Surface characterization of end-of-life reverse osmosis membranes from a full-scale advanced water reuse facility: Combined role of bioorganic materials and silicon on chemically irreversible fouling

Eight-year-old end-of-life reverse osmosis (RO) membranes from all three stages of a full-scale plant from the world's largest potable reuse facility were comprehensively characterized to discern the role of the co-existing foulants on performance decline and recovery by chemical cleaning. X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectra detected surficial silica foulants on all stages. High-resolution XPS and infrared spectra evidenced siloxanes among other forms of silicon foulants, which was confirmed by gas chromatography-mass spectrometry as cyclosiloxanes. Additionally, culturable bacteria were recovered, and other bioorganic foulants were identified by colorimetry, microscopy, and spectroscopy. Higher amounts of bioorganic foulants were measured in the first two stages, whereas silica fouling was more significant in the first-and third-stage elements. Chemical cleaning with either sodium tripolyphosphate - sodium dodecylbenzene-sulfonic acid mixture, sodium dodecyl sulfate - sodium hydroxide mixture, or hydrochloric acid did not completely restore membrane permeability demonstrating the need for membrane replacement. Siliceous fou-lants were most intractable to all chemical cleaning methods evaluated (including sodium hydroxide) and were the dominant cause of chemically-irreversible fouling leading to the membranes' end-of-life. Our results suggest that incorporating silicon pretreatment could improve RO performance and extend membrane life span during municipal potable reuse.

Automated summary

This study comprehensively characterizes the impact of co-existing foulants on the performance decline and recovery of eight-year-old reverse osmosis membranes. Silicon and bioorganic foulants were identified as the main causes of fouling. Chemical cleaning methods did not fully restore membrane permeability, indicating the need for membrane replacement. The study suggests that incorporating silicon pretreatment can improve reverse osmosis performance and extend membrane lifespan in municipal potable reuse.