Batch Series Research Articles

Direct Z-scheme heterojunction impregnated MoS2–NiO–CuO nanohybrid for efficient photocatalyst and dye-sensitized solar cell

In this present work, the preparation of ternary MoS2–NiO–CuO nanohybrid by a facile hydrothermal process for photocatalytic and photovoltaic performance is presented. The prepared nanomaterials were confirmed by physio-chemical characterization. The nanosphere morphology was confirmed by electron microscopy techniques for the MoS2–NiO–CuO nanohybrid. The MoS2–NiO–CuO nanohybrid demonstrated enhanced crystal violet (CV) dye photodegradation which increased from 50 to 95% at 80 min; The degradation of methyl orange (MO) dye increased from 56 to 93% at 100 min under UV–visible light irradiation. The trapping experiment was carried out using different solvents for active species and the Z-Scheme photocatalytic mechanism was discussed in detail. Additionally, a batch series of stability experiments were carried out to determine the photostability of materials, and the results suggest that the MoS2–NiO–CuO nanohybrid is more stable even after four continuous cycles of photocatalytic activity. The MoS2–NiO–CuO nanohybrid delivers photoconversion efficiency (4.92%) explored efficacy is 3.8 times higher than the bare MoS2 (1.27%). The overall results indicated that the MoS2–NiO–CuO nanohybrid nanostructure could be a potential candidate to be used to improve photocatalytic performance and DSSC solar cell applications as well.

Quality of beer from historical and current varieties of spring barley with addition of valerian and hops

Historic spring barley varieties can be a source of resistance to abiotic (drought) and biotic (diseases) environmental factors in breeding programs. They can be a source of the new technological characteristics of malt or sensory characteristics of beer. Beers made from Pilsner malt from two historical varieties – Chlumecky (1902) and Stupicky Starocesky (1926) and two contemporary varieties – Bojos and Sebastian (2005) were evaluated. These beers have beenflavoured with valerian, which in combination with hops has been shown to have anxiolytic and sedative effects. A comparison of elementary and sensory parameters of beers with addition of 0.5 g.L-1 and 1.5 g.L-1 of valerian to two different series of beers was carried out. The Chlumecky samples had the lowest content of alcohol by volume (6.17% and 5.12%) in both batch series of beer and the highest real extract in the first batch series (4.11%). The samples of beer from the Stupicky Starocesky variety had low real extract (3.57% and 3.60%) and high content of alcohol by volume in both batch series (6.34% and 5.96%). In terms of sensory analysis it means that beers brewed from the malt made from the older barley varieties – Chlumecky and Stupicky Starocesky with addition of 0.5 g.L-1 of valerian had the highest overall impression.

Artificial Intelligence Modeling of the Heterogeneous Gas Quenching Process for Steel Batches Based on Numerical Simulations and Experiments

High-pressure gas quenching is widely used in the metals industry during the heat treatment processing of steel specimens to improve their material properties. In a gas quenching process, a preheated austenised metal specimen is rapidly cooled with a gas such as nitrogen, helium, etc. The resulting microstructure relies on the temporal and spatial thermal history during the quenching. As a result, the corresponding material properties such as hardness are achieved. Challenges reside with the selection of the proper process parameters. This research focuses on the heat treatment of steel sample batches. The gas quenching process is fundamentally investigated in experiments and numerical simulations. Experiments are carried out to determine the heat transfer coefficient and the cooling curves as well as the local flow fields. Quenched samples are analyzed to derive the material hardness. CFD and FEM models numerically determine the conjugate heat transfer, flow behavior, cooling curve, and material hardness. In a novel approach, the experimental and simulation results are adopted to train artificial neural networks (ANNs), which allow us to predict the required process parameters for a targeted material property. The steels 42CrMo4 (1.7225) and 100Cr6 (1.3505) are investigated, nitrogen is the quenching gas, and geometries such as a disc, disc with a hole and ring are considered for batch series production.

