Optimization of commercial net spacers in spiral wound membrane modules

CFD simulations have been used to determine mass transfer coefficients and power consumption of commercial net spacers. The simulations show transversal and longitudinal vortices, vortex shedding and instationary flow behavior leading to the enhanced mass transfer in spacer filled-channels compared to empty channels. The results of the simulations were validated with experiments and compared with data reported in literature, showing satisfactory agreement. Furthermore, CFD simulations were used to optimize the geometry of commercial net spacers in terms of mass transfer and power consumption. The performance of these optimized spacer geometries will be used as reference for future work on the development of new high-performance spacer shapes

A whole-cell biosensor for the detection of gold

Geochemical exploration for gold (Au) is becoming increasingly important to the mining industry. Current processes for Au analyses require sampling materials to be taken from often remote localities. Samples are then transported to a laboratory equipped with suitable analytical facilities, such as Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) or Instrumental Neutron Activation Analysis (INAA). Determining the concentration of Au in samples may take several weeks, leading to long delays in exploration campaigns. Hence, a method for the on-site analysis of Au, such as a biosensor, will greatly benefit the exploration industry. The golTSB genes from Salmonella enterica serovar typhimurium are selectively induced by Au(I/III)-complexes. In the present study, the golTSB operon with a reporter gene, lacZ, was introduced into Escherichia coli. The induction of golTSB::lacZ with Au(I/III)-complexes was tested using a colorimetric β-galactosidase and an electrochemical assay. Measurements of the β-galactosidase activity for concentrations of both Au(I)- and Au(III)-complexes ranging from 0.1 to 5 µM (equivalent to 20 to 1000 ng g⁻¹ or parts-per-billion (ppb)) were accurately quantified. When testing the ability of the biosensor to detect Au(I/III)-complexes(aq) in the presence of other metal ions (Ag(I), Cu(II), Fe(III), Ni(II), Co(II), Zn, As(III), Pb(II), Sb(III) or Bi(III)), cross-reactivity was observed, i.e. the amount of Au measured was either under- or over-estimated. To assess if the biosensor would work with natural samples, soils with different physiochemical properties were spiked with Au-complexes. Subsequently, a selective extraction using 1 M thiosulfate was applied to extract the Au. The results showed that Au could be measured in these extracts with the same accuracy as ICP-MS (P<0.05). This demonstrates that by combining selective extraction with the biosensor system the concentration of Au can be accurately measured, down to a quantification limit of 20 ppb (0.1 µM) and a detection limit of 2 ppb (0.01 µM).Carla M. Zammit, Davide Quaranta, Shane Gibson, Anita J. Zaitouna, Christine Ta, Joël Brugger, Rebecca Y. Lai, Gregor Grass, Frank Reit

Bacterial Deposition of Gold on Hair: Archeological, Forensic and Toxicological Implications

Trace metal analyses in hair are used in archeological, forensic and toxicological investigations as proxies for metabolic processes. We show metallophilic bacteria mediating the deposition of gold (Au), used as tracer for microbial activity in hair post mortem after burial, affecting results of such analyses. Methodology/Principal Findings Human hair was incubated for up to six months in auriferous soils, in natural soil columns (Experiment 1), soils amended with mobile Au(III)-complexes (Experiment 2) and the Au-precipitating bacterium Cupriavidus metallidurans (Experiment 3), in peptone-meat-extract (PME) medium in a culture of C. metallidurans amended with Au(III)-complexes (Experiment 4), and in non-auriferous soil (Experiment 5). Hair samples were analyzed using scanning electron microscopy, confocal microscopy and inductively coupled plasma-mass spectrometry. In Experiments 1–4 the Au content increased with time (P = 0.038). The largest increase was observed in Experiment 4 vs. Experiment 1 (mean = 1188 vs. 161 µg Kg−1, Fisher's least significance 0.001). The sulfur content, a proxy for hair metabolism, remained unchanged. Notably, the ratios of Au-to-S increased with time (linear trend P = 0.02) and with added Au and bacteria (linear trend, P = 0.005), demonstrating that larger populations of Au-precipitating bacteria and increased availability of Au increased the deposition of Au on the hair. Conclusion/Significance Interactions of soil biota with hair post mortem may distort results of hair analyses, implying that metal content, microbial activities and the duration of burial must be considered in the interpretation of results of archeological, forensic and toxicological hair analyses, which have hitherto been proxies for pre-mortem metabolic processesGenevieve Phillips, Frank Reith, Clifford Qualls, Abdul-Mehdi Ali, Mike Spilde and Otto Appenzelle

Reflecting on gold geomicrobiology research: thoughts and considerations for future endeavors

