Flow-through Setup Research Articles

Removal of Phosphate Ions from Aqueous Solutions by Adsorption onto Leftover Coal

High loadings of wastewater with phosphors (P) require purification measures, which can be challenging to realize in regions where the technical and financial frame does not allow sophisticated applications. Simple percolation devices employing various kinds of adsorbents might be an alternative. Here, we investigated the application of leftover coal, which was collected from Ethiopian coal mining areas, as an adsorbent for the removal of phosphate from aqueous solutions in a classical slurry batch set-up. The combined effects of operational parameters such as contact time, initial concentration, and solution pH on P retention efficiency was studied employing the Response Surface Methodology (RSM). The maximum phosphate adsorption (79% removal and 198 mg kg−1 leftover coal) was obtained at a contact time of 200 min, an initial phosphate concentration of 5 mg/L, and a solution pH of 2.3. The Freundlich isotherm was fitted to the experimental data. The pseudo second-order equation describes the experimental data well, with a correlation value of R2 = 0.99. The effect of temperature on the adsorption reveals that the process is exothermic. The results demonstrate that leftover coal material could potentially be applied for the removal of phosphate from aqueous media, but additional testing in a flow-through set-up using real wastewater is required to draw definite conclusions.

On-line microcolumn-based dynamic leaching method for investigation of lead bioaccessibility in shooting range soils

In this work, a miniaturized flow-through leaching test is presented for rapid screening of potential chemical extractants to explore the bioaccessibility of lead (Pb) in contaminated shooting range soils in Valkeala, Finland. The method combines the versatility of microcolumn-based extraction methods with on-line inductively coupled plasma optical emission spectrometry (ICP OES) analysis for expedient assessment of the magnitude of the bioaccessible pools and the leaching kinetics of lead from polluted soils under variable physicochemical scenarios. Acids and salt solutions were studied as potential extractants. The efficiency of the extractants relative to the initial total amount of lead in the soil sample (509 ± 21 mg/kg) were found to increase in the following order: 0.11 M acetic acid (55%) < 1 M MgCl2 (58%) < 0.1 M NH2OH·HCl (61%) < 0.1 M citric acid (93%) < 0.1 M HCl (96%). The proposed on-line microcolumn-based method was further explored for implementation of the modified BCR (now termed Standards, Measurements and Testing Programme, SM&T) sequential extraction procedure to avail the information about different fractions available in the solid sample, and validated by mass balance calculations. The equivalent sequential procedure in a batch format was then studied and compared against the on-line microcolumn extraction method.The on-line dynamic extraction system presented in this work accepts a substantial amount of sample (2.5 g) as compared to previous flow-through mini-column setups (generally accommodating < 0.25 g of sample), thus maintaining sample representativeness and fostering comprehension of the extraction patterns for non-homogenous soil materials. The use of cotton buds and Teflon membranes and holders in the microcolumn setup facilitates the repeatable flow-through leaching of trace elements and restrict formation of preferential channels. Monitoring of the leachable trace elements in real time delivers detailed insight into the ongoing extraction process and provides a time-saving assessment of potential chemical extractants.

A combination of experimental and computational methods to study the reactions during a Lignin-First approach

Abstract Current pulping technologies only valorize the cellulosic fiber giving total yields from biomass below 50 %. Catalytic fractionation enables valorization of both cellulose, lignin, and, optionally, also the hemicellulose. The process consists of two operations occurring in one pot: (1) solvolysis to separate lignin and hemicellulose from cellulose, and (2) transition metal catalyzed reactions to depolymerize lignin and to stabilized monophenolic products. In this article, new insights into the roles of the solvolysis step as well as the operation of the transition metal catalyst are given. By separating the solvolysis and transition metal catalyzed hydrogen transfer reactions in space and time by applying a flow-through set-up, we have been able to study the solvolysis and transition metal catalyzed reactions separately. Interestingly, the solvolysis generates a high amount of monophenolic compounds by pealing off the end groups from the lignin polymer and the main role of the transition metal catalyst is to stabilize these monomers by transfer hydrogenation/hydrogenolysis reactions. The experimental data from the transition metal catalyzed transfer hydrogenation/hydrogenolysis reactions was supported by molecular dynamics simulations using ReaXFF.

