The use of forward osmosis (FO) for water purification purposes has gained extensive attention in recent years. In this review, we first discuss the advantages, challenges and various applications of FO, as well as the challenges in selecting the proper draw solution for FO, after which we focus on transport limitations in FO processes. Despite recent advances in membrane development for FO, there is still room for improvement of its selective layer and support. For many applications spiral wound membrane will not suffice. Furthermore, a defect-free selective layer is a prerequisite for FO membranes to ensure low solute passage, while a support with low internal concentration polarization is necessary for a high water flux. Due to challenges affiliated to interfacial polymerization (IP) on non-planar geometries, we discuss alternative approaches to IP to form the selective layer. We also explain that, when provided with a defect-free selective layer with good rejection, the membrane support has a dominant influence on the performance of an FO membrane, which can be estimated by the structural parameter (S). We emphasize the necessity of finding a new method to determine S, but also that predominantly the thickness of the support is the major parameter that needs to be optimized.

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In this paper, we introduce a single-step process that incorporates an intermediate layer on a hollow fiber to enhance the final membrane performance after interfacial polymerization (IP). This intermediate layer is applied during hollow-fiber spinning by complexation of two oppositely charged polyelectrolytes. Specifically, in this study, we consider the IP coating process an experimental success for a membrane sample with a NaCl rejection > 85%. The IP success rate is defined as the percentage of the samples with a NaCl rejection of > 85% within a studied group. The purpose of the intermediate layer is to increase the success rate of IP on the inner surface of the hollow fibers, typically a challenging task due to the cylindrical shape of the fibers. After the application of IP, the pure water permeance and NaCl rejection of the nascent membranes were tested to determine the success rate of IP. The IP success rate was 86-100% for the hollow fibers (HF) with intermediate layer, significantly higher than the 29% success rate achieved for IP on the support without intermediate layer. This surface modification approach is simple, time-efficient, and effective without any need for post-IP optimization that opens up new avenues for further developments for IP based dense hollow fiber membranes.

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Chokeberry (Aronia melanocarpa) pomace is a by-product from the juice industry very rich in anthocyanins and other bioactive components. Recovery and purification of anthocyanins from the pomace is a viable valorization strategy that can be implemented to produce high-value natural food colorants with antioxidant properties. In this study, chokeberry pomace was subjected to enzyme-assisted extraction using commercial pectinases. The extracts were further purified by adsorption–desorption using an acrylic resin and stabilized by co-pigmentation with ferulic acid. The anthocyanin concentration and antioxidant activity of the extracts were unaffected by the enzymatic treatment at the conditions tested. The total phenolic content of the extracts suffered minor variations depending on the enzyme formulation used, whereas the dissolved solid content increased in all cases. The adsorption–desorption strategy allowed a 96% recovery of the anthocyanins initially present in the extract, whereas the co-pigmentation treatment magnified the intensity of the color in terms of absorbance, and improved the stability during storage up to one month.