p>With "primary water" we means those natural waters (rivers, lakes, sea or ground water), which contain, in addition to the natural components, also varying amounts of dissolved and/or suspended substances. In order to be used as water for human use or for industrial use (water technology), they must be undergone to treatments of mechanical, physical or chemical nature, to make them meet the requirements.
Here are some examples of treatments:
- Quartz filter (QF) or disc filter (DF), for the removal of suspended solids and turbidity;
- Softener (SF) to reduce the water hardness; this system can be replaced by a RO 1st stage, which, in addition to removing calcium and magnesium, also reduces TDS, silica and organic components;
- Ultrafiltrazione (UF) + RO 1° stadio (come addolcimento);
- Ultrafiltration (UF) + RO 1st stage (as softening);
- Decarbonantore (DT) per la rimozione dei bicarbonati;
- Iron removal (DF) for the removal of the iron;
- Sistemi di disinfezione tramite dosaggio chimico, ozono o UV;
- Decarbonated filter (DT) for the removal of bicarbonates;
- Activated Carbon Filter (CF), for the removal of chemical elements such as chlorine, solvents, oils, pesticides, etc;
- Disinfection systems through chemical dosing, ozone or UV;
- Demineralization mixed bed resins;
- Ultrafiltration (UF) + RO double pass (as demineralization);
- EDI (electrodeionization);
In particular, the latest solutions are used to produce ultrapure water, which contains only H20, ions H+ and OH- in equilibrium, and it is characterized by very low conductivity. The processes, required to obtain demineralized water, are:
- Chemical-physical (the so-called “calcium-sodium” treatment);
- Through selective extraction of the ions of the salts, (ion exchange filters, mixed bed);
Distillation is now used only in very specific areas (such as pharmaceuticals and other similar), given the high-energy cost required. In the other industrial areas, only the reverse osmosis or ion exchange resins are used.
Basing on the data obtained from existing plants, reverse osmosis is the cheaper solution and this is the reason why today the market no longer requires systems with resins exchange, but only the reverse osmosis.
With this technology, the water produced may reach a purity of up to 3-5 mg/l. To obtain higher quality water, with values less than 1 mg/l, up to 0,055 micro Siemens, it is necessary a double stage installation: a reverse osmosis system, and a subsequent EDI system (Electrodeionization) with ion exchange resins with mixed bed, regenerated by electric current, or in the traditional way with exchange resins regenerated with acid and soda.
In addition to savings of operating costs, the reverse osmosis allows to abolish the use of acid and soda, very dangerous products in their use, transport, handling and storage.