Far from equilibrium basaltic glass alteration: The influence of Fe redox state and thermal history on element mobilization

Elemental release from basaltic glasses at far from equilibrium conditions was investigated as a function of the Fe redox state (Fe(II)/Fetot = 0.35 and 0.80) and thermal history (quenched ↔ annealed). A flow-through column setup was used to ensure disequilibrium of basaltic glass and solution during the entire runtime. Percolation experiments were performed at 25 °C for up to 500 h with intermediate sample collection. Two different pH values were adjusted, and the effect of organic matter was tested by adding oxalic acid. Element concentrations in the percolate were measured by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES).After an initial high release of elements from fresh glass surface, steady state was achieved after 240–430 h for Si at pH 5–7 and after 170–240 h for Al at pH 2. At near neutral conditions (pH 5–7) mobilization of Si is relatively high, while Fe and possibly Al are retained in precipitates. Under more acidic conditions (pH 2), the Si concentration of the solutions was very low compared to the other main constituents of the glass. Large amounts of Si-rich residues are formed after glass dissolution at pH 2. On the other hand, Fe (and Mn) is very mobile under acidic conditions, favored by complex formation with oxalic acid and chlorine. In the initial phase of the pH 2 experiments, the element release from reduced glasses is higher than from oxidized glasses. However, this trend is reversed when approaching steady state. Higher dissolution rates for oxidized glasses are predicted due to the progressive replacement of strong Si-O-Si with weaker Fe(III)-O-Si. At pH 5–7 the concentrations of elements in the percolate are too low to establish a systematic difference between oxidized and reduced glasses. Looking at the total amount of mobilized elements, the thermal history of the glasses has no significant effect in the case of oxalate-free solutions, but a noticeable increase of element release in the case of rapidly quenched glasses was observed when using 1 mM oxalic acid solution. The strong effect of oxalate on dissolution of quenched glasses is probably related to the more open glass network structure in quenched glasses.

Probing in Vitro Release Kinetics of Long-Acting Injectable Nanosuspensions via Flow-NMR Spectroscopy.

Novel treatment routes are emerging for an array of diseases and afflictions. Complex dosage forms, based on active pharmaceutical ingredients (APIs) with previously undesirable physicochemical characteristics, are becoming mainstream and actively pursued in various pipeline initiatives. To fundamentally understand how constituents in these dosage forms interact on a molecular level, analytical methods need to be developed that encompass selectivity and sensitivity requirements previously reserved for a myriad of in vitro techniques. The knowledge of precise chemical interactions between drugs and excipients in a dosage form can streamline formulation development and process screening capabilities through the identification of properties that influence rates and mechanisms of drug release in a cost-effective manner, relative to long-term in vivo studies. Through this work, a noncompendial in vitro release (IVR) method was developed that distinguished the presence of individual components in a complex crystalline nanosuspension environment. Doravirine was formulated as a series of long-acting injectable nanosuspensions with assorted excipients, using low- and high-energy wet media milling methods. IVR behavior of all formulation components were monitored using a robust continuous flow-through (CFT) dissolution setup (USP-4 apparatus) with on-line 1H NMR end-analysis (flow-NMR). Results from this investigation led to a better understanding of formulation parameter influences on nanosuspension stability, surface chemistry, and dissolution behavior. Flow-NMR can be applied to a broad range of dosage forms in which specific molecular interactions from the solution microenvironment require further insight to enhance product development capabilities.

Efficient Mild Organosolv Lignin Extraction in a Flow-Through Setup Yielding Lignin with High β-O-4 Content.