Biodegradation of Tetrachloroethene in Batch Experiment and PHREEQC Model; Kinetic Study

Introduction: Bioremediation and biodegradation are considered as environmental friendly techniques for contaminants’ removal in polluted environment. In this study, the removal and kinetics of Tetrachloroethene (PCE) and Trichloroethene (TCE) microbial degradation, their inhibitory effects and the rate of dehalogenation capacity at high concentration of PCE were investigated.Materials and Methods: Dechlorinating culture was provided by Bioclear B.V. from a PCE-contaminated site (Evenblij in Hoogeveen -The Netherlands). The batch apparatuses were placed in an orbital shaker at 150 rpm at room temperature. In all the 18 batches, 6 different concentrations of PCE were measured from 0.1 mM to 0.6 mM. The degradation rate of PCE, Trichloroethene (TCE), and cis-1,2-dichloroethene (cDCE) were determined by the PHREEQC model.Results: The results revealed that the final product was ethene and the rate of dechlorinating of PCE increased gradually. The degradation process started after 3 days in batch modes (0.1 mM). After 10 days, the dechlorination of PCE to TCE was obtained in a low concentration of PCE (0.1 mM). Also, the TCE concentration became close to zero after 10 days. However, the start point was longer than PCE and the rate of biodegradation of TCE was faster than PCE. PCE did not show any progress in the dechlorinating procedure at 13th and 14th batch series and none of the daughter products were observed.Conclusions: It should be concluded that there was no single organism that could dechlorinate PCE to ethene, directly. Therefore, the best consortium of microorganisms to dechlorinate PCE to ethene faster, with less production of VC as the most hazardous compound, should be studied.

Structural optimization of additively manufactured polymer tools for flexible sheet metal forming

Traditionally, dies are subtractively manufactured for sheet metal forming. Beside the forming process, high tooling costs, material exertion and energy consumption of the die production offers chances for economic improvements. Especially, product(ion) individualization and small batch series require sustainable low-cost tooling approaches, where advances in additive manufacturing (AM) have recently led to additive tooling approaches. In this work, sheet metal forming tools are structurally optimized and 3D printed from bio-based polymers to reduce the overall material effort. The deformation and wearing behavior of the optimized tool is investigated during a drawing operation for low batch size of an automotive typical sheet material and compared to a solid AM-die approach as well as a tool made by conventional subtractive manufacturing.

Comparison of FDM-printed and compression molded tensile samples

Abstract Since the processing of plastics by additive manufacturing techniques, for example, fused deposition modeling, has become quite common, it is mainly used for the production of unique pieces for private consumption as well as for prototyping in industry. In order to professionally manufacture plastic components in large amounts, due to time, cost, and quality factors, injection molding is more suitable. Nevertheless, it is of great interest to print plastic parts in small batch series for technical tasks. In this paper, FDM-produced tensile samples, made from 16 materials, printed in three orientations, are compared to compression molded components. In addition to ordinary filaments, composite materials with metal-, carbon-, wood-, and stone-additives are also examined. While some cavities emerged in both printed and molded samples, the results support the hypothesis that the mechanical properties depend on the components’ densities.

Comparison of FDM-printed and compression molded tensile samples

Abstract Since the processing of plastics by additive manufacturing techniques, for example, fused deposition modeling, has become quite common, it is mainly used for the production of unique pieces for private consumption as well as for prototyping in industry. In order to professionally manufacture plastic components in large amounts, due to time, cost, and quality factors, injection molding is more suitable. Nevertheless, it is of great interest to print plastic parts in small batch series for technical tasks. In this paper, FDM-produced tensile samples, made from 16 materials, printed in three orientations, are compared to compression molded components. In addition to ordinary filaments, composite materials with metal-, carbon-, wood-, and stone-additives are also examined. While some cavities emerged in both printed and molded samples, the results support the hypothesis that the mechanical properties depend on the components’ densities.

