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5. Investigate and describe the process used for ozone production.

5.1 Ozone: General Concept

Ozone is a powerful oxidant and sterilizing used to disinfect the water in water treatment plants, is used as a

substitute for chlorine in the water washing and disinfection of raw materials. Used in low concentrations

and have short contact time. It is very effective to inactivate bacteria, fungi, viruses and protozoa.

Ozone can be generated artificially by an ozone generator.

Ozone cannot be stored or transported. Is much less stable than diatomic oxygen and other industrial gases.

The reason for the instability is that quickly converts into oxygen, and therefore must be produced at thesite will be used. (Production SITE)

Scientific research conducted by the Environmental Protection Agency (EPA), USA, showed that ozone is

more benign in comparison with chlorine and chlorine dioxide is common disinfectants. This acceptance

allows extending the use of ozone in food processing operations.

5.2 Ozone Production

Ozone can be produced by different ways; however the corona discharge method is the most used in the

industry. The reaction is endoderm and requires application of a large amount of energy. In this method,

ozone is produced by means of an electric discharge applied to dry air or oxygen. Applying a high voltage

(6,000-20,000 V) to two electrodes and voltage produces an electric arc. In the arc of the O2 becomes O3.

Ozone is generated onsite because it is unstable and decomposes to elemental oxygen in a short amount oftime after generation. Ozone is a very strong oxidant and virucide. The mechanisms of disinfection using

ozone include:

Direct oxidation/destruction of the cell wall with leakage of cellular constituents outside of the cell.

Reactions with radical by-products of ozone decomposition.

Damage to the constituents of the nucleic acids (purines and pyrimidines).

When ozone decomposes in water, the free radicals hydrogen peroxy (HO2) and hydroxyl (OH) that are

formed have great oxidizing capacity and play an active role in the disinfection process. It is generally

believed that the bacteria are destroyed because of protoplasmic oxidation resulting in cell wall

disintegration (cell lysis). The effectiveness of disinfection depends on the susceptibility of the target

organisms, the contact time, and the concentration of the ozone. A line diagram of the ozonation process is

shown in Figure 1. The components of an ozone disinfection system include feed-gas preparation, ozone

generation, ozone contacting, and ozone destruction.

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FIGURE: OZONE PROCESS SCHEMATIC DIAGRAM

Air or pure oxygen is used as the feed-gas source and is passed to the ozone generator at a set flow rate. Theenergy source for production is generated by electrical discharge in a gas that contains oxygen.

Ozone generators are typically classified by:

The control mechanism (either a voltage or frequency unit).

The cooling mechanism (water, air, or water plus oil).

The physical arrangement of the dielectrics (either vertical or horizontal).

The name of the inventor.

However, generators manufactured by different companies have unique characteristics but also have some

common configurations.

The electrical discharge method is the most common energy source used to produce ozone. Extremely dry

air or pure oxygen is exposed to a controlled, uniform high-voltage discharge at a high or low frequency. The

dew point of the feed gas must be -60EC (-76EF) or lower. The gas stream generated from air will containabout 0.5 to 3.0% ozone by weight, whereas pure oxygen will form approximately two to four times that

concentration. After generation, ozone is fed into a down-flow contact chamber containing the wastewater

to be disinfected. The main purpose of the contactor is to transfer ozone from the gas bubble into the bulk

liquid while providing sufficient contact time for disinfection. The commonly used contactor types diffused

bubble (co-current and counter-current) are positive pressure injection, negative pressure (Venturi),

mechanically agitated, and packed tower. Because ozone is consumed quickly, it must be contacted

uniformly in a near plug flow contactor. The off-gases from the contact chamber must be treated to destroy

any remaining ozone before release into the atmosphere. Therefore, it is essential to maintain an optimal

ozone dosage for better efficiency. When pure oxygen is used as the feed-gas, the off-gases from the

contact chamber can be recycled to generate ozone or for reuse in the aeration tank. The ozone off-gases

that are not used are sent to the ozone destruction unit or are recycled.

The key process control parameters are dose, mixing, and contact time. An ozone disinfection system strivesfor the maximum solubility of ozone in wastewater, as disinfection depends on the transfer of ozone to the

wastewater. The amount of ozone that will dissolve in wastewater at a constant temperature is a function of

the partial pressure of the gaseous ozone above the water or in the gas feed stream.

It is critical that all ozone disinfection systems be pilot tested and calibrated prior to installation to ensure

they meet discharge permit requirements for their particular sites.

