The Combined Effect of Air Layers and Membrane Superhydrophobicity on Biofouling in Membrane Distillation

Previous studies of membrane distillation (MD) have shown that superhydrophobic membranes experience dramatically less inorganic and particulate fouling. However, little explanation for this improved performance has been given in the literature. Furthermore, studies comparing membrane superhydrophobicity and biofouling are lacking, though superhydrophobic surfaces are known to be more vulnerable to biofouling than other types. In non-membrane surfaces, visible air layers on superhydrophobic surfaces have been correlated with significant decreases in biofouling. Therefore, it was proposed here to use superhydrophobic MD membranes with periodic introduction of air to maintain an air layer on the membrane surface. Superhydrophobic membranes were created with initiated chemical vapor deposition (iCVD) of a fluorinated compound, perfluorodecyl acrylate (PFDA). The substrate membrane was PVDF. To test MD fouling, an MD membrane was placed on top of a fouling solution, with a heater and stirrer to caus e evaporation of water through the membrane. Results were analyzed with foulant mass measurements. Alginate gel fouling was examined, as this compound is a common proxy for biological fouling in ocean w ater. The introduction of air layers was found to dramatically decrease foulant adhesion to the membrane, by 95-97%. Membrane superhydrophobicity made a much smaller impact in reducing fouling. Keywords membrane distillation, superhydrophobic surfaces, alginate, air layers, anti-foulin

Selective sweeps on novel and introgressed variation shape mimicry loci in a butterfly adaptive radiation.

Natural selection leaves distinct signatures in the genome that can reveal the targets and history of adaptive evolution. By analysing high-coverage genome sequence data from 4 major colour pattern loci sampled from nearly 600 individuals in 53 populations, we show pervasive selection on wing patterns in the Heliconius adaptive radiation. The strongest signatures correspond to loci with the greatest phenotypic effects, consistent with visual selection by predators, and are found in colour patterns with geographically restricted distributions. These recent sweeps are similar between co-mimics and indicate colour pattern turn-over events despite strong stabilising selection. Using simulations, we compare sweep signatures expected under classic hard sweeps with those resulting from adaptive introgression, an important aspect of mimicry evolution in Heliconius butterflies. Simulated recipient populations show a distinct 'volcano' pattern with peaks of increased genetic diversity around the selected target, characteristic of sweeps of introgressed variation and consistent with diversity patterns found in some populations. Our genomic data reveal a surprisingly dynamic history of colour pattern selection and co-evolution in this adaptive radiation

Combining air recharging and membrane superhydrophobicity for fouling prevention in membrane distillation

In previous studies of the desalination technology membrane distillation (MD), superhydrophobicity of the membrane has been shown to dramatically decrease fouling in adverse conditions, but the mechanism for this is not well understood. Additionally, air layers present on submerged solid superhydrophobic surfaces have been shown to dramatically reduce biofouling, and air-bubbling has been used to reducing fouling and increase flux and efficiency in MD. The present work studies the effect of maintaining air layers on the membrane surface and superhydrophobicity as a new method for preventing fouling of MD membranes by salts, particulates, and organic particles. Superhydrophobic MD membranes were prepared using initiated chemical vapor deposition (iCVD) of perfluorodecyl acrylate (PFDA) on poly(vinyldene fluoride) PVDF membranes and used to study the effects of surface energy on fouling. A static MD setup with evaporation through an MD membrane but no condensing of permeate was used to examine the effect of air exposure on fouling, by measuring the increase in weight of the membrane caused by scale deposition. Theory was derived for the reduction of fouling on superhydrophobic surfaces, and a review of related theory was included. Air layers may displace fouling gels, reduce the area of feed in contact with the membrane, reduce foulant adhesion, and enhance superhydrophobicity in a Cassie–Baxter state. The study shows that the presence of air on the membrane surface significantly reduces biological fouling, but in some cases had mildly exacerbating effects by increasing crystal formation of salts, especially when the air was not saturated with water vapor. Air recharging combined with superhydrophobicity reduced fouling in several cases where hydrophobic membranes alone did little.National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (DMR-1120296)Masdar Institute of Science and Technology/MIT/UAE (Cooperative agreement, Reference no.02/MI/MI/ CP/11/07633/GEN/G/00

Selective sweeps on novel and introgressed variation shape mimicry loci in a butterfly adaptive radiation

Natural selection leaves distinct signatures in the genome that can reveal the targets and history of adaptive evolution. By analysing high-coverage genome sequence data from 4 major colour pattern loci sampled from nearly 600 individuals in 53 populations, we show pervasive selection on wing patterns in the Heliconius adaptive radiation. The strongest signatures correspond to loci with the greatest phenotypic effects, consistent with visual selection by predators, and are found in colour patterns with geographically restricted distributions. These recent sweeps are similar between co-mimics and indicate colour pattern turn-over events despite strong stabilising selection. Using simulations, we compare sweep signatures expected under classic hard sweeps with those resulting from adaptive introgression, an important aspect of mimicry evolution in Heliconius butterflies. Simulated recipient populations show a distinct 'volcano' pattern with peaks of increased genetic diversity around the selected target, characteristic of sweeps of introgressed variation and consistent with diversity patterns found in some populations. Our genomic data reveal a surprisingly dynamic history of colour pattern selection and co-evolution in this adaptive radiation. © 2020 Moest et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited