Degradation of polyamide reverse osmosis membranes in the presence of chloramine

Abstract

Exposure to relatively low concentrations of chlorinated chemicals such as hypochlorite can reduce the performance and ultimately result in the failure of polyamide (PA) reverse osmosis membranes. Whereas the tolerance of PA membranes to chloramine solutions is considerably higher than that of hypochlorite, the presence of some metal ions can potentially catalyze and accelerate degradation reactions. Spectroscopic techniques are commonly used to qualitatively assess the chemical degradation of membranes by observing changes in structural peaks. This paper presents a technique to quantitatively evaluate changes in PA membranes exposed to chloramine by means of a peak ratio derived from a typical amide peak and an invariant peak in the same spectrum. The effect of some common metal ions and combinations of these on the peak ratio parameter derived from a typical amide peak is also reported.

Production and characterisation of UF membranes by chemical conversion of used RO membranes

“…The converted membrane exhibits suppression and possibly elimination of the characteristic aromatic polyamide peaks which has been previously shown to be an indication of chlorine damage via the mechanism of Orton rearrangement [18]. When comparing these results to previous studies on free chlorine damage to PA membranes, the relative peak suppression is extreme and nearly complete [19,39], a difference which can be explained by the significantly higher oxidant exposures used. This suppression corresponds to breaking of various bonding groups and the subsequent deterioration of the chemical structure.…”

“…The PSf peaks can be seen in the spectra of the membrane due to the relatively deep penetration of the light probe compared to the PA layer thickness. This lack of suppression indicates that the PSf layer has not been negatively affected in this band by the conversion process [19]. Based on this qualitative assessment, the PA active layer has undergone significant changes to its chemical structure.…”

“…Once in contact with chlorinated oxidants, the active PA layer is degraded through a number of suggested reaction pathways including Nchlorination of amine groups and aromatic ring chlorination, which can be summarised as the weakening of PA intermolecular hydrogen bond interactions with the incorporation of chlorine [18,19]. In addition, limited evidence has also been presented that the supporting layers of the membrane were unaffected by moderate chlorine exposure [20].Another significant factor affecting membrane performance is the method used for storage and transportation.…”

“…However, radical chemical treatment on used RO membranes could facilitate conversion for additional applications. The effects of oxidative degradation and long-term chlorine exposure have been well documented [18,19], and the literature suggests that removing the active layer of a retired RO membrane via oxidative degradation has the potential to result in a separation device that has a similar physical structure to standard polyethersulfone (PES) UF membranes [28][29][30]. This technique of oxidative chemical treatment to remove the PA active layer of the RO membrane resulting in an UF membrane is referred to as membrane conversion.…”

Virus removal and integrity in aged RO membranes

“…Table S4 presents the average RMS (root-meansquare) roughness values from AFM images of the intact and aged membranes. ATR-FTIR spectroscopy is a technique widely used to investigate the chemistry change of the PA RO membrane surface induced by chlorine (Kwon and Leckie, 2006a;Tang et al, 2007;Kwon et al, 2008;Antony et al, 2010;Kim et al, 2010;Cran et al, 2011;Ettori et al, 2011;Do et al, 2012a;Gu et al, 2012;Donose et al, 2013). ATR-FTIR scans the membrane surface across several hundreds of nanometres at different IR frequencies and measures their absorbance (Tang et al, 2009).…”