Current lignin fractionation methods use harsh conditions that alter the native lignin structure, resulting in a recalcitrant material which is undesired for downstream processing. Milder fractionation processes allow for the isolation of lignins that are high in β-aryl ether (β-O-4) content, however, at reduced extraction efficiency. The development of improved lignin extraction methods using mild conditions is therefore desired. For this reason, a flow-through setup for mild ethanosolv extraction (120 °C) was developed. The influence of acid concentration, ethanol/water ratio, and the use of other linear alcohol co-solvents on the delignification efficiency and the β-O-4 content were evaluated. With walnut shells as model feedstock, extraction efficiencies of over 55% were achieved, yielding lignin with a good structural quality in terms of β-O-4 linking motifs (typically over 60 per 100 aromatic units). For example, lignin containing 66 β-O-4 linking motifs was obtained with an 80:20 n-propanol/water ratio, 0.18 M H2SO4 with overall a good extraction efficiency of 57% after 5 h. The majority of the lignin was extracted in the first 2 hours and this lignin showed the best structural quality. Compared to batch extractions, both higher lignin extraction efficiency and higher β-O-4 content were obtained using the flow setup.

Measuring Retardation Factors of Cesium133 and Strontium88 Cations Using Column Test

AbstractA flow-through column test setup was developed to measure the breakthrough curves of cesium133 (Cs) and strontium88 (Sr) cations in a natural silty sand. Advantages of this column setup inc...

Efficient treatment of brine wastewater through a flow-through technology integrating desalination and photocatalysis

Many current treatments for brine wastewaters are energy-intensive, chemical-intensive, and involve independent process in the removal of salts and contaminants. We demonstrate that through the integration of capacitive deionization and photocatalysis reactions within carbon nanotubes (CNTs) based membrane system, we are able to realize the purification and desalination of wastewaters via single-step, energy-efficient, and environmentally friendly route. We firstly designed the membrane system consisting of graphitic carbon nitride (g-C3N4), CNTs membrane, and poly(vinyl alcohol)-formaldehyde (PVF) foam. Then, two identical membrane systems were used as permeable electrodes and photocatalytic microreactors to construct the flow-through setup. The tests of the setup with a variety of dye solution, antibiotics solution, and actual wastewaters prove that wastewaters passing through the setup promptly turn to clean water with significantly decreased salinity. This is because the setup can use C3N4 modified CNTs membrane to adsorb organic contaminants and inorganic ions and decompose contaminants via photocatalysis reactions. In addition, by discharging the setup, its adsorption capacity towards salts is easily recovered. Consequently, the flow-through setup is observed to exhibit stable performance for concurrent removal of organic contaminants and inorganic salts in multiple cycles.

Reactive fronts in chemically heterogeneous porous media: Experimental and modeling investigation of pyrite oxidation

The spatial distribution of reactive minerals in subsurface porous media is an important control for groundwater quality. In this study we investigate pyrite oxidation reactive fronts in chemically heterogeneous porous media by combining laboratory experiments and reactive transport modeling. We performed experiments in different setups including batch, 1-D column, and 2-D flow-through systems. The flow-through experiments were performed in physically homogenous but chemically heterogeneous domains with embedded reactive pyrite inclusions at different spatial locations and with different concentrations. The setups were initially maintained under anoxic conditions and subsequently flushed with an inflowing oxic solution. A non-invasive optode technique was used for high-resolution monitoring of oxygen. This allowed us to capture the dynamics of the reactive oxygen fronts in the 1-D columns and in the 2-D flow-through chamber. Water quality analyses of the products of pyrite oxidation, iron (Fe) and sulfur (S), were also carried out in the different setups. The concentration of these species released in the 1-D columns (up to 6.2 × 10−5 mol/L Fe and 13.7 × 10−5 mol/L S) and in the 2-D setup (up to 3 × 10−6 mol/L Fe and 9 × 10−6 mol/L S) could be quantitatively related to the consumption of oxygen (up to 1.9 × 10−4 mol/L consumed in the 1-D and 2-D setups). The reaction rates were found to be different between the setups and dependent on the spatial location and concentration of the pyrite inclusions.A modeling approach coupling 1-D and 2-D transport codes with the geochemical simulator PHREEQC is proposed to simulate the spatial and temporal dynamics of oxygen transport, the kinetics of pyrite oxidative dissolution, and the changes in water quality in the chemically heterogeneous flow-through setups. The model allowed the quantitative interpretation of the experimental results and represents a valuable tool to capture the coupling between multidimensional transport and geochemical reactions both in laboratory and in field scale applications.

