Recirculating Flow System Research Articles

3D-printed indium oxide monoliths for PFAS removal

More efficient removal methods for per- and polyfluoroalkyl substances (PFAS), anthropogenic compounds with high persistence in the environment, are urgently needed due to their significant adverse health effects. Current technologies for PFAS removal in water are limited by incomplete degradation or practical concerns about the use of slurry-based adsorbents. In this study, self-supported indium oxide (In2O3) monoliths were produced via extrusion-based 3D printing and used for the removal of perfluorooctanoic acid (PFOA) via adsorption in a recirculating flow system. A detailed study of the sintering temperature, monolith geometry, and flow rate allowed maximising PFOA adsorption due to the improvement of PFOA diffusion and the increased number of active sites on the monolith, resulting in 53 % of PFOA removal with fast adsorption kinetics in 3 h. Additionally, a low-temperature pyrolysis process at 500 °C effectively regenerated the In2O3 monoliths, allowing reusing the monoliths for three adsorption cycles, while also improving the PFOA removal to 75 % in 3 h. The regenerated In2O3 monoliths not only have a high adsorption capacity (0.16 mg g−1), but also required a much shorter time to reach the adsorption equilibrium compared with other adsorbents reported in the literature. The effectiveness, robustness and reusability of the 3D printed In2O3 monoliths highlight their potential as an efficient and sustainable adsorbent for PFAS removal. The approach presented here represents an effective strategy for the fabrication of complex adsorbents, which are reusable and can be easily handled, eliminating the expensive downstream removal required for slurries while offering a clear route for scale-up towards industrial use.

Use of a turbulence promoter in an electrochemical filter-press reactor: Consolidated evidence of significant enhancement of organics mass transport and degradation rates

• Turbulence promotion enables a remarkable enhancement of the electrolysis performance. • The mass transfer coefficient is thus increased by approximately threefold. • The electrolysis time to attain 98% removal of bisphenol S is reduced by about 62%. • The organic load removal (mineralization) rate is almost doubled. • Significant energy savings are achieved for organics degradation by anodic oxidation. In this communication, consolidated evidence of the significant effect of turbulence promotion on organics anodic oxidation is presented. Thus, the performance of a filter-press reactor fitted or not with a turbulence promoter (three randomly superposed plastic meshes) is assessed using a recirculating flow system. For a given volumetric flow rate ( q V ), the mass transfer coefficient ( k m ) for the oxidation of the [Fe(CN) 6 ] 4− species at the surface of the boron-doped diamond anode (geometric area = 24.2 cm 2 ) is increased approximately threefold (e.g. to 9.44 × 10 −5 m s −1 at q V = 7.0 L min −1 ), indicating that mass transport is significantly enhanced by the presence of the turbulence promoter in the filter-press reactor. In fact, a given value of k m can be attained using a q V value that is only about one fifth that needed in the absence of the turbulence promoter. Using bisphenol S (BPS) as a model organic compound, an approximately threefold increase in its degradation rate is also brought on by the use of the turbulence promoter, which e.g. means a reduction of ~ 62% in the electrolysis time to attain 98% BPS removal. Additionally, the mineralization rate is doubled, which e.g. means a reduction of ~ 45% in the electrolysis time needed to remove 84% of the solution organic load. These results confirm that turbulence promoters in filter-press reactors indeed enable significant savings in the energy expenses associated to the electrochemical degradation of organics, greatly increasing the efficiency of the process.

Synthesis of Bi‐functional Immobilized Polymer Catalysts via a Two‐step Radiation‐induced Graft Polymerization Process

AbstractHere, we designed and synthesized two types of bi‐functional immobilized polymer catalysts based on the prolineamide‐acid combination for direct enantioselective aldol reaction in flow systems. Conventional bi‐functional catalysts in which the two functions are present on the same graft polymer afforded up to 99 % yield and >99 % enantiomeric excess (ee) in a recirculating flow system. We also investigated bi‐functional catalysts in which the two functions are located on different graft polymers. We present a straightforward catalyst immobilization method that allows two different catalysts located on different graft polymers to be introduced separately onto the same polymer by conducting two successive steps of radiation‐induced graft polymerization process (RIGP). We confirmed that the graft polymers (grafted polycatalyst and polyacrylic acid chain) interact with each other to promote the aldol reaction with high conversion and ee. This design strategy may be superior to the conventional approach for synthesizing catalysts in which multiple functions interact.

