Ozonation in Water Treatment

Ozone was first used in water treatment in the late 1800s and ozone is more widely used in Europe and Asia than the United States.

Ozone is an unstable gas consisting of three oxygen atoms (O₃); the gas will readily degrade back to oxygen (O₂), and during this transition a free oxygen atom, or free radical (O•) will form. The free oxygen radical is highly reactive and short lived; under normal conditions it will only survive for milliseconds.

Ozone is a colorless gas that has an odor similar to the sharp electric smell of the air after a major thunderstorm.

Ozone has a greater disinfection effectiveness against bacteria and viruses compared to chlorination. In addition, the oxidizing properties can also reduce the concentration of iron, manganese, sulfur and reduce or eliminate taste and odor problems. Ozone oxidizes the iron, manganese, and sulfur in the water to form insoluble metal oxides or elemental sulfur. These insoluble particles are then removed by post-filtration. Organic particles and chemicals will be eliminated through either coagulation or chemical oxidation. Ozone is unstable, and it will degrade over a time frame ranging from a few seconds to 30 minutes. The rate of degradation is a function of water chemistry, pH, and water temperature.

Ozonation Process

The formation of oxygen into ozone occurs with the use of energy. This process is carried out by an electric discharge field as in the CD-type ozone generators (corona discharge simulation of the lightning), or by ultraviolet radiation as in UV-type ozone generators (simulation of the ultraviolet rays from the sun). In addition to these commercial methods, ozone may also be made through electrolytic and chemical reactions. In general, an ozonation system includes passing dry, clean air through a high voltage electric discharge, i.e., corona discharge, which creates an ozone concentration of approximately 1% or 10,000 mg/L. In treating small quantities of waste, the UV ozonation is the most common while large-scale systems use either corona discharge or other bulk ozone-producing methods. Ozone test strips are a must.

The raw water is then passed through a venturi throat which creates a vacuum and pulls the ozone gas into the water or the ozonated air is then bubbled up through the water being treated. Since the ozone will react with metals to create insoluble metal oxides, post filtration is required.

Primary Advantages to Ozone

1 | Ozone is effective over a wide pH range and rapidly reacts with bacteria, viruses, and protozoans and has stronger germicidal properties than chlorination. It has very strong oxidizing power with a short reaction time.

2 | The treatment process does not add chemicals to the water.

3 | Ozone can eliminate a wide variety of inorganic, organic, and microbiological problems as well as taste and odor problems. The microbiological agents include bacteria, viruses, and protozoans such as Giardia, Cryptosporidium, and other waterborne pathogens

Pathogenic and waterborne disease screening test.‍

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Disadvantages to Ozone

1 | There are higher equipment and operational costs and it may be more difficult to find a  professional proficient in ozone treatment and system maintenance.

2 | Ozonation provides no germicidal or disinfection residual to inhibit or prevent regrowth of bacteria.

3 | Ozonation by-products are still being evaluated and it is possible that some by-products may be carcinogenic. These may include brominated by-products, aldehydes, ketones, and carboxylic acids. This is one reason that the post-filtration system may include an activated-carbon filter.

4 | The system may require pretreatment for hardness reduction or the addition of polyphosphate to prevent the formation of carbonate scale.

5 | Ozone is less soluble in water, compared to chlorine, and, therefore, special mixing techniques are needed.

6 | There are potential fire hazards and toxicity issues associated with ozone generation.

Important tool - ORP Monitoring

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