Non-reactive and reactive experiments to determine the electrical conductivities of aqueous geothermal solutions up to supercritical conditions

Electrolytes, dissolved in aqueous solutions, have the tendency to associate at near-critical temperature, which causes a removal of free charge carriers from the solution. This behavior is intensified in the “low” pressure range of the supercritical field and has become noticeable in a reduction of fluid conductivity by an order of magnitude. Thus, deep resistivity surveys are regarded to provide a convenient means for detecting supercritical roots of geothermal high-enthalpy reservoirs. In previous decades, the temperature dependence of electrical properties of single-component brines has been extensively studied up to supercritical conditions. Very few data are available for two-component brines, but none for multicomponent mixtures, representing natural geothermal fluids. Thus, we have developed a flow-through set-up to measure both the intrinsic temperature dependence of electrical properties of hydrothermal solutions and the effect of fluid-solid interactions on fluid conductivities in a temperature range of 23–422 °C at 31 MPa. Experimental conditions were adapted to those of two geothermally exploited areas on Iceland – the Krafla and the Reykjanes field – which are characterized by meteoric and by seawater controlled fluid systems, respectively.Our study shows that the intrinsic temperature dependence of mixed brines exhibit a similar left-skewed curve characteristic like those of single component brines with conductivities decreasing precipitously to a minimum at critical temperature. At further isobaric temperature rise conductivities remain on this level. The opposite was observed for reactive experiments, where fluid – solid interaction was allowed. In this case, conductivities re-increased by up to factor 7 within seconds, indicating a significant and immediate increase in solubility of rock and composite materials, which are in contact with supercritical aqueous solutions and suggest high reaction kinetics of this process. However, at supercritical conditions conductivities did not remain steady and the electrical properties of supercritical fluid-rock systems are characterized by a wide range of conductivities. The competing processes of mineral dissolution and new mineral formations are also evident from complementary micro-structural investigations as well as chemical analyses of the percolated fluids.

UV-vis Imaging of Piroxicam Supersaturation, Precipitation, and Dissolution in a Flow-Through Setup.

Evaluation of drug precipitation is important in order to address challenges regarding low and variable bioavailability of poorly water-soluble drugs, to assess potential risk of patient safety with infusion therapy, and to explore injectable in situ suspension-forming drug delivery systems. Generally, drug precipitation is assessed in vitro through solution concentration analysis methods. Dual-wavelength UV-vis imaging is a novel imaging technique that may provide an opportunity for simultaneously monitoring changes in both solution and solid phases during precipitation. In the present study, a multimodal approach integrating UV-vis imaging, light microscopy, and Raman spectroscopy was developed for characterization of piroxicam supersaturation, precipitation, and dissolution in a flow-through setup. A solution of piroxicam dissolved in 1-methyl-2-pyrrolidinone was injected into a flowing aqueous environment (pH 7.4), causing piroxicam to precipitate. Imaging at 405 and 280 nm monitored piroxicam concentration distributions during precipitation and revealed different supersaturation levels dependent on the initial concentration of the piroxicam solution. The combination with imaging at 525 nm, light microscopy, and Raman spectroscopy measurements demonstrated concentration-dependent precipitation and the formation, growth, and dissolution of individual particles. Results emphasize the importance of the specific hydrodynamic conditions on the piroxicam precipitation. The approach used may facilitate comprehensive understanding of drug precipitation and dissolution processes and may be developed further into a basic tool for formulation screening and development.

Laboratory Evaluation of a Novel Real-Time Respirator Seal Integrity Monitor.

