Revisiting membrane rejection: On the relationship between solute size and pore size in the nanofiltration regime

The molecular resolution of nanofiltration depends on resistance to solute transport along the permeation channel, manifesting steric hindrance and hydrodynamic friction. To date there is little direct experimental evidence of reporting on rejection in nanofiltration for ideal membranes with uniform pores, and defined size solutes. However the recent availability of defined nanoparticles in the range 1-20 nm makes new investigations feasible. Phenomenological models for predicting solute permeation through defined cylindrical channels started with the Hagen-Poiseuille equation, which includes viscosity as the key parameter for solvent permeation. The Bowen-Welfoot model was developed to incorporate several correction terms to account for solute-pore interaction. However, the Bowen-Welfoot model generates ideal rejection curves only under the conditions of low pressure-driven flow. Under high-pressure conditions, the rejection curve as predicted by Bowen-Welfoot model assumes a broad spread, similar to the rejection profile predicted by Ferry’s sieving model, demonstrating steric hindrance based on solute-pore interaction as the key parameter in rejection. We set out to obtain new fundamental experimental evidence to interrogate these nanofiltration models. In this work, transport of spherical nanoparticle (NP) imaging probes through model polycarbonate track etch (PCTE) and alumina (Al) membranes were studied empirically using citrate-coated gold nanoparticles of defined sizes (1, 5, 15 nm) and straight channel PCTE (nominal pore diameters 10 and 30 nm) and Al (nominal pore diameters 40 nm) membranes with uniform pore sizes. A priori calculations of theoretical rejections of the membranes with respect to different solute sizes were computed using Bowen-Welfoot pore-flow model. Two simulation approaches were used to describe both discrete and continuous (Gaussian distribution) pore size distributions using probability density functions and taking into account the solvent viscosity as a function of pore radii. Empirically measured rejections of nanoparticle imaging probes were compared with simulation results to confirm the phenomena of hindered transport of NPs inside defined cylindrical nanochannels. Given the experimentally observed evidence of hindered transport of solute moving through pores of commensurate dimensions, we revisited the measurement of rejection in nanofiltration regime in different operational modes: dead-end filtration, diafiltration and cross-flow using a same combination of nanoparticle solute size and membrane pore size. Our results show that dead-end and cross-flow measurements of rejection values do not always agree well with each other; while our diafiltration experiments provide evidence of solutes getting trapped inside membrane pores of commensurate sizes (permanent loss) or solutes in retarded movement through the pores due to much faster solvent flow (transient accumulation). In summary, this fundamental study will illustrate the relation between solute sizes and pore sizes, the implications of it on measurements of rejection values, and the applications of the use of nanoparticle imaging agents for quantifying pathway dimensions in commercial membranes such as reverse osmosis thin film composites and integrally skinned asymmetric nanofiltration membranes with tortuous pore channels that are otherwise difficult to imaging the sizes directly using electron micrographic techniques

Performance of the CSTR-in-series extractive membrane bioreactor in industrial wastewater treatment

The extractive membrane bioreactor (EMBR) is a treatment method which had demonstrated success in the removal of organic compounds such as phenol, nitrochlorobenzene, dichloroaniline from complex industrial wastewaters that are naturally hostile to bioprocessing (eg. extreme pH and salinity) (Livingston 1993, Brookes and A.G.Livingston 1994). As shown in Figure, the targeted organics from the feed wastewater are extracted by the membrane into the bioreactor downstream of the membrane while salt and acid/alkaline are retained at the feed side, creating an environment conducive to the bioremoval of organics downstream of the membrane. The biofilm on the downstream side of the membrane surface removes and biodegrades the organics, creating the concentration gradient required to sustain the organic flux across the membrane. In this study, the EMBR is applied for the first time in the CSTR-in-series configuration using in-house hollow fiber membranes (Loh, Zhang et al. 2016) in submerged EMBR systems. Preliminary studies were conducted using a synthetic feed solution comprising of 860 ppm phenol and 5 g/L NaCl. The phenol that diffused across the membranes served as a carbon source for the biofilm downstream of the membrane while additional inorganic nutrients comprising of MgSO4.7H2O, CaCl2.2H2O, KH2PO4, K2HPO4, FeCl3 and NH4Cl were supplied to the bioreactor on a daily basis. At a feed flow rate of 0.86 L/day, the effluent treatment concentration can be as low as 84 ppm (just 10% of the influent). No phenol was detected on the bioreactor side throughout the operation, indicating all phenol was removed by the biofilms on the membrane surface. Our study demonstrates that the EMBR is a promising system that can treat difficult industrial wastewater at source and could potentially reduce costs associated with other treatment strategies (eg. maintenance of activated carbon cartridges). Biofilm characterization results and the performance of the CSTR-in-series EMBR in treatment of actual industrial wastewater will be shared. Please click Additional Files below to see the full abstract

Effectiveness of an intervention to facilitate prompt referral to memory clinics in the United Kingdom: Cluster randomised controlled trial

