Regeneration, modification and stabilization of spent reverse osmosis membranes for their reuse

Abstract

Unlike 8-in. reverse osmosis elements, which are operated in different water treatment systems under controlled conditions and can often be regenerated through established protocols, small residential and commercial reverse osmosis membranes typically function with limited automation and monitoring, have much shorter lifespans of only 6–12 months, and are replaced rather than regenerated in different water treatment systems. Consequently, they generate a disproportionately high volume of plastic waste yet remain largely unexplored in regeneration studies. This paper investigates the four-stage regeneration process (alkaline and acidic cleaning, oxidative modification and stabilization) of spent residential and commercial reverse osmosis membranes, using a household membrane type as the test model. Following sequential alkaline and acidic regeneration, the membrane salt rejection was increased from 92 % to 95 % along with significant increase in membrane permeability. To ensure microbiological safety and achieve complete removal of residual biofouling from the membrane surface, an oxidative modification step using sodium hypochlorite was introduced. At an oxidant dosage of 30,000 ppm·h, a significant increase in membrane permeability was observed, accompanied by a reduction in salt rejection to 30 %, highlighting the need for subsequent membrane stabilization. Further stabilization was carried out using a 0.5 % sodium metabisulfite solution with a 24-h contact time, resulting in improved salt rejection from 30 % to 50 %. SEM and FTIR analyses confirmed structural integrity of the flatsheet, while the pore radius of the stabilized membrane was estimated to range from 4.03 Å to 4.80 Å, demonstrating that the pore radius remains largely unaffected during regeneration process. Quantum-chemical modeling was performed on selected model organic pollutants to calculate reactivity indices and assess their potential interactions with the regenerated polyamide membrane surface. These results demonstrate that regenerated residential and commercial RO membranes can be effectively repurposed for the growing segment of decentralized wastewater treatment systems, including households, hospitality, and healthcare facilities, where short service lifetimes currently generate significant plastic waste. By extending membrane usability and tailoring rejection performance, this approach offers both environmental benefits and practical opportunities for sustainable water reuse in the rapidly developing decentralized treatment market.