewater treatment plant effluent by thermogravimetric analysis (TGA)

For the elimination of potentially harmful micropollutants, powdered activated carbon (PAC) adsorption is applied in many wastewater treatment plants (WWTP). This holds the risk of PAC leakage into the WWTP effluent and desorption of contaminants into natural water bodies. In order to assess a potential PAC leakage, PAC concentrations below several mg/L have to be detected in the WWTP effluent. None of the methods that are used for water analysis today are able to differentiate between activated carbon and solid background matrix. Thus, a selective, quantitative and easily applicable method is still needed for the detection of PAC residues in wastewater.In the present study, a method was developed to quantitatively measure the PAC content in wastewater by using filtration and thermogravimetric analysis (TGA), which is a well-established technique for the distinction between different solid materials. For the sample filtration, quartz filters with a temperature stability up to 950 °C were used. This allowed for sensitive and well reproducible measurements, as the TGA was not affected by the presence of the filter. The sample’s mass fractions were calculated by integrating the mass decrease rate obtained by TGA in specific, clearly identifiable peak areas. A two-step TGA heating method consisting of N2 and O2 atmospheres led to a good differentiation between PAC and biological background matrix, thanks to the reduction of peak overlapping. A linear correlation was found between a sample’s PAC content and the corresponding peak areas under N2 and O2, the sample volume and the solid mass separated by filtration. Based on these findings, various wastewater samples from different WWTPs were then analyzed by TGA with regard to their PAC content. It was found that, compared to alternative techniques such as measurement of turbidity or total suspended solids, the newly developed TGA method allows for a quantitative and selective detection of PAC concentrations down to 0.1 mg/L. The method showed a linearity coefficient of 0.98 and relative standard deviations of 10%, using small water sample volumes between 0.3 and 0.6 L.

Preparation of functionalized Pd/Fe-Fe3O4@MWCNTs nanomaterials for aqueous 2,4-dichlorophenol removal: Interactions, influence factors, and kinetics

Magnetic multi-walled carbon nanotubes (MWCNTs) were prepared to support Pd/Fe nanoparticles, inhibit the aggregation and passivation, and achieve magnetic separation to avoid the environmental risk of nanoparticles. Rapid adsorption of initial contaminant, steady dechlorination, and gradual desorption of final product was observed. The micromorphology, chemical structure, and components of the nanohybrids were comprehensively characterized by a series of analysis technologies, such as EDX, XRD, SEM, TEM, and XPS. The interactions between the nanohybrids compositions were discussed according to the characterization and experimental data. The whole insight of 2,4-dichlorophenol (2,4-DCP) adsorption- dechlorination-desorption was studied in detail, including the pathways, influence factors, dechlorination kinetics and selectivity. Weak acidity (pH=5.0 and 6.5) favored the 2,4-DCP removal. Satisfactory reactivity of the Pd/Fe-Fe3O4@MWCNTs nanohybrids was observed in five consecutive runs, and 99.2%, 89.6%, 92.1%, 99.8%, and 99.9% of 2,4-DCP was removed, respectively. Most of the final product (phenol) was steadily desorbed to the liquid phase, resulted in the re-exposure of active sites on the nanohybrids and maintained a longer activity.

Remediation of contaminated soils by thermal desorption; effect of benzoyl peroxide addition

In situ remediation of contaminated sites by thermal desorption is a widely accepted technology that provides a permanent solution at an economically competitive cost. In this paper, thermal desorption of various model contaminants was tested at the bench scale. Polyaromatic hydrocarbons (benzene/toluene/xylene) and non-polar extractable compounds were selected as representatives. The electrically heated static oven worked up to 380 °C with temperature gradient 6 °C/min, under air flow (0.6 m3/h). Prior to an experiment, model contaminants (xylene, 2-methylnaphtalene or motor oil) were mixed with 18 kg of model soil in concentrations 2−10 g/kg. The desorption process was performed with and without addition of 1 wt. % of benzoyl peroxide as an oxidant. The aim of the oxidant addition was to facilitate the chemical catalytic decomposition and/or biodegradation of desorbed organics from the soil as an alternative to usually employed incineration. In the course of the desorption process, part of the organic contaminants was oxygenated and liquids obtained after condensation of the desorbed contaminant vapours were subsequently treated by biodegradation. The application of benzoyl peroxide significantly accelerated biodegradation of organic compounds present in the condensates by Pseudomonas sp. Moreover, it was shown that the presence of partial oxidation products in the condensates did not increase their eco-toxicity.

