Plasma activated water (PAW)
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Plasma activated water (PAW) is water that has been exposed to a plasma (see wikiarticle on cold plasma). In the cold plasma, radicals are present. These radicals produce other active species in water (nitrite, nitrate, hydrogen peroxide etc). These give plasma activated water a high degree of reactivity. Plasma activated water contains radicals, which are oxidizing agents, and has pH 2-3. When the plasma activated water is stored, the pH increases to 3-4 and the antibacterial effect is mostly lost. This loss of antibacterial effect takes about 7 days. The nitrite and nitrate components of the possibly present active components remain stable for the longest time.
The antibacterial effect is caused by very low pH, nitrite, nitrate, hydrogen peroxide plus other components.
Some suppliers call their product plasma activated water, but it is actually a combination of plasma treated electrolyzed water. This produces two streams: high pH and low pH stream. Benefits of the high pH water are similar to those ascribed to high-pH electrolyzed water.
A cold plasma is generated and directed on a water reservoir or water film. This can be done both in batch and in continuous systems.
Pros and cons
- No storage of chlorine compounds necessary
- Very low pH (2-3), causing corrosion and oxidation
- Limited shelf life (up to 1 week)
- Activity against microorganisms is decreased when organic matter is present
- Contact time is relative long (several minutes)
www. Plasmawater.org (systems for wastewater and drinking water disinfection), with capacity of 28-85 m3/hr for clean water.
Specific capital expenses for drinking water purification are 250 USD per 1000 litre per day.