Water pH changing under ozonation investigation

Ozonation is known as one of the most effective water purification methods that removes different water pollutants, disinfects and decontaminates water. In the present paper results of pH changing for different objects ozonation investigation are represented. Ozonation of several objects was investigated: distilled water, deionized water, tap water, river water, different inorganic salts model water solutions. The authors have shown that after a 30-minute ozone-air treatment of the investigated objects pH decreases down to 1-2. It was pointed out that at the beginning of the ozonation process the nature of the pH change is different for distilled, deionized, river water and for tap water. In case of tap water pH changes slowly in the first 10 minutes, and pH sharp change takes place later than during other samples ozonation. To find out the reasons of pH changing the concentration of dissolved ozone during ozonation was investigated. For this dissolved ozone concentration measurements were carried out simultaneously with pH measurements of the probes. It was shown that O3 concentration in water under ozonation increases systematically regardless of pH changing. Dissolved ozone concentration increase is a result of high O3 molecule stability in comparison with its low stability under basic pH. To find out the reason for different pH change nature for different water types the influence of some metal salts presence in the water on pH decreasing under ozonation was studied. It was found out that there is no pH decreasing at the presence of such salts as calcium carbonate, magnesium carbonate, iron sulfate and manganese sulfate. Thus, water hardness salts present in tap water do not influence the processes in water under ozonation that lead to pH decreasing. Some assumptions about the reasons of water acidification during ozonation were expressed. Firstly, gaseous mixture brings huge amount of CO₂ to the water treated. It can lead to the increase of carbonate and hydro-carbonate ions concentration in water. According to literature data that could significantly decrease water pH. On the other hand, the authors point out the possibility of nitric acid formation in water during ozonation with using air as the initial gas. In this case nitrogen can react with ozone to form nitrogen oxides up to N₂O₅, which dissolves in water with HNO₃ formation.

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