Ozone properties:

Ozone (O3) is an allotrope of oxygen (O2) and a strong oxidant and disinfectant. Ozone is composed of three oxygen atoms forming an isosceles triangle with a density of 2.144 kg/m3. Its solubility in water is more than 10 times that of oxygen. Ozone has a strong oxidizing ability, with an oxidation-reduction potential of 2.08 V, much higher than the commonly used disinfectant liquid chlorine in water plants (with an oxidation-reduction potential of 1.36 V).

Working principle

After ozone is added to water, its reaction with organic matter is divided into direct reaction and indirect reaction.

Direct reaction: Ozone directly oxidizes organic matter in water, which is selective and has a slower reaction rate;

Indirect reaction: Ozone oxidizes organic compounds through · OH radicals formed in water, which is non selective and has a fast reaction rate.

The main functions of ozone in water purification processes are pre oxidation and post oxidation.

Pre oxidation process:

In the pre oxidation process, the main function of ozone is to remove odor, taste, color, iron, manganese, heavy metals, and algae, stabilize colloidal particles in water, improve flocculation effect, reduce the dosage of coagulants, and remove the parent substances of THM and other three pathogenic substances, reducing the content of three pathogenic substances in water. It can oxidize large molecular organic matter into small molecular organic matter, and oxidize inorganic substances such as cyanide, carbide, and nitrate.

The amount of ozone added for pre ozone contact oxidation is very small, usually 0.5-1.5 mg/L. And the reaction time is short, usually 2-4 minutes, the reaction rate is fast, and the residual ozone in the water is generally zero or very little.

The treated water in the pre ozone contact oxidation system is usually raw water, which contains a certain amount of impurities. Therefore, its diffusion device can prevent blockage by impurities in the raw water, and generally uses a static mixer or jet diffuser. The static mixer requires a water head of 0.5~1m, so it is suitable for situations where there is surplus water head in the raw water. The jet diffuser does not consume the head of the raw water, but it requires additional power equipment to improve the transfer efficiency of ozone by mixing a small amount of raw water (1.2-1.6 m3/kgO3) with ozone.

The pre ozone contact oxidation system generally has one injection point at the front end of each process line, and the effective water depth is generally 6 meters.

Post oxidation process:

In the post oxidation process, ozone is generally used in combination with activated carbon, and its main functions are to kill bacteria and viruses; Oxidation of organic compounds, such as insecticides, cleaning agents, phenols, etc; Remove COD; Oxidative decomposition chelates, such as EDTA and NTA.

The reaction rate of post ozone contact oxidation is slow, and the reaction time is generally not less than 10 minutes. The ozone dosage is generally 1.5-2.5 mg/L, and the residual ozone in water is 0.2-0.4 mg/L. The effective water depth is also 6 meters.

The treated water in the post ozone contact oxidation system is generally sand filtered water, with clear water quality and no impurities. Therefore, its diffusion device generally uses microporous gas caps (discs). Micro porous cloth gas cap (disc) does not consume power, is inexpensive, and has high ozone transfer efficiency.

The post ozone contact oxidation system generally has 2-3 injection points per process line.

When using 2-point dosing, the proportion of ozone dosing at each point along the water flow direction is 80%~50% and 20%~50% of the total dosing amount, respectively; The contact time of two ozone injection points is 50% of the total time.

When using 3-point dosing, the proportion of ozone dosing at each point along the water flow direction is 80%~40%, 10%~30%, and 10%~30% of the total dosing amount, respectively; The contact time of three ozone injection points is 30%, 30%, and 40% of the total time in the direction of water flow.