Research in gold (Au) geomicrobiology has developed extensively over the last ten years, as more Au-bearing materials from around the world point towards a consistent story: That microbes interact with Au. In weathering environments, Au is mobile, taking the form of oxidized, soluble complexes or reduced, elemental Au nanoparticles. The transition of Au between aqueous and solid states is attributed to varying geochemical conditions, catalyzed in part by the biosphere. Hence, a global Au-biogeochemical-cycle was proposed. The primary focus of this mini-review is to reflect upon the biogeochemical processes that contribute to what we currently know about Au cycling. In general, the global Au-biogeochemical-cycle begins with the liberation of gold-silver particles from a primary host rock, by physical weathering. Through oxidative-complexation, inorganic and organic soluble-Au complexes are produced. However, in the presence of microbes or other reductants—e.g., clays and Fe-oxides—these Au complexes can be destabilized. The reduction of soluble Au ultimately leads to the bioprecipitation and biomineralization of Au, the product of which can aggregate into larger structures, thereby completing the Au cycle. Evidence of these processes have been “recorded” in the preservation of secondary Au structures that have been observed on Au particles from around the world. These structures—i.e., nanometer-size to micrometer-size Au dissolution and reprecipitation features—are “snap shots” of biogeochemical influences on Au, during its journey in Earth-surface environments. Therefore, microbes can have a profound effect on the occurrence of Au in natural environments, given the nutrients necessary for microbial metabolism are sustained and Au is in the system.Jeremiah Shuster and Frank Reit

Editorial for special issue "geomicrobiology and biogeochemistry of precious metals"

n/aFrank Reith and Jeremiah Shuste

Proteomic responses to gold(III)-toxicity in the bacterium Cupriavidus metallidurans CH34

Accepted 11th October 2016The metal-resistant β-proteobacterium Cupriavidus metallidurans drives gold (Au) biomineralisation and the (trans)formation of Au nuggets largely via unknown biochemical processes, ultimately leading to the reductive precipitation of mobile, toxic Au(i/iii)-complexes. In this study proteomic responses of C. metallidurans CH34 to mobile, toxic Au(iii)-chloride are investigated. Cells were grown in the presence of 10 and 50 μM Au(iii)-chloride, 50 μM Cu(ii)-chloride and without additional metals. Differentially expressed proteins were detected by difference gel electrophoresis and identified by liquid chromatography coupled mass spectrometry. Proteins that were more abundant in the presence of Au(iii)-chloride are involved in a range of important cellular functions, e.g., metabolic activities, transcriptional regulation, efflux and metal transport. To identify Au-binding proteins, protein extracts were separated by native 2D gel electrophoresis and Au in protein spots was detected by laser absorption inductively coupled plasma mass spectrometry. A chaperon protein commonly understood to bind copper (Cu), CupC, was identified and shown to bind Au. This indicates that it forms part of a multi-metal detoxification system and suggests that similar/shared detoxification pathways for Au and Cu exist. Overall, this means that C. metallidurans CH34 is able to mollify the toxic effects of cytoplasmic Au(iii) by sequestering this Au-species. This effect may in the future be used to develop CupC-based biosensing capabilities for the in-field detection of Au in exploration samples.Carla M. Zammit, Florian Weiland, Joël Brugger, Benjamin Wade, Lyron Juan Winderbaum, Dietrich H. Nies, Gordon Southam, Peter Hoffmann and Frank Reit

Cycling of biogenic elements drives biogeochemical gold cycling

Available online 13 DecemberMicroorganisms are key-drivers of carbon-, nitrogen-, sulfur- and metal cycling on Earth. Through their metabolic activities they directly and indirectly link element cycles. This leads to the cycling of elements through the Earth’s ecosystems from/to the atmosphere to/from the lithosphere. Gold (Au) is a rare, redox-active, noble transition metal, which is neither essential as a nutrient nor, reputedly, mobile in the environment. Therefore, observations published in recent decades, which have shown that gold is highly mobile and subject to biogeochemical cycling largely driven by microbiota, have surprised many. Questions concerning the fundamental biogeochemical processes mediating gold cycling, the organisms involved and the benefits they may gain have puzzled researchers. In this review we integrate the cycling of the major biogenic elements carbon, nitrogen and sulfur with that of gold. We identify key-processes that drive gold cycling and evaluate how different chemical Au(I/III)-species affect microbiota that form biofilms on gold-bearing minerals and placer gold particles. Additionally, we assess how the cycling of the gold-associated metal(loid)s silver, copper, iron, manganese, mercury and arsenic is linked to that of gold. Microbially produced compounds resulting from carbon, nitrogen, sulfur, iron and manganese cycling (e.g., organic acids, cyanides, (thio)sulfates, ammonium, iron sulfides/oxy-hydroxides and managanese oxides) can each play important roles for the mobilization of gold. Highly toxic, mobile Au(I/III)-complexes affect the phylogenetic and functional composition of microbial communities resident on gold particles. This leads to gold detoxification coupled to active and passive biomineralization, and ultimately the aggregation and (trans)formation of metallic gold particles. The complex interplay between gold, microbiota and physicochemical conditions modified by these organisms (e.g., redox or pH) has throughout the Earth’s history led to the aggregation of gold particles (grains to nuggets), led to the formation of the largest known gold deposit (i.e., Witwatersrand paleo-placer), and the largest gold reservoir in seawater. Today it opens up exciting biotechnological pathways for mineral exploration, processing and remediation.Santonu Kumar Sanyal, Jeremiah Shuster, Frank Reit