Physical processes and influencing factors of contaminants release due to resuspended sediments in water environment

Strong interaction exists in water flow, sediment movement and pollutants migration, resulting in an integrated environmental system of close contact with each other. Impact of sediment and suspended sediment on the water environment appears a combined dynamic coupling effect by complex hydrodynamic conditions. Three main ways of the pollutants entering water are studied by flume experiments. These three physical processes may be the static diffusion through sediment-water interface, the release due to sediment resuspension and the release of suspended sediment by turbulence. The results show that the sediment can be divided into two distinct muddy and sandy matters based on surface characteristics. Sediment grain size, porosity and initial contaminant amount are the main factors to determine static release of contaminants at the sediment-water interface. The pollutant quantity attenuation formula in sediment was established thereby, indicating that the contaminated attenuation time are proportional to the sediment thickness, density and distribution coefficient. The contaminant release process due to suspended sediment can be broadly divided into three stages: the initial stage, the alternating stage between suspension and settlement and the balance stage. The ratio of the solid/liquid distribution in the water body increases firstly and then decreases in the later two stages. Pollutants emission amount equations is derived based on the mass conservation law, and its contract with experimental results shows that the nature of the adsorption and desorption of contaminants to some extent alleviate the rate of its release. Water pollutant concentration distribution and velocity distribution as well as suspended sediment concentration distribution are closely related, showing the same variation. Vertical distribution difference of sediment contaminants becomes larger with the increase of flow velocity. The larger the initial sediment concentration is, the more uniform the distribution of sediment contaminants tends to be. The time to reach a uniform vertical concentration distribution takes more for sediment with smaller particle size.

Adsorption of phenol and Cu(II) onto cationic and zwitterionic surfactant modified montmorillonite in single and binary systems

Organo-montmorillonites (OMts) modified by cationic surfactant (hexadecyltrimethylammonium bromide, C16) and zwitterionic surfactant (hexadecyldimethyl (3-sulphonatopropyl) ammonium, Z16) were used to remove phenol and Cu(II) from aqueous solution. The OMts were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG), Fourier-transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), and C, H, and N elemental analyses. Besides the independent adsorption of single contaminants, simultaneous and sequential adsorption of phenol and Cu(II) onto OMts were also investigated. The organic carbon contents of the two OMts were similar but the basal spacing of Z16 modified montmorillonite (Z16-Mt) was larger than that of C16 modified montmorillonite (C16-Mt) indicating a higher packing density of surfactant and hydrophobicity in C16-Mt with a slight higher adsorption capacity toward phenol. On the other hand, C16-Mt showed much lower capacity in adsorbing Cu(II) as compared with raw montmorillonite. On the contrary, the adsorption capacity of Z16-Mt toward Cu(II) was comparable with that of raw montmorillonite. The equilibrium data of phenol and Cu(II) were fitted satisfactorily with Linear and Langmuir models, respectively. In the sequential adsorption system, the adsorption of one contaminant was not affected by the other pre-adsorbed one; desorption of pre-adsorbed contaminant was also investigated. For both two contaminants, one did not affect the adsorption of the other one onto Z16-Mt and C16-Mt in the simultaneous system. Z16-Mt could rapidly and efficiently remove both phenol and Cu(II) simultaneously. The adsorption kinetics followed the Pseudo-second order model. The results of this work might provide novel information for developing new effective adsorbents toward organic contaminants and heavy metals.