Electroforming on Additively Manufactured Mandrels

Manufacturing industry faces recently a new challenge. Production of parts require, for various reasons, more and more low batch size production, sometimes even batch size one. Not only the batch size is reduced, but a given design has to be produced in lower on lower number too. If previously only prototyping required batch size one prodcution, the new trend of mass personalization requires it as well.Manufacturing technologies developed over the past decades are able to produce cost effectively very complex products in high series. Low batch series production is often not possible or very costly. Additive manufacturing is a promising answer to this challenge. Additive manufacturing equipment represent however, in case of metal printing, very high investment costs and usually significant post-processing after printing is needed. An alternative way to create complex 3D printed parts in low volumes could be to use electroforming. Electroforming is commonly used to form parts on a model or, as termed in industry, a mandrel. Using additive manufacturing to create this mandrel could be a viable and cost-efficient solution. Since electroforming require less energy and less expensive equipment, it can be potentially used to create precise 3D structures. In order to create a 3D shape using electroforming.Electroforming has its own challenges. As the thickness of the electroforming increases, voids build up and create a rough, uneven surface that has undesirable physical properties. The mass transfer at the micro-scale also changes the contribution of migration, diffusion and convection phenomena due to the scaling effect [1]. In order to produce complex and micro-scale features with acceptable quality, profile and characteristics, this paper discusses some significant factors and several methods for the improvement.By applying appropriate potential and rotation on the mandrel during the electroforming process, deposition thickness ranging from few to several 100 microns with very low surface roughness (few microns Ra) could be achieved. The deposit thickness was very consistent too (less than 1% variation of the complete part). The homogeneity of the thickness was further investigated for various geometries to determine the limitations of the methodology.[1] Angel, K., Tsang, H. H., Bedair, S. S., Smith, G. L., & Lazarus, N. (2018). Selective electroplating of 3D printed parts. Additive Manufacturing, 20, 164–172. doi: 10.1016/j.addma.2018.01.006

Applicability of Palm Oil Fuel Ash in Interlocking Compressed Earth Brick – A Preliminary Assessment

This paper presents the preliminary assessment on the applicability of palm oil fuel ash (POFA) as one of the materials used to produce interlocking compressed earth brick (ICEB). Ultrafine size POFA was used to replace the main ingredient for ICEB production which is the clay soil. The percentages of replacement were limited to 0%, 10%, 20%, 30%, 40%, 50%, and 60% by weight of the total clay soil material. The main purpose of conducting the experiment is to identify the most desirable mix through compressive strength test. Result showed that, at the curing age of 28 days, the compressive strength of mixture that substituted with 30%–60% of ultrafine POFA achieved higher strength than the control mixture. Meanwhile, the highest compressive strength was obtained by batch series CP50 (50% clay soil + 50% ultrafine POFA). The experimental studies specified that ultrafine POFA has significant possibilities for application in manufacturing ICEB.

Critical evaluation of the material characteristics and environmental potential of laser beam melting processes for the additive manufacturing of metallic components

Abstract Nowadays, the main impetus to apply additive manufacturing (AM) of metals is the high geometric flexibility of the processes and its ability to produce pilot or small batch series. In contrast, resource and energy intensities are often not considered as constraints, even though the turnout of additive manufacturing is high, at least compared to chip removing processes. The study at hand analyses the material characteristics and environmental impacts of a hose nozzle as an example of a commercial product of simple geometry. The production routes turning (conventional manufacturing) and laser beam melting (additive manufacturing) are compared to each other in terms of natural resource use, climate change potential and primary energy demand. It is found, that the product shows a lower demand for natural resources when produced via AM, but higher carbon emissions and energy demand when using a steel, that is mainly (80%) produced from high-alloyed steel scrap. However, different case studies during the sensitivity analyses showed that a number of factors highly influence the results: the steel source as well as the source of electricity play a major role in determining the environmental performance of the production routes. The authors also found that other production processes (here cold forging of tubes) might be an eco-friendly alternative to both routes, if feasible from an economic point of view. In regard to the material characteristics, experimental testing revealed that the material advantages of AM produced hose nozzles (in particular higher yield strength) are reduced after a solution heat treatment is applied to the as-produced material, in order to increase corrosion resistance. However, products that do not require this production step might benefit from the higher yield strength, as a lower wall thickness could be realised.

Assessment of stability of Live Plague vaccine Manufacturing and Basic Preparation Quality Indicators

Objective of the study was to analyze the basic quality parameters of the produced live plague vaccine and stability of the preparation during the storage process. Materials and methods . Specifications for batch series of the live plague vaccine on the basis of Yersinia pestis EV NIIEG, manufactured between 2012 and 2017, in compliance with the regulations of the normative documentation were assessed. The parameters under investigation were: viability, thermal resistance, absence of extraneous substances and fungi, weight loss in the process of drying, immunogenicity. Results and conclusions . Comparative analysis of the vaccine viability (quantity of live microbe cells) in the batches manufactured over the past 6 years was carried out. All the studied vaccine series have the appropriate indicators stated in the Specification to the Pharmacopeia Monograph and master formula which testifies to the stability of manufacturing line and basic live plague vaccine quality parameters throughout the whole term of storage. It is outlined that the production of the vaccine, corresponding to the requirements of the normative regulations, depends upon the strict adherence to the rules by the personnel, usage of high-grade stock and materials, validation of equipment and technological processes of manufacturing.

