Ozone has been used for disinfections of drinking water in the municipal water industry in europe for over 100 years and is used by a large number of water companies, where ozone generator capacities in excess of 100 kg/h are common. But due to the absence of proper monitoring equipment ozonation is appearing to be ineffective. This is also one of the reasons why most industries do not take the ozone generator industry seriously.
What is Ozone?
Ozone is a molecule composed of three atoms of oxygen. Two atoms of oxygen form the basic oxygen molecule--the oxygen we breathe that is essential to life. The third oxygen atom can detach from the ozone molecule, and re-attach to molecules of other substances, thereby altering their chemical composition. It is this ability to react with other substances that forms the basis of manufacturers claims. Ozone (O3) is one of the strongest oxidizing agents that are readily available. It is used to reduce color, eliminate organic waste, reduce odor and reduce total organic carbon in water. Ozone is created in a number of different ways, including ultra violet (UV) light, corona discharge of electricity through an oxygen stream (including air), and several others. In treating small quantities of waste, the UV ozonators are the most common, while large-scale systems use either corona discharge or other bulk ozone-producing methods. Ozone is formed as oxygen (O2) is struck by a source of energy. The bonds that hold the O2 together are broken and three O2 molecules are combined to form two O3 molecules. The ozone begins to break down fairly quickly, and as it does so, it reverts back into O2. The bonds that hold the O atoms together are very weak, which is why ozone acts as a strong oxidant as readily as it does.
How Ozone works?
Ozone offers real advantages over chlorine bleach and other disinfectants used in the dialysis field because of its strong oxidizing power that inactivates pyrogenic lippopolysaccharides (endotoxin) and destroys total organic carbon (TOC). Additionally, ozone has a higher lethality coefficient than chlorine and other disinfectants against most organisms and readily destroys viruses. The action of ozone is through the agency of free radicals produced by the incorporation of ultraviolet radiation. The covalent bond connecting two atoms consists of the mutual sharing by these atoms of two bonding electrons. This valence may break in two ways: In one process, one of the atoms may acquire both bonding electrons, leaving the other with none. This type of bond cleavage gives rise to ions. The electron being the seat of negative electricity, one atom possesses more than its original share of negatively charged electrons, or an anion. The other atom is deprived of its normal complement of electrons and becomes positively charged, or a cation.
The covalent bond may also rupture, leaving each of the constituent atoms with one of the bonding electrons. These atoms are now free radicals, which require combinations with other free radicals to form stable molecules. Alternatively, a free radical may form a linkage with a molecule and abstract an atom and a bonding electron. This action stabilizes the free radical, but in the process forms a new free radical. A series of free radical attacks upon molecules results in a free radical chain. Eventually the free radical chain terminates. Free radicals have half-life durations whose length are inverse expressions of their stabilities. Thus, the more unstable the free radical, the more avid its need to bond, the shorter its half-life. Also, the more unstable the free radical, the broader the spectrum is of molecules it can interact with. Hydrogen abstraction from carbon atoms, as well as carbon-carbon bond cleavage to create free radical chains can be initiated by the hydroxyl free radicals caused by the action of the ozone upon water:
O3 + H2O O2 + 2OH
Hydroxyl free radicals are generated by ozone in water in a several step reaction. Carbon dioxide is the final product of the oxidative free radical chain.
Nearly all commercial ozone generators employ the corona discharge principle. Properly dried air, or oxygen itself, is passed between a high-voltage electrode and a ground electrode separated by a dielectric material. Considerable electrical energy is required for the ozone producing electrical discharge field to be formed. In excess of 80% of the applied energy is converted to heat that, if not rapidly removed, causes the ozone to decompose, particularly above 35° C (95° F). Proper cooling of the ozone generator is crucial to maintaining ozone yields. Some units include a composite mixing tank that mixes the fluid stream with ozone via a venturi side-stream. The side-stream venturi injection method is recognized by some as more efficient than the fine bubble diffuser type for transferring ozone to water. Electrolytic generation of ozone results in the formed ozone being rapidly dissolved in water. However, the small quantity of ozone containing water involved must be dispersed throughout the water being treated. The use of static mixers, storage tanks and distribution loops serve this purpose.
The first quantities of ozone introduced are consumed by reaction with the organics that are present. Only after these excessive initial requirements of ozone have been assuaged can maintenance of proper ozone residual level relative to the biocidal activity be made. Because not all the ozone gets dissolved and utilized, generators supplying 1 mg/L (1 PPM) of ozone are used though only tenths of a PPM are required. The gas stream exits from the generator at 10 to 15 psig. This is sufficient for introduction into storage tanks. If it must be introduced into a pressurized system, say at 80 psig, it is first dissolved in a small quantity of water that is then discharged by a pump.
The power of ozone generators is estimated in two ways ie - the production of ozone per hour or yield (g/H or grams per hour) and quantity of ozone in weight per unit of volume of the bearer gas (mg/L) or concentration. Aurozone designs and manufactures OGs with a capacity as high as 5 grams per hour, while the Swedish product caters to a range from five grams to 1000 grams per hour. A swimming pool of Olympic size would hardly require 20 grams of ozone per hour from high concentration machines, but over 60 grams from low concentration air fed generators. The reason is that the solubility of Ozone in water is proportional to the concentration of ozone in the bearer gas.
Ozone vs Chlorine
- The US Government for 8 HOURS installation rates ozone as toxic at 100PPT level only. Whereas, Chlorine is not only toxic; it is also a poisonous gas
- Ozone is generated on the premises and not stored or transported. But Chlorine is stored in high pressure containers on the premises and is hazardous.
- Ozone degrades all organic substances to make them into harmless ashes and does not leave any other by-products than Oxygen. Chlorine, on the other hand, when mixed with body fluids and perspiration, will form chloramines that will cause eye irritation and are carcinogenic by nature.
- Ozone has become less expensive due to an increase in efficiency and lower energy consumption. Whereas, the cost of chlorine is constantly increasing and it has become quite expensive
- Tests have proven that ozone is 600 to 3000 times more active in the destruction of bacteria and viruses than Chlorine in the same concentrations. Ecoli is killed within 5 seconds by ozone at a concentration of 1 mg/l. Even the cyst and spores cant resist ozone. But to be killed by chlorine Ecoli required 15,000 seconds at a concentrations of 1 mg/l
- Ozone does not require pH control, but some other chemicals use may require such control. While, Chlorine needs pH control ( 7.0 to 7.4 pH) for reliable results.
- Ozone is an excellent deodorizing agent for many substances, such as hydrogen sulfide, ammonia, smoke, cooking smells, paint, etc. Whereas, Chlorine is not a deodorizing agent.
- Ozone is effective against decomposition of wastes, mildew, and fungus and can be used to eliminate "locker room" odor in dressing room. Whilst Chlorine doesnt have such effect.
Industrial Applications of Ozone
Using ozone in industrial applications does not produce any by-product to contaminate the ecological system further. In the conventional methods, there would be by-products created in the process and this creates problems in one way or the other. However, Ozone leaves only pure oxygen and inert oxides as by-products. There is a vast potential for applications in sewage treatment industry, as there is a lot of opportunities for detoxifying, de-coloring and deodorizing. As OGs were capital intensive, it is not favourable in these industries and in the midst of recession. The support from the government such as decreasing taxes, offering other encouragements, higher depreciation or other benefits is lacking.
However, Ozone has more potential applications in other industries such as hospitality industry, fish farms, cooling towers beverage manufacturers, and mineral water plants.
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|Posted : 10/20/2005|