Determination of bisphenol S, simultaneously to bisphenol A in different water matrices or solely in electrolyzed solutions, using a cathodically pretreated boron-doped diamond electrode

A simple, accurate, and environmentally friendly method for the simultaneous determination of the analog endocrine disruptors bisphenol S (BPS) and bisphenol A (BPA) was developed and validated. The determination was performed by square-wave voltammetry using a cathodically pretreated boron-doped diamond (BDD) as the working electrode, with 0.1 mol L−1 H2SO4 as the supporting electrolyte. Under optimized conditions, a wide linear working range (R2 = 0.999) from 0.20 to 80.0 mg L−1 with a limit of detection (S/N = 3) of 0.060 mg L−1 was attained for BPS. For BPA, a linear correlation (R2 = 0.992) was attained from 0.10 to 50.0 mg L−1, with a limit of detection of 0.030 mg L−1. As far as we could ascertain, these are the lowest limits of detection and the widest linear ranges in the literature for this determination. The method was applied to the simultaneous determination of BPS and BPA in real water samples, with minimum sample preparation processes (dilution and acidification only). Excellent recovery values were achieved, ranging from 95 to 99%. Additionally, the method was successfully applied to the monitoring of the electrochemical degradation (anodic oxidation) of BPS using a recirculating flow system fitted with a BDD anode. The decay of [BPS] with time was also checked by an HPLC method, with results statistically similar to those obtained by the proposed electroanalytical method. Hence, the proposed method is a reliable, greener, and low-cost alternative to monitor simultaneously BPS and BPA in aquatic matrices or only BPS in wastewater treatment processes.

Release of Ag/ZnO Nanomaterials and Associated Risks of a Novel Water Sterilization Technology

Abstract: For water sterilization, a highly effective system utilizing electrophoresis and the antimicrobial properties of Ag/ZnO nanomaterials has been developed. However, the key component of this system, a sterilization carbon cloth containing Ag/ZnO nanomaterials, has not been evaluated with respect to the potential environmental and human health risks associated with the nanomaterials released. In this paper, a recirculation flow system and methodology were developed to study the release of Ag and ZnO during water treatment. Our study showed that the released silver nanoparticles and dissolved Ag from the carbon cloth were 50 µg/L and 143 µg/L in the United States Environmental Protection Agency (EPA) medium, respectively. The release of dissolved Zn in the EPA medium was 33 µg /L. The results indicate that the release of dissolved and nanoparticulate silver from the sterilization carbon cloth exceeded acceptable risk levels in the aquatic environment. However, if the sterilization carbon cloth was pre-washed two days prior to use, the concentration of Ag was below the drinking water limit of 0.1 mg/L. Our study provides important exposure data for a novel water sanitation technology for real-world application in waste water and drinking water treatment, and aid in assuring its safe use.

Electrochemical degradation of the antibiotic ciprofloxacin in a flow reactor using distinct BDD anodes: Reaction kinetics, identification and toxicity of the degradation products

The performances of distinct BDD anodes (boron doping of 100, 500 and 2500 ppm, with sp3/sp2 carbon ratios of 215, 325, and 284, respectively) in the electrochemical degradation of ciprofloxacin – CIP (0.5 L of 50 mg L−1 in 0.10 M Na2SO4, at 25 °C) were comparatively assessed using a recirculating flow system with a filter-press reactor. Performance was assessed by monitoring the CIP and total organic carbon (TOC) concentrations, oxidation intermediates, and antimicrobial activity against Escherichia coli as a function of electrolysis time. CIP removal was strongly affected by the solution pH (kept fixed), flow conditions, and current density; similar trends were obtained independently of the BDD anode used, but the BDD100 anode yielded the best results. Enhanced mass transport was achieved at a low flow rate by promoting the solution turbulence within the reactor. The fastest complete CIP removal (within 20 min) was attained at j = 30 mA cm−2, pH = 10.0, and qV = 2.5 L min−1 + bypass turbulence promotion. TOC removal was practically accomplished only after 10 h of electrolysis, with quite similar performances by the distinct BDD anodes. Five initial oxidation intermediates were identified (263 ≤ m/z ≤ 348), whereas only two terminal oxidation intermediates were detected (oxamic and formic acids). The antimicrobial activity of the electrolyzed CIP solution was almost completely removed within 10 h of electrolysis. The characteristics of the BDD anodes only had a marked effect on the CIP removal rate (best performance by the least-doped anode), contrasting with other data in the literature.

