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Demineralized water is produced using various technical processes, usually via ion exchange or reverse osmosis or a combination of the two techniques. The so-called water demineralization usually means a degree of purity in the form of conductance at 25°C between 1 and 50 µS/cm. At even higher purities, we no longer speak of demineralization but of pure water (Pure Water, up to 0.1 µS/cm) or ultra pure water (Ultra Pure Water, up to 0.056 µS/cm).
Technically, the production of demineralized water in the industry is implemented by:
- A demineralization cartridge to be regenerated externally with typically 30L – 1000L mixed bed resin, i.e. a flow rate between 1 – 25 m³/h with a capacity of 2 – 60 m³ (with city water of approx. 500 µS/cm)
- A demineralization system with up to 20 m³/h that can be regenerated on site. However, it should be noted that an additional wastewater treatment plant is required.
- A reverse osmosis system industry up to 20 m³/h in various designs, e.g. a permeate-staged reverse osmosis system, i.e. 2 reverse osmosis systems in series to achieve an even better conductance, or a concentrate-staged reverse osmosis system, i.e. 2 reverse osmosis systems in series to keep the amount of wastewater lower.
The main differences between the demineralization techniques used to produce demineralized water are as follows:
- Produce demineralization cartridge for demineralized water:
In the simplest application, demineralized water is produced using a demineralization cartridge. This contains a mixed bed ion exchanger, i.e. an ion exchanger consisting of a strongly acidic cation exchanger and a strongly basic anion exchanger. This combination removes ionogenic substances within the capacity of the demineralization cartridge up to a conductivity value of < 1 µS/cm. The ion exchangers used are then regenerated externally in a central regeneration plant. However, if the volume of demineralized water exceeds around 4 m³/week, the process is often no longer economical and it may make more sense to use a different treatment technology. - Demineralization system for producing demineralized water
Instead, either a self-regenerating demineralization system or a reverse osmosis system is available. Both processes have their advantages and disadvantages and can be adapted to the respective application, if necessary with further purification stages. The self-regenerating demineralization system is usually regenerated with hydrochloric acid and caustic soda. This means that chemicals are required on site and the wastewater produced must at least be neutralized in a wastewater treatment plant. If more than 10 m³/week of wastewater is produced from the process water treatment, the system is also subject to approval. In addition, the operational wastewater, i.e. the wastewater from the process to which the water from the demineralization is fed, is also subject to approval, but from the very first liter. - Reverse osmosis system for producing demineralized water
Although the reverse osmosis system does not require chemicals such as hydrochloric acid and caustic soda, it does require at least table salt or a temporary hardness stabilizer instead and constantly generates waste water during operation, the so-called concentrate, i.e. the city water “thickened” by an ingredient ratio of around 2-5:1. Although there are technical options for recirculating the concentrate to reduce the amount of wastewater in the reverse osmosis system, there is still a constant consumption of resources during operation of the reverse osmosis system.
Here you will find an example of a comparative cost calculation between the demineralization system and the reverse osmosis system. The demineralized water that is produced with a demineralization system differs from that of a reverse osmosis system, even if it has the same conductivity. These differences are due to the different active principles of the processes and are essentially limited to the anions, depending on the pre-treatment in the reverse osmosis system.
If further requirements are placed on the demineralized water in addition to the conductivity, further purification or a combination of the two techniques may be necessary, e.g. softening, reverse osmosis system, 2nd reverse osmosis system, membrane degasser, electrodeionization (EDI) and subsequent demineralization cartridge (mixed bed polisher) as shown.
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