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By Brant Smith, Ph.D., P.E. (XDD, LLC) Bench scale treatability tests are common for emerging technologies. Over time many technologies evolve to the point that bench tests are not always required as knowledge that has been gained is readily transferable from site to site. However, even as in-situ chemical oxidation and reduction (ISCO and ISCR) and in-situ bioremediation (ISB) have evolved, the need to bench scale test these technologies has remained. The reason is very simple: the performance of each of these technologies varies considerably from site to site and subtle differences can result in significant changes to cost or the actual effectiveness of the field application. To illustrate this point, let's take the application of catalyzed hydrogen peroxide (CHP). I have had people postulate to me that you can simply take the aqueous concentration of iron and use published kinetic rates to determine hydrogen peroxide's longevity in the subsurface and that this should be sufficient for all sites. On a preliminary level this makes sense as CHP is also commonly referred to in our industry as Fenton's reagent, which is based on the reaction of dilute hydrogen peroxide and ferrous iron. However, CHP is not Fenton's reagent and to better understand the reaction, think of iron as a transition metal that can donate an electron to facilitate the decomposition of hydrogen peroxide. Then, understand that any transition metal that can similarly donate an electron can also facilitate the decomposition of hydrogen peroxide. This is further complicated by the fact that each transition metal will have a different kinetic rate of reaction with hydrogen peroxide and that if organic material at the site happens to be chelating the transition metals, that the chelated transition metal will have a different rate of reaction than the non-chelated transition metal. To continue to understand the expected rate of decomposition of hydrogen peroxide, we would need to understand that as the hydrogen peroxide decomposes it will both react with natural organic material, forming new organic chelates, and with the organic chelates themselves, forming other organic compounds. Both of these reactions will have the net effect of changing the rate of decomposition of the hydrogen peroxide during the application. So, to understand the general rate of hydrogen peroxide decomposition in the subsurface at a specific site, you either need to quantify all of the transition metals, all of the organic chelates, and how they will degrade and interact with each other as they degrade over the course of the treatment... Or... ...You could run a bench test. Needless to say, we believe that it is more cost-effective to understand these types of parameters with ISCO, ISCR, metals stabilization and ISB by conducting bench tests rather than trying to theoretically model and predict every aspect of very complex reactions. And I didn't even mention that as organic chelates are being formed, they are likely liberating metals from the soils, that transition metals will need to cycle between reduced and oxidized states, what happens in reactions where the transition metals accept an electron rather than donate an electron, the interactions of inorganic chelates, the interaction of chelates and transition metals with soils, or any of the propagation reactions of the radicals that are formed. XDD's Bench Test Capabilities XDD, LLC conducts a wide assortment of bench scale treatability tests at our facility in Stratham, New Hampshire. XDD bench tests the technologies that we implement, including:
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