Reducing COD in Waste Water

A. Hi Abbas.
I assume there is a typo there, and you are asking how to reduce BOD?
If you have high BOD despite an acceptable COD, peroxide additions or ozone treatment should do it.

The usual way of dealing with BOD is biological treatment, but that is probably not economically & logistically appropriate for a waste treatment plant for electroplating wastewater.

Read on for what others have done re. high COD.
Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Sara,

I may be up a gum tree, as we say, but to increase the oxygen content of your waste water, have you ever tried to arrange a system such that nature will help?

In the fishery business a way they use is to discharge oxygen depleted water at a reasonably high level, 6 feet to 12 feet or so.

The discharge empties into a round plastic pipe or tube. There are a number of these identical tubes and each one is at least 9" above the next one. They are about 18" in diameter but could be larger.

Each tube has a perforated plate at the base to prevent 'packing', i.e. plastic mass transfer packing, from falling out ... although the Fisheries, being a little bit cheap, did use some fairly poorly designed packing.

The modus operandi is that this oxygen starved water falls down into and onto the packing where the flow is distributed and then dribbles out, reasonably evenly, from the perforated plate. Due to the 'fall' of the water, it automatically sucks in some ambient air = oxygen.

Ergo, ipso facto, you now have some somewhat oxygenated H20. OK? Let's hope it will work for you. If it does, please remit $ 10,000,000.00 so that I can afford to go on vacation! Good luck !

A. Sara,

I found on the web this site:
www.h2o2.com/industrial/applications.aspx?pid=104&name=BOD-COD-Removal ⇩
Maybe it can help you.

Good luck

[Ed. update: The above link has broken -- don't go there. Thankfully, The Internet Archive preserved a copy
These days information often never sees print, then disappears forever. If you find that concerning, please consider a donation to The Internet Archive.

A. Sara, Before I start looking for process technologies to solve various waste and pollution issues; I always like to take the process creating the waste back to ground zero and look at it from the point of view of what can be done to eliminate or change the various materials, process steps, equipment, etc. that is causing the waste or pollution in the first place and yet still maintain product specification. Or if that is not possible, change the product spec. such that, process changes can be made. I.E., "Change the process and material and spec., eliminate the waste". In order to do this effectively, this requires a little work and creativity.

If this is ineffectual or impossible, then end of pipe treatment technology is required. As for solving a high COD problem, this can be normally masked by oxygenating the waste stream by contacting the waste process stream with air or by the injection of oxygen. But remember, this is adding on additional equipment, materials, energy, etc. (hence increased maintenance and operations costs) There are plenty of vendors world wide that can supply this process technology. Check any of the waste water or chemical process websites.

A. Sara,

Removing or reducing chemical oxygen demand can be done with a variety of ways including utilizing some chemical pretreatment, biological remediation or bio-augmentation in activated batch reactors wastewater pretreatment units. Depending on the upstream source that is contributing the high loads of COD in question and the daily volume loads needing treatment you may discover that you might be able to adjust the upstream contributing problems areas process control and reduce any problem areas. Small daily volume loadings ( less than 500 gallons ) may be cost effectively evaporated at $0.03-$0.10 per gallon. Pretreatment of high COD loadings is a bit of a challenge in the real world. Be cautious of any "Blue-Sky" remedies. COD loadings and the difficulties in treating them will vary as they are impacted by pH, various chloride loadings, temperature, presence of heavy metals, surfactants, F-M food to microbial loadings ratios, etc.

Fill in more info on your process, COD loadings, COD characteristics, goals, etc., to help paint a better picture of what you are facing.

A. Sara,
You can reduce the COD using various methods. The best method I suggest to you if the COD of your effluent is more than 20000 mg/L.Then you should go for AOP (advanced oxidation processes). First bring the effluent pH to around 5-6 and treat with Fentons Reagent, wait for the flocs to settle.Then filter the supernatant using Activated Carbon filter. You will be surprised to see much reduction of COD after filtration.

Hi Hashim. Please see
www.h2o2.com/industrial/fentons-reagent.aspx?pid=84&name=Fenton-s-Reagent ⇩
and/or Wikipedia .

Regards,

[Ed. update: The above link has broken -- don't go there. Thankfully, The Internet Archive preserved a copy
These days information often never sees print, then disappears forever. If you find that concerning, please consider a donation to The Internet Archive.

A. Hi cousin Prajapati. Five answers were offered above.

If you can express your question in terms of someone's previously posted response, people may be able to help you :-)
Or maybe your need is for a tutorial textbook on the subject? ⇨

Best of luck!

Regards,

A. Hi Meeta. It may be possible to chemically precipitate most of the contaminant to remove it, or to chemically oxidize it, or to biologically treat it in a trickling filter or activated sludge. But what type of waste please? Consider the ideas previously offered on this page. Is this just one drum of waste or thousands of gallons per day?

I probably can't personally answer your question, but readers & I want to help. Please try to offer readers a fuller description of your situation. Thanks.

Regards,

A. TO REDUCE COD NEEDS CHEMICAL AND BIOLOGICAL TREATMENT ON WASTE.

A. Hello,
You don't mention what type of industry you are involved in. Is your system closed looped? Anyway, have you considered using activated carbon? There are in-line carbon filters that could be installed to reduce organics. If the organics are reduced, the natural reaction of organics/oxygen will also be reduced.

A. Hi. I don't know the answer, but you might read up on New York City's sewerage treatment approach. NYC was built before the days of separated sanitary sewers and storm sewers, so they have the same problem when storm waters run into their system.

Regards,

A. Aeration is a good way to go. I believe you could also use a swimming pool floating chlorinator with a couple of chlorine tablets added daily. Make sure to check with your POTW before using the chlorine.