Ultra Pure Water Device

What is an ultrapure water manufacturing device?

The system, which includes A/C filter, Ion-Exchange filter, and 0.2µm Final filter, produces 18.3M³ of ultra-pure water treated through the DI (Deionized) and RO system.

When ultra-pure water is produced too slowly, it often cannot supply the necessary amount when needed. To address this, a certain amount of ultra-pure water is produced in advance and stored so that it can be used when necessary. However, problems may occur when water is stored for too long in the tank, as the ultra-pure water can dissolve ions from the inert materials (like Teflon) or plastic present in the storage tank. This causes the water’s quality to degrade, and organic matter can also mix into the stored water.

To prevent contamination, it is common to circulate stored ultra-pure water continuously in order to maintain its purity. Some ultra-pure water tanks even have ultraviolet lamps installed to prevent bacterial growth, but bacteria can still multiply within the tank or pipes.

In semiconductor factories, where ultra-pure water must be produced at a precise schedule, it is common to produce ultra-pure water using tanks. It is crucial to have systems that prevent ion leakage from the tank walls and constantly supply pure water.

The ultra-pure water used in laboratories is the most common type. In laboratories, ultra-pure water is produced using mixed-bed cartridges that remove ions from the water. If bacteria are included in the system, a biofilm forms, which contaminates the water. This ultra-pure water is called ELGA in some parts of the world, and this term is widely used globally in laboratories and research centers.

How does ion exchange work?

Ion exchange replaces the ions in the water supply with H+ ions, and cations with OH- ions. Ion exchange resin is made up of tiny porous particles that allow water to pass through while retaining ions. Over time, as the water passes through the resin, the active H+ ions attached to the resin are gradually replaced with other ions, and when this happens, the resin must be regenerated or replaced.

What are the advantages of ion exchange?

Ion exchange offers many advantages compared to other purification methods.

  1. It can produce the required level of purity:
    Ion exchange is capable of producing very high-purity water.

  2. Effective at removing all ions:
    By using both cation and anion exchange resins, the system can effectively remove all ionic impurities in the water, maintaining ultra-pure water quality up to 18.2 MW·cm (at 25°C).

  3. Efficiency and minimal loss of water:
    The small residual components in the resin can be efficiently flushed out, preventing them from leaking into the treated water. For applications requiring ultra-high-purity water, the resin needs to be periodically replaced or regenerated.

However, if bacteria multiply rapidly in the treated water, the resin can become contaminated and must be replaced if it cannot be reused.

Challenges with ion exchange:

The key issue with ion exchange is that the resin needs to be regularly regenerated or replaced to maintain optimal performance. In some cases, chemical agents are used for this process, or the resin is regenerated by backwashing with a special solution to prevent contamination.

Additionally, ion exchange resin tends to degrade when it absorbs non-ionic organic materials, which can impact the performance of the system. In certain cases, reverse osmosis systems are used before ion exchange to extend the resin’s lifespan and improve water quality.

To combat the limitations of ion exchange, many advanced methods have been developed. Some use a mix of different types of resins, and others use hybrid methods to increase efficiency. However, if not properly maintained, ion exchange systems can become ineffective, and installing new systems requires careful consideration to ensure they can produce the required water quality efficiently.

Electrodeionization

Electrodeionization (EDI) is a water purification method that uses electricity to remove ions, combining ion exchange resins and selective ion membranes. EDI is often used alongside reverse osmosis (RO) as a useful alternative to other purification methods. It offers the advantage of not requiring ion exchange resins to be regenerated using chemicals like in conventional systems. This method not only avoids the need for frequent resin replacement but also eliminates the issue of resin degradation over time.

How does Electrodeionization work?

EDI was developed from the principle of electrodialysis (ED). EDI’s principle is based on ion-selective membranes: cations pass through one membrane, and anions pass through another, driven by an electric current. The current separates the charged ions from the water. As a result, the ions are removed, and the water passing through the membrane becomes deionized.

In comparison to traditional ion exchange methods that use resin regeneration, EDI continuously removes ions without requiring external regeneration chemicals. This leads to consistent production of high-purity water.

In fact, EDI systems can be very useful in achieving high levels of water purity, as they are effective even in environments where lower conductivity (200 µS/cm or more) is difficult to achieve with conventional methods.

By using the conductive flow produced between the ion exchange membranes, EDI systems can continuously remove cations and anions, producing a high-purity, low-conductivity output stream. This constant removal of ions ensures that the water remains pure and free of contaminants over time. One advantage of EDI is that it doesn’t require the periodic replacement or recharging of resins, as the system regenerates itself as part of its regular operation. The ions removed from the water are continuously flushed out of the system, and this process reduces maintenance costs and downtime.

Some EDI systems use mixed ion exchange resins to increase the efficiency of the process. These are often used in pharmaceutical or specialized water purification processes. The ELGA® module or Vivendi Water system are examples of systems that use advanced EDI technologies to achieve the highest levels of water purity, often used in critical applications requiring ultra-pure water.

