Forward Osmosis vs Reverse Osmosis – What’s the Difference?
Written by: Alexandra Uta // Last Updated: Jun 30, 2023
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As if reverse osmosis wasn’t tricky enough to get your head around, did you know there are other kinds of osmosis? Such as forward osmosis.
While it makes sense that reverse osmosis should have an opposite counterpart, what exactly is it? And what’s the difference between forward osmosis and reverse osmosis?
Let’s find out!
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Key Takeaways
- Forward osmosis uses osmotic pressure to move water through a membrane in order to extract it from a solution. One application of FO is in the beverage industry to concentrate fruit juices.
- Reverse osmosis uses external pressure in order to move water through a membrane and separate it from contaminants. It is used to produce highly pure water in applications like seawater desalination or home water purification.
Forward Osmosis vs Reverse Osmosis
So, forward osmosis vs reverse osmosis – here is everything you need to know:
In the world of osmosis, you have reverse, forward, and “traditional” osmosis.
- Traditional osmosis is a natural process. It happens all around us, such as when tree roots absorb water from the surrounding soil. Water flows from a low-concentrate solution (soil) to a high-concentrate solution (roots). Essentially, it tries to equalize both solute concentrations.
- Forward osmosis is an engineered process that uses a highly concentrated solution to move water through a membrane via osmotic pressure. Here, water also flows from a low-concentrate to a high-concentrate solution, only that the high side was artificially concentrated in order to increase osmotic pressure and make the process more effective.
- Reverse osmosis also uses pressure, but instead of pushing water from an area of lower concentration to one of a higher concentration like traditional osmosis does, reverse osmosis moves water in the opposite direction, from higher concentrations of dissolved solids to lower concentrations, with the assistance of external water pressure.
What Is Forward Osmosis and How Does It Work?
Forward osmosis (FO) is a process that separates water from dissolved substances by utilizing a semi-permeable membrane and the natural force of osmotic pressure. This pressure drives water through the membrane, leaving the dissolved particles behind.
In FO, dirty water flows on one side of a membrane, while another solution with more dissolved particles flows on the other side. The difference in the number of dissolved particles between the two sides creates a natural force called osmotic pressure, which causes the water to move from the dirty side through the membrane to the side with more dissolved particles, leaving the contaminants behind.
Applications
FO is used for a few kinds of industrial applications.
- Product concentration: Forward osmosis can be used to extract water from products with liquid to leave behind a more concentrated solution. This is often utilized in the food and beverage industry and does not remove tastes and aromas like other concentrating methods can, meaning it maintains its original flavor when reconstituted.
- Wastewater concentration: FO can be used as part of wastewater treatment to extract water and leave a concentrated waste product that is easy to dispose of.
- Extracting clean water for reuse: FO water recovered from industrial applications is of high quality and can be used for cooling, rinsing, irrigation, and drinking water.
What Is Reverse Osmosis and How Does It Work?
Reverse osmosis filtration refers to using a semipermeable membrane that separates pure water molecules from contaminants. Pressure forces water through this membrane, which allows only tiny molecules like H2O through and rejects larger ones. Those larger molecules are then flushed down the drain with the wastewater. Reverse osmosis can remove salt, bacteria, heavy metals and other contaminants from the water to make it almost pure.
The process is widely used in industries such as desalination but is also gaining popularity for home applications.
Applications
Reverse osmosis is primarily used for large-scale water desalination, home water purification (like removing harmful chemicals and other pollutants from drinking water) and wastewater treatment.
Reverse osmosis is employed in some food production industries, such as beer brewing and winemaking, to produce clean water needed for their processes.
What’s the Difference Between Forward Osmosis and Reverse Osmosis?
Forward osmosis and reverse osmosis are both water filtration methods, but they vary in their operation. Both utilize a semipermeable membrane, though, in reverse osmosis, water is forced through the membrane using external pressure, whereas, with forward osmosis, the water moves through the membrane based on natural osmotic pressure.
Pressure
As such, one difference between forward osmosis and reverse osmosis is that the latter requires external pressure. The former is based on naturally-occurring osmotic pressure.
Flow Direction
With reverse osmosis, water flows from the higher to the lower concentrated side. Forward osmosis is the exact opposite.
Scaling and Fouling
RO tends to have a higher rate of scaling and fouling than FO. Scaling is when the total dissolved solids or other particulates in the feed water stick to the surface of the membrane and clog the pores. Scaling and fouling can be cleaned with specific processes and chemicals, but FO doesn’t usually require this, meaning the maintenance could be reduced.
Energy Efficiency
A study looked at combining forward osmosis with reverse osmosis for desalination. Two different salts were tested as the solution. The performance of both FO and RO processes was compared, and the findings showed that RO alone used less power than the combined FO-RO process.
However, the difference in power consumption was small. The energy used by the FO process was only 2-4% of the total power used in the FO-RO process in this study. The gap in power consumption between the RO and FO-RO processes decreased when dealing with saltier seawater.
Benefits of Forward Osmosis
- Reduced membrane fouling and scaling: As FO is a more passive process, buildup on the membrane is not as common. This means the membrane is less sensitive to fouling, and the lifespan of the membrane is extended.
- Doesn’t rely on hydraulic pressure: For reverse osmosis to work effectively, the feed water pressure must sit within a certain range. This is not the case with FO, which uses natural osmotic pressure to function.
Further Reading:
Benefits of Reverse Osmosis
- Clean drinking water without contaminants: If you want to drink water without contaminants, reverse osmosis water is likely your best choice. It’s one of the most thoroughly filtered options on the market, with up to 99% fewer contaminants than regular tap water. Reverse osmosis water treatment can remove the following:
- Dirt and particles
- Disinfectants like chlorine and chloramine
- Volatile organic compounds
- Nitrites and nitrates
- Pesticides
- Herbicides
- Heavy metals
- Salts and minerals
- Microorganisms
- And more
- Improved water taste: RO water is exceptionally pure and tastes better than other water sources. This is because chemicals, such as chlorine, can significantly impact the taste and odor of water.
- Enhanced flavor of food: Water plays a significant role in your kitchen – from cooking to washing fruits and vegetables. The taste of your tap water can significantly influence the quality of your culinary creations, which is another reason to use reverse osmosis water.
- Enhanced hydration: Some individuals consume minimal water, opting for soft drinks and other less healthy options instead. If you’re one of them, a potential reason might be that you don’t enjoy the taste of your drinking water. Since reverse osmosis water typically tastes better than regular water, it might encourage you to drink more.
- Reduces the need for single-Use plastic bottles: Another great reason to consider reverse osmosis water. It’s available as needed and stored without single-use plastic. It also works out cheaper than bottled water in the long run, and in a lot of cases, it is actually safer than bottled water.
If you have any questions about the difference between forward osmosis and reverse osmosis please don’t hesitate to leave a comment below!
About the Author Alexandra Uta
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