Methods for Removing Inorganic, Soluble CODs

[aljosa_90]

Hi All,

I have an interesting case where a client who primarily deals in the removal of ink from rags & such is trying to lower the COD levels of their discharge effluent. The wastewater is probably highly toxic, inorganic and soluble. Total COD levels are over 120,000 mg/L.

What methods would you recommend for treating this kind of wastewater? Most of the articles I see written on COD removal are primarily concerned with biological processes, however I don't believe that will be possible in this case due to the inorganic makeup of my effluent. Is AOP the way to go for primary treatment? Some other chemical process?

Any input is appreciated.

Thanks,
A.M.

 

[bimr]

Hard to tell with the very limited information that you have presented. The answer will depend on the volume of wastewater, biodegradability of the COD, permit limitations, and TDS. An anaerobic processes is generally the first recommendation for high strength wastewater. The AOP process will likely have unaffordable operating costs

 

[aljosa_90]

Thanks for the response bimr. I don't have TDS readings, but for the sake of this discussion I would say it's safe to assume low biodegradability. (As I understand it, an anaerobic process is only done in biological wastes, which would rule it out in this case).

There may be a way to store the wastewater and over time dilute it in a less-polluted stream. But I still have to confirm a few things regarding the volume. Also, even if we were to dilute it we would still have COD levels approaching 80,000 mg/L. I am trying to remove it to sub-10,000 mg/L, but I understand this may not be achievable without undue costs - right now I'm just trying to pinpoint the most-reasonable primary treatment, and working from there.

I agree about the high costs of the AOP, which is why I'm searching for other options... unfortunately, I'm hitting a brick wall. Would you have any recommendations on how further to approach this problem?

Many thanks.

 

[bimr]

If the waste is not treatable, you should be investigating disposal options.

Send the material off-site to a dispoal firm or thermally process it.

 

[aljosa_90]

Ok, to give you an update: it turns out that the plant is using a lot of organic solvents for cleaning the ink. These include acetates, alcohols, glycol ethers and white spirits - I believe these are all polar in nature. Methinks you can break the solution either by biodegrading the solvents through an anaerobic process as you mentioned, or by neutralizing them through some other chemical means. This could be followed by flocculation and sedimentation of the processed stream. Please correct me if I'm wrong; I believe this will produce good results.

Unfortunately, the polar nature of the solvents rules out adsorption through activated carbon.

I'm also a bit worried that the required retention time of any biological process will call for a large footprint, high construction costs, etc. However, if that's the typical way to remove these solvents, it's better than nothing.

 

[bimr]

If you have solvents, suggest you look into a distillation process. Distillation is a BAT for some of the industries that use solvents.

Examples of treatment

That may able to reduce the wastewater COD enough that it is suitable for municipal treatment.

 

[aljosa_90]

bimr,

I want to thank you for all the advice you offered so far. The distillation process is something I considered, but ruled out based off of the high evaporation temperatures of the glycol and white spirits.

I've started considering different variations of the advanced oxidation process (via Fenton's regent or ozone).

Thanks again and best regards.

 

[bimr]

Good luck to you. Interested to know your results. Consider reporting back on the project outcome