A low-cost real-time Respirator Seal Integrity Monitor (ReSIM) was recently developed to monitor a respirator's actual performance at a workplace. The objective of this study was to evaluate the capability of the new ReSIM prototype in manikin-based laboratory experiments to rapidly detect induced leakage of a half-mask elastomeric respirator. Two phases of testing were conducted in this study. First, the accuracy of ReSIM measuring an aerosol concentration was assessed by comparing the outputs of ReSIM against a reference optical aerosol spectrometer (OAS) in a flow-through set-up. Second, the capability to detect a leak was tested using a manikin-based set-up to simulate leaks into a functional respirator. The regression curve of ReSIM versus OAS had an R2 of 0.936, indicating its high accuracy within the targeted particle size range of 0.5-2 µm. The ReSIM provided a leak detection sensitivity (probability of correctly identifying intervals with the true leak) of 98.4% when challenged with a combustion aerosol, compared to 71.8% when challenged with a NaCl aerosol. Its specificity (probability of identifying intervals without a leak) was 99.8% after adjusting for persistent false positives for both types of challenge aerosol. The ReSIM prototype not only can estimate the particle concentration with high accuracy but also can rapidly detect respirator faceseal leakage in real time with sufficient sensitivity and specificity. In addition, it can trigger an alarm when the faceseal integrity is compromised.

Invasive versus native brachyuran crabs in a European rocky intertidal: respiratory performance and energy expenditures

The invasive Asian shore crab Hemigrapsus sanguineus is now the second most abundant intertidal crab in the North Sea after the native European green crab Carcinus maenas. To compare their respiratory performance and energy expenditures, we measured standard respiration rates of both species from around the island of Helgoland, North Sea, Germany (54°11′N, 7°53′E) in 2015. Oxygen consumption was recorded in a flow-through setup between 5 and 20 °C. At lower temperatures, H. sanguineus had similar respiration rates as C. maenas, but approximately twofold higher rates at higher temperatures. Numerical models for the calculation of individual respiration rates were established and applied to the entire intertidal populations around Helgoland to compare the energy expenditures of both species. Abundance and biomass data recorded in August 2014 showed that H. sanguineus reached values as high as 21 and 59%, respectively, compared to those of C. maenas. Based on these data and the numerical respiration models, the energy expenditures of both populations were calculated for the whole year 2014. The H. sanguineus population reached, depending on the assumed diet of both species (complete herbivory versus complete carnivory), 86–135% of the expenditure value of C. maenas. As population densities of H. sanguineus are likely to increase in the North Sea, the energy expenditure of the invader and thus its impact on the energy flux in the intertidal habitat will further increase. Whether this will lead to an impact on the local intertidal community depends on species-specific dietary preferences and remains to be investigated.

Promoter nature effect on the sensitivity of Ni–Mo/Al2O3, Co–Mo/Al2O3, and Ni–Co–Mo/Al2O3 catalysts to dodecanoic acid in the co-hydrotreating of dibenzothiophene and naphthalene

The promoter nature effect on the sensitivity of Mo/Al2O3, Ni–Mo/Al2O3, Co–Mo/Al2O3, and Ni‒Co–Mo/Al2O3 catalysts to dodecanoic acid in the hydrotreating of a mixture containing dibenzothiophene and naphthalene has been investigated. The experiments have been carried out using a flow-through setup. The catalysts have been prepared using the PMo12 heteropoly acid, Сo(Ni) citrates, and Co2Mo10 heteropoly acid and have been characterized by high-resolution transmission electron microscopy. The highest hydrodesulfurization activity in the presence of dodecanoic acid is shown by the trimetallic catalyst Ni–Co–Mo/Al2O3. The introduction of Ni is favorable for dodecanoic acid conversion via the hydrogenation route, thus increasing the С11: С12 ratio in the conversion products. Effective dodecanoic acid adsorption constants under the hydrotreating conditions have been calculated using the Langmuir–Hinshelwood model.

Dissolution enhancement of griseofulvin from griseofulvin-sodium dodecyl sulfate discs investigated by UV imaging

The purpose of study was to investigate the dissolution rate enhancement obtained when sodium dodecyl sulfate (SDS) is co-compressed with griseofulvin into discs using a UV imaging-based flow-through dissolution testing setup. Griseofulvin dissolution rates obtained from discs containing 5.92 and 10.6% (w/w) SDS in phosphate buffer (pH 6.5) were similar to dissolution rates from pure griseofulvin discs when applying 20 and 100 mM SDS as dissolution medium, respectively. Dynamic light scattering of effluent samples revealed nanosized particles (approximately 135 nm in diameter) escaping the discs during dissolution. Scanning electron microscopy of co-compressed griseofulvin-SDS discs prior to dissolution testing showed surfaces apparently consisting of granules (100 and 200 nm in diameter) as well as particles present on the disc surfaces possibly related to the high initial dissolution rates. Material swelling or precipitation was observed for discs containing 10.6 or 15.8% (w/w) SDS. UV imaging revealed increased griseofulvin concentrations near the solid-liquid interface of griseofulvin-SDS discs, e.g., a 45-fold increase in concentration was observed for discs containing 10.6% (w/w) SDS as compared to discs without SDS, which is the likely cause of the enhanced dissolution rates found for the co-compressed griseofulvin-SDS discs.

