The Fundamental Concept Behind Ultra-Pure Water Equipment used in Laboratories

Some advanced experiments such as animal and plant cell culture, high-performance liquid chromatography, mass spectrometry, plasma coupled spectroscopy, atomic fluorescence, gel analysis, cell immunity, in vitro fertilization, total organic carbon analysis, PCR experiments, organic compound analysis, trace element detection, two-dimensional electrophoresis, molecular biology experiments, genetic experiments, atomic absorption/emission spectroscopy, etc.

Figure 1 Ultrapure water in laboratories

These experiments have very demanding requirements for the quality of the water used. Not only is a specific level of resistivity required, but there are also requirements for the organic matter, particles, bacteria, and heat sources present in the water. An experimental pure water machine can meet these requirements.

In the future, there will be many experiments with high demands for water quality that will require further development of ultrapure water. Not only must the cost of producing water be reduced, but the requirements for the quality of the water produced must also become even more stringent. Only through continued development can the rapidly changing market demands be met. The market share of experimental pure water machines will continue to increase in the future, but there will be even higher demands for product quality and after-sales service in the industry.

Laboratory ultrapure water equipment has solved the complex problem of producing ultrapure water in laboratories. It is no longer necessary to rely on large-scale equipment to produce ultrapure water; it can be easily prepared using small-scale equipment, making the process simpler and more convenient.

The Working Principle of Pure Water and Ultrapure Water Machines

Laboratory pure water machines generally use advanced reverse osmosis technology to produce pure water. The working principle of a pure water machine is to apply a certain pressure to water so that water molecules and ionized mineral elements pass through the reverse osmosis membrane.

Figure 2 Working principle of reverse osmosis

The vast majority of inorganic salts (including heavy metals), organic matter, bacteria, viruses, and other substances dissolved in the water cannot pass through the reverse osmosis membrane. This strictly separates the permeated pure water from the concentrated water that cannot be permeated. The pore size on the reverse osmosis membrane is only 0.0001 micrometers, while the diameter of viruses is generally 0.02-0.4 micrometers, and the diameter of common bacteria is 0.4-1 micrometers. The water produced by the pure water machine meets drinking water standards.

Figure 3 Ion exchange, terminal treatment, RO technology

Ultrapure water machines add ion exchange and terminal treatment technology based on reverse osmosis technology. Some also have deep ion desalination, ultrafiltration, and UV photocatalytic oxidation equipment, and the water produced meets water quality requirements that are higher than the laboratory grade one water quality requirements of the national standard GB/T6682-2008.

Purification Process of Ultra-Pure Water Machine

Common impurities in natural water include soluble inorganic substances, organic matter, particulate matter, microorganisms, and soluble gasses. The goal of an ultra-pure water machine is to remove these impurities as thoroughly as possible.

Figure 4 Ultra-Pure Water Machine

Currently, common purification methods include:

  • Distillation
  • Reverse osmosis
  • Ion exchange
  • Filtration
  • Adsorption
  • Ultraviolet oxidation

The purification process of an ultra-pure water machine can generally be divided into four major steps:

  • Pre-treatment (primary purification)
  • Reverse osmosis (production of pure water)
  • Ion exchange (production of 18.2 MΩ.cm ultra-pure water)
  • Terminal treatment (production of ultra-pure water that meets specific requirements)

1. Pretreatment

Pretreatment water system flow chart

The water after pretreatment will undergo further purification through reverse osmosis, so it is necessary to remove impurities that may affect the reverse osmosis membrane as much as possible. This mainly includes large particles, residual chlorine, and calcium and magnesium ions. It should be noted that different pretreatment units must be equipped according to the differences in the quality of the incoming water.

Most manufacturers of pure water machines cannot help customers solve this problem well, which can lead to the inability to achieve ideal results in subsequent purification and shorten the service life of key components such as reverse osmosis membranes and ultra-purification columns.

To solve this problem well, precision filters, activated carbon adsorption filters, and softening resins are designed to selectively remove large particles, residual chlorine, and calcium and magnesium ions in water to achieve the best pretreatment effect. Timely replacement of pretreatment consumables (which are relatively low in price) is essential for the long-term stable operation of ultra-pure water machines and the protection of core components.

2. Reverse Osmosis

Figure 6 RO process

Reverse osmosis uses a high-pressure pump to provide pressure greater than the osmotic pressure of a high-concentration solution. Water molecules are forced through a semipermeable membrane to the low-concentration side. 

Reverse osmosis can filter out 99% of pollutants, including inorganic ions. Reverse osmosis is a very effective technology for water purification systems because it can remove most of the pollutants. Due to its outstanding purification efficiency, it is often used as a pretreatment method to significantly extend the life of ion exchange columns.

Given that reverse osmosis is a critical step in the water purification process and the cost of replacing reverse osmosis membranes is high, we recommend that users choose an ultra-pure water machine that has protective functions for reverse osmosis membranes.

Figure 7 Reverse osmosis membranes

To extend the service life of reverse osmosis membranes as much as possible and improve their filtration efficiency, NEWater uses unique technology and combines it with a leading reverse osmosis limiting design. At the outset, there is a flow restrictor to ensure that the reverse osmosis membrane is always immersed in water and does not dry out, thus affecting its lifespan. Extending the service life of the reverse osmosis membrane ensures water quality and also enhances the cost-effectiveness of the ultra-pure water system.

The quality of the reverse osmosis membrane has a significant impact on its service life and the service life of the ultra-purification column, so we recommend that users pay attention to the brand of reverse osmosis membranes, such as those from Dow and DuPont.

3. Ion Exchange

Figure 8 Ion exchange process

Ion exchange is the process of exchanging positive ions in water with H+ ions in an ion exchange resin, and exchanging negative ions in water with OH- ions in an ion exchange resin, to purify water.

Through ion exchange, theoretically, almost all ion substances can be removed, and the water resistivity resin reaches 18.2 MΩ·cm at 25℃. The quality of ion exchange resin and the efficiency of exchange between water and resin inside the exchange column mainly determine the water quality of the water after ion exchange.

Figure 9 Ion exchange resin

The quality of ion exchange resin directly affects the water quality and service life of the ultra-pure water machine, so we recommend that users pay attention to the brand of resin, such as Dow, Rohm, and Haas. Additionally, the amount of ion exchange resin filling is directly proportional to its service life.

4. Terminal Treatment

Figure 10 Terminal treatment process

This process mainly produces ultra-low organic, sterile, and heat-free ultra-pure water according to customers’ special requirements. There are various processing methods for different requirements, such as ultrafiltration for removing heat sources, dual-wavelength ultraviolet oxidation for reducing total organic carbon (TOC) in water, and microfiltration for removing bacteria.

Figure 11 Ultrafiltration membrane

Ultrafiltration (UF) membrane is a molecular sieve that separates different-sized molecules in a solution by allowing it to pass through an extremely fine filter membrane based on size. It can reduce the heat source content in ultra-pure water to below 0.001EU/ml. The dual-wavelength ultraviolet oxidation method can use photo-oxidation of organic compounds to reduce the total organic carbon concentration in ultrapure water to below 5 ppb.

The application scope of laboratory ultrapure water machines includes:

Figure 12 Laboratory ultrapure water machines applications

  • Hospitals
  • University research
  • Quality inspection units
  • Chemical plants
  • Pharmaceutical factories
  • Water quality monitoring centers
  • Water supply plants
  • Disease control centers
  • Battery factories
  • LCD screen factories
  • Precision circuit factories
  • Dust-free product production
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