To comply with the Final Long Term 1 Enhanced Surface Water Treatment rule of EPA, they have listed some best available technologies that include ozone and UV as well. It has long been known that ultraviolet light (UV) and ozone are effective at inactivating pathogenic organisms that exist in water and wastewater systems. Ozone and UV both have a long history of being used in water treatment.
Ozone is the most powerful commercially available disinfectant on earth due to its high oxidizing potential. Combined with bottled water, clean-in-place sanitation, processing of produce, meat, and industrial reuse, ozone has been used in municipal water treatment for more than 100 years.
Combination of Ozone and UV
Ozone combined with ultraviolet radiation is effective in destroying organic contaminants, largely because the hydroxyl radical (2.8 eV) has a high oxidation potential. A photolytic ozonation reaction (also known as ozone/UV reactions) in aqueous solution involves the creation of OH, which is a more powerful and less selective chemical oxidant than either oxygen or chlorine.
In addition to reacting with organic contaminants, ozone can produce two radicals per molecule with remaining residual ozone. Multiple enemies attack oxidation targets simultaneously, altering the oxidation landscape dramatically. Ozone molecules are able to function more effectively when highly active and nonselective hydroxyls attack many targets. In addition, AOPs such as ozone/UV have the benefit that they can partially oxidize organic materials that are hard to destroy. This allows them to be more easily biodegraded.
Ozone dosage, UV irradiation level, and pH are the three parameters that make ozone/UV systems successful. An effective transfer of ozone gas into aqueous solution is required for proper ozone dosing with a high dissolved ozone rate. Pressurized injection secondary mix UV/O3 reactors are an effective design for ozone/UV systems, creating microbubbles, continuously renewing the gas-to-liquid mixing zone and enhancing gas solubility for UV irradiation to be used to its fullest extent.
In addition to increasing pH, ozone will also convert more readily to hydroxyl, which increases cyanide and pesticide oxidation rates. Design and control of a system must consider pH level, UV photolysis, and ozone dosage to make it as effective as possible.
The wastewater produced by the sanitation, processing, and agricultural infrastructure that serves these same communities is a major obstacle to providing clean water to developing municipalities and industries. Water in municipalities is often obtained from surface sources such as rivers, lakes, and reservoirs. They are contaminated by air, water, and soil in their immediate surroundings. Contaminants may include metals or parasites in unhealthy concentrations, harmful bacteria or viruses such as E. colitis, Listeria, and Cryptosporidium.
As a result of increasing public awareness and scrutiny, efficient treatment of wastewater is essential to ensure long-term sustainability of water resources.
The combination of UV and ozone can be ideal to treat wastewater, however, it is important to ensure the treatment processes are being used appropriately.