In this post we would like to talk about pilot and lab testing of ozone water treatment and advanced oxidation applications. Typically, pilot and lab tests are conducted to first see if ozone or other advanced oxidation processes will address the water treatment objectives, or to assess the economics of using ozone or other advanced oxidation processes.
As we have discussed in other posts, it is difficult to predict with accuracy the amount of oxidant required to destroy dissolved organics in water. This is especially true if the specific organic constituents are not known or the variety of such contaminants is large. In many cases, the only analytical data available are broad based measures of organic species such as BOD, COD and TOC. In the case of ozone, some organic species react readily with ozone while others are not reactive at all.
In the case of advanced oxidation processes, the primary reactant involved, the hydroxyl radical, will react with most organic species; other materials in the water may interfere with these reactions. One such species are carbonate ions that can scavenge hydroxyl radicals out of the water. High concentration of these ions will limit the effectiveness of advanced oxidation processes.
Given the complexity of the chemistry that can be involved, it is sometimes better to run laboratory and pilot tests to measure actual results which can then be scaled up to predict the results in a commercial scale installation. To be effective, proper measurement of the amount of oxidant applied is important.
In the case of ozonation, we first need to know how much ozone has been produced. Ozone generators are usually supplied with production curves that show ozone production as a function of gas feed and power applied. With time ozone generator characteristics may change, so these curves should be checked using a high quality flow meter and a high concentration ozone monitor.
Only a portion of the ozone applied to the water will dissolve and thus be able to react with the organics in the water. The percentage of ozone that transfers to the water is measured as the ozone transfer efficiency. Using a high concentration ozone monitor, one can measure the off gas from the process to see how much ozone did not dissolve into the water. By subtraction one can arrive at the amount that did enter the water and is available to react.
While not as critical, measuring dissolved, but unreacted oxidant at the end of the process can be done with a dissolved ozone monitor or other analytical method depending on the oxidant used. This information might suggest what will need to be done to maximize the use of the reactant. Being able to measure a oxidant residual may also point to a process control option. If ozone residual is present it might be able to serve as an indication that the organic destruction reaction has reached its end point. This could be useful in the final design of the commercial installation.
While the economics of the process are dictated by the total amount of ozone applied, regardless of whether it dissolved or not, pilot processes may not be as efficient as commercial scale processes. A short bubble column that allows the ozonated gas to enter in large bubbles could easily have a ozone transfer efficiency of less than 10% while a well design ozone injection and mixing system can achieve 95% efficiency. Such a large difference would make the applied dose useless to know without the ozone transfer efficiency data.
Using the information gathered at the pilot stage, adjustments can be made to accurately assess the amount of ozone needed in an efficient commercial process. In other advanced oxidation processes, measurement of peroxide and UV radiation applied would be needed as well.
Besides the amount of oxidant applied, before and after results for the relevant measure of the dissolved organic (BOD, COD and/or TOC) will be needed. This will be correlated to the amount of applied oxidant, e.g. mg Ozone/mg COD removed. This ratio along with the ozone transfer efficiency data will allow for a cost estimate to be made for the entire system.
Spartan Environmental Technologies can provide both laboratory and pilot testing of ozone and advanced oxidation processes. Contact us if you would like to see if ozone or advanced oxidation processes may be able to solve your dissolved organic contamination issue.