Abstract
This work explores the application of Reverse Osmosis (RO) upcycled membranes, as Anion Exchange Membranes (AEMs) in Donnan Dialysis (DD) and related processes, such as the Ion Exchange Membrane Bioreactor (IEMB), for the removal of nitrate from contaminated water, to meet drinking water standards. Such upcycled membranes might be manufactured at a lower price than commercial AEMs, while their utilization reinforces the commitment to a circular economy transition. In an effort to gain a better understanding of such AEMs, confocal µ-Raman spectroscopy was employed, to assess the distribution of the ion-exchange sites through the thickness of the prepared membranes, and 2D fluorescence spectroscopy, to evaluate alterations in the membranes caused by fouling and chemical cleaning The best performing membrane reached a 56% average nitrate removal within 24 h in the DD and IEMB systems, with the latter furthermore allowing for simultaneous elimination of the pollutant by biological denitrification, thus avoiding its discharge into the environment. Overall, this work validates the technical feasibility of using RO upcycled AEMs in DD and IEMB processes for nitrate removal. This membrane recycling concept might also find applications for the removal and/or recovery of other target negatively charged species.
Highlights
Reverse Osmosis (RO) desalination market is in constant growth [1]
These results indicate that the employed organic solvent in the coating mixture (i.e., THF) has dissolved the PSf layer of the recycled membrane support, causing the percolation of dissolved PSf inside the PET layer, while the solvation of the PSf layer promotes the penetration of the polymer binder (i.e., Polyvinyl chloride (PVC)) into the recycled membrane support, as it is demonstrated by the presence of the PVC signal at point h
The feasibility of using Anion-Exchange Membranes (AEMs) prepared from upcycled end-of-life RO membranes for the removal of nitrate from water using Donnan Dialysis (DD) and Ion-Exchange Membrane Bioreactor (IEMB) systems is demonstrated
Summary
Reverse Osmosis (RO) desalination market is in constant growth [1]. due to RO performance deterioration, an annual membrane replacement rate ranging between 5% in brackish water RO desalination to 20% in sea water RO desalination is estimated [2]. The upcycling of end-of-life RO membranes for the preparation of Anion-Exchange Membranes (AEMs) has been proposed [4,5,6]. This alternative entails the deconstruction of the RO module, allowing for the individual management of flat sheet membranes and plastic components. ED necessarily removes both cations and anions (i.e., leading to demineralization), and it might be less appropriate in certain applications, such as drinking water or beverages production, in which the ionic composition should be preserved as much as possible. The IEMB has been reported as an efficient technology for removal and degradation of target ionic pollutants, such as nitrate, from drinking water supplies [10]
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