COD reduction 1

[imans]

Dear Readers,

Does anyone know how to reduce COD from wastewater? What type of chemical compounds can influence COD value? Is caustic soda can influence the COD value?

Thanks a lot.

Regards

 

[bimr]

Yes, there are ways to reduce COD.

The most common and economical method is the activated sludge process with will remove the COD that is organically biodegradable.

Some compounds may not be biodegradable, and other methods such as peroxide for example are used.

Your question is too general to discuss in detail. The subject is broad and complex. If you would like a specific recommendation, you need to provide more specifics such as flow rate and type of wastewater.

 

[mbeychok]

imans:

I agree with the response from bimr that the subject is broad and complex. Perhaps the following discussion will help you to better understand the subject.

Any oxidizable material present in a natural waterway or in an industrial wastewater will be oxidized both by biochemical (bacterial) or chemical processes. The result is that the oxygen content of the water will be decreased. Basically, the reaction for biochemical oxidation may be written as:

Oxidizable material + bacteria + nutrient + O₂ => CO₂ + H₂O + oxidized inorganics such as NO₃, SO₄, etc.

Oxygen consumption by reducing chemicals such as sulfides and nitrites is typified as follows:

S^-- + 2 O₂ => SO₄^--
NO₂^- + 0.5 O₂ => NO₃^-

Since all natural waterways contain bacteria and nutrient, almost any waste compounds introduced into such waterways will initiate biochemical reactions (such as shown above). Those biochemical reactions create what is measured in the laboratory as the Biochemical or Biological Oxygen Demand (BOD).

Oxidizable chemicals (such as reducing chemicals) introduced into a natuaral water will similarly initiate chemical reactions (such as shown above). Those chemical reactions create what is measured in the laboratory as the Chemical Oxygen Demand (COD).

Both the BOD and COD tests are a measure of the relative oxygen-depletion effect of a waste contaminant. Both have been widely adopted as a measure of pollution effect.

The so-called 5-day BOD measures the amount of oxygen consumed by biochemical oxidation of waste contaminants in a 5-day period. The total amount of oxygen consumed when the biochemical reaction is allowed to proceed to completion is called the Ultimate BOD. The Ultimate BOD is too time consuming, so the 5-day BOD has almost universally been adopted as a measure of relative pollution effect.

There are also many different COD tests. Perhaps, the most common is the 4-hour COD.

It should be emphasized that there is no generalized correlation between the 5-day BOD and the Ultimate BOD. Likewise, there is no generalized correlation between BOD and COD. It is possible to develop such correlations for a specific waste contaminant in a specific wastewater stream ... but such correlations cannot be generalized for use with any other waste contaminants or wastewater streams.

If you want even more details, read "Aqueous Wastes from Petroleum and Petrochemical Plants" written by M.R. Beychok and published by John Wiley & Sons in 1967. It is available in most university libraries.

Milton Beychok
(Contact me at www.air-dispersion.com)
.

 

[appy1]

imans,
bmir is right and its very effective solution to remove COD by activated sludge treatment stage. you can easily innoculaye seed in your system by having sludge from nearby municipal wastewater treatment plant. some municipal plants may have very good growth of nitrifiers, so that u can remove NH4-N from your efflent stream
Another important point is caustic soda can not impart COD to the waste, because it can give inorganic carbon not the oragnic one and COD measures oxygen consumed for total organic carbon present in the waste. I am adding bicarbonate in our process for alkalinity and there is no increase in COD due to bicarbonates!