In our last post we talked about BOD reduction using ozone and advanced oxidation processes (AOP). We noted that that ozone reacts differently under different conditions. In this posting, we will discuss these differences in a little more detail. You can also read more about ozone reactions at www.spartanwatertreatment.com/reactions.html.
In general ozone can react along two pathways: as molecular ozone (O3) or as the hydroxyl radical. In the former case it is a selective oxidant where the reactions are relatively slow. Without getting into chemistry lesson there are certain types of organic compounds that are readily oxidized by ozone and others that do not react at all. For example, phenol is readily oxidized by ozone, but formaldehyde does not react at all.
Under certain condition conditions ozone reacts to form the hydroxyl radical. This compound is not selective in its reactions and will attack most organic compounds very quickly. Ozone forms the hydroxyl radical at elevated pH, in the presence of hydrogen peroxide and with exposure to UV radiation. Processes that produce the hydroxyl radical are called advanced oxidation processes. These processes are used to oxidize compounds that are not readily oxidized by ozone or hydrogen peroxide alone.
Hydroxyl radicals are relatively expensive to produce and short lived, so it is important to use them efficiently. Since they are not selective in what they react with, it is important o design the process to avoid reactions with compounds that will consume the hydroxyl radicals before they react with the intended targets. For example if the water has high alkalinity this will tend to consume the radicals as would easily oxidized species such as dissolved iron to hydrogen sulfide.
Because of the chemistry of ozone and the hydroxyl radical, the design of the process is just as critical as the equipment that is used. AOP that use the same basic process, for example ozone/hydrogen peroxide, will not necessarily work equally as well. As a result considerable thought needs to go into the design of these processes along with a good understanding of the water chemistry involved. In some cases pilot studies may be required.
If you have questions about AOP technology please contact Spartan with your question: www.spartanwatertreatment.com/contactus.html.