CHALLENGES, TRENDS AND APPROACHES OF FUTURE RELIABILITY ENGINEERING IN HIGH PRECISION MANUFACTURING PROCESSES

The progress within the development of manufacturing processes leads to complex failure modes and reliability problems within the product life cycle. This fact is valid in the case of mass production of consumer goods, e.g. automobiles, as well as small batch series of industrial goods, e.g. machine tools. Especially micro product platforms with a high amount of derivate and variants are challenging regarding to the planning of high precision manufacturing processes to ensure product reliability. This paper discusses challenges, trends and approaches of future reliability engineering in planning and realisation of high precision manufacturing processes. It considers e.g. mathematical models for uncertainty quantification, additive manufacturing, hydro micro forming, 3D printing and multivariate process validation models. The paper contains contributions of universities, institutes and original equipment manufacturers of industrial nations: Germany, United Kingdom, Japan, Turkey, Poland and U.S.A.

Melt pool monitoring for laser beam melting of metals: inline-evaluation and remelting of surfaces

Laser Beam Melting of Metals (LBM-M) is an additive manufacturing technique that is applied successfully for the production of complex parts, small batch series and prototypes. In LBM metallic parts are generated layer by layer directly from sliced CAD data. For each layer a thin powder layer is deposited and subsequently irradiated by a focused laser beam which is guided by a galvanometer scanner. Due to variations in the powder stock, plain parameter sets and unresolved machine maturity problems, quality fluctuations are a major problem for a future series production. Surface roughness of parts during manufacturing is a quality issue. In this paper, we address it with a coaxial melt pool monitoring system and show a method for inline evaluation of surfaces by means of melt pool monitoring and the results of applied remelting strategies.

Melt pool monitoring for laser beam melting of metals: assistance for material qualification for the stainless steel 1.4057

Laser Beam Melting of Metals (LBM-M) is an additive manufacturing technique that is successfully applied for the manufacturing of complex parts, small batch series and prototypes. In LBM metallic parts are generated layer by layer directly from sliced CAD data. For each layer a thin powder layer is deposited and subsequently, irradiated by a focused laser beam, which is guided by a galvanometer scanner. A major drawback of this relatively new manufacturing technology is a limited material portfolio. Today, the whole procedure of material qualification is time-consuming and resource intensive because a fast and reliable modelling of the process is not yet possible. In this work we are going to show the results of a qualification procedure applying a coaxial melt pool monitoring system to determine suitable processing parameters for a material, which has not yet been processed. In this work, a stainless steel material was exemplarily used to proof the feasibility. Furthermore, we are discussing the usability of this methodology for the material qualification in LBM-M in general.

3D - Material Extrusion - Printing with Biopolymers: A Review

Additive Manufacturing represents a well-known and fast growing material processing technology. Printed part is formed by adding material layer by layer until the part is finished without requiring any additional molds. Therefore, using Additive Manufacturing can save time and costs in comparison to commercial production methods particularly when manufacturing complex prototypes or small batch series. Another advantage of Additive Manufacturing is its freedom of design. This review is focused on material extrusion, a specific Additive Manufacturing technology. It begins with a short overview of the most common materials processed with this technology. Subsequently, we discuss several processes and machine parameters in material extrusion as well as their influence on the printing process and on the final properties of the printed part. Based on this knowledge, various challenges in material extrusion are also identified. These challenges must be resolved in order to improve the material extrusion process.