Abatement of aqueous anionic contaminants by thermo-responsive nanocomposites: (Poly(N-isopropylacrylamide))-co-silylanized Magnesium/Aluminun layered double hydroxides

A series of novel thermo-responsive composite sorbents, were prepared by free-radical co-polymerization of N-isopropylacrylamide (NIPAm) and the silylanized Mg/Al layered double hydroxides (SiLDHs), named as PNIPAm-co-SiLDHs. For keeping the high affinity of Mg/Al layered double hydroxides towards anions, the layered structure of LDHs was assumed to be reserved in PNIPAm-co-SiLDHs by the silanization of the wet LDH plates as evidenced by the X-ray powder diffraction. The sorption capacity of PNIPAm-co-SiLDH (13.5mg/g) for Orange-II from water was found to be seven times higher than that of PNIPAm (2.0mg/g), and the sorption capacities of arsenate onto PNIPAm-co-SiLDH are also greater than that onto PNIPAm, for both As(III) and As(V). These sorption results suggest that reserved LDH structure played a significant role in enhancing the sorption capacities. NO3− intercalated LDHs composite showed the stronger sorption capacity for Orange-II than that of CO32−. After sorption, the PNIPAm-co-SiLDH may be removed from water because of its gel-like nature, and may be easily regenerated contributing to the accelerated desorption of anionic contaminants from PNIPAm-co-SiLDHs by the unique phase-transfer feature through slightly heating (to 40°C). These recyclable and regeneratable properties of thermo-responsive nanocomposites facilitate its potential application in the in-situ remediation of organic and inorganic anions from contaminated water.

Evaluation of soil flushing of complex contaminated soil: An experimental and modeling simulation study

The removal of heavy metals (Zn and Pb) and heavy petroleum oils (HPOs) from a soil with complex contamination was examined by soil flushing. Desorption and transport behaviors of the complex contaminants were assessed by batch and continuous flow reactor experiments and through modeling simulations. Flushing a one-dimensional flow column packed with complex contaminated soil sequentially with citric acid then a surfactant resulted in the removal of 85.6% of Zn, 62% of Pb, and 31.6% of HPO. The desorption distribution coefficients, KUbatch and KLbatch, converged to constant values as Ce increased. An equilibrium model (ADR) and nonequilibrium models (TSNE and TRNE) were used to predict the desorption and transport of complex contaminants. The nonequilibrium models demonstrated better fits with the experimental values obtained from the column test than the equilibrium model. The ranges of KUbatch and KLbatch were very close to those of KUfit and KLfit determined from model simulations. The parameters (R, β, ω, α, and f) determined from model simulations were useful for characterizing the transport of contaminants within the soil matrix. The results of this study provide useful information for the operational parameters of the flushing process for soils with complex contamination.

Tenax extraction of sediments to estimate desorption and bioavailability of hydrophobic contaminants: a literature review.

Characterizing sediment-associated hydrophobic contaminants is problematic, because assessing the total amount of a compound available for chemical exchange with an organism is difficult. To address this, contaminant concentrations have been normalized for specific sediment characteristics (including organic C content) or the chemical activity has been estimated using passive samplers. Another approach to assess compound availability is to determine the extent of readily desorbed compound using resin extractions of sediment slurries. The present paper reviews the literature that uses Tenax® TA, a 2,6-diphenylene-oxide polymer as an extraction tool to measure bioavailability of hydrophobic organic contaminants in sediment. Some work has assessed the extent of desorption with sequential extractions to characterize the maximum rate and pool sizes for different desorbing fractions of bound contaminant. As such, the rapidly desorbing fraction has been well correlated with the extent of degradation, bioaccumulation, and toxicity of hydrophobic contaminants. A shortcut to measuring the full desorption curve to determine the rapidly desorbing compound is to use a single-point extraction, with 6 h or 24 h extractions being the most common. The Tenax extraction has been shown to be effective with laboratory-spiked sediments, field-collected sediments, laboratory-exposed organisms, field-collected organisms, and studies among laboratories. Furthermore, a literature-based model has described the bioaccumulation of polychlorinated biphenyls from independently measured field-collected sediments. Despite the success of this approach, applying the Tenax method to manage contaminated sediments is limited by the absence of a standard set of conditions to perform the extractions, as well as standard methods for using field sediments.

