Population growth, climate change, drought, etc. are increasingly necessitating reclamation of municipal wastewater to meet our drinking water demands. Reverse osmosis (RO) is universally employed as the final filtration step during potable water reuse. However, fouling (or clogging) of these membranes is a serious operational issue that is countered by periodic chemical regeneration to restore permeability. Importantly, long-term exposure to foulants and chemical cleaning agents diminshes membrane performance; a phenomenon termed as ageing. The primary objective of this research is to quantify the ageing kinetics of a polymeric thin-film composite RO membrane (ESPA2, Hydranautics) donated by Orange County Water District California. Virgin and fouled membranes are being repeatedly exposed to sodium tripolyphosphate + Na-dodecylbenzene sulfonic acid (STPP), a common cleaning solution. Ageing is being evaluated in terms of changes in (i) water permeability, (ii) NaCl rejection, (iii) surface zeta potential, and (iv) organic functionalities via attenuated total reflectance – Fourier transform infrared spectroscopy after 1, 3, 5, and 10 cleaning cycles. The water flux across the virgin membrane and after 1-cleaning cycle was statistically indistinguishable (46 L/m2/h at 150 psig pressure). However, after 3 exposures to STPP, the flux increased by ~15% to 54 L/m2/h indicating degradation of the polyamide layer. Preliminary FTIR spectra of virgin, fouled, and cleaned membranes (Figure 1) show the loss of intensity of many peaks (e.g. 1151, 1170, 1245 cm-1, etc.) from the polysulfone support layer and its incomplete recovery after 1 cycle of STPP cleaning. Interestingly, amide I and II peaks were prominent in the virgin membrane but were highly attenuated after only 1 cleaning cycle. The zeta potential of membrane surfaces also changed upon cleaning (Figure 2), which will be discussed in more detail in the poster.

Impacts of cleaning agents and fouling on ageing of reverse osmosis membranes employed for potable water reuse

255th National Meeting (2018)

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