Unveiling the presence of toxic transformation products and microfibers on end-of-life RO membranes

Point-of-use (PoU) drinking water treatment systems using reverse osmosis (RO) are becoming increasingly popular. Over time, the membrane cartridges in these systems accumulate a concentrated layer of contaminants on their surfaces. This study focuses on analysing this fouling layer by performing autopsies on spent membrane cartridges from PoU units. Four used RO membranes were collected from rural and urban locations in Kerala, India. Two of these membranes treated groundwater in rural areas, while the other two were supplied by municipal water and groundwater in urban settings. The foulants desorbed from the membrane surfaces were analysed using a combination of spectroscopic, microscopic, and chromatographic methods. Non-target analysis (NTA) revealed the presence of micropollutants, including herbicides, personal care products, and pharmaceuticals. Toxic transformation products of diuron, namely 3,4-dichloroaniline and 3,4-dichlorophenyl-N-methylurea, were also detected. Raman spectroscopy identified polyethylene terephthalate (PET) and cotton microfibers, while inorganic foulants such as calcium, iron, silicon, and aluminium were also found. Infrared spectra confirmed that the membranes were composed of polypropylene, polysulfone, and polyurethane. Improper disposal of these end-of-life membranes risks reintroducing these contaminants into the environment. • End-of-life PoU membranes are substrates containing toxic substances. • Toxic transformation products of diuron (3,4-dichloroaniline and 3,4-dichlorophenyl-N-methylurea) were identified. • PET microfiber was identified on the membrane surface. • Thrown-away membrane can reintroduce toxic substances into the environment.