Impact Of Operating Conditions Research Articles

Biodegradation kinetics of organic micropollutants in biofilters for advanced wastewater treatment – Impact of operational conditions and biomass origin on removal

Biofiltration processes are often part of advanced wastewater treatment (aWWT) technologies for the removal of organic micropollutants (OMP) from conventional wastewater treatment plant (WWTP) effluents. Although biological effects are not always the main focus of these technologies (e.g. filtration through granular activated carbon), they have been shown to contribute significantly to total OMP removal. While OMP biodegradation kinetics in conventional biological wastewater treatment are well researched, no systematic comparison to biomass from aWWT is available. This biomass faces different growth conditions and higher OMP concentrations relative to the background organic matter. Adaptation to these conditions could be possible and could lead to faster OMP biodegradation kinetics, which would show in a larger pseudo first-order biodegradation kinetic constant kbiol. In this work, kbiol values for biomass obtained from aWWT biofilters were determined by evaluating OMP removals measured in lab-scale biofilters using a mechanistic model of the experimental setup. A comparison to kbiol values from literature for conventional wastewater treatment (with nutrient removal) revealed similar OMP biodegradation kinetics without any advantages of biomass from aWWT. A conceptual evaluation of influencing factors on OMP removal in biofilters showed that operational parameters (such as the biomass concentration or the empty bed contact time) and the affinity of OMPs to adsorb on biomass have a significant additional effect on biological OMP removal. Therefore, kbiol values alone are not sufficient to estimate biological OMP removal in biofilters and further information about the system is required.

Impact of operational conditions on drinking water biofilm dynamics and coliform invasion potential.

The revelation that even low concentrations of coliforms can infiltrate into mature drinking water biofilms highlights a potential public health concern. Nowadays, the measurement of coliform bacteria is used as an indicator for fecal contamination and to control the effectiveness of disinfection processes and the cleanliness and integrity of distribution systems. In Flanders (Belgium), 533 out of 18,840 measurements exceeded the established norm for the coliform indicator parameter in 2021; however, the source of microbial contamination is mostly unknown. Here, we showed that mature biofilms, are susceptible to invasion of Serratia fonticola. These findings emphasize the importance of understanding and managing biofilms in drinking water distribution systems, not only for their potential to influence water quality, but also for their role in harboring and potentially disseminating pathogens. Further research into biofilm detachment, long-term responses to operational changes, and pathogen persistence within biofilms is crucial to inform strategies for safeguarding drinking water quality.

Nickel promoted Si-rich ZSM-5 nanocatalyst remarkably converts LDPE plastic waste to gasoline range hydrocarbons in a dual-bed semi-batch reactor at atmospheric pressure

Catalytic pyrolysis is an environmentally friendly recycling method, which has attracted remarkable attention due to worldwide issues of the production and accumulation of plastic wastes. In this work, the catalytic pyrolysis of Low-density polyethylene (LDPE) was carried out in a dual-bed semi-batch reactor over the Si-rich Ni/ZSM-5 nanocatalyst at atmospheric pressure. The parent nanocatalyst was prepared by hydrothermal technique and modified with nickel promoter (0–25 wt%). The properties of the nanocatalysts were characterized by XRD, FTIR, FE-SEM, EDX, TEM, BET, NH3-TPD, and TG-DTA techniques. The results showed the high crystallinity, spherical particles, and high specific surface area (376 m2g−1). The impact of operational conditions was evaluated to maximize the production of the high value-added compounds. The high percentage of the Ni promoter (25 wt%) led to the highest amount of gasoline range hydrocarbons (61%). The appropriate operational conditions were temperature of 525 °C, catalyst to plastic ratio of 1:20, and 2.5 ml min−1 nitrogen flow rate, resulting in the best product distribution: aromatics (39.4%), olefins (28.3%), and paraffins (15%). The reusability of the nanocatalyst showed high performance and more aromatic production. The characterization results of the used nanocatalyst confirmed the high stability through the pyrolysis reaction and lack of significant structural defect. The developed nanocatalyst represented the high activity through the pyrolysis of the real LDPE plastic waste, including the major product distribution in the gasoline range hydrocarbons.