Soft and flexible piezoelectric smart patch for vascular graft monitoring based on Aluminum Nitride thin film

Vascular grafts are artificial conduits properly designed to substitute a diseased blood vessel. However prosthetic fail can occur without premonitory symptoms. Continuous monitoring of the system can provide useful information not only to extend the graft’s life but also to optimize the patient’s therapy. In this respect, various techniques have been used, but all of them affect the mechanical properties of the artificial vessel. To overcome these drawbacks, an ultrathin and flexible smart patch based on piezoelectric Aluminum Nitride (AlN) integrated on the extraluminal surface of the prosthesis is presented. The sensor can be conformally wrapped around the external surface of the prosthesis. Its design, mechanical properties and dimensions are properly characterized and optimized in order to maximize performances and to avoid any interference with the graft structure during its activity. The sensorized graft is tested in vitro using a pulsatile recirculating flow system that mimics the physiological and pathological blood flow conditions. In this way, the ability of the device to measure real-time variations of the hemodynamics parameters has been tested. The obtained high sensitivity of 0.012 V Pa−1 m−2, joint to the inherent biocompatibility and non-toxicity of the used materials, demonstrates that the device can successfully monitor the prosthesis functioning under different conditions, opening new perspectives for real-time vascular graft surveillance.

Experimental device for the study of Liquid–Solid coupled flutter instability of salt cavern leaching tubing

A salt cavern underground gas storage is typically constructed by water solution mining, in which slender leaching tubings are used as the channel for water injection and brine production. Cavern leaching and well workover operations are accident prone owing to leaching tubings being bended excessively and even ruptured. These accidents are caused primarily by flow-induced vibration of leaching tubings. To investigate these flow-induced vibration phenomena, an in-house laboratory device for liquid–solid coupled flutter instability of salt cavern leaching tubing was developed. This experimental device consists primarily of a recirculating flow system, vertical cantilevered pipe test section, and instruments for parameter measurement. The experimental device can be utilized to investigate multiple factors involved in the flow-induced vibration of the leaching tubing, including flexural rigidity, overhang length, and support conditions of tubing string. To verify the adequacy of this device, two sets of experiments have been performed in the air without external space constraints by using a cantilevered silicon rubber and polycarbonate pipes, respectively. Flutter instability phenomena were observed in these experiments. Furthermore, through the study on the length effect, an asymptotic behavior with the critical flow velocity reaching limiting values as the lengths of the pipes increase, is discovered. The present study is conducive to the subsequent experimental step that considers additional factors. Consequently, the device provides adequate in-house experimental conditions for researching the instability mechanism and safety control measures of the leaching tubing.

Real-time Imaging and Quantification of Fungal Biofilm Development Using a Two-Phase Recirculating Flow System.

In oropharyngeal candidiasis, members of the genus Candida must adhere to and grow on the oral mucosal surface while under the effects of salivary flow. While models for the growth under flow have been developed, many of these systems are expensive, or do not allow imaging while the cells are under flow. We have developed a novel apparatus that allows us to image the growth and development of Candida albicans cells under flow and in real-time. Here, we detail the protocol for the assembly and use of this flow apparatus, as well as the quantification of data that are generated. We are able to quantify the rates that the cells attach to and detach from the slide, as well as to determine a measure of the biomass on the slide over time. This system is both economical and versatile, working with many types of light microscopes, including inexpensive benchtop microscopes, and is capable of extended imaging times compared to other flow systems. Overall, this is a low-throughput system that can provide highly detailed real-time information on the biofilm growth of fungal species under flow.

