5. ozone
TRANSCRIPT
-
7/30/2019 5. Ozone
1/8
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.
-
7/30/2019 5. Ozone
2/8
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
-
7/30/2019 5. Ozone
3/8
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.
-
7/30/2019 5. Ozone
4/8
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.
-
7/30/2019 5. Ozone
5/8
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
-
7/30/2019 5. Ozone
6/8
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
-
7/30/2019 5. Ozone
7/8
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.
-
7/30/2019 5. Ozone
8/8
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