GDE vs RDE: Impact of operation conditions on intrinsic catalytic parameters of FeNC catalyst for the oxygen reduction reaction

We present a comprehensive comparison of the catalytic evaluation of a FeNC catalyst using two different approaches, i.e., employing the rotating ring disk electrode (RRDE) technique and a gas diffusion electrode (GDE) setup. With both techniques, the FeNC catalyst is evaluated in acidic as well as in alkaline environment. The oxygen reduction reaction (ORR) is studied and parameters such as ORR kinetic activity, Tafel slope, and the apparent activation energy are determined at different applied temperatures/overpotentials. The obtained results offer clear evidence that in alkaline medium, the GDE offers reaction conditions with improved reactant mass transport enabling an evaluation of the FeNC catalyst closer to membrane electrode assembly (MEA) testing. As compared to the RRDE evaluation, the ORR rate is higher in the GDE setup and the potential range for extracting kinetics and activation energies is substantially improved. However, in acidic environment only minor differences between the two reaction environments (RRDE and GDE) are observed. The difference between alkaline and acidic conditions is rationalized based on the different reaction pathway in the two environments.

Electrical Life Assessment of the Low-Voltage Circuit Breaker (LVCB) Considering Arc Voltage

The low-voltage circuit breaker (LVCB) is commonly utilized in the distribution network. An accurate evaluation of its electrical life is related to the safety and reliability of electric energy output. The traditional arc erosion model only considers the effect of current on contact wear while ignoring the impact of operation conditions (supply voltage and power factor) on electrical life. As a result of the arc voltage, the original circuit topology changes, resulting in an early current zero. At 220–660 V AC supply voltages, arc voltage causes the distortion of the breaking current waveform, and the contact erosion amount (CEA) is smaller than that in the ideal case. This work investigates the effect of arc voltage on breaking current, develops an arc erosion model that includes arc voltage, and compares the CEA curves for various supply voltages and power factors. The electrical life of the LVCB is then simulated using the Monte Carlo approach to determine the distribution of electrical life under various operating situations. The results reveal that the LVCB’s electrical life diminishes as the supply voltage increases under the same power factor; it first declines and then increases as the power factor grows under the same supply voltage. For the combination of two parameters (220 V, 0.95) and (660 V, 0.65), the electrical life difference of the LVCB can reach 21.4%. The method solves the low accuracy problem of the LVCB life assessment under different operation conditions. It improves the efficiency of overhaul and maintenance on the LVCB in power distribution systems.

Impacts of Operating Conditions on the Recovery of Proton Exchange Membrane Fuel Cells Exposed to Sulfur Dioxide in an Air Stream

Impacts of Operating Conditions on the Recovery of Proton Exchange Membrane Fuel Cells Exposed to Sulfur Dioxide in an Air Stream

Materials Engineering toward Durable Electrocatalysts for Proton Exchange Membrane Fuel Cells

AbstractProton exchange membrane fuel cells (PEMFCs) have penetrated many commercial markets, especially in the automotive market as Toyota has launched the first commercially mass‐produced fuel cell vehicle, the Mirai in 2014. Electrocatalysts play an irreplaceable role in determining the PEMFCs, performance and account for half of the total cost. Despite substantial progress in exploiting highly active platinum group metal (PGM) and PGM‐free electrocatalysts, current electrocatalysts are faced with significant durability challenges, i.e., high‐performance electrocatalysts usually suffer from rapid degradation during PEMFC operation. The lifetime of the reported electrocatalysts is far from the requirement of performing steadily over the 8000 h of operation in commercialized PEMFCs. To this end, addressing the durability issues of oxygen reduction reaction (ORR) electrocatalysts is imperative for their practical employment in PEMFCs. Herein, the state‐of‐the‐art advances in understanding the durability issues of PGM and PGM‐free catalysts for ORR under fuel cell conditions and the materials engineering strategies to tackle these issues are summarized. The insights into the durability issues, involving the degradation mechanisms and the impact of operation conditions are reviewed. Establishing strategies to mitigate catalyst degradation through rational design of stable PGM and PGM‐free catalysts is highlighted.

