TECHNOLOGY OVERVIEW
AOP Chemistry — Advanced Oxidation Processing (AOP) uses hydroxyl radicals (•OH) to oxidize organic contaminants in water. Hydroxyl radicals are the most powerful natural oxidizing agents for the destruction of hazardous organic compounds in water treatment applications.
There are several processes for generating hydroxyl radicals including; ozone and hydrogen peroxide, ultraviolet light and ozone, ultraviolet light and hydrogen peroxide, Fenton's chemistry, cavitation and titanium dioxide. Ozone and hydrogen peroxide is generally viewed as the most economical process for generating hydroxyl radicals.
Hydroxyl radicals can be formed by the dissociation of ozone in water as well as by the reaction of ozone with hydrogen peroxide. The overall, balanced reaction of ozone with hydrogen peroxide to form hydroxyl radicals is:
Due to their behavior as extremely aggressive oxidizers, hydroxyl radicals react very rapidly with hazardous organic contaminants to form non-hazardous compounds such as carbon dioxide and water. The oxidation of the organic contaminants does not significantly increase the temperature or pressure in the reaction system. Therefore, the water is ready for use or discharge when it exits the HiPOx reactor.
The amount of ozone and hydrogen peroxide and the number of reaction zones required for a given water treatment situation are determined by the water flow rate, the composition and concentration of organic compounds in the influent, and the desired effluent concentrations.
Historical AOP Applications — Industrial applications of AOP using ozone and hydrogen peroxide for drinking water have not met with a great deal of success because of the formation of bromate from bromide. This may have more to do with how the chemistry is applied than the chemistry itself. In historical AOP processing, hydrogen peroxide is added to the contaminated water and the water is then passed through an atmospheric pressure contactor where the ozone is introduced. The ozone is a gas generated from dry air with an ozone generator. The concentration of the ozone is typically 2-3% by weight. See figure 1 below.
Figure 1. Historical Advanced Oxidation Process
Applied's HiPOx™ Technology Approach — The HiPOx process developed by Applied is an Advanced Oxidation Process (AOP) that uses ozone (O3) and hydrogen peroxide (H2O2) to form hydroxyl radicals to subsequently destroy organic compounds in water while controlling bromate formation. The simplified block flow diagram of the HiPOx process is shown in figure 2 below.
Figure 2. HiPOx In-Line Continuous Flow Oxidation System
To effectively utilize the short-lived hydroxyl radicals (less than 10-6 seconds) and thus minimize the cost of hydroxyl-radical generation, HiPOx technology enhances and maximizes mass transfer of ozone into the water. Improved mass transfer is accomplished with higher ozone concentration (8-10% by weight versus 2-3% wt.), higher operating pressure (35-45 psig versus ambient pressure) and efficient mixing. The higher ozone concentration is achieved by using oxygen instead of ambient air as the feed to a solid-state ozone generator.
Installing multiple reaction zones further enhances the system efficiency. With multiple injections of ozone, the formation of bromate is avoided or minimized by minimizing the ozone concentration at any one point in the HiPOx system’s serpentine reactor.
VOC Destruction — HiPOx technology is very effective at treating a wide range of volatile organic compounds found in groundwater including PCE, TCE, benzene, toluene, ethyl benzene, xylenes and phenol. However, HiPOx is far superior to conventional technologies in treating waters containing recalcitrant contaminants such as the fuel oxygenate MTBE and its degradation product TBA and the solvent stabilizer 1,4 dioxane, which is now being detected in many industrial solvent plumes. Conventional water treatment technologies such as carbon adsorption and air stripping are not effective in remediating these contaminants. The oxidation of the MTBE molecule is shown below in figure 3.
Figure 3. HiPOx Destruction of the MTBE Molecule
The destruction of MTBE, and subsequently of TBA, is shown in the following destruction curve (figure 4).
Figure 4. Destruction Curve of MTBE in the HiPOx Reactor
HiPOx Scalability — Applied uses mobile 1 — 10 gpm systems to perform field tests. Data obtained during these tests allow the proper design of full scale treatment systems. Test data and subsequent operating data from full scale systems have consistently confirmed that the HiPOx process is scalable and will destroy contamiants at virtually the same efficiency no matter what the flow rate. This has been demonstrated repeatedly over a wide range of flows (10 to 1,000 gpm) at many treatment sites. Below are examples of destruction curves for the 10 and 1,000 gpm applications on the same water containing the contaminants, PCE and TCE (figure 5).
 
Figure 5. HiPOx Scalability
The scalability of the HiPOx technology from field tests to commercial scale installations has also been demonstrated for a number of other contaminants including 1,4-dioxane, MTBE, TBA and others.
Competitive Advantages —The HiPOx technology has a demonstrated competitive cost advantage when compared with treatment methods such as carbon, air stripping, and ultraviolet oxidation processes over a wide range of influent concentrations and flow rates. The following graphs (figures 6 and 7) illustrate the Comparative Operating Costs differential between HiPOx and other technologies.
Figure 6. Comparative Operating Cost VOCs with Moderate Adsorption (TCE)
Figure 7. Comparative Operating Cost Contaminants with Poor GAC Adsorption (TBA)
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