Reverse Osmosis vs Nanofiltration, What is The Difference?

When selecting filtration technologies and purchasing water filters, have you ever wondered about the differences between reverse osmosis and nanofiltration? How do you choose between them? Keep reading to find the answers in this article.

What are Reverse Osmosis and Nanofiltration?

Reverse Osmosis

Reverse Osmosis (RO) process is a technology that produces purified water by applying high pressure to force water through a reverse osmosis membrane. The working principle involves using a high-pressure pump to apply pressure (usually around 4 MPa) greater than the osmotic pressure to pre-treated feed water, causing water molecules to pass through the semi-permeable reverse osmosis membrane against the natural direction of osmosis.

The pores size of the RO membrane are extremely small, with a precision of up to 0.0001 microns, effectively removing 99% of dissolved salts, heavy metals, microorganisms, suspended particles, and other impurities from the water. Due to the selective permeability of the semi-permeable membrane, only water molecules are allowed to pass through, while impurities are retained on one side of the membrane and highly concentrated as wastewater. The other side produces high-purity RO water.

NF vs RO

Nanofiltration

The nanofiltration (NF) system removes contaminants using the charge adsorption and selective permeability of the nanofiltration membrane. Its working principle is similar to that of the RO system, requiring external pressure and using a semi-permeable membrane for selective permeability. However, the filtration precision of nanofiltration membranes is 0.001 microns, and the operating pressure required for the NF process is lower than that of RO, typically ranging from 0.5 to 2.5 MPa.

Nanofiltration technology can remove some of the substances that RO can remove, but the difference lies in the fact that a small amount of divalent ions (such as calcium and magnesium) and monovalent ions (such as sodium and potassium) will pass through the semi-permeable membrane along with the water molecules. Therefore, the purified water treated by nanofiltration contains trace elements and minerals.

What are the Pros and Cons of the Two?

Reverse Osmosis Pros: RO technology is highly regarded for its exceptional filtration precision, capable of removing a wider range of impurities. The maturity of reverse osmosis process ensures stable water quality, making it an ideal choice for producing high-quality, drinkable purified water. This makes RO water widely used in various fields, particularly in industries with high water purity requirements such as the electronics industry, industrial processes, laboratories, household water supply, seawater desalination, and the food processing industry.

For example, in the semiconductor electronics industry, RO water can be used for cleaning and other processes in the production, reducing the impact of impurities in the water and ensuring the quality and performance of the chips. High-purity RO water used as boiler feedwater can effectively prevent scaling and corrosion, thereby improving equipment operational efficiency and extending its lifespan.

Cons: However, the reverse osmosis process also has some disadvantages. The price of equipment and reverse osmosis membrane materials is typically higher than that of nanofiltration systems, and pretreatment of feed water is required before entering the system.

The complexity of the system means higher initial investments are needed during setup. Operating RO systems require higher operational pressures to overcome osmotic pressure, resulting in significantly increased energy consumption. Compared with nanofiltration systems, reverse osmosis systems have higher electricity prices for processing a certain amount of water per hour.

Additionally, RO systems require regular maintenance and cleaning. Apart from costly maintenance expenses, a notable drawback of reverse osmosis process is their recovery rate, which typically ranges from 50% to 75%. This means that for every unit of pure water produced, nearly one unit of wastewater is generated.

­čöŚRead this article to learn more about the pros and cons of reverse osmosis water.

Nanofiltration system Advantages: Compared to RO filters, nanofiltration water filters are relatively simpler with lower overall investment and operational costs. NF can produce high-quality purified water at a more economical price, making it highly suitable for water treatment projects with limited budgets.

Principles of membrane filtration

Due to its unique filtration precision and low energy consumption, nanofiltration technology is widely used in bottled water production, food and beverage processing, electroplating wastewater treatment, agricultural irrigation, landfill leachate treatment, and softening of drinking water.

Disadvantages: However, nanofiltration filters are not suitable for industries that do not require minerals and trace elements. As a membrane treatment technology, nanofiltration systems are prone to membrane fouling and contamination. Therefore, regular maintenance is required, including frequent cleaning and replacement of NF membranes, to ensure extended lifespan and stable water production quality. Additionally, improper handling of nanofiltration systems used for wastewater treatment may pose risks of secondary pollution.

Reverse Osmosis or Nanofiltration?

When selecting a filtration system, it is advisable to conduct a detailed water quality analysis first to understand common parameters such as TDS (Total Dissolved Solids), heavy metals, suspended solids, and organic compounds in the incoming water.

Additionally, clearly defining the desired water quality standards and intended use scenarios is crucial. Based on the types of contaminants to be removed, concentration requirements, water production needs, and project budget, suitable pretreatment processes and filtration system configurations can be chosen.

If your water quality requirements are not particularly stringent and focus mainly on removing large particles, colloids, bacteria, viruses, and some dissolved substances, nanofiltration is a good choice. However, if you need to achieve high purity water standards and remove specific substances such as heavy metals, minerals, and most dissolved salts, it is recommended to choose a reverse osmosis (RO) system.

For ultra-pure water needs in demanding fields like laboratories and pharmaceuticals, consider adding EDI (Electrodeionization) equipment to an RO system or using a combination of secondary reverse osmosis filters and deionization filters.

Therefore, ensuring clarity on the water quality requirements for the produced water is crucial. If you still feel uncertain or need further advice, please consult our experts, and we will tailor the most suitable solution for you.

Faqs:

Nanofiltration vs Ultrafiltration vs MF vs Reverse Osmosis

Microfiltration, ultrafiltration, nanofiltration, and reverse osmosis are all membrane filtration-based water treatment technologies. In terms of filtration precision, reverse osmosis > nanofiltration > ultrafiltration > microfiltration. Microfiltration and ultrafiltration do not require external pressure, making them simpler to operate, while NF consumes less energy compared to RO. Below is a visual comparison among them:

Nanofiltration vs Ultrafiltration vs MF vs Reverse Osmosis

What is the Difference Between Sand Filter and Membrane Filter?

Membrane filtration and sand filtration are two common water treatment technologies.

Membrane filters are based on membrane-based physical filtration techniques, suitable for treating pre-treated water  that have already removed most of the sediment, colloids, suspended solids, viruses, and residual chlorine. Semi-permeable membranes with different pore sizes can remove harmful substances from water to varying degrees. Membrane filters generally have higher costs and operational maintenance requirements.

Sand filters are also a type of physical filtration technology. By utilizing multiple layers of sand with different particle sizes (such as quartz sand, silica sand, or silicon sand), they can effectively remove larger particles, suspended solids, colloids, and odors from water. The water quality after sand filtration is generally lower and is often used as pretreatment for membrane filtration systems to protect the membranes from damage. Additionally, sand filters are suitable for treating tap water and well water, producing water for basic domestic uses like garden irrigation, but are not recommended for direct drinking.

When selecting the appropriate water treatment method, consider the quality of the raw water, the intended use of the treated water, and economic cost considerations.

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