A Multiphysics System-to-Cell Framework to Assess the Impact of Operating Conditions of Standalone PV Systems on Lithium-Ion Battery Lifetime

This paper proposes a multiphysics simulation structure for predicting Li-ion batteries’ useful life by consolidating battery cell electrochemical and thermal-aging models into the electrical domain of PV-battery standalone systems. This model can consider the effect of operating conditions at the system level, such as charge/discharge patterns and energy management strategies, to evaluate battery capacity fade at the cell level. The proposed model is validated using experimental observations with a RRMSE of 1.1%. Results show that the operating conditions of the battery bank affect its lifetime significantly. A wide range of 2.7 to 12.5 years of battery lifetime is predicted by applying the model to different case studies. In addition, the model predicts that managing the maximum cell state of charge level can enhance the battery bank lifetime by 60%. The developed model is a generic multiscale decision-making framework to investigate the effect of operating conditions on battery service life.

Impact of operational conditions on methane yield and microbial community composition during biological methanation in in situ and hybrid reactor systems

BackgroundBiogas can be upgraded to methane biologically by adding H2 to biogas reactors. The process is called biological methanation (BM) and can be done in situ in a regular biogas reactor or the biogas can be transferred to a separate ex situ upgrading reactor. The hybrid BM concept, a combination of in situ and ex situ BM, has received little attention, and only a few studies have been reported. The hybrid BM has the advantage of resolving the issue of pH increment during in situ BM, while the size of the ex situ BM reactor could be reduced.ResultsIn this study, the efficiency of in situ and hybrid biological methanation (BM) for upgrading raw biogas was investigated. The hybrid BM system achieved a CH4 yield of 257 mL gVS−1 when degrading a feedstock blend of manure and cheese waste. This represented an increase in methane yield of 76% when compared to the control reactor with no H2 addition. A 2:1 H2:CO2 ratio resulted in stable reactor performance, while a 4:1 ratio resulted in a high accumulation of volatile fatty acids. H2 consumption rate was improved when a low manure–cheese waste ratio (90%:10%) was applied. Furthermore, feeding less frequently (every 48 h) resulted in a higher CH4 production from CO2 and H2. Methanothermobacter was found to dominate the archaeal community in the in situ BM reactor, and its relative abundance increased over the experimental time. Methanosarcina abundance was negatively affected by H2 addition and was nearly non-existent at the end of the experiment.ConclusionsOur results show that hybrid BM outperforms in situ BM in terms of total CH4 production and content of CH4 in the biogas. In comparison to in situ BM, the use of hybrid BM increased CH4 yield by up to 42%. Furthermore, addition of H2 at 2:1 H2:CO2 ratio in in situ BM resulted in stable reactor operation.

(Energy Technology Division Research Award) The Emerging Research Needs of Polymer Electrolyte Membrane Electrolysis Cells

