Reuse of Seawater RO Membranes as Brackish RO Membranes: A Sustainable Approach in Water Treatment

In the realm of water treatment, reverse osmosis (RO) is a widely adopted technology, particularly for seawater desalination and brackish water treatment. However, one of the major challenges the industry faces is the disposal of membranes after they have reached the end of their operational life for seawater desalination. As sustainability becomes more critical, exploring innovative ways to extend the life cycle of these membranes can significantly reduce environmental impact and costs.

The reuse of seawater reverse osmosis (SWRO) membranes as brackish water reverse osmosis (BWRO) membranes is an emerging strategy in water treatment that offers both economic and environmental benefits, aligning with sustainability goals. This approach takes advantage of the fact that many end-of-life (EoL) SWRO membranes, though no longer efficient for seawater desalination, still retain enough functionality to treat lower-salinity water such as brackish water. By repurposing these membranes, the water industry can reduce waste and prolong the lifespan of expensive RO materials, which is a critical consideration given the growing demand for fresh water and the environmental impacts of membrane disposal.

Technical Mechanism :

SWRO membranes are designed to operate at high pressures (typically 55 to 82 bar) to handle seawater salinity levels of around 35,000 ppm. Over time, these membranes may lose efficiency in salt rejection and permeate flux due to fouling, scaling, and general wear. However, brackish water, with much lower salinity levels (around 1,000 to 10,000 ppm), requires lower operational pressures (17 to 27 bar), which means that EoL SWRO membranes can still perform adequately under these less demanding conditions.

Several studies have demonstrated that used SWRO membranes can achieve a salt rejection rate of 84-92% when applied to brackish water applications. These results show that the membranes can still offer reliable performance, albeit with some reduction in efficiency compared to new membranes .

Advantages of Repurposing SWRO Membranes :

1. Cost Savings: Repurposing EoL SWRO membranes as BWRO membranes can lead to significant cost reductions. By extending their operational life, treatment plants can avoid the high capital expense associated with purchasing new membranes .

2. Reduction of Waste: Each year, over 840,000 end-of-life RO membranes are discarded globally. Repurposing them for brackish water treatment provides a sustainable alternative to landfill disposal, contributing to a circular economy in membrane usage .

3. Energy Efficiency: Since brackish water requires lower pressures, the repurposed SWRO membranes operate under less energy-intensive conditions, contributing to lower overall energy consumption for the water treatment plant. This efficiency is critical in reducing the carbon footprint of desalination processes .

Considerations and Challenges :

1. Membrane Performance: Before being repurposed, EoL SWRO membranes must undergo thorough performance assessments, including testing for salt rejection and permeability. Cleaning and chemical treatment are often necessary to remove fouling and restore the membrane’s functionality .

2. Fouling and Scaling: Although brackish water is less prone to severe scaling and fouling than seawater, some residual buildup from prior SWRO use may still affect membrane performance. Regular maintenance and proper pretreatment of the feed water are required to ensure optimal operation .

3. Pressure System Adjustments: Some adjustments to the existing brackish water treatment systems may be needed to accommodate the reused SWRO membranes, such as recalibrating the high-pressure pumps to work with membranes that have lower flux or slightly compromised salt rejection .

Future Prospects :

The concept of reusing RO membranes is gaining traction as part of a broader effort to enhance sustainability in the water treatment industry. Ongoing research is exploring ways to chemically rejuvenate or alter the surface properties of these membranes to further improve their efficiency in lower-pressure environments, such as brackish water treatment . This innovative approach could pave the way for the widespread adoption of membrane recycling technologies, reducing both environmental impact and operational costs in desalination plants worldwide.

By implementing these techniques, the water treatment industry can take a significant step towards a more sustainable future, while continuing to provide clean, safe water to growing populations.

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Ahmed Khaled

Certified Maintenance & Reliability Professional (CMRP)

Water and Wastewater Treatment Specialist