End-of-life reverse osmosis membranes: Recycle procedure and its applications for the treatment of brackish and surface water

Abstract

As a result of population growth and potable water scarcity, an increasing number of reverse osmosis desalination plants are being installed and operated (more than 15,000 in the world). Reverse osmosis membranes tend to reach the end of the life cycle in around two to five years, becoming a solid waste. Recycling/repurposing these aged membranes could be a sustainable and profitable solution. This project aimed to transform end-of-life reverse osmosis membranes through the oxidation of their active layer using chlorine into nanoporous/microporous membranes, while searching possible applications for the resulting membranes. The results show that membranes oxidized at 10,000 ppm.h had a significant increase in permeability (3.1x), reaching NF-like capacity. On the other hand it was observed a decrease in the rejection of salt (4.35x) and acetaminophen (1.5x). Scanning Electron Microscopy (SEM) shows the positive effect of chlorine in the complete removal of particles deposited over the membrane. This oxidation condition also increased the average roughness (2.42x) of the membrane, as shown by Atomic Force Microscopy (AFM). Analysis by Fourier Transform Reflectance Spectroscopy (FTIR) suggests that chlorine oxidation replaced the hydrogen in the amide nitrogen. Both FTIR and SEM suggests the polyamide layer was not fully degraded. Application tests suggests that the recycled membrane can be used for the treatment of brackish and surface waters. The recycling of reverse osmosis membranes can be an alternative to simple landfill disposal, allowing owners to shift from disposal cost to revenue, as well as being a sustainable solution. The high permeability achieved on these oxidized membranes suggest many other NF/UF functions could potentially use recycled RO membranes.

Keywords

• reverse osmosis
• membrane recycling
• oxidation
• desalination
• membrane second life
• nanofiltration