Proton conducting polymer electrolyte membrane (PEM) electrolysis has emerged as the currently favored research area to enable a global transformation of the energy system with hydrogen from renewable sources as a critical central feature. The hydrogen council has suggested that hydrogen impacts by 2050 could be $2.5T annually and 18% of total global energy demand.[1] While other electrolysis routes including traditional alkaline (based on aqueous KOH), alkaline membrane (emerging) and solid oxide electrolysis are all also being explored, and other possible hydrogen production pathways exist. The ability of PEM electrolysis to fit the needs of the emerging energy system as a dispatchable resource meeting cost, performance and durability requirements most effectively has led to a greater focus on PEM electrolysis than other electrolysis approaches within the global R&D community. The extent PEM electrolysis will establish itself commercially will depend largely on the advances made in the next several years.Much of the focus on PEM electrolysis has been centered around the advances made in PEM fuel cells, and the belief that these advances can be translated to PEM electrolysis systems. In particular, PEM fuel cells have largely been designed for transportation applications where they operate at low duty cycles (mostly off), and experience significant start-stop cycling (multiple times per day) while still achieving requisite performance and durability (several years).[2] Renewable energy sources are dramatically impacting the cost and availability of electricity and the ability to translate these resources into other energy sectors – most notably transportation and industry. While it is hoped that PEM electrolyzers can achieve cost, performance and durability targets, the research needs and challenges are not identical to PEM fuel cells.A new Department of Energy Consortium (H2NEW – Hydrogen from Next-generation Electrolyzers of Water) funded out of the Hydrogen and Fuel Cell Technologies Office is focused on enabling the cell-level fundamental understanding and advances required to address achieving $2/kg hydrogen through electrolysis. The primary focus of this effort is PEM electrolysis, the focus of the talk.A challenge in meeting the cost, performance and durability of PEM electrolysis systems is that current systems have had a strong emphasis on efficiency and durability. This means that cost has not been a primary concern such that systems could be “over-engineered” using extra or more expensive components and processing techniques. This approach has meant that little is understood about fundamental degradation rates relevant to systems that have not been over-engineered. Additionally, the markets that these devices have been sold into have typically operated under continuous conditions rather than the variable, intermittent load profiles that could couple to renewable or low-cost electricity inputs expected in the future. A clear understanding of the optimum system and operating conditions is not well understood at this time, nor is the impact of such operating conditions on performance and durability.Research needs place a high priority on durability under variable operating conditions. Specific components have susceptibility to different performance and durability impacts. In this talk, the impact of operating conditions and a discussion of projected operating conditions will be discussed. The concerns for both performance and durability will be discussed at the cell level with consideration of various cell components including catalyst, polymer, electrode, and porous transport layers. Accelerated stress tests for components in cells is a critical need and will also be presented. Finally, system and techno-economic considerations will also be included.References Hydrogen Council. “Hydrogen Scaling Up.” November 2017. http://hydrogencouncil.com/hydrogen-scaling-up/ B Pivovar, N Rustagi, S Satyapal, Electrochemical Society Interface 27 (1), 47.

An Elementary Kinetic Model for the LSCF and LSCF-CGO Electrodes of Solid Oxide Cells: Impact of Operating Conditions and Degradation on the Electrode Response

