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  • Exploration of several core conceptual issues related to ISCR
  • How oxidation-reduction potential (ORP) is related to dechlorination rates
  • What controls the amount of intermediate “stall” dechlorination products like dichloroethene and vinyl chloride

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What is a stronger biogeochemical reductant? And they give three options here, ferrous sulfides, ferrous hydroxides or ferrous oxides.

So I’m hesitating because we’re actually working on this right now and we’re… and the more we work on this the more subtle the problem becomes. I guess a couple things I can say that as generalizations that are certainly gonna be true. One of them is that when you compare the numbers the iron sulfides almost always are the fastest they reduced dechlorinate say TCE faster than anything else. The one thing that’s surprising is that magnetite tends to be slow. And an iron(II) added to an iron(III) oxide like greigite is surprisingly actually faster than magnetite. Maybe beyond that, I can’t give more simple set of rules.

Does ZVI reduce sulfate in groundwater?

So that’s an interesting question it’s actually a very good question. And when we first started working on ZVI a long time ago I got quite invested a fair amount of time into that problem. Because thermodynamically, that is definitely a favorable reaction and so we thought, “Oh, wouldn’t that be cool if we could do abiotic reduction of sulfate to sulfide.” But there is no evidence that that reaction occurs. So thermodynamically, it’s favorable, but kinetically it doesn’t happen.

And this is John here. I’m going to put in my two cents from a practical perspective. It’s actually a good thing that doesn’t happen because there’s a lot of sulfate in groundwater. And that actually could be a pretty high reductive demand and you’d be using your iron to reduce you know, 500 milligrams per liter of sulfate. Instead of them you know, 500 ppb of TCE what you’re actually trying to address. So from a practitioners standpoint, it’s actually good that it doesn’t reduce sulfate.

How much water is reduced to hydrogen by… this is an acronym but I think what they’re saying is sulfidated nano zerovalent iron. So how much water is reduced to hydrogen by sulfidated nano zerovalent iron?

Well, the general generalization here is that unsulfidated iron is fairly inefficient and that the majority of the electrons actually go to reducing water and not reducing contaminants. When you sulfidated ZVI, that balance shifts and so it’s actually more favorable to reduce the contaminants than to reduce the water? The putting the exert numbers to that is a little bit TBD that data are just sort of coming out now from different groups about what that amounts to. But I think from what I can recall the sulfidated ZVI the amount of water reduction goes down to like 2010, 1% so really pretty low.

And from a practical perspective that’s great too is when you’re spending money on a reductant you wanted to go to your contaminant, not to water.

What is the viscosity of AquaZVI when it is injected into the ground?

So the way this works is that when the material ship it comes as a fairly viscous suspension like I said earlier 2,000 to 3,000 centipoise. But when it is diluted in water in field applications it’s typically somewhere about 1% to 2% of the material in your mix tank. And when it’s mixed it’s mixed and suspended the viscosity is essentially the same as water. So injecting an AquaZVI or MicroZVI product or most loyal remediation amendments. The real benefit you get out of that is that you’re basically injecting water. Which means that you can use you know, simple pump such as pneumatic diaphragm pumps and you don’t have to get into the realms of multihundred psi injections.

Does ZVI reduce the stall COCs like DCEs and VC in ground water?

I will defer this to Paul. I’m trying to give basically the answer is yes, but slowly. You can do a treatability study of sulfonated ZVI with this and it will go away. I would say with the half-life’s are probably two to three times as what they would be with TCE. But there is certainly abiotic degradation there are some compounds that are basically recalcitrant dichloromethane is basically recalcitrant and 1,2-DCA is also recalcitrant. Those are the two compounds that if you have them in your groundwater it’s strong related… strongly recommended that you use some sort of biological process using the dehalobacters or some other sort of engineered anaerobic bacteria. You have a comment on that Paul?

