Jar testing for Oxidation of BOD/COD

[DrLewinstein]

Hi, folks,
I am going to be doing some jar testing to remove BOD/ COD from an industrial waste stream. BOD is about 1200 mg/L, COD 2000 mg/L. Need to knock this down to 300 mg/L BOD, 750 mg/L COD. Waste stream is small (5,000 gpd), so we're trying to avoid biological if possible.

We're looking at oxidizing with chlorine (sodium hypochlorite?) or peroxide. Also, looking at removal by activated carbon.

I'd love to have some words of wisdom on jar testing these kinds of things. e.g., concentration of chemicals, can we use an ORP meter, a general test procedure.

Any help out there from the gallery?

Thanks

 

[bimr]

It would be helpful to know the type of waste.

In general, it will not be feasible to reduce the BOD significantly with chemicals. However, if you have floatables or solids, you may be able to remove some of it.

 

[DrLewinstein]

We are treating the wastewater from a process that is removing a coating off of "off-spec" plastic so that the plastic can be recycled.

When the pH is dropped to about 3.5, about half of the BOD/COD comes out as a precipitant. The numbers I gave at first are after this step. We're trying to treat the rest of it.

 

[bimr]

Would not expect that the chemicals would do much to oxidize that type of mixture.

About the only thing that may work is a catalytic oxidation process. Probably not economical either.

Have you considered an evaporation process?

 

[ChemOxGuy]

Your situation helps -- small flow and ca. 60% COD removal. This can probably be done using Fenton's Reagent (iron-catalyzed H2O2) in a batch treatment process. The process is described at

http://www.h2o2.com/pages.aspx?pid=143&name=General-Chemistry-of-Fenton-s-Reagent

and its use for BOD/COD removal is described at

http://www.h2o2.com/industrial/applications.aspx?pid=104&name=BOD-COD-Removal.

For personal safety reasons, read this info (and MSDSs) carefully before conducting bench tests. Since you're already at pH 3.5, the recipe would be: 1) add a ferrous salt e.g., FeSO4 at a dose of 4-10 lbs (as Fe) to a 5,000 gal batch and mix thoroughly - equal to 100-250 mg-Fe/L; 2) slowly or incrementally add 25-50 gals H2O2-50% while continuing to mix for 2-4 hrs - equal to 2500-5000 mg/L; and 3) after confirming substantial H2O2 reaction (H2O2 residual < 100 mg/L), raise the pH of the reacted wastewater to pH 8.0 - 8.5 to flocculate/settle the hydrous ferric oxide flocs (cationic polymer can help).

The big downside to this approach is sludge production. You may be able to forego Step-3 if COD targets can be met without dragging out the adsorbed COD, in which case I'd raise the pH only enough to meet discharge requirements (pH 6?) so as to minimize Fe precipitation.

Just a reality check ... the chemical costs for should be in the range of $125 - 250 per day (5,000 gals WW).