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A second life for membranes

Reverse osmosis (RO) is the most employed technology for water desalination. However, membrane fouling is inevitable and one of the main reasons for a regular membrane replacement. Due to the continuous growth of this technology, end-of-life RO membrane management has created an economic and environmental concern. Therefore, alternative management routes need to be faced by the industry and academia. 

The study of the direct recycling process as a feasible alternative to produce nanofiltration (NF) and ultrafiltration (UF) recycled membranes has been the subject of the doctoral thesis of Raquel García Pacheco, researcher in the Membrane Technology Group from IMDEA Water and participant in the LIFE-TRANSFOMEM project. The Doctoral Thesis, “Nanofiltration and ultrafiltration membranes from end-of-life reverse osmosis membranes. A study of recycling”, was directed by Dr. Eloy García and Dr. Junkal Landaburu and defended on May 11 at the University of Alcalá.

In this study membrane fouling was characterized through thermo-gravimetric, spectrometric and microbiological techniques.

In the study at laboratory scale, the effect of exposure time, pH solution and membrane storage (dry and wet) on the recycling process, were investigated.

The impact created on the membranes was evaluated in terms of permeability and rejection coefficients, during brackish water treatment.

The results were compared with several pristine commercial membranes (RO, NF and UF) obtaining in the recycled membrane performance values within the range values observed using comercial nanofiltration membrane models. Moreover, membranes exposed to high exposure level were also compared to a commercial UF membrane. Recycled membranes showed rejection coefficients similar or higher than the commercial one, when treating urban wastewater.

The recycling process at pilot scale required analogous exposure doses (ppm·h) to those used at laboratory scale. At both scales, membrane scaling affected significantly the recycling process.

This study demonstrates that direct passive recycling could be a feasible alternative that can further boost the RO membrane technology towards circular economy approach.