Additional Information

The ELGA® module, developed by ADEPT (Advanced Deionization by Electric Purification Technology), extends the lifespan of the resin by using advanced regeneration techniques. This innovation allows ions like sodium or bicarbonates to be more efficiently captured, extending the operational time of the system. This method is more eco-friendly and reduces the need for chemical regeneration processes, which are common in traditional systems.

Reverse Osmosis

Reverse Osmosis (RO) is a purification technology that supplements the shortcomings of ion exchange purification methods.

In order to operate reverse osmosis effectively, high pressure must be applied. When water is naturally divided by osmosis, water moves from low-concentration solutions to high-concentration ones. However, reverse osmosis works in the opposite way—water is forced from the high-concentration side to the low-concentration side by applying pressure, which separates the water from dissolved substances.

With high-pressure water flow, the process prevents dissolved particles from passing through the membrane, resulting in clean water passing through the membrane and leaving contaminants behind. If sufficient pressure is applied, the concentrated contaminants stay on one side while clean water, or permeate, flows through. This principle is also known as hyper-filtration.

In practice, the water supply is pumped through hollow fiber sets or spiral wound membranes using pressure. The clean water, called permeate, passes through the membrane, while the contaminants are trapped on the other side as a concentrate and are flushed out of the system. High-performance thin-film composite (TFC) membranes made of polyamide are commonly used in place of older cellulose membranes. These membranes can remove 95-98% of all dissolved solids and are effective at filtering organic compounds with molecular weights over 100. However, they do not remove all dissolved gases.

TFC membranes are used in all reverse osmosis systems manufactured by ELGA.

Due to their high filtration efficiency, RO systems are commonly used in ultrapure water systems, providing the best results in terms of ion removal efficiency. However, they are generally slower in production rate, so they are often used alongside ion exchange systems to protect against bacteria and pyrogen (toxins) and to further improve water quality.

Adsorption Media

Activated carbon, made from coconut shells or other carbon sources, is processed by heating to create a highly porous structure. Activated carbon is commonly used to remove chlorine and other organic contaminants from water. In water purification, activated carbon is used to prevent membrane fouling and protect the RO membrane. The TFC (thin-film composite) membranes are susceptible to damage from free chlorine, which can also affect the removal efficiency of organic compounds.

Activated carbon filters are often used in the pretreatment stage of water purification systems, providing essential protection before the water enters more sensitive ion exchange or reverse osmosis systems.

In addition to activated carbon, other adsorption media are used in purification processes. ELGA uses a variety of other adsorbents as well. These include adsorbers that remove specific ions, such as heavy metals, as well as acidic gases and organic substances. The adsorption media traps harmful substances that may not be removed by reverse osmosis alone.

Microporous Filtration

Microporous filtration membranes are used to filter out particles and microorganisms larger than 0.1 µm. Many ELGA systems use ultra-micro filters that filter as finely as 0.05 µm. Most of these particles are slightly negatively charged colloids (measured by zeta potential), and microporous filters can retain them on the surface of the membrane through the size and charge of the pores. The filters can capture much smaller natural colloids on the surface, preventing them from passing through. Absolute pore size (0.2 µm) micro-filters are widely used in ultrapure water systems. These micro-filters remove debris and contaminants that may form in the deionized water storage tanks, including tiny carbon particles from organic adsorption cartridges.

Sub-micron filters below 1 µm are often installed at the point where the water is dispensed (e.g., a dispenser), ensuring that the water used is filtered right before it is consumed. These sub-micron filters act as the final filtration step.

Another approach is using sub-micron filters in a recirculation loop within the ultrapure water system, which continuously removes bacteria from the water. In cases where very high levels of purity are required, these sub-micron filters are installed at the point of use to prevent bacteria from entering the system downstream.

Microporous membranes should also be considered essential elements in systems where UF (ultrafiltration) is not used, especially in ultrapure water production systems.

Water Purification Method

Photo-oxidation

Photo-oxidation uses high-intensity ultraviolet (UV) light to destroy bacteria and other microorganisms and oxidize all organic compounds into simpler forms, which are later removed by ion exchange resins. UV light with a wavelength of 254 nm is most effective for disinfection, while shorter wavelength UV light, such as 185 nm, is highly effective in oxidizing organic compounds.

Ultra-Pure Water Purification Method

Distillation is the oldest method for purifying water by boiling it and then condensing the steam into a collection container. Although distillation equipment is relatively inexpensive, it consumes a lot of energy.

Typically, it takes about 1 kW of electricity to purify 12 liters of water. Depending on the design of the distillation system, the efficiency may vary, but the usual production level is about 1 MW·cm of purity. However, after the water is stored, its quality degrades if the storage tank is not well-maintained, and the water will lose its purity.

Moreover, volatile compounds, such as carbon dioxide, silica, ammonia, and various organic substances, are often carried along with the steam, lowering the purity of the distilled water.

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