Type, volatility, and quantity of organic compounds in wastewater can influence the COD/TOC correlation. Nevertheless, there are some studies that actually analyse the correlation between COD and TOC, which have found a 3:1 mass ratio (2.81 approx.). Thus, TOC analysis may be more suitable for determining organic matter content since it takes into account all of its different oxidation states without producing toxic analytical waste.

http://dx.doi.org/10.1007/978-3-642-23756-0_39

http://dx.doi.org/10.1080/10934529.2010.506116

Chemical oxygen demand (COD) is widely used for waste water monitoring, design, modelling and plant operational analysis. , and  Total organic carbon (TOC) indirectly measures the total amount of organic substances present in water. 

COD represents quantification of oxygen requires for oxidizing the carbon and TOC represents quantification of oxidizable carbon. The amount of oxygen required (COD or BOD) may change while the carbon concentration (reflected by the TOC value) does not. Industrial Influent wastewater it could vary from 1.67 and 6.65 and Influent sewage it could be in range of 2 to 3. Treated effluent COD:TOC ratio might be same or change based on type of treatment. These ratios vary based on type of wastewater and need to be standardize for particular type of wastewater stream.

Article Rapid determination of indirect cod and polyvinyl alcohol fr...

 Thank you Ciro Fernando Bustillo-Lecompte from Ryerson University ,Manoj Kumar Tiwari from NIT, Raipur and Sandip S. Magdum from University of Pune.I will go through your suggestions.

Dear Sandip Magdum,

I need another clarification that what will happen  in the COD to TOC  after the treatment process of wastewater.We always expect that the TOC of the wastewater should be decreased after the treatment. comparatively the reduction of COD.Is it possible the value of TOC greater than COD value?  How I will correlate when the amount of TOC was greater than COD after the treatment.?

Thank you.,

Expanding Dr.Magdum's explanations, TOC is the carbon content of an organic compound/substrate, whereas COD is the oxygen equivalent of the same compound/substrate, serving as electron donor during full oxidation. Therefore TOC/COD ratio is a function of the oxidation state of carbon in the compound. For example, this ratio is 5.4 for methane and 2.65 for glucose and acetic acid.

COD testing is simple and less sensitive in lower concentrations, whereas TOC requires instrumental analysis but much more precise. Therefore, it is advisable to use TOC for following biodegradation reactions of compounds at low concentration (below COD 10-20 mg/L).

Bothe COD and TOC of wastewater to be reduced due to biomass formation and CO2 generation associated with energy reaction. If COD and TOC are measured in the filtrate (i.e. soluble values) in the effluent a similar ratio would be expected.

Regarding, TOC greater than COD in the effluent, I would advise repeating the measurements or... firing the technician!..

Expanding Dr.Magdum's explanations, TOC is the carbon content of an organic compound/substrate, whereas COD is the oxygen equivalent of the same compound/substrate, serving as electron donor during full oxidation. Therefore TOC/COD ratio is a function of the oxidation state of carbon in the compound. For example, this ratio is 5.4 for methane and 2.65 for glucose and acetic acid.

COD testing is simple and less sensitive in lower concentrations, whereas TOC requires instrumental analysis but much more precise. Therefore, it is advisable to use TOC for following biodegradation reactions of compounds at low concentration (below COD 10-20 mg/L).

Bothe COD and TOC of wastewater to be reduced due to biomass formation and CO2 generation associated with energy reaction. If COD and TOC are measured in the filtrate (i.e. soluble values) in the effluent a similar ratio would be expected.

Regarding, TOC greater than COD in the effluent, I would advise repeating the measurements or... firing the technician!..

   Thank you Dr.Derin Orhon..But I need to firing myself as your suggestion.Because me only the technician for TOC analyser as well as for COD estimation.I also shocked about the COD and TOC results got from the analysis. 

  Thank you sir for your response.I will repeat my TOC and COD estimation again and check the treatability of wastewater.

I'd like to say that the explanations are getting more sophisticated and accurate as time goes on.  in our lab putting sewage through  TOC analyzer is not really allowed.  Anything that is sensitive to high temperatures that can be oxidized to CO2 in an oxygen rich environment is measured.  Its mostly used to measure drinking water.  COD is chemically oxidized by dichromate and liberated chromium is measured as a surrogate for oxygen demand.  By thinking about the methods you can probably come up with reasonable alternatives for explaining the discrepancies and thus changing ratios.  Just a word of note in our lab using ozone to treat sewage although the COD decreased in the effluent, the TOC went up.  Good luck and I always enjoy reading some of the other comments.  Good job everyone!

Thank you Dr.Angus Chu for your comments...

Please note that TOC only measures the carbon in your sample, not other organics such as N, P, S, etc. If your wastewater/water is domestic one, it is mainly carbon. If not, it depends on the source/type of wastewater. 

Thank you Dr.Chinagarn Kunacheva and 

Ms.Shalini Gupta for your comments...

