This article reviews the many innovative strategies that have been developed to specifically design the support layers of forward osmosis (FO) membranes. Forward osmosis (FO) is one of the most viable separation technologies to treat hypersaline wastewater, but its successful deployment requires the development of new membrane materials beyond existing desalination membranes. Specifically, designing the FO membrane support layers requires new engineering techniques to minimize the internal concentration polarization (ICP) effects encountered in cases of FO. In this paper, we have reviewed several such techniques developed by different research groups and summarized the membrane transport properties corresponding to each approach. An important transport parameter that helps to compare the various approaches is the so-called structural parameter (-value); a low -value typically corresponds to low ICP. Strategies such as electrospinning, solvent casting, and hollow fiber spinning, have been developed by prior researchers—all of them aimed at lowering this -value. We also reviewed the quantitative methods described in the literature, to evaluate the separation properties of FO membranes. Lastly, we have highlighted some key research gaps, and provided suggestions for potential strategies that researchers could adopt to enable easy comparison of FO membranes.
This study focuses on developing and demonstrating feasibility of an integrated chemical precipitation and membrane filtration method for recovering phosphorus (P) and ammonia (NH 3 -N) in two separate streams from anaerobic digestate generated from municipal wastewater. Nutrient recovery from waste streams creates alternative raw material sources of fertilizers and offers opportunities for reduced energy usage and CO 2 emissions compared with their conventional production processes.Using both synthetic and real anaerobic digestates, the effects of ferrous dosage and precipitation pH on P recovery through vivianite precipitation was examined. Fe/P molar ratio 2.1 at circumneutral pH was found as an optimal condition for ~100% P recovery. The P-free digestate was further treated with polyelectrolyte-modified nanofiltration (NF) membranes to separate NH 3 -N and the organic constituents as a means of N recovery. The surface-modified membranes demonstrated ~2X NH 3 -N/ organic carbon selectivity versus commercial NF membranes. This integrated Fe-enabled chemical precipitation and membrane-based process demonstrates a unique approach to sustainably recover critical nutrients from wastewater.
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