In this posting, we will discuss different advanced oxidation processes and where they might be best applied. As we have explained in the past, all advanced oxidation processes (AOP), by definition, produce hydroxyl radicals. These are short lived molecules that are the strongest oxidants known. They can attack virtually any organic compound and given the proper dose, can mineralize (convert to CO2 and salts) most molecules. Thus they have found use in a variety of applications including the treatment of industrial wastewater and groundwater remediation.
Some of the major advanced oxidation processes are UV with hydrogen peroxide, UV with ozone, ozone with peroxide and Fentonâ€™s Reagent (Fe salt with peroxide). Each will produce hydroxyl radicals that can be used in water treatment. This is where the similarities end.
UV-Ozone is the most capital intensive of the processes. On the other hand, no purchase or storage of chemicals is required. The ozone can be produced from air (either directly or from concentrating oxygen) and the UV only requires electrical energy. Thus the UV-Ozone approach is self contained. There are no byproducts left in the water from the process. They hydroxyl radicals and ozone break down into oxygen and water. The water will also be thoroughly disinfected due to exposure to all of the agents used or produced. The foot print of the process can be quite small, especially since no storage tanks are needed.
UV-Peroxide requires less capital than UV-Ozone since peroxide is substituted for the ozone, but storage and purchase of peroxide is required. The Ozone-Peroxide system is similar to UV-Peroxide except the capital is spent of the ozone system versus UV.
Fentonâ€™s Reagent or other systems that employ catalysts to activate peroxide require low capital investments, but require the storage and ongoing purchase of chemicals to run the system. In addition, Fentonâ€™s reagent results in the formation of Fe hydroxide sludge that must be disposed of. This reaction also needs to take place at acidic conditions which may require multiple changes in pH of the treated water. This means additional chemicals on site.
So, which is the best solution? It depends on the conditions for the particular application. For example, if the water is already acidic and will flow into a conventional wastewater treatment plant after treatment, Fentonâ€™s reagent might be a good choice. The pH adjustment may already be part of the existing process and most conventional treatment processes such as an SBR would have sludge handling capabilities. So, if the handling of chemicals is not an issue, say at a facility that already handles many chemicals, Fentonâ€™s might be the perfect solution.
Another advantage of Fentonâ€™s is that the process can handle variation in load with little capital. Essentially, the key capital items are dosing pumps and tanks. The more capital intensive processes must be sized for the maximum amount of load the system would see, if the peak load is infrequent, most of the capital is unused. This provides an economic advantage to Fentonâ€™s, assuming the issues with sludge and pH adjustment are not significant.
On the other hand, if provisions for sludge handling are not already in place and the load on the system is fairly consistent, purchase and storage of chemicals is a problem and system size is important, UV-Ozone may be the best alternative.
There are also technical factors that can impact the decision. In UV based systems, the UV Transmittance (UVT) is a critical factor for sizing the system. A UVT of 100% corresponds to water that transmits UV radiation without any impedance. High organic loads and color impact UVT negatively. On the other hand, certain organic compounds are damaged by UV directly. In fact, heavily chlorinated organic compounds may require UV to initiate the breakdown of the compound. Ozone solubility is strongly affected by temperature, so in very hot water, ozone may not be a very good choice. On the other hand, ozone becomes more active as pH increases, so in high pH water ozone may be a good oxidant to add to the mix.
The last aspect of the decision making process is economics. The different processes will be impacted to a greater or lesser degree by the cost of electrical energy, project life time, transportation costs, distance to peroxide supply points, required pay back periods and other related factors.
Essentially, all of these factors must be taken into account in order to select the optimal advanced oxidation process.
Spartan Environmental Technologies supplies an array of advanced oxidation processes, so we can select the process that is the best fit for the clientâ€™s application. Contact Spartan to learn if AOP can solve your water treatment challenge. Call (800-492-1252) or e-mail (firstname.lastname@example.org).