Background on the Use of Ozone Generator Technology
Best known for its superior disinfection capability and efficiency, ozone has been commercially used since 1893 when the first full-scale drinking water treatment application was implemented in Germany and is now receiving considerable attention in the United States, the most rapidly growing market, and several other countries.
Ozone is generated by passing oxygen or dry air though a high-energy electrical field where molecular oxygen is broken down into 2 oxygen atoms. Some of the atoms of oxygen liberated will reform into loosely-bonded tri-atomic oxygen called ozone (O3). Due to the loose bond in this oxygen molecule, ozone is recognized to be the strongest commercially available oxidizing agent. Since it possesses high reactivity in an aqueous environment, ozone can oxidize material between 10 and 1,000 times faster than most oxidants used in water treatment and this means significant reaction time for effective removal of contaminants can be reduced. Hence, ozonation has received significant attention though it cost higher than conventional methods due primarily to high costs for ozone generation equipment.
The use of chlorine as a water disinfectant has come under scrutiny because of its potential to react with trace organic compounds and form carcinogenic by-products such as chloramines, trihalomethanes (THMs) and haloacetic acid (HAAs) (Dojlido et al., 1999) which create further water quality problems. As stricter rules on both the range and amount of disinfection needed has been placed and the concentrations of disinfection-by-products allowed in drinking water, the use of free chlorine and other common disinfectants such as chloramines, chlorine dioxide are becoming less cost-effective. Like chlorination, ozonation also forms a residual, however due to its short life span, it is negligible for preventive measures in distribution systems.
In addition, ozone is one of the few disinfectants that can effectively inactivate Cryptosporidium, Giardia and protozoan cysts, which constitute the most frequently identified cause of waterborne diseases in developed countries. The industrial use of ozone’s disinfection properties has also been reported (Viera et al., 1999). Its superior performance in disinfection and pesticide removal (Beltran, 1999) over other currently used methods is compared in Table 1. In general, ozonation is a viable solution in case of higher requirements for water quality.
|Comparison of the Commonly Used Methods||OZONE||UV||HEAT||FILTRATION|
|Purification of drinking water||YES||YES||YES||YES|
|Disinfection of chopping board, tableware and cooking utensil||YES||X||YES||X|
|Disinfection of nipple and feeding bottles||YES||X||YES||X|
|Disinfection of foods to be served without cooking||YES||X||X||X|
|Disinfect and improve quality and shelf-life of viable food, e.g. clams||YES||X||X||X|
|Food washing and prevent loss of vitamin||YES||X||X||X|
|Removal of residual pesticide on fruits and vegetables||YES||YES/NO||YES/NO||YES/NO|
|Removal of aflatoxin||YES||X||X||X|
Beside the superior performance of ozone in drinking and municipal water treatment, numerous studies have also been conducted to investigate its performance on disinfecting and extending the freshness of fruits, aquacultures (Kotters et al., 1997; Simons and Sanguansri, 1997) and vegetables. Some commercial use has occurred with a few commodities such as apples (Ong et al., 1996), cherries, grapes (Sarig et al., 1996), carrots, onions, and potatoes. Ozonation is found to be effective in complete inactivation of E. coli (Komanapalli and Lau, 1998; Hunt and Marinas, 1999) and Candida albicans (Komanapalli and Lau, 1998) which are common contaminants on some of the organic produces due to the application of natural waste as a fertilizer. Its use in post-harvest disease control (Perez et al., 1999) and other storage use have also been evaluated for many years. There is increasing interest and empirical activity in the evaluation of ozone for a diversity of water treatment and air treatment uses in post-harvest quality management. Examples include ethylene degradation (within a confined reactor), odor elimination for mixed storage, disinfection of humidification systems (including retail supermarkets), fungal spore elimination in storage room aerosols, and treatment of superficial mold after long-distance shipping of onions.