An elementary kinetic model was developed to predict the electrochemical response of porous LSCF and LSCF-CGO electrodes. The model was validated thanks to experiments performed on symmetrical cells using a three-electrode setup. After the model calibration on polarization curves, it has been shown that the model is able to simulate accurately the experimental impedance diagram at OCP and under polarization without additional fitting. Moreover, the evolution of the electrode polarization resistance with the oxygen partial pressure is well reproduced by the model. The electrodes reaction mechanism was thoroughly analyzed and it has been shown that the transition from the bulk path to the surface path depends on the temperature, the polarization and the oxygen partial pressure. The rate-determining steps for the LSCF electrode have been identified at OCP as function of the oxygen partial pressure. Finally, a sensitivity analysis has been performed to study the impact of LSCF demixing on the electrode performances. For a given decomposition, it has been highlighted that the surface passivation would be more impacting than the decrease of the ionic conductivity. Moreover, the impact of the LSCF decomposition would be more detrimental for the electrode performances evaluated in electrolysis mode. List of symbols Roman Symbols: Surface double layer capacitance(F m−2) Double layer capacitance at the LSCF/CGO interface(F m−2) Maximum concentration of neutral oxygen atoms in LSCF(mol m−3) Vacancies concentration in LSCF(mol m−3) Vacancies concentration in LSCF at equilibrium(mol m−3) Bulk oxygen chemical diffusion coefficient in LSCF(m2 s−1) Effective diffusion for the i-th species(m2 s−1) Oxygen vancancies self-diffusion coefficient(m2 s−1) Knudsen diffusion coefficient(m2 s−1) Molecular diffusion coefficient(m2 s−1) Diffusion coefficient of the oxygen ad-ions(m2 s−1) Diffusion coefficient of the oxygen ad-atoms(m2 s−1) Diffusion coefficient of the oxygen ad-molecules(m2 s−1) Local electrode potential(V) Activation energy for the i-th species(kJ mol−1) Faraday’s constant(C mol−1) Total inlet gas flow rate(mol s−1) Hole defect in LSCF(–) Ionic current density in CGO/Electronic current density in LSCF(A m−2) Thermodynamic equilibrium constant for the i-th species(–) Forward reaction kinetic constants for R1 for the LSCF(*) or LSCF-CGO(**) electrode (*) (mol m−1 s−1) or (**) (mol m−2 s−1) Forward reaction kinetic constants for R2(m3 mol−1 s−1) Forward reaction kinetic constants for R3 for the LSCF(*) or LSCF-CGO(**) electrode (*) (m s−1) or (**) (s−1) Forward reaction kinetic constants for R4(s−1) Forward reaction kinetic constants for R5(mol2 m−1 s−1) Forward reaction kinetic constants for R6(s−1) Electrode thickness(μm) CGO Electrolyte thickness(μm) Molar mass for the i-th species(g mol−1) m Reaction order(–) Molar flux of the i-th species(mol·m−2·s−1) Oxygen atom in the LSCF lattice(–) Oxygen atom in the CGO lattice(–) Oxygen ad-ion on LSCF surface(–) Oxygen ad-atom on LSCF surface(–) Oxygen ad-molecule on LSCF surface(–) O 2 Gaseous oxygen molecule(–) Oxygen partial pressure(atm) Total pressure(atm) Mean pore radius(m) universal gas constant(J mol−1 K−1) Serial resistanceΩ cm2 Polarization resistanceΩ cm2 Adsorption site on LSCF surface(–) Specific surface area between CGO and LSCF for the LSCF(*) or LSCF-CGO(**) electrode (*) (–) or (**) (m−1) Specific surface area between LSCF and gas phase(m−1) Electrode surface(cm2) Absolute temperature(K) Fuller’s volume for the i-th species(–) Oxygen vacancy in the LSCF lattice(–) Oxygen vacancy in the CGO lattice(–) Molar fraction of species i-th species(–)Greek Symbols: Charge transfer coefficient for oxidation or reduction for the reaction Ri(–) Surface density of available sites on LSCF(mol m−2) ε X Phase volume fraction for the phase X(–) η Overpotential(V) Coverage of oxygen ions on LSCF(–) Coverage of oxygen atoms on LSCF(–) Coverage of oxygen molecules on LSCF(–) Free sites on the LSCF surface(–) Coverage rate of oxygen ions on LSCF at equilibrium(–) Coverage rate of oxygen atoms on LSCF at equilibrium(–) Coverage rate of oxygen molecules on LSCF at equilibrium(–) Free site on LSCF at equilibrium(–) Kinetic rate of chemical/electrochemical reaction (i) in the electrode(*) or at the electrolyte interface(**) (*) (mol m−3 s−1) or (**) (mol m−2 s−1) Electrochemical potential(J mol−1) Density of triple phase boundary lengths for the LSCF(*) or LSCF-CGO(**) electrode (*) (m−1) or (**) (m−2) Electronic conductivity of LSCF(S m−1) Ionic conductivity of CGO(S m−1) Effective conductivity for th i-th species(S m−1) φ i Potential(V) χ Surface electrostatic potential(V) τ X Tortuosity factor for the phase X(–)

Methanol Production from Pyrolysis Oil Gasification—Model Development and Impacts of Operating Conditions

A novel process model simulating methanol production through pyrolysis oil gasification was developed, validated, then used to predict the effect of operating conditions on methanol production yield. The model comprised gasification, syngas post-treatment, and methanol synthesis units. The model was validated using experimental data from the literature, and the results obtained by the model were consistent with reference data. The simulation results revealed that gasification temperature has a significant impact on syngas composition. Indeed, rising temperature from 400 °C to 600 °C leads to higher syngas stoichiometric number (SN) value. Conversely, SN value decreases when the gasifier temperature is above 1000 °C. Moisture content in pyrolysis oil also affects both syngas composition and SN value; an increase in the first (from 10 to 30%) leads to an increase in SN value. The Rectisol unit deeply influences the syngas SN value and methanol yield, the best results being obtained with operating conditions of −20 °C and 40 bar. Increasing the operating temperature of the methanol synthesis unit from 150 °C to 250 °C leads to an increase in the yield of methanol production; the yield decreases beyond 250 °C. Although high pressures favor the methanol production yield, the operating pressure in the synthesis unit is limited at 50 bar for practical considerations (e.g., equipment price, equipment requirements, or operational risks).

