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Pure water equipment
In many industrial processes, water purer than potable water is required. Particularly in the semi-conductor and pharmaceutical processes, a great amount of ultra-pure water is required. The higher degree of precision and safety required in the process, the higher level of purity is required. As far as the pure water quality is concerned, the degree of purity and requirements of water quality in each process also vary. Among which, the water treatment technical units that are commonly used include the techniques such as, pre-treatment (e.g. coagulation, floating removal), ion exchange, reverse osmosis, electrodialysis with ion exchange, degassing, ultra-filtration, UV disinfection and UV/ozonation. Different combinations of the techniques will result in different water quality control and management characteristics.
Pre-treatment system
The main purpose of the pre-treatment system is to remove SS and TOC in the original water to ensure effective operation of the RO or ion exchange equipment in the later section. For example, if the turbidity of original water is below Level 1~3, first conduct the coagulation treatment by adding 10~20mg/l of PAC before filtration. There are quite a few examples of coagulation separation, activated carbon absorption, biodegradation, UF membrane separation. The filtration method after coagulation includes pressurized floating removal, MF or UF membrane.
Pre-treatment section (activated carbon absorption)
The purpose of the pure water system is to remove salts, organic substances, dissolved oxygen and micro-particles in water. It is often used with the RO and ion exchange equipment for treatment.
RO membrane
The removal rate of salts for the RO membrane can be up to 99% or more. Its removal rates of TOC and micro-particles are also high. Good and stable quality of water can be obtained under continuous operation. However, if the salt concentration in the original water is high, treated water may not meet the requirement of water quality. At neutral pH, the removal rate of weak acid ions such as, fluoric acid, carbonate, etc. are very low, and further treatment with the non-regenerative ion exchange equipment is required.
Ion exchange system
The ion exchange system is to replace each kind of anions and cations in water by the cation-anion exchange resin. An ion exchange positive-bed system, ion exchange negative-bed system and ion exchange mixed-bed (double bed) system can be formed with a different proportion of cations and anions. However, the mixed bed (double bed) system is often used in the RO treatment, and is widely used for industrial pure water treatment in electronics, power pure-water, chemical-engineering, electroplating pure water, boiler water supply and pure water for medicines.
With the ion exchange method, cations and anions in water can be removed. If we take sodium chloride (NaCl) for example as the inorganic salt in water, the basic reaction of desalting in water can be expressed as the following reaction formula:
| 1. | Cation exchange resin: R-H+Na+→ R-Na++H+ |
| 2. | Anion exchange resin: R-OH+Cl- → R-Cl+OH- The total reaction formula for the cation and anion exchange resin can be expressed as follows: RH + ROH + NaCl——R-Na++RCl-+H2O NaCl in water is replaced by H+ and OH- contained in resin and resulting in only H2O, achieving the desalting purpose in water. |