Evaluation of HT-PEM Fuel Cells via Load Cycling at High Current Densities

Polymer electrolyte membrane (PEM) fuel cells have a wide range of applications: stationary, transportation and portable communication [1]. Irrespective of type or operating temperature, for all fuel cells persist the same requirements like long term stability and reproducibility. To assemble an entire fuel cell stack, the utilized membrane electrode assemblies (MEA) should not only be the same type, they are also required to exhibit similar performances and power outputs. Vision of the German project QUALIFIX, funded by the Ministry of Economic Affairs and Energy (SC: 03Et6046A), is the development of consistent conditions for improved batch production to analyze and monitor quality of fuel cells, systems and components. With help of defined quality standards, the lifetime of fuel cell systems should be improved and cost-intensive losses can be minimized at an early production stage. Within QUALIFIX, the reproducibility of MEAs has been screened by evaluating several small batch series. One operation strategy, which has been used for this investigation, is load cycling between high current densities of 0.6 and 1.0 A/cm² and under equal test conditions. High temperature (HT) PEM MEAs with PBI-membranes of four different providers have been tested and their results will be presented in this work. All MEAs passed identical break-in procedures and activation phase under 0.3 A/cm². These start time intervals lasted 48 hours for each MEA respectively followed by initial characterization including polarization curves, impedance spectroscopy, cyclic and linear sweep voltammetry. Afterwards the load cycling operation started with 16 min of 1.0 A/cm² followed by 4 min of 0.6 A/cm². At the end of tests (EoT), after 500 h of operation, a second complete characterization has been performed. The characterizations have been replenished by ante- and post-mortem analysis via micro-computed tomography (µ-CT) and by product water and MEA analysis to provide phosphoric acid concentration changes. In Figure 1 the voltage changes for four MEAs from different suppliers are displayed as function of time. Indeed, all four MEAs are from the same type but their performances differ strongly; only MEA B and D show a good and similar performance but unequal degradation rates. All degradation rates are listed in Table 1. Table 1: Degradation rates at 0.3 A/cm² of load cycling tests after 500 h of operation. MEA Degradation Rate [µV/h] A -37 B +36 C -94 D -6 In addition, another MEA of the batches of MEA B and D have been adducted for inner-batch evaluations and comparisons. For both MEA-types (two different providers), the degradation rates vary within the batches of identical assemblies and under same operation conditions of load cycling at high current densities. Hence the production of MEAs with reproducible performances seem to be still of major concern. The in-situ electrochemical and ex-situ post- and ante-mortem evaluation (e.g. MEA acid content and µ-CT investigations) of all tested MEAs will be presented and compared. Figure 1: Voltage changes as function of time under load cycling conditions, (0.6 A/cm²: 4 min, 1.0 A/cm²: 16 min, 160 °C) under H2 and air supply (λH2=1.5; λair=2.0), MEAs of 4 different suppliers.

Bio-Gasification Under Partially Aerated Conditions

Anaerobic digestion (AD) under mild aerobic loading is investigated. Aeration can apparently have both positive and negative impacts on biogas generation. This study aims to recognize and describe these different aeration effects on AD. Seven series of batch experiments (BT 1- 7) were conducted under varying feed and oxygenation conditions at 35 oC. Oxygen was introduced as headspace air in four of the batch experiments and as pure oxygen in two series. Effects of extensive initial aeration of inoculum were investigated in one batch series. The methane yield of the reactors fed with starch (1.09 g COD/LReactor) was positively influenced by oxygenation in the load range up to 38 % O2 (as % of feed COD). A negative influence of oxygen was observed at the next experimental level of 79 % O2. For the glucose fed reactors under similar operating conditions, the oxygen impact was near linearly negative in the tested range of 0 - 49 % O2. These results demonstrate that digestion of soluble substrates like glucose is not enhanced by O2, while substrates requiring hydrolysis are. Thus, limited aeration can enhance biogas production from non-soluble substrates under batch conditions. According to the experiment where the effects of extensive initial aeration was investigated, lengthening of the aeration period increasingly slowed down the gas generation rate but eventually resulted in the same methane yield. The lag period before gas generation started was three times longer for the aerated inoculum reactors than un-aerated. These observations suggest that oxygen induced inhibition of the biomass activity is mostly reversible. Reduced biogas production rates with initial aeration extent suggest some permanent damage to the anaerobes. Extensively aerated inoculums generated less methane compared to the un-aerated inoculum, probably due to the loss of some biogas potential initially present in the inoculum. Oxygen assisted degradation of some recalcitrant organic matter, including biomass cells themselves, present in the inoculum is also detected in an unfed inoculum test series.

