Treating Saltwater Intrusion with Reverse Osmosis Systems

Saltwater is getting into freshwater supplies in many coastal areas, making drinking water and irrigation water too salty to use. One of the best ways to remove salt from water is by using reverse osmosis (RO). This process filters out salt and other contaminants, making water safe for drinking, farming, and industry. However, to get the best results, an RO system needs to be properly chosen, optimised, and maintained. This articles explains how to choose the right RO system, improve its efficiency, and ensure overall longevity.

• Choosing the Right Reverse Osmosis System
• Optimising Reverse Osmosis System Operation
• Keeping Your Reverse Osmosis System Working
• Conclusion

Choosing the Right Reverse Osmosis System

A reverse osmosis system works best when it is matched to the specific conditions of the water it treats. That means understanding the quality of your water, the amount of water you need, and what additional treatments may be required.

1. Check the Water Quality

Before selecting an RO system, you need to know what’s in your water because different impurities require different filtration methods.

✔️ Salt Levels (Total Dissolved Solids - TDS):

• If your water has low to moderate salt levels (1,000 - 5,000 mg/L TDS), a brackish water RO system (BWRO) is sufficient.
• If the water has very high salt levels (over 35,000 mg/L TDS), a seawater RO system (SWRO) is needed, which operates at a higher pressure.

✔️ Other Contaminants:

• Iron & Manganese: These metals can clog RO membranes, so a pre-treatment system (such as oxidation and filtration) is needed before RO.
• Sediments & Particles: If the water contains dirt, sand, or algae, a sediment filter must be used before RO to prevent clogging.
• Chlorine & Organic Compounds: RO membranes are sensitive to chlorine, which can damage them over time. A carbon filter is required to remove chlorine beforehand.
• Bacteria & Viruses: While RO can remove many microorganisms, if the water is heavily contaminated, additional UV sterilisation or chlorination may be required.

✔️ Water Temperature and pH Levels:

• RO membranes work best at moderate temperatures. If the water is too hot or too cold, adjustments may be needed.
• Extreme pH levels can also damage membranes, so pH adjustment may be necessary.

2. Make Sure the System Meets Your Needs

The best RO system is one that fits your daily water demand and can operate efficiently over time. More energy is required to produce more water so optimising will save you money.

✔️ Daily Water Demand:

• Small systems can handle 90-100 liters per hour, while large systems can produce thousands of liters per hour.
• If an RO system is too small, it will be overworked and wear out quickly. If it’s too large, it wastes energy.

✔️ Water Recovery Rate:

• RO systems typically recover 15-50% of the water while rejecting the rest as brine. A more efficient system wastes less water.
• Some systems use advanced energy recovery devices to reduce water waste and improve efficiency.

✔️ Backup & Redundancy:

• If a system is critical for drinking water, having spare membranes and backup power sources (such as solar or generators) ensures continuous operation.

Optimising Reverse Osmosis System Operation

Reverse osmosis systems can last many years if properly maintained. The key to longevity is keeping the membranes clean, using energy wisely, and managing waste properly.

1. Protect the RO Membranes

The RO membranes are the most important part of the system, but they can become clogged, scaled, or damaged if not protected.

✔️ Use Pre-Filters:

• Sediment and dirt can clog RO membranes, reducing efficiency. A pre-filter (5-10 micron) removes large particles before they reach the RO unit.

✔️ Prevent Scaling with Anti-Scalant Chemicals:

• Hard water minerals like calcium and magnesium form scale that clogs the membrane. An anti-scalant chemical or a water softener can prevent this buildup.

✔️ Remove Chlorine with a Carbon Filter:

• RO membranes are sensitive to chlorine, which can degrade them quickly. A carbon pre-filter removes chlorine before it reaches the membrane.

✔️ Flush the System Regularly:

• Over time, minerals and contaminants build up in the membrane. Flushing with clean water keeps the system running efficiently.

2. Reduce Energy Use

RO systems require high pressure to push water through membranes, which can lead to high energy costs. However, efficiency upgrades can save money and extend the system’s lifespan.

✔️ Use Energy Recovery Devices (ERDs):

• ERDs recycle energy from the brine stream, reducing power use by up to 60%, making them ideal for large-scale desalination.

✔️ Install Variable Speed Pumps:

• Instead of running at full speed all the time, these pumps adjust power based on demand, reducing wear and tear.

✔️ Consider Solar Power:

• In off-grid or coastal locations, solar-powered RO systems can reduce operational costs and increase sustainability.

3. Manage Brine Waste Properly

RO systems produce brine, a concentrated salty wastewater that must be disposed of carefully to avoid harming the environment.

✔️ Evaporation Ponds:

• Letting water evaporate naturally leaves behind solid salt, which can be collected and disposed of.

✔️ Deep Well Injection:

• In some areas, brine is injected into deep underground wells where it won’t affect freshwater supplies.

✔️ Dilution with Seawater:

• In coastal areas, controlled mixing with seawater reduces environmental impact.

✔️ Use Brine for Salt-Tolerant Crops or Aquaculture:

• Some plants and fish species thrive in slightly salty water, making use of brine for agriculture or fish farming.

Keeping Your Reverse Osmosis System Working

Reverse osmosis systems must be regularly maintained to keep them running. The situation may also change over the years meaning a flexible solution should be considered from the start.

1. Maintaining Your System

Preventative maintenance is essential for keeping an RO system in top condition.

✔️ Clean the Membranes Regularly:

• Scaling and biological buildup reduce efficiency, so membranes should be cleaned every 6-12 months or as needed.

✔️ Replace Filters on Time:

• Pre-filters should be changed every 3-6 months.
• RO membranes last 1-3 years, depending on water quality.

✔️ Monitor Pressure and Water Flow:

• A drop in pressure can signal a clogged filter, while a sudden pressure increase could indicate scaling.

✔️ Use Remote Monitoring Systems:

• Smart RO systems can track performance and send alerts for maintenance needs.

2. Preparing for the Future

As climate change makes saltwater intrusion worse, RO systems must be designed to adapt and remain sustainable.

✔️ Use a Modular Design:

• If water demand increases, the system should be easily upgradable with more membranes or pumps.

✔️ Ensure Compatibility with Renewable Energy:

• Solar and wind power can reduce costs and carbon footprint.

✔️ Have Emergency Water Storage:

• Backup water tanks provide security in case of power failures or maintenance downtime.

Conclusion

A reliable reverse osmosis (RO) system is crucial for ensuring safe drinking water in coastal communities facing saltwater intrusion, particularly following natural disasters or ongoing climate change impacts. By carefully selecting an RO system tailored to specific water quality, usage demands, and local conditions, communities can greatly enhance water security and sustainability.

To optimise performance and longevity, systems must be well-maintained, incorporating preventative measures like regular membrane cleaning, efficient pre-treatment, and energy-saving technologies such as Energy Recovery Devices (ERDs) and variable-speed pumps. Smart, remote monitoring further ensures the system operates reliably, providing early warnings for maintenance requirements.

Companies like LEDI offer innovative solutions such as Aquagen Troop and Garrison water purification systems, which integrate robust, flexible, and energy-efficient designs. These solutions make RO desalination accessible and reliable, helping communities to secure their potable and non-potable water needs efficiently and sustainably, even in challenging conditions.