A number of clients that call us regarding ozone water treatment systems often don’t know how much ozone they will need. They know the amount of water they treat and the treatment objective, but they don’t know how much ozone will be required to meet that treatment objective.
This is not much of a surprise since it is difficult to predict the required ozone dosage. In some applications well informed estimates can be made based on theoretical requires to oxidize a specific species, such as Fe or Mn. Even in these applications, other elements in the water might also exert a demand on the ozone making the estimates based on the Fe or Mn concentrations low.
A thorough water analysis can often provide most of the information for making a good estimate for the size of the ozone system. In a smaller system with well understood compounds, it may be possible to use the water analysis with a margin of safety to eliminate the need for pilot testing. It is certainly possible to use such information to provide a rough estimate of the cost of an ozone system so a client can determine if ozone is likely to be a viable solution for their application.
In many cases, the amount of ozone required for treating certain compounds and the full range of contaminants that might consume the ozone are not known. So while an educated guess of the system size and cost might be possible, the actual design and a firm cost estimate would not be. In order to achieve this type of information, laboratory and pilot studies are needed.
The testing can be done on site or off site. Testing off site assumes that the nature of the materials in the water do no change with time and can be preserved in shipping. This can be a problem if BOD reduction is a goal of the ozonation process. BOD levels can decrease with time, the presence of naturally occurring bacteria and oxygen. If samples can be kept cold and tested within 24 hours, it might be possible to do the testing off site; otherwise doing the testing at the ultimate place of use would make more sense.
The laboratory or pilot testing equipment should be such that the results can be scaled to full size. Fortunately, typical ozone water treatment equipment is scalable. The vendors of the various components offer different sized pieces of equipment with technical data that allows for this scale up. The testing facility has to be able to estimate the amount of ozone produced, the amount of ozone transferred to the water and how much of the ozone has been consumed. In the case of the ozone production, either the testing facility must have monitors to measure the concentration of the ozone gas, or have ozone generators that have been well characterized using such devices with accurate and reproducible production curves.
Normally there is a specific objective for the ozonation process, for example color removal. Colorimeters can measure when the ozonation process has achieved its objective. If we know how much ozone we applied, from production curves or ozone concentration monitors/flow meters, we can then design a larger system to achieve the color removal. Color removal, COD reduction, Fe/Mn/H2S removal, destruction of specific organic compounds, e.g. phenol, are typical applications for ozone. A curve can be plotted to show the treatment objective versus the applied dose of ozone, allowing a full scale system to be designed. In disinfection applications, it is important to know the ozone residual over a period of time (CT) in order to estimate the degree of pathogen inactivation. In these circumstances one needs a dissolved ozone monitor or wet chemical method for measuring ozone.
If you want to know how efficiently the applied dose is being used, which would be useful for optimizing the design, it is necessary to be able to measure the ozone in the off gas from the process. It is extremely rare or 100% of the ozone to dissolve into the water. So measuring the ozone in the off gas will allow you to know the ozone transfer efficiency and the effectiveness of the ozone dissolving equipment. For larger applications this efficiency can be very important.
Spartan Environmental Technologies can provide on-site or off-site testing for a number of applications. This information will allow for detailed designs and firm price estimates. If you are just trying to get a feel for whether ozone might be an economical process for your application, we can also provide rough estimates based on a water analysis.