What is Reverse Osmosis？

Reverse Osmosis (RO) technology is widely regarded as one of the most efficient water filtration methods, providing clean, great-tasting drinking water. RO systems are widely used in a variety of applications, including whole-house water use, tap terminals, the restaurant industry, and aquariums.

 

Reverse Osmosis (RO) technology is widely regarded as one of the most efficient water filtration methods, providing clean, great-tasting drinking water. RO systems are widely used in a variety of applications, including whole-house water use, tap terminals, the restaurant industry, and aquariums. No matter what aspect of water quality you are concerned about, there is always an RO system that can meet your needs.

What Is Osmosis?

Remember high school biology? Osmosis is when water moves from a less concentrated solution to a more concentrated one through a semi-permeable membrane. It’s how plants drink through their roots.

What Makes It Reverse?

Now flip that idea. Reverse osmosis pushes water from a more concentrated solution to a less concentrated one using pressure. The key? That semi-permeable membrane that acts like a microscopic bouncer—letting in only the clean Hâ‚‚O and blocking out everything else.

What Contaminants Can Reverse Osmosis (RO) Remove?

Reverse Osmosis (RO) is one of the most effective water purification methods available. It can remove a wide range of contaminants, including:

1. Dissolved Salts and Minerals

• Sodium

• Chloride

• Calcium

• Magnesium

• Sulfates

2. Heavy Metals

• Lead

• Arsenic

• Mercury

• Cadmium

• Chromium

3. Organic Contaminants

• Pesticides

• Herbicides

• Volatile Organic Compounds (VOCs)

• Industrial solvents

4. Microorganisms

• Bacteria (e.g., E. coli)

• Viruses

• Protozoa
  Note: While RO membranes can block many microorganisms, RO is often combined with UV or other disinfection systems for complete microbial control.

5. Chemical Contaminants

• Fluoride

• Nitrates & Nitrites

• Chlorine & Chloramine

• PFAS (in some advanced systems)

6. Aesthetic Impurities

• Bad taste

• Odors

• Cloudiness (turbidity)

RO membranes are rated to remove up to 95%–99% of total dissolved solids (TDS), making RO systems highly effective for delivering clean, safe, and great-tasting water.

How Does Reverse Osmosis Work?

Reverse Osmosis (RO) is a water filtration process that uses a semi-permeable membrane to remove unwanted substances from water. Here's a detailed breakdown of how it works:

1. Pre-Filter Stage
Before the water reaches the RO membrane, it passes through a pre-filter. This stage typically involves carbon or sediment filters that remove large particles like dirt, sand, chlorine, and other sediments. This step ensures that the RO membrane stays clean and free from larger impurities that could cause damage or clogging.

2. Water Pressure
To initiate the RO process, the water needs to be pressurized. A pump applies pressure to the incoming water, which forces it through the semi-permeable RO membrane. The pressure must be strong enough to overcome the natural osmotic pressure of the water, pushing the molecules through the membrane.

3. The Semi-Permeable Membrane
The core of the reverse osmosis system is the semi-permeable membrane. This membrane has incredibly tiny pores—around 0.0001 microns in diameter—that allow only water molecules to pass through while blocking larger molecules like salts, chemicals, bacteria, and other contaminants. This selective permeability ensures that only pure water is allowed to pass, while the contaminants are filtered out.

4. Separation of Contaminants
As the pressurized water moves through the RO membrane, the clean water molecules pass through, while the contaminants (including salts, metals, and other harmful substances) are left behind. The membrane essentially separates pure water from the impurities.

5. Post-Filtration
After the water has passed through the RO membrane, it may go through an additional post-filter (typically a carbon filter) to further polish the water. This step helps remove any remaining odors, tastes, or chemicals that might still be present, ensuring the water tastes clean and fresh.

6. Storage Tank
The purified water is stored in a tank for later use. The water is now free from contaminants and is ready for consumption or other applications.

7. Waste Water (Concentrate)
The contaminants that are left behind by the RO membrane are flushed away as waste water or concentrate. This is usually sent to a drain. On average, for every gallon of purified water, 3 to 4 gallons of waste water may be produced, depending on the efficiency of the RO system.

Benefits of Drinking RO Water

Why should you consider installing a reverse osmosis (RO) system? Let's take a deeper look into the key advantages of choosing RO filtration:

Superior Purity

RO systems can remove up to 99% of dissolved salts, particles, colloids, organic substances, bacteria, and pathogens from water. This significantly reduces the presence of harmful contaminants, thereby lowering the risk of health issues caused by these pollutants.

Better Taste

By eliminating impurities like chlorine and sediments, RO water offers a cleaner, fresher taste compared to tap water. However, it’s worth noting that the removal of minerals can alter the taste. To ensure the best overall drinking experience, it’s recommended to use a water filtration system that combines reverse osmosis with mineral additives.

