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Hexavalent Chromium Removal from Groundwater Leachate

2006

We are recommending a co-precipitation method (add FeSO4, bring pH down to 2 and then raise to 8.5) to remove hexavalent chromium from water. Someone mentioned to that the system proposed is great in theory but that in practice we would have difficulty in achieving settling, which would manifest as both a scum on top of the batch, and a poorly settled precipitate with little better than 1% solids.He suggested that I use Dissolved Air Flotation (DAF) to remove metal sludges, which will give greater success achieving 4-5% solids, and a cleaner supernatant.

Does anyone have a thought on it. Please note that I am not removing hex Cr from industrial wastewater.
Does anyone know of any vendor that uses co-precipitation method for Cr removal?

Regards,

Prakhar Prakash
- Philadelphia, USA

How much Cr VI are you starting with and to what level are you trying to reduce it to? What is the targeted design flow rate of the system?

Chad Dannemann
- Houston, Texas
2006

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2006

Thanks Chad,

a) We are treating 20-30 ppm of Hexavalent Chromium and hoping to bring it down to 0.1-0.3ppm in the effluent. The treatment is in a batch process with the total volume of leachate treated being 12.5 m3 in a batch reactor.

b) Any thoughts on how far should we raise the pH and whether we would need additional coagulants?

Regards.

Prakhar Prakash [returning]
Consulting - Philadelphia, Pennsylvania

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I hate to mention it because of some past over-statements seen here, but electrolytic treatment is perfect for hex or tri chromium. It will reduce and remove both in a single step at a pH of 6.5.

Paul Morkovsky
- Shiner, Texas, USA
2006

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2006

Anything is possible depending on your selection of co-precipitants (calcium, ferric, etc.) and dosage of polymer, but my experience has been that this sort of sludge is normally settled vs. floated in a DAF.

However, since this is landfill leachate, you may want to think about floating the sludge further if it contains a lot of oil and grease or other organics.

I would suggest that you work with an experienced supplier of water treatment chemicals/polymers to conduct some jar tests to determine which technology would be best suited for this particular wastewater as every wastewater behaves a little differently.

Chad Dannemann
- Houston, Texas

Have you considered treating the groundwater leachate at a neutral pH or the incoming pH of the water. This would eliminate the use of acid to take down to pH 2 and eliminate (reduce)caustic to bring back up. There are a number of products that reduce and coagulate that may work as a 1 product fix. With these low levels of Chrome this may be a good fix. With these products gravity settling works best.

Gordon Djani
- Greenville, South Carolina
2006

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Treating the batch at a pH of around 8.5 would do the trick. There are several additives as Gordon said--Coagulants, Precipitants, etc. That will easily reduce the Cr level to what you are looking for. I see no need to Drop the pH down low unless you have some chelating agents in the water you are worried about. I have treated LOADS of this stuff before with Non- Detectable Cr as a byproduct.

Ryan Cook
Toccoa, Georgia
2006

Can you try RO system for water extraction before chemical treatment as this will reduce the hydraulic load on the treatment facility and recover water for reuse.

Aravind A Narayan
- Coimbatore, Tamilnadu, India
2006