A genomic perspective of metal-resistant bacteria from gold particles: Possible survival mechanisms during gold biogeochemical cycling

Advance Access Publication Date: 4 June 2020.A bacterial consortium was enriched from gold particles that 'experienced' ca. 80 years of biotransformation within waste-rock piles (Australia). This bacterial consortium was exposed to 10 µM AuCl3 to obtain Au-tolerant bacteria. From these isolates, Serratia sp. and Stenotrophomonas sp. were the most Au-tolerant and reduced soluble Au as pure gold nanoparticles, indicating that passive mineralisation is a mechanism for mediating the toxic effect of soluble Au produced during particle dissolution. Genome-wide analysis demonstrated that these isolates also possessed various genes that could provide cellular defence enabling survival under heavy-metal stressed condition by mediating the toxicity of heavy metals through active efflux/reduction. Diverse metal-resistant genes or genes clusters (cop, cus, czc, znt, ars) were detected, which could confer resistance to soluble Au. Comparative genome analysis revealed that the majority of detected heavy-metal resistant genes were similar (i.e. orthologous) to those genes of Cupriavidus metallidurans CH34. The detection of heavy-metal resistance, nutrient cycling, and biofilm formation genes (pgaABCD, bsmA, hmpS) may have indirect yet important roles when dealing with soluble Au during particle dissolution. In conclusion, the physiological and genomic results suggest that bacteria living on gold particles would likely use various genes to ensure survival during Au biogeochemical cycling.Santonu Kumar Sanyal, Frank Reith and Jeremiah Shuste

Biogeochemical gold cycling selects metal-resistant bacteria that promote gold particle transformation

Bacteria catalyze the dissolution and re-precipitation of gold, thereby driving the biogeochemical cycle of gold. Dissolution of gold/silver and re-precipitation of gold transforms gold particles by increasing gold purity. While soluble gold complexes are highly cytotoxic, little is known about how gold cycling affects bacterial communities residing on gold particles. Micro-analysis of gold particles obtained from Western Australia revealed porous textures and aggregates of pure gold nanoparticles, attributable to gold dissolution and re-precipitation, respectively. By interpreting structure and chemistry of particles, the kinetics of gold biogeochemical cycling at the site was estimated to be 1.60 × 10−9 M year−1. Bacterial communities residing on particles were composed of Proteobacteria (42.5%), Bacteroidetes (20.1%), Acidobacteria (19.1%), Firmicutes (8.2%), Actinobacteria (3.7%), and Verrucomicrobia (3.6%). A bacterial enrichment culture obtained from particles contained a similar composition. Exposure of enrichments to increasing concentrations of soluble gold decreased community diversity and selected for metal-resistant bacteria. Lower gold concentrations, which corresponded well with the concentration from the kinetic rate, provided a selective pressure for the selection of metal-resistant organisms while retaining the overall diversity. In conclusion, biogeochemical gold cycling directly influences bacterial communities on gold particles, thereby contributing to a continuum of particle transformation.Santonu Kumar Sanyal, Jeremiah Shuster, Frank Reit

Modelling double skin façades (DSFs) in whole-building energy simulation tools: Validation and inter-software comparison of a mechanically ventilated single-story DSF

Double skin façades (DSFs) have been proposed as responsive building systems to improve the building envelope's performance. Reliable simulation of DSF performance is a prerequisite to support the design and implementation of these systems in real buildings. Building energy simulation (BES) tools are commonly used by practitioners to predict the whole building energy performance, but the simulation of the thermophysical behaviour of DSFs may be challenging when carried out through BES tools. Using an exhaust-air façade case study, we analyse and assess the reliability of four popular BES tools when these are used to simulate a DSF, either through available in-built models or through custom-built representations based on zonal models. We carry out this study by comparing numerical simulations and experimental data for a series of significant thermophysical quantities, and we reflect on the performance and limitations of the different tools. The results show that no tool is outstandingly better performing over the others, but some tools offer better predictions when the focus is placed on certain thermophysical quantities, while others should be chosen if the focus is on different ones. After comparing the different models’ limitations and challenges, we conclude that BES tools can simulate the performance of DSF systems over long periods. However, their use alone is not recommended when the simulation's scope is to replicate and study short-term phenomena and dynamic aspects, such as sizing the building's HVAC system