SPR gas sensor with corona discharge

Surface plasmon resonance (SPR)-based sensors are widely used today for express analysis of liquid biological mediums in microbiology, medicine and genetic engineering. They are also used for detecting different contaminants in gaseous mediums. In this case, the main problem of such sensors development is choosing of selective sorbents applied to the sensor surface of for detecting a specific contaminant. Sorbent properties in combination with SPR high sensitivity define the achievable sensor parameters. At nanometer thicknesses of sorbents, the surface condition defines the main contribution to the sensor properties. The impact of the positive corona discharge plasma leads to an effective desorption of extraneous contaminants that block active adsorption centers. Furthermore, the sensor surface is exposed to radicals generated in the discharge plasma under ionization of contaminants. In the present paper, we discuss the possibility of using the corona discharge effects for developing SPR sensors, allowing one to detect trace contaminants in gaseous mediums.

Sorption and desorption of diverse contaminants of varying polarity in wastewater sludge with and without alum.

Sewage sludge sorption and desorption measurements were conducted for nine diverse contaminants of varying polarity: caffeine, sulfamethoxazole, carbamazepine, atrazine, estradiol, ethinylestradiol, diclofenac, and, for the first time desethylatrazine and norethindrone. Two types of sorption behaviour were observed. Compounds with a log octanol-water partition coefficient, log Kow, below 3 showed little or no sorption over 48 hours of shaking, while compounds with log Kow over 3 showed 30 to 90% sorption within the first few minutes. After 6 hours of shaking, mass loss through suspected biotransformation became evident for some compounds. At the pH range considered (5.7-6.7), diclofenac (pKa 4.0, log Kow 4.5) was the only compound in which pH dependent sorption could be quantified. The log sewage sludge-water distribution coefficients, log Kd, ranged from 0.2 to 2.9, and, as expected, increased with increasing log Kow of the compound and organic carbon (OC) content of the sewage sludge. A sewage sludge precipitated with alum had a substantially lower Kd values, as well as lower OC content, compared to alum-free sludge. Desorption was studied by sequentially replacing supernatant water. With each water replacement, log Kd values tended to either remain similar (following a linear isotherm) or in some cases increase (following a Freundlich-type isotherm). The length of time required to restore equilibrium increased with each rinsing step. A literature review of reported Kd values compared well with the alum-free sludge data, but not the alum-sludge data. Sewage sludge Kd across the literature appear more consistent with increasing Kow.

토양 세척 시 초음파 적용에 따른 유기 오염물 제거 특성 평가

ABSTRACT Cavitation generated by ultrasonic irradiation can enhance the diffusional transport of organic contaminants from soilsurfaces or pores. Therefore, ultrasound soil washing can be an alternative of traditional soil washing process. In this study,soil was artificially contaminated with n-tetradecane, n-hexadecane and phenanthrene. A plate type ultrasonic reactor at25 kHz frequency and 1000 W power was used for laboratory soil washing experiments. Ultrasonic soil washingefficiency was compared with those of traditional soil washing using mechanical mixing. Various operational parametersuch as soil/liquid ratio, irradiation time, particle size, and soil organic matter content was tested to find out the optimumcondition. It was found that ultrasonic soil washing demonstrates better performance than mechanical soil washing.Optimum soil:liquid ratio for ultrasonic soil washing was 1 : 5. Desorption of organic contaminants from soils by ultrasonicirradiation was relatively fast and reached equilibrium within 10 minute. However, decrease in the soil particle sizes byultrasonic irradiation results in re-adsorption of contaminants to soil phase. It was also observed that soil particle sizedistribution and soil organic matter content have significant effects on the efficiency of ultrasonic soil washing. Key words :Ultrasound, Desorption, Soil Washing, Soil organic matter, Particle size distribution

Sequential Soil Flushing for Remediation of Complex Contaminated Soils: A Pilot-Scale Test

