EN Rx Reagent™
What is EN Rx Reagent and How is it a Different ISCO Strategy?
As the remediation industry grows, there has been a parallel expansion of strategies and methods to address various challenges and specialized knowledge is needed to make the best decisions. First, one must consider the nature and extent of contamination to determine what protocols to apply at a site. One strategy, that is often recommended for moderately to severely impacted sites, is In-Situ Chemical Oxidation (ISCO). As part of the expansion of strategies there are a several options to choose from.
First, we need to identify the dominant criteria to get the most value for the “time and treasure” that is invested. Consequently, there are many features to consider in choosing an ISCO reagent and, while cost issues are primary, other factors come into account such as efficacy, safety and ease of use. In this regard, we will compare EN Rx Reagent to the other dominant ISCO product sodium persulfate. To begin, let us explain what EN Rx Reagent is for an effective comparison before looking at the comparative economics which are very favorable with this product.
EN Rx Reagent is an inorganic additive that is added to hydrogen peroxide, with a cost advantage therein since it is a commodity chemical not subject to certain proprietary processes and higher costs. It is established that hydrogen peroxide is a historical standard for ISCO in the form of Fenton’s Reagent. In this process, the hydrogen peroxide is catalyzed, typically with iron, to generate powerful free radicals that are the currency of contaminant destruction. The problem with this, however, is the reaction has a violent exotherm. This may not seem be a problem if the reagent is successfully injected into the subsurface – but that is not the whole picture. While the tempest is hidden below the surface, it has the capacity to generate levels of heat and pressure that desorb contaminants and makes the situation worse for an indeterminate period of time.
While it seems counterintuitive, EN Rx Reagent is actually a catalyzed hydrogen peroxide that is simultaneously activated and stabilized such that it literally forms a slow release hydrogen peroxide-based generation of the desired free radicals. This creates a treatment longevity profile of several months which considerably longer than other quasi-stabilized hydrogen peroxide additives. To be more specific, claims for those other Fenton’s-based products are on the order of one to two weeks.
It gets better. The inorganic component is added in relatively low doses, on the order of 2.5% by weight to 35% hydrogen peroxide. This simple action suppresses the normally violent exotherm and keeps the solution in the range of 70 to 80 degrees Fahrenheit – yes Fahrenheit. What this means is that this form of activated hydrogen peroxide can be handled with impunity above ground and then injected into the subsurface. The alternative is to mobilize the injection of hydrogen peroxide in the field, then chase with iron and then more hydrogen peroxide and on it goes. This involves more equipment and field time and gives EN Rx Reagent and operational advantage over and above the inherent efficiencies grounded in comparative chemistry – which we will now examine next. As an additional note, one would not deploy 35% hydrogen peroxide to the subsurface directly, but rather safely dilute it on the order of 10X which is in line with established protocols (between 4% and 12% final concentration). This is therefore an ideal application for the EN Rx Support Platform or SP Unit (please see details on the Website) that can draw up the mixture, effect the dilution and pump it out to the subsurface without extensive field manipulations.
An In-Depth Examination of the Chemistry and Economics
As noted, all the oxidants of relevance, with the exception of ozone that has a more complex infrastructure requirement, need to be catalyzed. We have established that EN Rx Reagent is a superior oxidizer, by the nature of the hydrogen peroxide component which is very powerful, universal in its application, versus say sodium permanganate that is only effective on certain double bonds, e.g., chlorinated ethenes. Also, a significant benefit is that the activator is “clean” resulting in no impurities left behind, which in some cases and interfere with secondary biological activity. To this set of qualifications, we then add the fact that we have the controlled exotherm and all of the value which that adds. With that said, let’s look at the comparative efficacy and cost.
To do this we must first look at the stoichiometry of the reactions and evaluate the required dosages for equivalent impact on the contaminants of concern. In this case we will use benzene (C6H6) as a common representative contaminant. Therefore:
Table 1 takes all the key factors into account including the weight of various activator chemicals, which is a critical feature. This is due to the fact that our activator is only needed at 2.5% by weight to hydrogen peroxide versus multiples of that for other activators. In that regard, we then use a low estimate of activator for persulfate at 10%.
Multiplying the stoichiometric coefficient by the adjusted total weight we get the actual mass of oxidant and activator needed to oxidize a Mole of contaminant. From this we can derive an Efficiency Ratio among the three options as follows.
|Oxidant||Molar Weight||Activator Weight Factor||Adjusted Total Weight||Stoichiometry||Weight of Oxidant and Activator per Mole Benzene||Ratio of Need to EN Rx Reagent|
|Na Persulfate||238||g/mol||1.1 X||261.8||15 to 1||3927||7.51|
|EN Rx Reagent||34||g/mol||1.025 X||34.85||15 to 1||523||1.00|
In summary, if we were to compare the total mass delivered to the site EN Rx Reagent would be as effective as 7.51 X sodium persulfate on a weight basis. This has huge implications not only in direct cost, but also for shipping and application times. Further, with a highly stabilized hydrogen peroxide, other benefits include reduced infrastructure requirements and safety factors given the relative behavior of each oxidant.
Back on the economics. The rough bulk price for EN Rx Reagent is $4.77 per lb. For persulfate, which as noted is variable, we will use $1.60 a pound, including the cost of an iron salt activator. The cost differences is 2.98 X. Taking this ratio and factoring the efficiency calculation we can see the true comparative values of these products.
If we convert the efficiency ratios to cost differences, we can see the following in Table 2.
|Oxidant||Ratio of Need to EN Rx Reagent||Approx. Cost Difference||Relative Value Ratio/Cost Advantage|
|EN Rx Reagent||1.0||1.0||2.52|
Because pricing is a function of many factors, these are ballpark relationships, but they certainly create a sense of what the savings can be. What the Table represents is that for every dollar spent on EN Rx Reagent, $2.52 would have to be spent on Na persulfate.
Over and above this feature is the fact that there are significant operational costs that favor the use of EN Rx Reagent.
The Unique Ability for EN Rx Reagent to be Both Activated and Stabilized at the Same Time
Below is a graph of the longevity of EN Rx Reagent from a field. Performance was tracked using ORP. Note we see 97 days back to baseline, but baseline is +100 mV in this case. One could make the argument if we had 0 mV as the endpoint, the longevity would be almost twice as long. That said, three months is more than enough.
As noted, Temperature and Pressure are attenuated in remarkable ways, compared to Fenton’s Reagent which is hydrogen peroxide catalyzed with iron in an uncontrolled reaction. This “bomb” is set off in the subsurface, and risks include daylighting and severe disturbance of mass that is driven into solution.
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