Ozone

Destruction

Ozone Contact

Basin

Ozone Generation

Feed Gas preparation

Oxigen Production

Oxigen Storage

Air/ Oxigen Treatment

Wastewater In

Recycle

Wastewater In

Discharge

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5.3 Ozone Treatments Features

1. Improved water organoleptic characteristics.2. Color, smell and taste undesirable, attenuated or eliminated.3. Total destruction and fast (3000 times faster than chlorine) of bacteria, viruses and spores, with

short contact times.

4. Destruction of iron and magnesium salts in the form of hydrates, resulting in easily removableproducts by decantation or filtration.

5. Clarifies water, leaving it particularly clean.6. Its disinfectant covers a wide range of both temperatures and pH's.7. Not create any type of chemical bond or halogenated compounds.8. Totally tasteless.9. It is unnecessary to use chemicals such as hypochlorite (stable) or chlorite (toxic), that only

qualified and empowerment, can handle.

10. Immediate oxidizing action against organic impurities therefore reduces the BOD and COD.11. Removes THMs and their precursors.12. Improves water coagulation-flocculation.13. Destroy sulfates.14. Oxidized phenols, pesticides, etc.

Consequently, ozone has great advantages, since this active oxygen leaves any residue or foreign substances

contributes to the elements that have been treated. The use of ozone extends every day, thanks to the

convenience of their employment, their cool effects to your excess decompose and its simplicity in terms of

production, it does not need more power.

ADVANTAGES DISADVANTAGE

Ozone is more effective than chlorine in destroying

viruses and bacteria.

Low dosage may not effectively inactivate some viruses,

spores, and cysts.

The ozonation process utilizes a short contact time

(approximately 10 to 30 minutes).

Ozonation is a more complex technology than is chlorine or

UV disinfection, requiring complicated equipment and

efficient contacting systems.

There are no harmful residuals that need to be

removed after ozonation because ozone decomposes

rapidly.

Ozone is very reactive and corrosive, thus requiring

corrosion-resistant material such as stainless steel.

After ozonation, there is no regrowth of

microorganisms, except for those protected by the

particulates in the wastewater stream.

Ozonation is not economical for wastewater with high levels

of suspended solids (SS), biochemical oxygen demand (BOD)

chemical oxygen demand, or total organic carbon.

Ozone is generated onsite, and thus, there are fewer

safety problems associated with shipping and handling.

Ozone is extremely irritating and possibly toxic, so off-gases

from the contactor must be destroyed to prevent worker

exposure.

Ozonation elevates the dissolved oxygen

(DO) concentration of the effluent. The increase in DO

can eliminate the need for reaeration and also raise the

level of DO in the receiving stream.

The cost of treatment can be relatively high in capital and in

power intensiveness.

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5.4 Costs

The cost of ozone disinfection systems is dependent on the manufacturer, the site, the capacity of the plant,

and the characteristics of the wastewater to be disinfected. Ozonation costs are generally high in

comparison with other disinfection techniques.

Table shows a typical cost estimate (low to medium) for ozone disinfection system used to disinfect one

mgd of wastewater. The costs are based on the wastewater having passed through both primary andsecondary treatment processes of a properly designed system (the BOD content does not exceed 30

milligrams per liter [mg/L] and the SS content is less than 30 mg/L). In general, costs are largely influenced

by site-specific factors, and thus, the estimates that follow are typical values and can vary from site to site.

Because the concentration of ozone generated from either air or oxygen is so low, the transfer efficiency to

the liquid phase is a critical economic consideration. For this reason, the contact chambers used are usually

very deep and covered. The overall cost of an ozonation system is also largely determined by the capital and

O&M expenses. The annual operating costs for ozone disinfection include power consumption, and supplies,

miscellaneous equipment repairs, and staffing requirements. Another consideration for the cost is that each

ozonation system is site specific, depending on the plants effluent limitations. Chemical suppliers should be

contacted for specific cost information.

Table typical cost estimate of and ozone disinfection

Items CostsCapital Costs

Oxygen feed gas and compressor $245,500

Contact vessel (500 gpm) $4,000-5,000

Destruct unit:

Small (around 30 cfm) $800

Large (around 120) $1,000-1,200

Non-component costs $35,000

Engineering 12,000-15,000

Contingencies 30%

Annual O&M Costs

Labor $12,000

Power 90 kW

Other (filter replacements, compressor oil, spare dielectric, etc.) $6,500

gpm = gallons per minute

cfm = cubic feet per minute

Source: Chapion Technology, 1998.