Development of an Advanced Zinc-Air Flow Battery

In recent years, zinc-air flow batteries have regained importance as promising energy storage system for mobile and stationary applications. This revived importance is driven by the increased demand of high-performance, efficient, safe and environmentally friendly energy storage solutions to meet the challenges of modern energy supply systems with high amounts of renewable energy. These energy storage systems need to address variable power, capacity and profitability requests. Zinc-air batteries with a specific energy density higher than lithium-ion and low cost, highly available, eco-friendly active materials are suitable to fulfill these requirements. The use of a flow battery type with zinc-particles suspended in alkaline solution (zinc-slurry) in addition with oxygen reduction electrodes developed for the chloralkali process allows the development of high-power zinc-air batteries. This setup also enables the independent scaling of capacity and power. The cooperative research project ZnMobil, supported by the Federal Ministry of Economic Affairs and Energy in Germany, combines the experience of industrial and academic partners (Covestro Deutschland AG; Grillo-Werke AG; VARTA Microbattery GmbH; Accurec Recycling GmbH; Technical University Freiberg, Gottfried Wilhelm Leibniz University Hannover; University of Duisburg-Essen; The fuel cell research center ZBT GmbH) to develop a low-cost zinc-air flow battery with high performance. Here we present the electrochemical performance of the new zinc-air flow battery with respect to different zinc-slurry compositions. The battery system consists of a 100 cm² copper plate as current collector for the zinc-suspension electrode and an oxygen reduction electrode with gas-diffusion layer (supplied by Covestro). The zinc-slurry contains zinc particles (supplied by Grillo) suspended in alkaline solution (30 wt-% KOH) and stabilized with polyacrylic acid. Current voltage curves and depth of discharge were measured as a function of slurry composition (e.g. zinc content, additives) and different flow velocities of the zinc slurry. Corresponding zinc-slurry conductivities were evaluated in a flow-through conductivity measurement setup. Depending on the selected parameters, it is possible to achieve discharge current densities higher than 4 kA/m².

Bioelectrochemical anaerobic sewage treatment technology for Arctic communities.

This study describes a novel wastewater treatment technology suitable for small remote northern communities. The technology is based on an enhanced biodegradation of organic carbon through a combination of anaerobic methanogenic and microbial electrochemical (bioelectrochemical) degradation processes leading to biomethane production. The microbial electrochemical degradation is achieved in a membraneless flow-through bioanode-biocathode setup operating at an applied voltage below the water electrolysis threshold. Laboratory wastewater treatment tests conducted through a broad range of mesophilic and psychrophilic temperatures (5-23°C) using synthetic wastewater showed a biochemical oxygen demand (BOD5) removal efficiency of 90-97% and an effluent BOD5 concentration as low as 7mgL-1. An electricity consumption of 0.6kWhkg-1 of chemical oxygen demand (COD) removed was observed. Low energy consumption coupled with enhanced methane production led to a net positive energy balance in the bioelectrochemical treatment system.