Real-time Imaging and Quantification of Fungal Biofilm Development Using a Two-Phase Recirculating Flow System

Real-time Imaging and Quantification of Fungal Biofilm Development Using a Two-Phase Recirculating Flow System

Characterization of temporal variations and feedback timescales of exhaust gas recirculation gas properties using high-speed diode laser absorption spectroscopy for next-cycle control of cyclic variability

Dilute combustion offers efficiency gains in boosted gasoline direct injection engines both through knock-limit extension and thermodynamic advantages (i.e. the effect of γ on cycle efficiency), but is limited by cyclic variability at high dilution levels. Past studies have shown that the cycle-to-cycle dynamics are a combination of deterministic and stochastic effects. The deterministic causes of cyclic variations, which arise from feedback due to exhaust gas recirculation, imply the possibility of using active control strategies for dilution limit extension. While internal exhaust gas recirculation will largely provide a next-cycle effect (short-timescale feedback), the feedback of external exhaust gas recirculation will have an effect after a delay of several cycles (long timescale). Therefore, control strategies aiming to improve engine stability at dilution limit may have to account for both short- and long-timescale feedback pathways. This study shows the results of a study examining the extent to which variations in exhaust gas recirculation composition are preserved along the exhaust gas recirculation flow path and thus the relative importance and information content of the long-timescale feedback pathway. To characterize the filtering or retention of cycle-resolved feedback information, high-speed (1–5 kHz) CO2 concentration measurements were performed simultaneously at three different locations along the low-pressure external exhaust gas recirculation loop of a four-cylinder General Motors gasoline direct injection engine using a multiplexed two-color diode laser absorption spectroscopy sensor system during steady-state and transient engine operation at various exhaust gas recirculation levels. It was determined that cycle-resolved feedback propagates through internal residual gases but is filtered out by the low-pressure exhaust gas recirculation flow system and do not reach the intake manifold. Intermediate variations driven by flow rate and compositional changes are also distinguished and identified.

Numerical estimation of air core length in two-phase free surface vortex

ABSTRACTThe free-surface vortex is simulated with the homogeneous mixture approach. In order to define suitable boundary conditions in the two-phase flow field, a numerical strategy is proposed on the air mass conservation in a recirculating flow system. The numerical approach is verified from an experiment. Numerical results agreed well with the experiment not only in the vortex circulation but also in the axial velocity gradient. On the homogeneous mixture assumption, the compressibility corrections for the turbulence modelling had almost no effect on the result in this case study. In order to estimate the continuous air–core length, the visible air–core interface was assumed to be characterized by the constant void fraction. With validated numerical results, vortex air core was visualized by the air volume fraction, based on the air–core length in not only the experiment but also the analytical model in the applicable range.

Light-based methods for whole blood bacterial inactivation enabled by a recirculating flow system.

Light of certain wavelengths can be used to inactivate pathogens. Whole blood is opaque; thus, the penetration of light is reduced. Here, we overcame this limitation using a thin transparent tube that is illuminated from all angles. Three light-based techniques were evaluated: photodynamic therapy (PDT) using a 660-nm light and antibody-photosensitizer conjugates, ultraviolet, and violet light. We observed a reduction of 55-71% of Staphylococcus aureus after 5h of exposure (starting concentration 107 CFUmL-1 ) and an 88-97% reduction in methicillin-resistant Staphylococcus aureus (MRSA) (starting 104 CFUmL-1 ). An 83-92% decrease for S.aureus and 98-99.9% decrease for MRSA were observed when combined with an immunocapture approach. Complete blood count with differential analysis did not reveal any significant changes in the blood cell numbers. Genotoxicity studies showed that violet and ultraviolet did not induce any significant level of single strand breaks and alkali labile sites in the peripheral blood mononuclear cells (PBMC). In contrast, ultraviolet did induce a very low level of cyclobutane pyrimidine dimers, a UV damage indicator. PDT generated a significant level of single strand breaks and 8-oxoGua in these cells. The approaches showed promise for whole blood pathogen inactivation with minimal collateral damage to PBMC.

