The Operation Principle of Ozone Disinfection

The Operation Principle of Ozone Disinfection

Ozone is a very strong oxidant and virucide. Ozone (O3) is produced when oxygen (O2) molecules are dissociated by an energy source into oxygen atoms and these subsequently collide with other oxygen molecules. Most wastewater treatment plants generate ozone by imposing a high voltage alternating current across a dielectric discharge gap that contains an oxygen-bearing gas. Ozone is generated onsite because it is unstable and decomposes to elemental oxygen in a short amount of time after generation.

Ozone decomposes spontaneously in water by a complex mechanism and generates hydroxyl (OH- ) and hydroperoxide (HO2) free radicals, which also have a great oxidizing capacity. Hence, ozone can react by either or both modes in an aqueous solution: direct oxidation of compounds by molecular ozone, or oxidation of compounds by the free radicals produced during the decomposition of ozone. It is generally believed that the bacteria are destroyed because of protoplasmic oxidation resulting in cell wall disintegration (cell lysis).

The effectiveness of ozone disinfection depends on the susceptibility of the target organisms, the contact time, and ozone concentration. Since ozone has limited solubility and decomposes rapidly in water, the ozone contactor must be well covered to ensure the ozone diffuses into the wastewater as effectively as possible.

The advantages of ozonation systems include the following: few safety problems associated with transportation and storage (onsite generation); more effective than chlorine in destroying viruses and bacteria; short contact time; less observed dependency on pH and temperature; no harmful residuals need to be removed after ozonation because ozone decomposes rapidly; ozonation elevates the dissolved oxygen concentration of the effluent; wastewater quality improvements (including effluent color, odor, and turbidity).

On the other hand, some of the disadvantages of ozone disinfection are: low dosage may not effectively inactivate some viruses, spores, and cysts; it is a complex technology, requiring complicated equipment and efficient contacting systems; ozone is very reactive and corrosive, thus requiring corrosion-resistant materials; it is not economical for wastewater with high levels of suspended solids, biochemical oxygen demand, chemical oxygen demand, or total organic carbon; the cost is generally high in comparison with other disinfection techniques.