Water quality is becoming an increasingly important issue in the US and around the world. Pollution of both ground water and surface water has resulted from the disposal of pharmaceuticals, personal care products and industrial wastes into our water supplies. Often the contaminants are found in low concentrations and are very difficult to remove by conventional means. Even when conventional methods do work, for example with activated carbon treatment, we are simply moving the pollutant from the water to the carbon which must be disposed of in a safe manner. In recent years, advanced oxidation processes (AOP) have been developed that can treat these pollutants without further disposal issues.
So what are advanced oxidation processes or AOP? The most familiar oxidation process is fire. Oxygen combines with carbon based materials to form carbon dioxide, CO2. Advanced oxidation processes work in a similar fashion, but in the water. Organic compounds are oxidized, you could say burned, to CO2. This eliminates the toxicity of the pollutants and makes the water safe for drinking or other uses.
An AOP combines multiple oxidants like ozone and hydrogen peroxide to form a much stronger oxidant known as the hydroxyl radical. This compound is capable of oxidizing virtually any organic compound. There are a variety of advanced oxidation processes such as UV and ozone, UV and peroxide, peroxide and ozone, peroxide with various catalysts, etc. UV with ozone is an intriguing combination since the ozone can be made from air and the entire process does not require any purchase or storage of chemicals. The oxidants are produced on site and with proper design produce no byprodusts.
Advanced oxidation processes can be used to solve a number of difficult environmental problems not readily solved by any other method. One such problem is 1,4 Dioxane. This industrial solvent was widely used in industry and has ended up in groundwater. Ozone/peroxide based AOP have been successfully applied to treat the groundwater to safe levels permitting it to be used for applications like drinking water. Another example is MTBE, a gasoline additive. Leaks of gasoline have contaminated ground water with MTBE around the US. While the compound can be treated with simple oxidants like ozone alone, the byproducts can be more toxic than the MTBE. AOP can be used to break down the MTBE to safe compounds that require no further treatment. Advanced oxidation processes have also been used to treat byproducts of pharmaceutical and personal care products, algal toxins such as microcystin, pesticides and herbicides, and chlorinated hydrocarbons such as TCE and PCE.
While treatment with an AOP is not inexpensive, it is a relatively simple process. For a UV Ozone process, ozone is made in an ozone generator and mixed with water. Ozonation of water is a process that is used routinely in drinking water treatment. In fact, about 30% of all public drinking water is treated at some point with ozone. The ozonated water then passes through a chamber with UV lamps. The UV light reacts with the ozone to form the hydroxyl radicals which convert the pollutants to carbon dioxide and other minerals. Other than the pumps, there are usually no moving parts in the system. The treated water can be returned to the ground or whatever source it came from or immediately put to use.
The continued development and deployment of advanced oxidation processes will allow industry and communities to recover contaminated ground water or reuse water that was once discarded. With high quality water resources in decline in the US and elsewhere, AOP can improve both the quality and availability of water. The costs are certainly reasonable at around $0.10/1,000 gallons treated.
So, we have the technology to recover contaminated water and reuse water that normally would be discarded. All that is really required is the will to do so.