Well, yeah, just to reinforce that. So the advantage of ZVI is not so much that it degrades the stall intermediates, like DCE like John said. It does sort of but that’s very slow the advantage is it doesn’t make them in the first place because it goes by the other pathway so it avoids making those intermediates. So you have a site where there’s by in situ biodegradation that’s already produced a bunch of DCE and dichloride. ZVI in principle could be useful but that’s not an ideal application.

Can you address the feasibility of injecting chemical reductants into fractured bedrock any success with treating contaminants that have been sorbed in the rock matrix?

I’ll answer that question there’s been colloidal products that have been injected into bedrock oh say I’d say at least the number of the injections at least in the tens. The material, the advantage of a colloidal material is that it doesn’t sink they’re buoyant or they sink very slowly. So they’re not going to fall down to the bottom of your injection while you’re tooling so you can get them out into a formation. I mean, obviously fractured bedrock has got large channels so it’s not that difficult to get it there but you got to keep it suspended before it goes in there. Sometimes the challenges with bedrock would be you know, using Packers or some other engineered injection techniques to make sure that you get good vertical distribution and also horizontal distribution. If it’s saturated you’re gonna be injecting to a saturated zone which is incompressible and doesn’t work too well. But you can give me a call or the RRS crew could also help you with that if you have a project related to bedrock.

Dane: Hello and welcome, everyone. My name is Dane Menke. I am the digital marketing manager here at REGENESIS and Land Science. Before we get started I have just a few administrative items to cover. Since we’re trying to keep this under an hour, today’s presentation will be conducted with the audience audio settings on mute. This will minimize unwanted background noise from the large number of participants joining us today.

If the webinar or audio quality degrades, please disconnect and repeat the original login steps to rejoin the webcast. If you have a question, we encourage you to ask it using the question feature located on the webinar panel. We’ll collect your questions and do our best to answer them at the end of the presentation. If we don’t address your question within the time permitting, we’ll make an effort to follow up with you after the webinar.

We are recording this webinar and a link to the recording will be emailed to you once it is available. In order to continue to sponsor events that are of value and worthy of your time, we will be sending out a brief survey following the webinar to get your feedback. Today’s presentation will focus on “in situ Chemical Reduction Core Concepts and their Engineering Implications.” With that, I’d like to introduce our presenters for today. We are pleased to have with us Dr. Paul Tratnyek, professor in the Division of Environmental and Biomolecular Systems and Institute of Environmental Health at the Oregon Health & Science University. Dr. Tratnyek research concerns the physicochemical processes that control the fate and effects of environmental substances, including minerals, metals, organic contaminants and nanoparticles for remediation, as contaminants, and in biomedical applications. Dr. Tratnyek is best known for his work on the degradation of groundwater contaminants with zerovalent metals.

We’re also pleased to have with us today Dr. John Freim. Dr. Freim is well-known throughout the environmental industry for his work in developing breakthrough in situ chemical reduction technologies. He has over 30 years of experience in materials processing, and 15 years in the environmental remediation industry. And currently leads the first REGENESIS state-of-the-art colloidal product manufacturing facility. In his role with REGENESIS, Dr. Freim is responsible for the manufacture of colloidal materials, including PlumeStop Liquid Activated Carbon, the colloidal zerovalent iron technologies AquaZVI and MicroZVI. As well as other new products used in environmental remediation.

All right, that concludes our introduction, so now I’ll hand things over to Paul Tratnyek to get us started.

Dr. Tratnyek: Thank you, and good morning to everybody. This is Paul Tratnyek, and I’m speaking from Portland, Oregon. This is the first time that I’ve been able to use this cover slide from my office so this is, in fact, the view from just around the corner from where we are. I’m gonna give a talk today that’s primarily based on the work that we roll it up in a chapter from a sort of book back in, you know, in 2014. And I wanna use this first slide here to basically make a little plug for the book and to give you a perspective on how we got started on this particular topic.