The Impact of Operating Conditions on the Performance of a CH4 Dry Reforming Membrane Reactor for H2 Production

Biogas is a promising resource for the production of H2 since it liberates energy by recycling waste, along with the reduction of CO2. In this paper, the biogas dry reforming membrane reactor is proposed to produce H2 for use in fuel cells. Pd/Cu alloy membrane is used to enhance the performance of the biogas dry reforming reactor. This study aims at understanding the effect of operating parameters such as feed ratio of sweep gas, pressure in the reactor, and reaction temperature on the performance of the biogas dry reforming membrane reactor. The effect of the molar ratio of the supplied CH2:CO2, feed ratio of the sweep gas, and the valve located at the outlet of the reaction chamber on the performance of biogas dry reforming are investigated. Besides, the thermal efficiency of the proposed reactor is also evaluated. The results show that the concentration of H2 in the closed valve condition is higher than that of the open valve, and the optimum feed ratio of the sweep gas to produce H2 is 1, irrespective of the molar ratio of supplied CH2:CO2. Also, H2 selectivity and CO selectivity increases and decreases respectively when the reaction temperature increases, irrespective of the molar ratio of supplied CH2:CO2. Therefore, the thermal efficiency of the closed valve is higher than that of the opened valve. Also, the thermal efficiency is the maximum when the feed ratio of the sweep gas is 1 due to high H2 production performance.

The Impact of Operational Conditions on Commercial Membranes using in Removing Nitrate from Drinking Water

It is a great advantage to reduce the energy requirement for the provision of consumable groundwater to an absolute minimum. Reverse osmosis (RO) and nanofiltration (NF) are two of the most commonly used technologies for desalination water to provide potable water with lowest energy consumption. However, there is still lack of a thorough comparison between these two methods providing the better option in different conditions. Therefore, in this paper, nitrate rejection and the effects of operation conditions on the performance of RO and NF systems are compared. Several wells in Zarch District, Iran, are polluted by nitrate and groundwater is a major drinking water source in the region. The aim of this research was to evaluate the efficiency of nitrate removal by two commercial membranes NF90 and BW30 (both Dow Filmtec) using natural water under different operating conditions. Experiments were conducted to assess the influence of temperature and pressure on nitrate removal by the membranes. The results indicated that BW30 (reverse osmosis) performs better removing nitrate than NF90 (Nano-filter). With a feed of 200 mg-NO3-.L-1 (as nitrate), only permeate from the BW30 membrane met the required quality standard for drinking purposes (50 mg-NO3-.L-1). When the feed concentration increased to 250 mg-NO3-.L-1, both membranes failed to achieve the standard in the permeate. The membranes showed similar nitrate removal behaviour under different applied temperatures and pressures. It was concluded that the BW30 membrane can be used to produce drinking water in the study area with influent concentrations below 200 mg-NO3.L-1.

Multiphysical modelling of planar solid oxide fuel cell stack layers

Anode supported (ASC) and electrolyte supported cells (ESC) represent the most common cell concepts in solid oxide fuel cell (SOFC) technology. In ASCs, mechanical manageability is provided by a porous nickel/yttria-stabilized zirconia (Ni/YSZ) substrate, whereas in ESCs a self-supporting dense YSZ electrolyte is applied. Naturally, the electrical loss contributions arising in ASCs and ESCs differ in quantity, leading to different temperature profiles within planar SOFC stacks.A two-dimensional, finite element method model was developed which considers the underlying chemical and physical processes, and calculates both the electrical performance and the thermal distribution of planar SOFC stack layers operated with reformate fuels. It was then validated by comparing simulation results with extensively measured (i) temperature profiles in SOFC stacks, (ii) gas composition changes along the fuel gas channel of planar ASCs, and (iii) current-voltage characteristics in a temperature range from 650 °C to 800 °C.The subsequent numerical study reveals (i) the different performances of ASC and ESC, (ii) the impact of operation conditions on performance and temperature profile and (iii) how the individual loss contributions generate temperature distributions in the stack layer.

Impact of Operating Conditions on Measured and Predicted Concentration Polarization in Membrane Distillation.