Dye wastewaters treatment using batch and recirculation flow electrocoagulation systems

An electrocoagulation (EC) process was employed to remove the Reactive Black 5 (RB5) dye from aqueous solutions using batch-stirred and recirculation flow reactor configurations. Different operating conditions, such as current density, initial pH value, initial dye concentration, sacrificial anode materials and stirring rate were tested with the synthetic wastewater in order to optimise the treatment. The best operating conditions achieved for both systems were: current density of 16mAcm−2, initial pH of 6, 100mgL−1 of RB5 and Al anodes, as well as 800rpm for the batch-stirred setting. These parameters, at the batch-stirred EC system, led to 76% and 97% of decolourisation after 45 and 120min of operation, with an energy consumption of 5 and 14kWhm−3, respectively. Similar colour removals were achieved for the recirculation flow system in 10 and 120min, requiring 2kWhm−3 and 22kWhm−3 of electrical energy, respectively. The behaviours observed in each one of the EC systems (−batch and –recirculation flow) are related to the way how the liquid was mixed and the location where samples were taken. In the batch-stirred system, a real textile wastewater was also treated applying Al or Zn anode materials. Results clearly show that these two EC configurations are alternatives to depurate effluents containing dyes, since they guarantee the legal limits values so that a treated wastewater can be discharged into aquatic ecosystems.

Synthesis of ZSM-5 and SAPO-34 membranes in a high temperature-pressure recirculating-flow system

MFI and SAPO-34 type zeolite membranes were prepared on tubular alumina supports in a recirculating flow system at elevated temperatures and reported for the first time in the literature. During membrane synthesis, the synthesis mixture flowed between the reservoir and the membrane module, which includes the membrane support. The highest synthesis temperatures were 180°C and 220°C, and the corresponding system pressures were approximately 20 and 30bar for MFI and SAPO-34, respectively. The best performing MFI membrane had a CH4 single gas permeance of 2.8×10−7mol/m2sPa and CH4/n-C4H10 ideal selectivity of 24 at 25°C. The n-C4H10/CH4 separation selectivity was 43.6 with n-C4H10 permeance of 8×10−7mol/m2sPa at 25°C. The ideal selectivities of CO2/CH4 of SAPO-34 membranes synthesized at 220 and 200°C in an autoclave without flow were 227 and >1000, respectively. However, the membranes synthesized by flow-induced crystallization exhibit CO2/CH4 ideal selectivities of less than 10.

Initial in vitro and in vivo evaluation of a self-monitoring prosthetic bypass graft

ObjectiveProsthetic grafts used for lower extremity revascularization and dialysis access fail because of hyperplastic stenosis and thrombosis. Graft surveillance is advocated to monitor function; however, graft failure can occur between episodic examinations. An innovative sensor with wireless, microchip technology allows automated surveillance with assessment of graft function using a “cloud”-based algorithm. We performed proof-of-concept experiments with in vitro and in vivo models to assess the feasibility such a real-time graft surveillance system. MethodsA self-monitoring graft system was evaluated consisting of a prosthetic conduit of expanded polytetrafluoroethylene and a sensor unit, and a microsensor, microelectronics, battery, and remote processor with a monitor. The sensor unit was integrated on the extraluminal surface of expanded polytetrafluoroethylene grafts without compromise to the lumen of the conduit. The grafts were tested in vitro in a pulsatile, recirculating flow system under physiologic flow parameters. The hemodynamic parameters were varied to assess the ability to obtain wireless signal acquisition reflecting real-time flow properties in vitro. Segments of custom tubing with reduced diameters were inserted into the model to mimic stenosis proximal and distal to the grafts. After characterization of the initial data, the self-monitoring grafts were implanted in an ovine carotid model to assess proof of concept in vivo with 30-day follow-up of signal acquisition as well as arteriographic and histologic analysis. ResultsIn vitro flow data demonstrated the device was able to determine factors related to prosthetic graft function under varied hemodynamic flow conditions. Wireless signal acquisition using Bluetooth technology (Bluetooth SIG, Inc, Kirkland, Wash) allowed remote data analysis reflecting graft flow parameters through changes in microsensor voltage and frequency. Waveform analysis was applied to construct an algorithm using proprietary software and determine a parameter for graft flow characteristics. This algorithm allowed determination of the degree of stenosis and location of stenosis location (proximal or distal) for display on a remote monitor in real time. Subsequent in vivo experiments confirmed the ability of the system to generate signal acquisition through skin and soft tissue under biologic conditions with no arteriographic stenosis and a favorable healing response at 30-day harvest. ConclusionsInitial in vitro and in vivo experiments demonstrate the ability for a self-monitoring graft system to remotely monitor hemodynamic parameters reflecting graft function using wireless data transmission. This automated system shows promise to deliver real-time data that can be analyzed by cloud-based algorithms alerting the clinician of a change in graft function or development of stenosis for further diagnostic study or intervention before graft failure.