In this study, an efficient soil flushing process was developed for the remediation of soil complex contaminated with heavy petroleum oils (HPOs) and heavy metals. In most cases, remediation of contaminated soil is carried out after all industrial activity is suspended and removal of facilities. Therefore, in-situ remediation becomes more favored over ex-situ technologies albeit relatively long remediation periods are needed. In particular, soil flushing has been employed as an efficient in-situ technology most frequently in many railroad and industrial sites still in business. The objective of this study was to develop an in-situ soil flushing method using horizontal injection/suction channels. A pilot-scale box reactor (1 m × 0.6 m × 0.7 m) was employed to evaluate desorption of complex contaminants from complex contaminated soils by flushing agents. Since HPOs and heavy metals can be removed by different mechanisms, various flushing agents were required for the treatment of HPOs and heavy metals. Hydrogen peroxide (H2O2) and citric acid were selected and injected sequentially as flushing agents for HPOs and heavy metals, respectively. Soils complex contaminated with HPOs, Zn, and Pb were collected from a railroad site, Seoul, Korea, and they were packed into the pilot-scaled reactor. Two horizontal channels were installed: injection channel was placed 10 cm below the top of soil surface and suction channel was placed 10 cm above the bottom of the reactor. Flushing agents were injected at a flow rate of 3.86 mL/min for 1 month. After flushing, soil samples were collected separately from various points of the reactor (divided into 5 vertical layers and 15 horizontal sections), and then each soil sample was analyzed for the soil flushing efficiency. The initial concentrations of HPOs, Zn and Pb were 4685.5±374.4 mg/kg, 204.9±60 mg/kg, and 139.8 mg/kg (n = 3). After soil flushing, the concentrations were decreased to 1448.4±166.7 mg/kg, 143.4 mg/kg, and 99.5 mg/kg (total removal rates = 69%, 30% and 28.9%, for HPOs, Zn, and Pb, respectively). Hence, it was confirmed in this pilot-scale study that sequential soil flushing by combination of flushing agents was effective for soils complex contaminated with HPOs and heavy metals. These results must be useful for field-scale application of soil flushing remediation for the complex contaminated soils.

Pharmaceutical wastewater treatment using granular activated carbon and UV/H2O2 processes: Experimental analysis and modelling

The treatment of a synthetic pharmaceutical wastewater was studied using granular activated carbon (GAC) adsorption, UV/H2O2 process, and their combination. Experimental results reveal that GAC adsorption alone has 79% efficiency in total organic carbon (TOC) removal in 10 min breakthrough time with the dosage of 333.33 mg activated carbon/L. The adsorption data are fitted well with the Langmuir adsorption isotherm. The UV/H2O2 process alone at 6 h hydraulic retention time with optimum dosage of 4.25 mgH2O2/mgCOD shows 29 and 26% TOC reduction using 185 and 254 nm UV lamps, respectively. The kinetic modelling of the UV254/H2O2 process is developed using chemical oxygen demand (COD) and TOC as lumped parameters. A good agreement between model predictions and experimental data is confirmed. In combined processes, pre‐treated pharmaceutical wastewater by UV254/H2O2 followed by GAC adsorption process along with the desorption of contaminants from GAC and the subsequent treatment of the condensed steam by UV254/H2O2 process leads to 82 % TOC removal efficiency. On the other hand, the GAC adsorption along with UV254/H2O2 treatment of regenerant (condensed steam) from the desorption process leads to 88 % TOC removal at optimum conditions.

Molybdenum-rhenium superconducting suspended nanostructures

Suspended superconducting nanostructures of MoRe 50%/50% by weight are fabricated employing commonly used fabrication steps in micro- and nano-meter scale devices followed by wet-etching with Hydro-fluoric acid of a SiO2 sacrificial layer. Suspended superconducting channels as narrow as 50 nm and length 3 μm have a critical temperature of ≈6.5 K, which can increase by 0.5 K upon annealing at 400 °C. A detailed study of the dependence of the superconducting critical current and critical temperature upon annealing and in devices with different channel widths reveals that desorption of contaminants is responsible for the improved superconducting properties. These findings pave the way for the development of superconducting electromechanical devices using standard fabrication techniques.