Concentration polarization (CP) occurs in almost all membrane-based separation processes. In this study, the concentration profile of the dissolved salt has been accurately characterized using a previously developed laser-based spectrophotometric method which had a spatial resolution of 4.5 μm. The objective of the current work was to probe the concentration profile of the solute and analyze the impact of operating parameters, such as feed concentration, hydrodynamic conditions, and feed temperature, on the solute concentration profile in the boundary layer. This study also examined the validity of the conventional approach, where semi-empirical models are used to estimate the boundary layer thickness (BLT) and concentration polarization coefficient (CPC)-based on experimental results. Nusselt correlations were developed specifically for the membrane cell and validated through experimental observations at the operating conditions used in this study. A key finding of this study is that the conventional approach of estimating the effect of CP severely underpredicts the BLT and CPC. The results of this study highlight the need to develop new methods to estimate the BLT and CPC as the conventional approach of using semi-empirical Nusselt and Sherwood correlations does not agree with experimental observations obtained for a membrane distillation system employed in this study.

Chromium(VI) bioreduction and removal by Enterobacter sp. SL grown with waste molasses as carbon source: Impact of operational conditions

A technology utilizes bacteria Enterobacter sp. SL grown in an anaerobic reactor with waste molasses as carbon source to bio-reduce hexavalent chromium [Cr(VI)] in wastewater and then remove total chromium has been developed. The performance was elucidated through different initial and operating experiments conditions, and the associated mechanism of Cr(VI) reduction was explained. Results show that Cr(VI) removal is 99.91% at 25 h in the anaerobic reactor initially containing bacteria of 5% (v/v), (NH4)2Fe(SO4)2·6H2O of 0.5 g·L−1, waste molasses of 2.5 g·L−1, Cr(VI) of 100 mg·L−1, pH of 6.0, and with the operational temperature of 45 °C. After 120 h reaction, Cr(total) removal reached 91.10%. The major reduction products [FeS, Cr2O3, Cr(OH)3, S0 granules] together with microbes was removed by sludge separation with Cr(VI) in the supernatant (0.027 mg·L−1) being much lower than that (not excess 0.2 mg·L−1) of Electroplating Pollutant Emission Standard.

Impact of Operating Conditions on PEMFC Durability

PtCo-alloy catalysts have achieved mainstream application approximately 20 years after they were first reported. The current state of art PEM fuel cell cathode catalyst is represented by Pt-alloy nanoparticles dispersed on high surface area carbon (HSC) supports. [1] Mass activity > 0.6 A/mgPt has been reported consistently for such catalysts. Unfortunately, the high BOL activity of the Pt-alloy nanoparticle catalysts can suffer fairly rapid degradation in mass activity (MA) over time on exposure to fuel cell operating conditions, especially under voltage cycling (V-cycling). The prevalent mechanism for loss of specific activity is due to dissolution of the non-noble alloying element and thickening of Pt shell during voltage cycling. [2] Not withstanding the advances and numerous impactful studies, the degradation of Pt-alloy nanoparticles and its impact on electrode performance is poorly understood. For example, a recent article reviews the conflicting results on the impact of alloying on Pt nanoparticle stability, from positive, to neutral, to negative. [3] Additionally, the existing literature on durability of PtCo alloys are focused on the activity and nanoparticle characterization rather than on associated V-loss in the composite electrode. Given the criticality of this issue, a careful systematic study of this phenomenon with best-in-class materials in a state of art (SOA) membrane electrode assembly (MEA) is desired. In this present work, the use of operating conditions as a key factor to mitigate electrode degradation is explored. This was accomplished by conducting voltage cycling tests in H2/N2 environment at different operating conditions up to 60,000 voltage cycles. To identify the factors affecting the degradation, fractional factorial design of experiments was implemented. The fractional design allows to identify the impact of individual factors and its interactions while reducing the total number of tests needed to be run. Factors in the test matrix include temperature, relative humidity, upper potential limit and upper potential hold time etc. In-situ electrochemical diagnostics such as electrochemical surface area (ECSA), mass activity (MA), specific activity (SA) was measured to understand the kinetics and degradation mechanism. Transport properties such as proton transport resistance and oxygen transport resistance was measured using H2-N2 impedance [4] and oxygen limiting current measurements [5]. The end of test (EOT) MEAs were characterized by ex-situ characterization measurements such as TEM for particle size distribution, electron micro probe analysis (EPMA) and EDS measurements to quantify the cobalt composition and loss up on voltage cycling at different operating conditions. In addition to multi-factor design of experiments, few key factors like RH and temperature were studied independently. Figure 1 shows the impact of relative humidity (RH) on H2-air performance and measured electrochemical surface area. Up to 100 mV loss at high current density (2.0 A/cm2) and ~30% ECSA loss observed for MEAs cycled up to 30,000 voltage cycles. Both performance and ECSA loss decreases with decreasing relative humidity. Almost zero ECSA loss after 30,000 voltage cycles at 25% RH observed. This example indicates that PtCo alloy catalyst degradation can be mitigated by carefully identifying the operating condition. The effect of various such operating condition and degradation mechanisms will be discussed. References S. Kumaraguru, 2018 Annual Progress Report, https://www.hydrogen.energy.gov/pdfs/progress18/fc_kumaraguru_2018.pdf C.E. Carlton, S. Chen, P.J. Ferreira, L.F. Allard, Y. Shao-Horn, J. Phys. Chem.Lett. 3, 161 (2012)J.A. Gilbert, A.J. Kropf, N.N. Kariuki, S. DeCrane, X. Wang, S. Rasouli, K. Yu, P.J. Ferreira, D. Morgan, D.J. Meyers, J. Electrochem. Soc., 162 (14), F1487 (2015)R. Makharia, M. F. Mathias, D. R. Baker, J. Electrochem. Soc., 152 (5), A970 (2005)T.A. Greszler, D.A. Caulk, P. Sinha, J. Electrochem. Soc., 159, F831 (2012) Figure 1