The COD effectively is a measur efor the amounts of electrons avialable in the organic carbon for reduction of oxygen to water. TOC is the amount of carbon. The ratio is therefoore a measure for the degree of reduction of the carbon compounds (Add your answeri.e. low for formiate and high for a lipid).

Thank you Dr.Mark Van Loosdrecht for your valuable comments...

Nice Q and Replies.

COD is a parameter that indicates what potential the waste water sample has towards Dissolved Oxygen for its degradation and TOC is what amount of Carbon (Organic compound derived Carbon) that is actually is available. Both differs. and values vary from effluents of varied industries and also for organic compounds..  

Please dont get confused with COD theor and COD exprtl..  

Correlationship may be possible theoritically but not experimentally for different WW composiitons... 

Thank you Dr.Udaya Bhanu for your comments...

To Udaya:   The amount of dissolved O2 needed to degrade the organic compounds is effectively the BOD. The amount of O2 needed to fully oxidise (burn) organics to CO2 is the COD. The theoretical COD is usually the same as the experimental COD, although one has to consider that some compounds are not oxidized in the Chromic acid test. For the permanganate test (as sometimes stil is used) many compounds are not oxidised and permanganate COD has a very weak correlation with theoretical COD.

I enjoyed a nice discussion series. I also have similar question as Maharaha. What does negative TOC value signifies? 

Also in my test of Greywater, TOC values are always higher than COD. One explanation could be: In greywater nutrients are very low. Are there other explanations too?

Which one is higher, TOC or COD?

COD = chemical oxygen demand since the COD test oxidizes all organics except for those which are totally resistant to dichromate oxidation

Stoichiometrically, the COD/TOC ratio should be approximately the molecular ratio of oxygen to carbon: COD/TOC =32/12= 2.66 —4

The ratio actually ranges from 0 (when organic material is resistant to dichromate oxidation  to 6 (when inorganic reducing agents are present).

In a wastewater treatment plant, when wastewater gets oxidized, the BOD5/TOC ratio  drops. Following treatment the treated effluent may have as low BOD5 /TOC ratio as  0.5 because by the time effluent wastewater is having very low biodegradable organic compound.

Thank you Prof.Jayanta Biswas for your valuable comments. But i found that in many cases, COD/TOC ratio goes beyond the limit what you mentioned theoretically. Because, the wastewater from various industries are very typical in nature. At that time i think that we have to validate other parameters such as BOD5, organic nitrogen etc., to confirm the treatment of particular wastewater.

Regards,

Maharaja.P 

Dear Maharaja

Conventional COD methods are based on the principle of the dichromate oxidation, so that often customary environmental and safety conditions are not met. Furthermore, the method is difficult to implement for the online operation. This leads to an increased tendency to replace the COD by TOC.

Correlations between TOC and COD are defined in the German waste water ordinance (AbwV) and can be determined for each substance. Of course, using such measurements, correlation factors for unknown mixtures can also be detected. However, to be able to use such a factor with online measurements, it is required that the water and its mixture of substances does not change in their composition...

Also you can find some useful informations from following links:

https://link.springer.com/chapter/10.1007/978-3-642-23756-0_39

https://www.ncbi.nlm.nih.gov/pubmed/20721800

http://rofacts.com/Treatment/Activated_Sludge/BOD-COD-TOC/bod-cod-toc.html

http://www.tandfonline.com/doi/abs/10.1080/10934529.2010.506116?src=recsys&journalCode=lesa20

http://www.ingentaconnect.com/content/wef/wefproc/2001/00002001/00000009/art00021

Reagrds,

Ata

Dear Ata Rafiee,

Thanks a lot for your valuable comments and the mentioned references. Shall we use COD: TOC ratio to describe the biodegradable nature of the wastewater instead of taking BOD test?

Regards, 

Maharaja.P

Dear Maharaja Pounsamy

Thanks for your warm messege. Also I record my thanks for your valuable guide.

Regards,

Ata

Good discussions on the topic. Many experts have lucidly explained the significance of COD/TOC ratio in waste water.

Thanks and regards

Dear Dr.Asit Kumar Batabyal,

Thanks for your comments.

Regards,

Maharaja Pounsamy

very fruitful discussion.

Regard to all participants

Thana Noor

Thanks for your comments.@Thana Noor

Regards,

Maharaja Pounsamy

Really a healthy discussion

Received clarity in correlation between COD and TOC

Regards

Anantha Singh T S

What an educative discussion! Thank you Mr. Maharaja Pounsamy for igniting the intellectual discussion.

Also, regards to all participants.

The 'Q & A Section' is the most interesting part of RG. This gives us scope to interact with others and to improve our knowledge. In the present thread, the discussion was really educative.

Thanks Mr. Musa Abubakar Tadda and Dr. Asit Kumar Batabyal for your comments.

Regards,

Maharaja Pounsamy