Cost-Effectiveness

Investing in an RO system can save you money in the long run, especially when compared to buying bottled water. It provides a reliable and affordable source of healthy water at a fraction of the cost of bottled alternatives.

Health Benefits

RO water helps reduce the risk of consuming harmful contaminants, improving your overall health by providing clean, purified water free from harmful substances.

Sustainability

Drinking RO water can help reduce your reliance on plastic water bottles. Over time, this contributes significantly to lowering plastic waste and pollution, promoting environmental sustainability.

Versatility

RO systems are suitable for both residential and commercial use, ensuring clean water for drinking, cooking, and any other water-related needs.

RO System Performance and Design Calculations

When designing or evaluating a Reverse Osmosis (RO) system, it’s crucial to understand the factors that influence its performance. Proper calculations ensure the system functions efficiently, providing the desired level of purification while minimizing waste and operating costs. Below are some key performance aspects and design calculations involved in setting up an RO system.

1. Membrane Flux Rate

The flux rate is the amount of water that passes through the RO membrane per unit area. It is typically expressed in gallons per square foot per day (GFD) or liters per square meter per day (LMH). The flux rate depends on several factors:

• Water quality: Higher levels of contaminants lead to lower flux rates.
• Pressure applied: The more pressure applied, the higher the flux rate.
• Temperature: Warmer water usually results in better flow rates due to lower viscosity.

2. Recovery Rate

The recovery rate refers to the percentage of feed water that is converted into permeate (treated water) after passing through the RO system. It is essential to balance the recovery rate to avoid excessive brine (wastewater). A typical recovery rate for a residential RO system is 40-60%, while commercial systems can vary depending on the design.

Recovery Rate Formula:

Recovery Rate (%) = (Permeate Flow / Feed Flow) × 100

For example, if the feed water flow rate is 100 liters per hour and the permeate flow rate is 50 liters per hour, the recovery rate would be 50%.

3. Salt Rejection Rate

The salt rejection rate (or percentage of contaminants removed) indicates the efficiency of the RO membrane. A higher salt rejection rate means the system is better at removing dissolved salts, chemicals, and other impurities. High-quality RO membranes can reject up to 99% of contaminants, while some systems may have a slightly lower rejection rate.

Salt Rejection Formula:

Salt Rejection (%) = ((Concentration_feed - Concentration_permeate) / Concentration_feed) × 100

If the feed water has a salt concentration of 500 mg/L and the permeate concentration is 5 mg/L, the salt rejection rate would be:

Salt Rejection = ((500 - 5) / 500) × 100 = 99%

4. Pressure and Flow Rate Requirements

The pressure required to drive water through the RO membrane is a key factor in system performance. Typically, the feed water pressure should be between 40-100 psi (pounds per square inch) for residential systems and can go higher for industrial or commercial systems. Insufficient pressure will reduce the water flow and efficiency of the system.

The flow rate is determined based on the system’s size and application. For example:

• Residential RO system: Usually provides a flow rate of 2-10 gallons per day (GPD).
• Commercial RO system: Can produce anywhere from 1,000 to 10,000 gallons per day.

5. Recovery vs. Wastewater (Concentrate)

As the RO process separates pure water from contaminants, the remaining concentrated wastewater must be discharged. Balancing recovery and wastewater production is essential for an efficient system. Higher recovery rates generally result in more wastewater, which may require special management or disposal solutions.

6. Pre-Treatment Considerations

Proper pre-treatment of feed water is vital for optimal RO performance. Common pre-treatment options include:

• Sediment filtration: Removes large particles that could clog the RO membrane.
• Activated carbon filtration: Reduces chlorine and organic compounds that can damage the RO membrane.
• Softening: Removes hard water minerals like calcium and magnesium that could cause scaling on the membrane.

7. Post-Treatment

After the water passes through the RO membrane, post-treatment steps such as UV sterilization or additional carbon filtration may be required to remove any remaining microorganisms or improve taste and odor.

8. Membrane Cleaning

Over time, RO membranes can become fouled or clogged with contaminants, reducing their effectiveness. Regular cleaning using specialized chemicals helps maintain optimal performance and extends the lifespan of the membrane.

9. System Size and Scaling

To calculate the size of an RO system, it's important to consider the total water demand (per day or per hour) and the required permeate flow rate. You also need to factor in the expected TDS (Total Dissolved Solids) level of the feed water, as systems designed for high TDS water will need more energy and possibly larger membranes.

Sizing Calculation Example:

If the daily water requirement is 1,000 liters and the desired permeate flow rate is 75%, the required feed water flow rate would be:

Feed Flow = Required Permeate Flow / Recovery Rate = 1,000 / 0.75 = 1,333.33 liters per day