Effects of electric infrared heating with light source penetration on microbial and entomological loads of dried currants and their organoleptic characteristics

A series of field bioassays was conducted to evaluate the effects of electric infrared (IR) penetration on microbial disinfection and insect control as well as on the organoleptic characteristics of dried black currants (Corinthian currants, Vitis vinifera L. var. Apyrena). A continuous IR processor was placed in the production line of an industrial facility and was used for the field assays. In a series of bioassays, currants were fed into the IR processor and examined with and without process agitation at different treatment parameters including retention times (ranging from 30 to 35 s) and various peak temperatures (45, 50, 55, 60, 65, 70 and 75 °C). Samples of processed currants were randomly selected for microbial analysis, as well as for determination of organoleptic characteristics. Infrared treatment resulted in a significant reduction of total viable counts, yeasts and moulds by factors ranging from 10 to 300. Increase of treatment time and peak temperature was positively correlated with microbial reduction. Sensory attributes were not affected up to 60 °C, while crystalline texture and overall acceptance were affected by IR treatment at 70 °C. With respect to currant phenolics, antioxidants that have potential benefits to human health, IR heating resulted in almost the same effect up to 65 °C, i.e. approximately 20 % reduction; higher peak temperatures further lowered total phenolic values. 5-hydroxymethylfurfural (HMF) formation was low up to 55 °C, while increased at higher temperatures; however, values still remained low as compared with dried fruit HMF levels. In another series of bioassays, golden sultanas were artificially infested with larvae of Ephestia elutella and adults of Oryzaephilus surinamensis and Tribolium confusum and treated with IR in agitating flow process at different peak temperatures (45, 50, 55, 60, 65 and 70 °C). Finally, a batch series of non-agitated flow process tests were conducted in glass Petri dishes. Briefly, O. surinamensis and T. confusum adults were exposed to IR penetration for different time exposure intervals (1, 2, 3, 4, 5, 8, 10 and 20 s) with and without the presence of currants and sultanas. In the bioassays with infested sultanas, all IR treatments with agitation provided complete control of the insect species tested, since IR-treated sultanas were found free of insects even 1 year after treatment. For exposure intervals higher than 4 s in the non-agitated flow process, all adults of O. surinamensis and T. confusum were killed in glass Petri dishes consisting of insects only and without the presence of currants and sultanas. In contrast, the presence of currants and sultanas in the non-agitated flow process reduced significantly the killing rate efficacy of IR against the insect species tested, especially on the individuals located beneath the sultanas and currants and where the infrared light could not penetrate them. Our results suggest that electric infrared heating with light source penetration could be a valuable tool for rapid and successful reduction of the microbial load and post-harvest insect disinfestation of dry currants and sultanas, provided that adequate agitation within the infrared process chamber is achieved so that sultanas and currants could be penetrated consistently in a three-dimensional manner.

Mechanism of Cutting Elastomers with Cryogenic Cooling

Machining of elastomers offers more flexibility of product shape in comparison to the common compression moulding, especially for small batch series. In this context the entropy-elastic behaviour of the material with low Young's modulus is the main barrier for high-quality manufacturing. This material behaviour could be temporarily adapted by cryogenic cooling for precise cutting. In this article, the different mechanisms, e.g. forces, friction and separation procedures, are analysed for elastomers with different material behaviours. Different chip formation mechanisms are shown in comparison to metal machining. As a result, the friction (μ≈1) between work piece, chip and tool dominates. An analytic chip formation model has been applied.

Oxygen-Enriched Gas in Bioleaching Stirred Reactors and its Impact on the Consortium Behaviour

In bioleaching processes, gas transfer is often considered as one of the key mechanisms that will influence the leaching efficiency and more precisely the leaching rate. Oxygen can be a limiting factor in bacterial leaching because of its low solubility. One way to overcome this phenomenon consists in increasing the oxygen partial pressure in the gas stream supplied to the leach pulp. The primary objective of this work was to investigate the use of oxygen-enriched gas in bioleaching stirred reactors and its impact on the consortium dynamics. First tests were performed at lab scale in four successive series of 2-L bioreactors alimented either with air or with oxygen enriched gas. The microbial consortium used has proven its efficiency on several ores such as cobaltiferous pyrite and polymetallic ores in former research projects (BioMine, BioShale, ProMine). The community diversity was remarkably reproducible irrespective of the type of gas supply, in each of the successive series of reactors. Only minor changes occurred after subculturing from one batch series to the next one, highlighting the high stability of the established consortium. Different oxygen partial pressures (from 20% to 50%) were then tested in a 20-L continuous reactors pilot experiment. There was no impact on the community diversity, showing the high tolerance to oxygen of the bioleaching strains and their capacity to easily survive 50% oxygen input. The bioleaching efficiency in terms of rate and metal leaching did not seem to be changed. The use of enriched oxygen gas is not detrimental to the bioleaching strains and may be used in order to improve process operation (gas transfer, heat management...).