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5.5 Operation of Water Ozonation

The ozonation system consists of 6 components to achieve the irrigation water ozonation and washing.

a. Gas preparation: The purpose of the gas preparation device is dry oxygen containing gas. Typegenerators use corona discharge dry air or pure oxygen as the oxygen source to be converted into

ozone. When air is used, drying is critical, in order to maximize the yield of ozone and to minimize

the formation of nitrogen oxides, which accelerate the corrosion of the electrodes. Another option

is to deliver concentrated oxygen to the ozone generator; with this option the ozone production

efficiency is much higher.

b. Ozone Generators: Ozonation systems used in water treatment ozone generated at the site ofapplication, and almost all do through a corona discharge between two dielectrics produced,

through which passes oxygen or dry air to produce ozone gas.

c. Ozone injection system: To fulfill its function ozone disinfection and oxidation, should contact withwater and dispersed as finely as possible. Generally, this is done through fine bubble diffusers,

venturi injectors and static mixers, and the mixture is performed in a contact tank.

Preparation of Gas

Ozone Generator

Dry Air

Ozone

Ozone Injection System

Static Mixer

Water InletContact Tank

Ozone/WaterOzone Water Oulet

Ozone Monitoring

Excess Ozone

Destruction

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d. Contacting Tank: Ozonation systems use a touch tank for transferring the generated ozone into thewater to be disinfected. The touch tank volume depends on the volume of water and ozone

concentration to be applied.

e. Destruction of surplus ozone: The ozone concentration reaches dissolved in water is directlyproportional to the partial pressure of ozone gas therein. Often, excess ozone gas is recirculated to

the previous process, to improve the oxidation and disinfection and maintain a concentration of

ozone. Although the recirculation is generally ozone (excess) in the exhaust gases, which must be

destroyed or dilute.

f. Monitoring: Not all ozone is dosed as ozone dissolved in water, some is lost in the air released fromthe water and some oxygen is reversed. The dose 1 mg / l, is generally between 0.3 to 0.4 mg / l of

residual ozone in water. The residual ozone is the only direct indicator of the presence of ozone in

water and for its determination there are different types of meters and sensors available on the

market.

Application methods of ozone in water

To do its job ozone disinfection and oxidation, should contact with water and dispersed as finely as possible.

Generally, this is done through fine bubble diffusers, venturi direct injection and static mixer.

Bubble diffusers: Relatively small bubble size Compressor needed Simple Application System

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Venturi Injection:

Ozone injection via a vacuum Small bubble size Mixing efficiency 80%

Static Mixer

Easy installation and low pressure loss Very small bubble size Dissolution of ozone on 90%

5.6 Monitoring of ozone in water

Not all ozone is dosed as residual ozone is dissolved in water, partly to meet demand consumes oxidizing

water, some leaves with the air escaping from the water and some oxygen is reversed, the 1 mg dose / l, is

generally between 0.3 to 0.4 mg / l of residual ozone. The residual ozone is the only direct indicator of the

presence of ozone in water, this must reach different types of meters, and chemical sensors that give us

information about the amount of ozone present in the water.

5.7 International regulations ozone

In 1997, the ozone is declared by the FDA (Food and Drug Administration) as GRAS (GenerallyRecognized as Safe) as a disinfectant for food.

The use of ozone as a disinfectant and sanitizer for the treatment, storage and food processing wasapproved as safe by the Food and Drug Administration (FDA), USA. The FDA issued a final ruling in

June 2001, in response to the request of Electric Power Research Institute (EPRI), modifying the

previous regulations and legislation approving the use of ozone as a food additive.

The Environmental Protection Agency Environmental Protection Agency (EPA) standard averageozone concentration of 0.08 ppm in air for 8 hrs.

The Administration of Occupational Safety and Health (Occupational Safety and HealthAdministration, OSHA) states that workers should not be exposed to a concentration greater than

1.0 ppm ozone for more than 8 hrs of work.

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REFERENCES:

Ozone

http://www.feragus.cl/index.php?option=com_content&view=article&id=119&Itemid=77

http://www.electrozono.com/produccion.asp

EPA Wastewater Technology Fact Sheet - Ozone Disinfection

1. Crites, R. and G. Tchobanoglous. 1998. Small and Decentralized Wastewater Management Systems. The

McGraw-Hill Companies. New York, New York.

2. Martin, E. J. and E. T. Martin. 1991. Technologies for Small Water and Wastewater Systems.

Environmental Engineering Series. Van Nostrand Reinhold (now acquired by John Wiley & Sons, Inc.). New

York, New York. pp. 209213.

http://www.feragus.cl/index.php?option=com_content&view=article&id=119&Itemid=77http://www.electrozono.com/produccion.asphttp://www.electrozono.com/produccion.asphttp://www.feragus.cl/index.php?option=com_content&view=article&id=119&Itemid=77