What is Forward Osmosis ?
Forward Osmosis: Process, Principle & Benefits
Water scarcity due to the unavailability of pure drinking water is a pressing concern worldwide. Various technologies are used to overcome it, such as reverse osmosis, desalination, ion exchange, and advanced oxidation. The Forward osmosis process is a robust and promising technology capable of overcoming the limitations of conventional water treatment techniques. Although its roots go back to the 1970s, it's still being widely explored. Find out how it is a viable solution to obtain clear water for various purposes.
What Is Forward Osmosis?
Forward Osmosis (FO) is an osmotic membrane process. It uses a partially permeable membrane and the energy from osmotic pressure to separate water from the solutes mixed into the wastewater. The energy from this pressure carries water forward through the membrane and pushes the dissolved impurities or TDS (total dissolved solids) to the other side.
Forward osmosis is slightly different than RO as it does not use applied pressure to produce freshwater from dissolved particles and impurities. So, considerably less energy is used in FO than in RO. If the fed solution's salinity is higher, more pressure is required. As a result, in a forward osmosis system, high-pressure pumps and vessels capable of using massive energy are used.
Forward osmosis also occurs automatically and requires no additional hydraulic energy, unlike reverse osmosis. However, in this process, the draw solution is controlled for a specific amount and quality of concentration. Control over the draw solution ensures that unwanted dissolved solutes are avoided by trading water into it. This process has gained popularity in the last few years due to its list of advantages over reverse osmosis.
How Forward Osmosis Works?
To understand forward osmosis, you should first know what natural osmosis is. Osmosis is a biological process wherein water molecules automatically move from a solution where the concentration of dissolved components is low (low osmotic pressure) to a solution where the concentration of dissolved solids is high (high osmotic pressure). The movement takes place across a semipermeable membrane.
In an FO system, the role of the semipermeable membrane to separate water from dissolved solids is similar. The industrial feedwater flows on a particular part of the membrane. A solution with a higher dissolved salinity flows on the other side. The osmotic pressure is a result of the difference between the two sides. This makes water pass from the TDS solution through the system's membrane and into the draw solution. It has all the impurities that are in the feed stream.
Difference Between Forward Osmosis and Reverse Osmosis
The key difference between forward and reverse osmosis is how water is compelled to go through the membrane. Forward osmosis system leverages the natural osmotic pressure to force the flow of water via the membrane. Thus, feedwater passes through through it at a low pressure. In contrast, reverse osmosis does the opposite of natural osmosis through external pressure. The pressure given on the side of the membrane with a high concentration of impurities creates the osmotic potential to compel water through the membrane, which results in the separation of impurities like salt.
| Feature | Forward Osmosis (FO) | Reverse Osmosis (RO) |
|---|---|---|
| Driving Force | Utilizes natural osmotic pressure from a saline draw solution | Requires external hydraulic pressure to drive water through the membrane |
| Operating Pressure | Operates at low pressure, reducing energy costs | Operates at high pressure, increasing energy consumption |
| Fouling and Scaling | Lower risk of fouling and scaling due to low pressure | Higher risk of fouling and scaling, necessitating frequent maintenance |
| Membrane Sensitivity | Less sensitive to contaminants, allowing for longer lifespan | More sensitive to contaminants, leading to quicker degradation |
| Water Recovery Efficiency | Generally higher recovery rates in specific applications | Efficient but can be affected by fouling and scaling |
| Applications | Suitable for wastewater treatment, food processing, dewatering, and desalination | Commonly used for drinking water purification and seawater desalination |
| Salt Rejection | Moderate salt rejection; some reverse salt flux occurs | High salt rejection, effectively removing dissolved solids |
| Maintenance Requirements | Lower maintenance due to reduced fouling | Higher maintenance required due to frequent cleaning needs |
Advantages of Forward Osmosis
Forward osmosis uses low energy and operational pressure by using the natural osmosis process. This makes it ideal for dewatering feeds filled with fibers, sugars, and salts. It is a great energy-efficient alternative to costly pre-treatment systems in reverse osmosis plants. Some major benefits of forward osmosis are given below:
Energy Efficiency
Minimal energy is required to pump the solution with impurities through forward osmosis technology. The natural osmotic pressure drives wastewater across the membrane, so less external pressure is used. Moreover, novel FO technologies are designed for minimal or zero liquid discharge with reduced specific energy consumption. The energy consumption can be as low as 0.0285 kWh/m3 to produce diluted draw and concentrated feed solutions.
Moreover, the treated water from an FO plant is suitable to be reused for wash-downs, boiler feed and cooling tower feed makeup, irrigation, and dilution of other feed streams with high discharge limits.
Reduced Scaling and Fouling
The low energy required to force water passage removes the concern related to membrane scaling and fouling because fewer particles are deposited on the membrane's surface. The low hydraulic pressure and use of draw solution reverses membrane fouling while providing a high recovery rate. This is why FO is used to treat wastewater with high fouling potential, like municipal wastewater, gas and coal seam gas-produced water, and landfill leachate.
Preserves Color and Nutrients in Food Processing
Forward osmosis concentrates are better than concentrates left out by other methods because they are not restricted by the osmotic pressure of the concentrate. The concentrates of this process are similar to those produced by thermal evaporation, but there is no effect on the key flavor compounds. It also does not cause food browning, so the vibrancy, smell, taste, and texture of the original product stays intact.
Dewatering Water-Solvent Mixtures
FO is a low-energy solution for dewatering water-solvent mixtures, offering efficient separation with minimal membrane fouling. Economic extraction of ethanol from aqueous solutions in the food industry is a significant challenge. FO is capable of dewatering extracts in alcohol and maintaining or reducing it in the final product. Forward osmosis membranes have been shown to de-alcoholize a 12% v.v. synthetic ethanol solution. The membranes work optimally for dewatering water-solvent mixtures when they have an ethanol/water flux ratio.
Rely on AMPAC USA for the Best Forward Osmosis Technology
The global market for forward osmosis technology is projected to reach approximately USD 1.73 billion by 2030. In the upcoming years, technological advances will make it an integral part of other water treatment processes, such as RO and electrochemical methods. This will enhance the treatment efficiency of feedwater with high. As a large-scale manufacturer of water purification systems, AMPAC USA is at the forefront of forward osmosis technology. Our advanced FO membranes are capable of a higher rejection of contaminants through natural osmotic pressure. They also retain valuable compounds and have a low fouling propensity. Contact us to learn more about our systems.