Background Most people with dementia do not receive timely diagnosis, preventing them from making informed plans about their future and accessing services. Many countries have a policy to increase timely diagnosis, but trials aimed at changing general practitioner (GP) practice have been unsuccessful. We aimed to assess whether a GP’s personal letter, with an evidence-based leaflet about overcoming barriers to accessing help for memory problems—aimed at empowering patients and families—increases timely dementia diagnosis and patient presentation to general practice. Methods and finding Multicentre, cluster-randomised controlled trial with raters masked to an online computer-generated randomisation system assessing 1 y outcome. We recruited 22 general practices (August 2013–September 2014) and 13 corresponding secondary care memory services in London, Hertfordshire, and Essex, United Kingdom. Eligible patients were aged ≥70 y, without a known diagnosis of dementia, living in their own homes. There were 6,387 such patients in 11 intervention practices and 8,171 in the control practices. The primary outcome was cognitive severity on Mini Mental State Examination (MMSE). Main secondary outcomes were proportion of patients consulting their GP with suspected memory disorders and proportion of those referred to memory clinics. There was no between-group difference in cognitive severity at diagnosis (99 intervention, mean MMSE = 22.04, 95% confidence intervals (CIs) = 20.95 to 23.13; 124 control, mean MMSE = 22.59, 95% CI = 21.58 to 23.6; p = 0.48). GP consultations with patients with suspected memory disorders increased in intervention versus control group (odds ratio = 1.41; 95% CI = 1.28, 1.54). There was no between-group difference in the proportions of patients referred to memory clinics (166, 2.5%; 220, 2.7%; p = .077 respectively). The study was limited as we do not know whether the additional patients presenting to GPs had objective as well as subjective memory problems and therefore should have been referred. In addition, we aimed to empower patients but did not do anything to change GP practice. Conclusions Our intervention to access timely dementia diagnosis resulted in more patients presenting to GPs with memory problems, but no diagnoses increase. We are uncertain as to the reason for this and do not know whether empowering the public and targeting GPs would have resulted in a successful intervention. Future interventions should be targeted at both patients and GPs. Trial registration Current Controlled Trials ISRCTN1921687

275 Candidates and 149 Validated Planets Orbiting Bright Stars in K2 Campaigns 0-10

Since 2014, NASA's K2 mission has observed large portions of the ecliptic plane in search of transiting planets and has detected hundreds of planet candidates. With observations planned until at least early 2018, K2 will continue to identify more planet candidates. We present here 275 planet candidates observed during Campaigns 0-10 of the K2 mission that are orbiting stars brighter than 13 mag (in Kepler band) and for which we have obtained high-resolution spectra (R = 44,000). These candidates are analyzed using the VESPA package (Morton 2012, 2015b) in order to calculate their false-positive probabilities (FPP). We find that 149 candidates are validated with an FPP lower than 0.1%, 39 of which were previously only candidates and 56 of which were previously undetected. The processes of data reduction, candidate identification, and statistical validation are described, and the demographics of the candidates and newly validated planets are explored. We show tentative evidence of a gap in the planet radius distribution of our candidate sample. Comparing our sample to the Kepler candidate sample investigated by Fulton et al. (2017), we conclude that more planets are required to quantitatively confirm the gap with K2 candidates or validated planets. This work, in addition to increasing the population of validated K2 planets by nearly 50% and providing new targets for follow-up observations, will also serve as a framework for validating candidates from upcoming K2 campaigns and the Transiting Exoplanet Survey Satellite, expected to launch in 2018.Comment: Published in AJ, 47 pages, 18 figures, 7 tables, associated supplementary dataset available at https://zenodo.org/record/116479

Association of Alcohol-Induced Loss of Consciousness and Overall Alcohol Consumption With Risk for Dementia

