Reducing COD in Waste Water

A. Chlorination is a bad idea, IMHO. It might help you pass but It'd be by "fooling" the test.

You might try adding some hydrogen peroxide and aerating. Seeding with some microorganisms wouldn't hurt.

A. Hi Hardik. You may consider my response to be "ducking the question", but please listen anyway because so many people get themselves into rapidly escalating trouble by making the same huge mistake --

You NEVER determine wastewater treatment regimens or reagent usage by theory; you always do beaker [beakers on eBay or Amazon [affil links] tests and, after you have proven a successful treatment regimen, you scale up proportionately from there. Good luck.

Regards,

Hi Keshava. I'm all for that, but how do you propose to use COD to advantage?

Regards,

A. The so called wastes, mainly liquid wastes, are used in agriculture irrespective of bod, cod, pH, etc. ... and good, high quality organic food is produced. We have been doing it since long.

Hi keshava. You may have been doing it for a long time in India, but I don't think it's ever going to happen in the USA :-)

We are very queasy about using wastewater for agricultural irrigation -- but not the least bit queasy about importing uninspected food from places where they do so :-)

Regards,

Hi Daph. We're pleased to post your inquiry but must remind you that this site focuses on metal finishing. So, few of our readers probably have much experience with poultry wastewater, nitrification, or de-nitrification.

Regards,

You might be able to remove the turbidity by applying a suitable flocculant (polymer).

I'd suggest you also pose your question in one of the wastewater groups on LinkedIn. You might have better luck there.

Hi Loreli. I hope someone helps you :-)

This is a free public forum where people must help each other if help is to be gotten. While you are waiting for help, please see if you can help answer one of the unanswered questions preceding yours. Thanks!

Regards,

A. Hi Sandip. You never combine wastes except:

If this is a plan for ongoing treatment, you must change it and separate those wastes -- for example, solvents & surfactants can make acid/alkali neutralization and precipitation of metals nearly impossible. If this is a one-time mess, such as a floor spill after a fire, you could try to carefully characterize the waste for us and see if you get any good hints, but you may need to ship the tank truck (or whatever) of waste to a competent facility. Good luck.

Regards,

A. You need to specify the volume per day to be treated, and also whether or not the analysis is on a filtered or an unfiltered sample before any advice can be given.

A. Hi again. So you are saying that this is one bad batch of wash-water waste you must get rid of? You should probably send this to a treatment facility which is able to thoroughly analyze and treat it . . . and make sure you separate your processes in the future so you don't generate any more. It should be very practical to keep the solvents away from the strong acids, for example.

Unfortunately, you could read a 400-page book and still not know what to do with it, but you must start with a pretty good analysis of what it is, as Lyle notes. Sadly, uncategorized mixed wastes with solvents, COD, strong acids, surfactants, etc., may contain powerful organic acids, and might possibly even be explosive -- they are not ideal for trial-and-error learning. Again, you must keep the solvents away from the acids.

Regards,

 Hi Sandip. If there is a lot of water in this batch, it's very unlikely to be explosive ... sorry, I'm not trying to frighten you. But I am suggesting that you can't allow various types of waste, like strong acids & solvents, to mix together randomly and then later treat it for disposal inexpensively, and without analysis & instrumentation.

In any case, if you must treat this batch in-house, the way to do it is by experimenting on one beaker of the mixed solution, keeping careful notes about what you do. When you have developed a successful protocol, you repeat it several more times with a beaker to be sure before you scale up to mixing any further chemicals into the whole batch. You never experiment with the whole batch, turning waste into witches' brew. Good luck.

Regards,

A. Hi Sean,

I would think chrome based chemicals shouldn't make the COD go up, and I don't know about silane-based chemicals as I haven't worked with them and don't know how you treat your wastewater.

Please, specify how you treat your wastewater, and if you know which chemicals are present in your final effluent water. If not, I would search for:

- Reducing agents
- Solvents
- Hydrocarbons (oils, greases?)
- Chelating/wetting agents

I can't say what is the problem without further data, and I can't assure we can solve this, but I think that while you are searching for data, you will learn something more about your process.

Regards and best of lucks!

A. Hi Hassan,

You say the sample you measured was taken just before the grease trap, so I would advise to take another one after it to see if it lowers that value somehow.

For BOD and COD, chlorine is always my first choice if applicable, there are many other choices but every one is more expensive than the first one. Controlled chlorination may be helpful lowering those values down to your requirement.

You may have to adjust pH to the best precipitation value if you have any metals in solution. If not, don't and just adjust if the chlorination performance needs it.

AFTER you have treated all oils and organics, sedimented and filtrated your wastewater, adjust pH to your requirement.

You could make all these steps in lab and try to extrapolate what could occur in your plant.

I hope this can help you! Best of luck!

A. Hi Logesh. There is perhaps a language issue here because inorganic minerals are probably chemicals. But you probably mean some mineral or material that you can dig up from the earth and add to your wastewater without any further processing, like sand or mud or peat or coal?

My very limited understanding is that the bacteria in activated sludge can reduce COD depending on exactly what is the source of the COD because some portion may be biologically reducable, and some portion may not. I would say that, in theory, adding a bacteria-rich inorganic material could constitute an activated sludge process … although obviously a carefully researched & designed process is more likely to be successful than a haphazard one.

Please give us the details of your situation.

Regards,

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A. Hi Noor. You should try to minimize your waste by returning rinsewater to the process tank when possible, then keep the cyanide separate from the nickel because treatment gets very difficult once combined. Then you oxidize the cyanide (probably via alkaline chlorination with sodium hypochlorite bleach) ⇦ bleach/sodium hypochlorite in bulk on eBay or Amazon [affil links] , precipitate the nickel by high pH, and settle or filter out the solids.

You can start with the free Metal Finishing Guidebook ⇨
which has chapters on wastewater treatment, minimization of waste, and similar topics .

You can also search the site for topics like "Cyanide Treatment" and "Nickel Waste" -- you'll find dozens of threads on those subjects.

It's not that I don't want to try to answer your question more fully, but treatment of plating waste fills whole shelves in technical libraries, with books like:
Kushner's "Water and Waste Control for the Plating Shop" ⇦[this on eBay, Amazon, AbeBooks affil links],
Cherry's "Plating Waste Treatment" ⇦[this on eBay, Amazon, or AbeBooks affil links], and
Clarence Roy's "Operation and Maintenance of Surface Finishing Wastewater Treatment Systems" ⇦[this on eBay, Amazon, or AbeBooks affil links]
and many others devoted to it. We can probably answer carefully delimited questions, but for a highly generalized one like how to treat electroplating wastewater we can only refer you to references. Good luck!

Regards,

A. Hello, Noor:

It's worth a try to add some hydrogen peroxide to the wastewater prior to settling or whatever method you use to reduce solids. I can't say how much, since you provide no numbers, but a few percent of the 35% grade might be more than enough.

Hydrogen peroxide is not terribly expensive in industrial quantities, and, possibly, might solve all your problems simultaneously.