How does a reverse osmosis plant work?

Reverse osmosis is a Water Filtration technology that uses a thin, semi-permeable membrane with tiny pores that allow pure water to pass through while blocking larger molecules. So how exactly does a reverse osmosis device work? And what's the science behind it?

About Reverse Osmosis Plant Membrane

The reverse osmosis system is built around the membrane, the core of which is a spirally wound semipermeable material membrane with diameters of 2 inches, 4 inches, and 8 inches. The 4-inch and 8-inch membranes are commonly used in the Water Treatment industry, and the standard length is 40 inches to facilitate the interchange of membranes from different manufacturers. The membrane surface area is 350-450 square feet. The semipermeable membrane was originally made of cellulose acetate (CA), and later the industry mainly turned to thin film composite materials (TFC) and placed on a solid substrate. Currently, TFC membranes are the main type used.

What is the scientific principle behind reverse osmosis plant?

The principle of reverse osmosis is to apply an external pressure that exceeds the osmotic pressure of the solution on the concentrated solution side, forcing water molecules to flow through the semipermeable membrane in the opposite direction, from the concentrated solution side to the dilute solution side, thereby achieving the separation of water and impurities. The key to this process is the selective permeability of the semipermeable membrane - it only allows water molecules to pass through, while impurities such as dissolved salts (such as sodium chloride), colloids, organic matter, bacteria, viruses, etc. are intercepted, and finally high-purity fresh water is produced.

How does XJY's reverse osmosis plant work?

1. Pretreatment stage: the first critical step

Raw water (such as tap water, groundwater or surface water) usually contains impurities such as suspended matter, colloids, organic matter, microorganisms and dissolved ions. If it enters the reverse osmosis membrane directly, it will cause membrane pollution or blockage. 

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● Mechanical filtration: Use a quartz sand filter to remove suspended matter, silt and other particulate impurities with a particle size greater than 5 microns to make the water initially clear. 

● Adsorption purification: Use an activated carbon filter to adsorb organic matter, residual chlorine, pigments and odors in the water.

● Anti-scaling treatment: Add antiscaling agents (such as polyphosphates) to inhibit the scaling of calcium and magnesium ions in the water on the membrane surface (such as the formation of calcium carbonate and calcium sulfate precipitation) to extend the service life of the membrane. 

● Precision filtration: Use a 5-micron precision security filter to intercept fine particles remaining in the pretreatment stage.

2. Membrane separation stage: core desalination process

The pretreated water enters the reverse osmosis membrane assembly. The reverse osmosis membrane is a rolled composite membrane, consisting of an ultra-thin desalination layer, a porous support layer and a protective layer, with a desalination rate of more than 97%.

● High-pressure drive: The high-pressure pump increases the water pressure to 1.0-1.5MPa, forcing water molecules to penetrate the membrane pores, while salt and impurities are retained.

● Water flow distribution: Water is divided into two streams on the membrane surface - about 75% of pure water (product water) passes through the membrane into the product water side, and the remaining 25% of concentrated water (containing high-concentration impurities) is discharged along the membrane surface to form concentrated water runoff.

● Operation control: The inlet water temperature (20-25℃ is the best, and the water output increases by 3% for every 1℃ increase in temperature) and pH value (polyamide membrane is suitable for pH 4-11) need to be strictly controlled to avoid degradation of membrane performance.

3. Post-treatment stage: optimize water quality on demand

Depending on the purpose, the produced water needs further treatment:

● Drinking water scenario: disinfect with ultraviolet light to inactivate residual bacteria and viruses.

● Industrial water scenario: For example, the electronics industry requires ultrapure water, which needs to be combined with electrodeionization (EDI) technology to further remove trace ions; boiler water needs to adjust the pH value to prevent equipment corrosion. 

4. Brine management: balance between environmental protection and efficiency

Due to the high salt content of brine produced during the reverse osmosis process (usually 3-5 times that of raw water), modern equipment is often equipped with a brine recovery system:

● Partial return: return brine to the pretreatment stage for backwashing of sand filters to improve water utilization (recovery rate can reach 75%-85%).

● Salt concentration: through multi-stage reverse osmosis, brine is further treated to achieve zero discharge or salt recovery (such as brackish water desalination projects). 

What contaminants can reverse osmosis palnt remove from water?

Arsenic, barium, calcium, chlorine, colloids, dyes, fluoride, herbicides, mercury, nickel, nitrates, proteins, pesticides, phosphates, precipitation, sodium, sulfates, volatile organic compounds, etc.

Some reverse osmosis systems can also remove organic contaminants from water, such as certain viruses and bacteria, although they may not remove 100% of these contaminants.

Benefits of reverse osmosis

●  Reduced total dissolved solids

●  Economical and efficient

●  Low energy consumption and environmentally friendly

●  Removes alkalinity and hardness

Reliable XJY Reverse Osmosis Plant

If you need a proven, reliable, economical and environmentally friendly water treatment solution, XJY is your trusted supplier of reverse osmosis systems. We provide free quotes and 24/7 support, and are happy to provide you with consultation to meet your unique industrial water purification needs.

For more information about reverse osmosis, please contact  “Cliff Mok”  Water Treatment Experts.

Contact us:

Name: Cliff Mok

Mobile phone: +86 17817887719