This cohort study examines the association of overall consumption of alcohol and resultant loss of consciousness with risk for dementia. Question Are alcohol-induced loss of consciousness and heavy weekly alcohol consumption associated with increased risk of future dementia? Findings In this multicohort study of 131x202f;415 adults, a 1.2-fold excess risk of dementia was associated with heavy vs moderate alcohol consumption. Those who reported having lost consciousness due to alcohol consumption, regardless of their overall weekly consumption, had a 2-fold increased risk of dementia compared with people who had not lost consciousness and were moderate drinkers. Meaning The findings of this study suggest that alcohol-induced loss of consciousness is a long-term risk factor for dementia among both heavy and moderate drinkers. Importance Evidence on alcohol consumption as a risk factor for dementia usually relates to overall consumption. The role of alcohol-induced loss of consciousness is uncertain. Objective To examine the risk of future dementia associated with overall alcohol consumption and alcohol-induced loss of consciousness in a population of current drinkers. Design, Setting, and Participants Seven cohort studies from the UK, France, Sweden, and Finland (IPD-Work consortium) including 131x202f;415 participants were examined. At baseline (1986-2012), participants were aged 18 to 77 years, reported alcohol consumption, and were free of diagnosed dementia. Dementia was examined during a mean follow-up of 14.4 years (range, 12.3-30.1). Data analysis was conducted from November 17, 2019, to May 23, 2020. Exposures Self-reported overall consumption and loss of consciousness due to alcohol consumption were assessed at baseline. Two thresholds were used to define heavy overall consumption: greater than 14 units (U) (UK definition) and greater than 21 U (US definition) per week. Main Outcomes and Measures Dementia and alcohol-related disorders to 2016 were ascertained from linked electronic health records. Results Of the 131x202f;415 participants (mean [SD] age, 43.0 [10.4] years; 80x202f;344 [61.1%] women), 1081 individuals (0.8%) developed dementia. After adjustment for potential confounders, the hazard ratio (HR) was 1.16 (95% CI, 0.98-1.37) for consuming greater than 14 vs 1 to 14 U of alcohol per week and 1.22 (95% CI, 1.01-1.48) for greater than 21 vs 1 to 21 U/wk. Of the 96x202f;591 participants with data on loss of consciousness, 10x202f;004 individuals (10.4%) reported having lost consciousness due to alcohol consumption in the past 12 months. The association between loss of consciousness and dementia was observed in men (HR, 2.86; 95% CI, 1.77-4.63) and women (HR, 2.09; 95% CI, 1.34-3.25) during the first 10 years of follow-up (HR, 2.72; 95% CI, 1.78-4.15), after excluding the first 10 years of follow-up (HR, 1.86; 95% CI, 1.16-2.99), and for early-onset (= 65 y: HR, 2.25; 95% CI, 1.38-3.66) dementia, Alzheimer disease (HR, 1.98; 95% CI, 1.28-3.07), and dementia with features of atherosclerotic cardiovascular disease (HR, 4.18; 95% CI, 1.86-9.37). The association with dementia was not explained by 14 other alcohol-related conditions. With moderate drinkers (1-14 U/wk) who had not lost consciousness as the reference group, the HR for dementia was twice as high in participants who reported having lost consciousness, whether their mean weekly consumption was moderate (HR, 2.19; 95% CI, 1.42-3.37) or heavy (HR, 2.36; 95% CI, 1.57-3.54). Conclusions and Relevance The findings of this study suggest that alcohol-induced loss of consciousness, irrespective of overall alcohol consumption, is associated with a subsequent increase in the risk of dementia.Peer reviewe

Two Small Transiting Planets and a Possible Third Body Orbiting HD 106315

The masses, atmospheric makeups, spin–orbit alignments, and system architectures of extrasolar planets can be best studied when the planets orbit bright stars. We report the discovery of three bodies orbiting HD 106315, a bright (V = 8.97 mag) F5 dwarf targeted by our K2 survey for transiting exoplanets. Two small transiting planets are found to have radii 2.23^(+0.30)_(-0.25)R⊕ and 3.95^(+0.42)_(-0.39)R⊕ and orbital periods 9.55 days and 21.06 days, respectively. A radial velocity (RV) trend of 0.3 ± 0.1 m s^(−1) day^(−1) indicates the likely presence of a third body orbiting HD 106315 with period ≳160 days and mass ≳45 M⊕. Transits of this object would have depths ≳0.1% and are definitively ruled out. Although the star has v sin i = 13.2 km s^(−1), it exhibits a short-timescale RV variability of just 6.4 m s^(−1). Thus, it is a good target for RV measurements of the mass and density of the inner two planets and the outer object's orbit and mass. Furthermore, the combination of RV noise and moderate v sin i makes HD 106315 a valuable laboratory for studying the spin–orbit alignment of small planets through the Rossiter–McLaughlin effect. Space-based atmospheric characterization of the two transiting planets via transit and eclipse spectroscopy should also be feasible. This discovery demonstrates again the power of K2 to find compelling exoplanets worthy of future study

Micro-to nano-scale characterisation of polyamide structures of the SW30HR RO membrane using advanced electron microscopy and stain tracers

The development of new reverse osmosis (RO) membranes with enhanced performance would benefit from a detailed knowledge of the membrane structures which participate in the filtration process. Here, we examined the hierarchical structures of the polyamide (PA) active layer of the SW30HR RO membrane. Scanning electron microscopy combined with focused ion beam milling (FIB-SEM) was used to obtain the 3-D reconstructions of membrane morphology with 5 nm cross-sectional resolution (comparable with the resolution of low magnification TEM imaging in 2D) and 30 nm slice thickness. The complex folding of the PA layer was examined in 3 dimensions, enabling the quantification of key structural properties of the PA layer, including the local thickness, volume, surface area and their derivatives. The PA layer was found to exhibit a much higher and convoluted surface area than that estimated via atomic force microscopy (AFM). Cross-sectional scanning transmission electron microscopy (STEM) was used to observe the distribution of a tracer stain under various conditions. The behaviour of stain in dry and wet PA indicated that the permeation pathways have a dynamic nature and are activated by water. High resolution STEM imaging of the stained PA nano-films revealed the presence of <1 nm pore-like structures with a size compatible with free volume estimations by positron annihilation lifetime spectroscopy (PALS). This study presents a comprehensive map of the active PA layer across different length scales (from micro- to sub-nanometre) and mechanistic insight into their role in the permeation process