Effect of a solar Fered-Fenton system using a recirculation reactor on biologically treated landfill leachate

The effects of electrochemical oxidation (EO), Fered-Fenton and solar Fered-Fenton processes using a recirculation flow system containing an electrochemical cell and a solar photo-reactor on biochemically treated landfill leachate were investigated. The most successful method was solar Fered-Fenton which achieved 66.5% COD removal after 120min treatment utilizing the optimum operating conditions of 47mM H2O2, 0.29mM Fe2+, pH0 of 3.0 and a current density of 60mA/cm2. The generation of hydroxyl radicals (OH) are mainly from Fered-Fenton process, which is enhanced by the introduction of renewable solar energy. Moreover, Fe2+/chlorine and UV/chlorine processes taking place in this system also result in additional production of OH due to the relatively high concentration of chloride ions contained in the leachate. The energy consumption was 74.5kWh/kg COD and the current efficiency was 36.4% for 2h treatment. In addition, the molecular weight (MW) distribution analysis and PARAFAC analysis of excitation emission matrix (EEM) fluorescence spectroscopy for different leachate samples indicated that the organics in the leachate were significantly degraded into either small molecular weight species or inorganics.

A simple recirculating flow system for the calibration of polar organic chemical integrative samplers (POCIS): Effect of flow rate on different water pollutants

A calibration system for POCIS was developed and used to calculate the sampling rates of eight analytes belonging to pesticides, non-steroidal anti-inflammatory drugs and perfluorinated compounds: atrazine, propazine, terbutylazine, diclofenac, ibuprofen, ketoprofen, perfluorooctanoic acid and perfluorooctanesulfonate. Experiments with a linear velocity of 2.0, 5.1, 10.2 and 15.3 cm/s were carried out for 96 h using two different analyte concentrations. POCIS extracts were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), using multiple reaction monitoring to maximize sensitivity. Results highlighted that the calculated sampling rates are rather constant at the considered concentrations and flow rates. Obtained values of sampling rates were then employed to calculate Time-Weighted Average concentration of the analytes in river and drinking waters.

Low temperature synthesis of SAPO-34 in a recirculating-flow system

SAPO-34 was synthesized both in recirculating-flow system and in autoclaves at low temperatures. A two-stage, varying temperature synthesis procedure was applied to reduce the crystallization time. The effects of synthesis temperature and synthesis system on the purity, particle size and BET surface area of the crystalline phase were examined. Pure SAPO-34 with high crystallinity was synthesized from a gel with Si/Al ratio of 0.2 at 130 °C following aging at 80 °C. The particle sizes of SAPO-34 crystals produced in stagnant mixture were in the 250–600 nm range, depending on the synthesis temperature. Flow induced crystallization caused a slight increase in the average particle size. SAPO-34 synthesized in the recirculating-flow system had a BET surface area of approximately 470 m2/g with a micropore volume of 0.28 cm3/g. From industrial standpoint, the stirring-recirculating-flow of synthesis mixture can be beneficial since uniform synthesis conditions can be accomplished during the production of SAPO-34 in large quantities.

Effect of Midsynthesis Addition of Silica to the Synthesis Medium on the Properties of MFI-Type Zeolite Membranes

Thin zeolite membranes of MFI type were prepared on α-Al2O3 supports by midsynthesis addition of silica in a recirculating flow system at 95 °C. The synthesis was started with the batch composition...