Modern hydroprocesses for the synthesis of high-quality low-viscous marine fuels

Basic physicochemical and service properties inherent in middle distillate fractions from hydrocatalytic and thermodestructive processes are studied for one Russian refinery from the viewpoint of using them as potential components for low-viscous marine fuels (LMFs) with improved environmental and low-temperature properties. A laboratory-scale flow-through setup loaded with an industrial nickel–molybdenum catalyst is used for the hydrocracking of vacuum gasoils (with T ebp ranging from 500 to 580°C) at 340–380°C and 15.0 MPa. The highest yield of the light hydrocracking gasoil (LHCG) is observed upon the processing of vacuum gasoil (T ebp, 350–500°C) at 360°C, the highest cetane index (53 points) and the lowest sulfur content (7 ppm) being characteristic of the obtained LHCG. With heavier vacuum gasoil, the total yields of target distillates and the yield of LHCG decrease. In terms of physicochemical and service properties, the obtained LHGC is a high-quality component of LMFs. Comparative properties of the hydrorefined virgin diesel fraction, light gasoils obtained via catalytic cracking, slow coking, and the promising hydrocracking process are analyzed. The physicochemical, environmental, and main service properties inherent in the middle distillate fractions of secondary processes are determined depending on their hydrocarbon and nonhydrocarbon compositions, and on the content of key components. Based on these dependences, recommendations are made for the production of optimum low-viscous marine fuels with improved environmental and low-temperature properties.

Mimicking natural systems: Changes in behavior as a result of dynamic exposure to naproxen

Animals living in aquatic habitats regularly encounter anthropogenic chemical pollution. Typically, the toxicity of a chemical toxicant is determined by the median lethal concentration (LC50) through a static exposure test. However, LC50 values and static tests do not provide an accurate representation of exposure to pollutants within natural stream systems. In their native habitats, animals experience exposure as a fluctuating concentration due to turbulent mixing, temporal variations of contamination (seasonal inputs), and contaminant input type (point vs. non-point). Research has shown that turbulent environments produce exposures with a high degree of fluctuation in frequency, duration, and intensity. In order to more effectively evaluate the effects of pollutants, we created a dynamic exposure paradigm, utilizing both flow and substrate within a small mesocosm. A commonly used pharmaceutical, naproxen, was used as the toxicant and female crayfish (Orconectes virilis) as the target organism to investigate changes in fighting behavior as a result of dynamic exposure. Crayfish underwent either a 23h long static or a dynamic exposure to naproxen. Following exposure, the target crayfish and an unexposed size matched opponent underwent a 15min fight trial. These fight trials were recorded and later analyzed using a standard ethogram. Results indicate that exposure to sublethal concentrations of naproxen, in both static and flowing conditions, negatively impact aggressive behavior. Results also indicate that a dynamic exposure paradigm has a greater negative impact on behavior than a static exposure. Turbulence and habitat structure play important roles in shaping chemical exposure. Future research should incorporate features of dynamic chemical exposure in order to form a more comprehensive image of chemical exposure and predict the resulting sublethal effects from exposure. Possible techniques for assessment include utilizing flow-through experimental set-ups in tandem with behavioral or physiological endpoints as opposed to acute toxicity. Other possibilities of assessment could involve utilizing fine-scale chemical measurements of pollutants to determine the actual concentrations animals encounter during an exposure event.

Investigation of geometry-dependent sensing characteristics of microfluidic electrical impedance spectroscopy through modeling and simulation

Microfluidic electrical impedance spectroscopy (EIS) has been widely used for the identification of single cells based on the detection of cell size or morphology. However, the obtained impedance data are highly affected by the design of microfluidic setup and by the geometric parameter and orientation of samples. Here, we systematically investigated the geometry-dependent sensing characteristics of microfluidic EIS by using finite-element modeling. We considered two different detection units of microfluidic EIS: One is a sample-immobilization system where samples are immobilized at a narrow orifice and subsequently measured by using EIS; The other one is a flow-through system where samples are detected when flowing through the sensing unit. Spherical microparticles with different diameters and combinations were used as samples in the experiment and modeling. Linear regression calculation between the EIS data and the geometric parameters of samples revealed that EIS signal is highly sensitive to the height or the cross-sectional area of immobilized samples, while the flow-through setup enables the detection of sample volume. Simulation of non-spherical samples, i.e. budding yeast cells and erythrocytes, demonstrated that sample orientations have significant influence on the impedance measurements and thus may discredit the volume detection of non-spherical cells by using microfluidic impedance cytometry. The results could conduct the future design and application of microfluidic EIS systems for single-cell studies, especially the cell discrimination based on size or morphology.