Preparation and Characterization of Al-Diatomite Composite for the Remedial of Pb(II) from Aqueous Solution

Aluminum-diatomite (Al-D) composite adsorbent is synthesized in one pot by heating natural diatomite in NaOH and subsequently mixed with a solution of aluminum salt. The chemical, surface, textural and structural properties of the prepared material were characterized by XRF, XRD, SEM, FTIR, and Nitrogen adsorption methods. The adsorption efficiency of the composite sample was evaluated towards Pb(II) species in batch technique and compared with the raw diatomite. The impact of operational conditions, such as pH, adsorption time, temperature, an initial concentration of adsorbate, and the adsorbent dose was also evaluated. As confirmed by XRD and FTIR, the partial dissolution of silica in NaOH leads to the formation of an alumina-silicate compound at the addition of an aluminum salt. SEM image showed that aluminum is successfully loaded both on the surface of the diatomite and on the inner surface of the meso- and macropores, which leads to the advance of the specific surface area from 19.7 m 2 /g to 80.9 m 2 /g. It was observed that the Al-Diatomite adsorbent showed a noticeable higher Pb (II) sorption capacity (67.9 mg/g) than the natural diatomite (17.2 mg/g). This result can be explained by the higher surface area, mesoporous structure and uniform deposition of small-sized Alumina particles. Keywords: Aluminum, Composite, Lead ion, Modification, Sorption DOI : 10.7176/CPER/60-02 Publication date :March 31 st 2019

Analytical Methodology for Loss Calculation of SiC MOSFETs

For evaluating and optimizing the efficiency of power converters, the loss model of the power semiconductor devices is needed. The analytical loss model is favorable for its simplicity. However, the model accuracy needs to be improved. This paper proposes an analytical loss model for the commutation pair of silicon carbide (SiC) MOSFETs and SiC Schottky barrier diodes. Compared to the conventional loss calculation method, the proposed model is derived based on the conservation of energy, which considers the impact of the displacement currents on estimating the turn-on and turn-off losses. The modeling and extraction methodology of the model parameters are given, and the impact of operational conditions on the model parameters is studied. Using the proposed model, the losses can be calculated analytically and also the switching trajectories can be predicted with good consistency. A double pulse tester is built to verify the proposed model. The results show that an average modeling error is reduced from 20% using the conventional piecewise linear model, to around 10% using the proposed model under various operational conditions, and the time cost is at least 3000 times smaller compared to the existing SiC MOSFETs models.