January 2012 Archives

Furthermore, the Ultra-filtration using lifelike semi-permeable membrane and reverse osmosis methods becoming available enabled separation of colloids and ions from water.

[Fig.1] Shows the principle of reverse osmosis.

When pure water and salt water placed in a tank divided with a semi-permeable membrane (a membrane with extremely fine size holes on the surface), the pure water permeates the membrane and enters the salt water side of the tank, diluting the salt water. This is called Osmosis. The energy for this is called Osmotic Pressure, and depends on the concentration of the salt water. If the diameter of the membrane's holes is larger than the diameter of the salt molecules, the salt will migrate to the pure water side until both tanks are of the equal concentration level. This would be called Divergence.

As shown in [Fig.1] above, pressurizing the salt water using a membrane with very fine holes, only the water of the salt water solution migrates to the water side. This is called Reverse Osmosis. In actual application, a tubular formed semi-permeable membrane (for improved pressure resistance) is used. Filtered water and concentrated water are obtained when precision filtered water is pump pressurized and sent through the tube.

[Fig.3] shows a water purification system with a reverse osmosis module integrated

Manufacturing of the ultra pure water such as: electrical resistance 18MΩ•cm, particulates (>0.2μm) 20 or less, viable bacteria 0.2/mL or less has been made possible by the advent of new technologies such as reverse osmosis, ultrafiltration, electro dialysis, and ion exchange method, along the traditional filtering systems.

[Fig.1] below shows the filtering particle diameter limits of various filter methods.

Filtering with wire mesh and filter cloth have been in traditional use for Sake and soy sauce. This method applies a pressure on the liquid contacting the membrane to cause a pressure difference on each side of the membrane to cause a separation between the material able/unable to pass through the membrane, and is called "Filtering". The membrane used is called "Filter material". The filtering limits of this method using filter cloth is approx. 10μm of solids. The advent of micro-filters using ultra fine fiber material has enabled filtering to 0.1μm.

By using further fine filtering grids such as Cellophane membrane, it became possible to separate colloids. This type of separation method is able to filter bacteria, proteins and colloids, smaller than the normal particles and is called Ultrafiltration method.

With the immergence of semi-permeable lifelike membrane and reverse osmosis methods, high molecular particles and ions are able to be seprated.

[Fig.2] shows the principle of Ultrafiltration
Small sized molecules such as water can pass the membrane, but the larger ones such as colloids and proteins cannot.

The quality of water used for metal cleaning processes is extremely important. The level of cleanliness required will differ depending on the applications and purposes of the subject products to be cleaned. For products requiring precision cleaning such as electronic equipment, optical components and semiconductors, any impurities, however minute in quantity within the cleaning water will affect the product accuracies and yield, so the water must be of in extremely high purity. This is called "Ultra Pure Water". An example of such water is of quality: Electrical resistivity 18MΩ•cm, Particulate count (>0.2μm) 20/mL or less, Viable bacteria 0.2/mL or less.

Ultra pure water production system is shown in [Fig.1] below.

Firstly, the source water from wells and city tap is filtered to remove the relatively larger particles, then pumped to a reverse osmosis system where ions are removed and loads on the ion exchange tower are reduced, as well as other soluble organic compounds. Then the air removal system removes carbon dioxide. The mixed bed deionizer, an ion exchange tower raises the water's electrical resistance up to the standard value. The pure de-ionized water obtained here is sent to the primary pure water tank, ultraviolet germicide system, polisher (resin ion exchange tower) to remove remaining minute amounts of ions, ultra-filtration system to remove submicron particulates, then supplied to the use point (where the water is actually used).

The ultra pure water, as produced as such, stored in air can be contaminated with carbon dioxide and oxygen as well as various germs. The basic rule is to use the water on-line and not store, but for unavoidable cases where storage is necessary such as for the primary pure water storage tanks, ultraviolet germicide lamps are used for sterilization and nitrogen gas is used to isolate the water from the air.