BOD, COD and Suspended solids  all are different parameters. BOD and COD are quite different. Therefore there is no correlation between them.

BOD is the mount of oxyegn required by by micororganism to degrade the oragni compounds while COD is the mount of oxygen are used by chemical oxidizing agent to oxide the organic an iorganic compound. and always COD is higher than BOD for the same efflunets.

you may also refre to this discussion which will help you :

https://www.researchgate.net/post/Is_there_any_relationship_between_BOD_Biochemnical_oxygen_demand_COD_chemical_oxygen_demand_SS_conductivity_in_the_water_analysis_parameter

regards,

Just to build on Mohamed's comments, while you can find correlations between COD and BOD, these correlations are specific to the particular wastewater.  So, for instance, domestic wastewater might tend to be approximately COD/BOD=2.3, but that number could vary considerably depending on the fraction of industrial wastewater in the domestic system, water shortages and water reuse, and even the extent of food/grease disposal in the wastewater system.

Thank you for great addition Dr. Randall

Kind regards

Can I use my COD results to predict my BOD?

YES. Although COD should be considered an independent test from BOD, and will generate a higher concentration reading than BOD for a particular wastewater sample, it is generally accepted that COD and BOD share an empirical relationship. Extensive observation of the COD and BOD levels on the same wastewater has shown that the COD to BOD ratio of a particular wastewater will remain constant over time.

For example, food processing wastewater will generally have a COD:BOD ratio of ~2:1, while textile wastewater that can contain dyes will often have a much higher COD:BOD ratio of ~5:1.

To establish the COD:BOD ratio for your wastewater, simply have both COD and BOD run on several wastewater samples. Divide the COD concentration by the BOD concentration for each sample and average the results. For example, below is the COD:BOD ratio developed using three wastewater samples from a food processor:

sample 1: COD = 2,150 mg/L BOD = 1,100 mg/L

COD ÷ BOD = 2,150 ÷ 1,100 = 1.95

Sample 2: COD = 1,990 mg/L BOD = 1,050 mg/L

COD ÷ BOD = 1,990 ÷ 1,050 = 1.89

Sample 3: COD = 1,850 mg/L BOD = 997 mg/L

COD ÷ BOD = 1,850 ÷ 997 = 1.86

(1.95 + 1.89 + 1.86) ÷ 3 = 1.9

COD:BOD Ratio = 1.9:1

Note: Three samples are used for this example, but 3 samples are too few to calculate an accurate ratio. It is recommended that a minimum of 10 samples be used to develop an initial ratio and that the ratio is consistently updated based on additional periodic sample results.

The important point is that once you have established an average COD:BOD ratio for your wastewater stream, then the relatively simple and quick COD test can be used to predict BOD with relative reliability.

Yes!! I do agree with Dr. Randall and Dr. Ali. You can correlate COD and BOD only for very specific type of water/wastewater. Otherwise it can produce misleading image of water quality. And both parameters are very tricky.

Thank you for all the informative answers above.

Since the COD is the amount of oxygen needed to chemically oxidize the organic and inorganic compounds in the water.   I am just wondering, for the TSS in the water samples (especially organic matter), will these solids  contribute to the increase of BOD and COD? I have one sample test results where the TSS increased, BOD increased but COD decreased (from influent, Daf the final discharge)

Furthermore, the samples for COD are preserved with concentrated sulphuric acid, pH

Solids will contribute to the increase of COD and BOD. You can check my paper for further readings at http://dx.doi.org/10.1016/j.ibiod.2016.04.028

@Nik Azimatolakma Awang Thank for your info, can i request for full paper for further details?

Daphne Ling

Universiti Sains Malaysia

Upon reviewal of the answers given, comment as follows :                                           The parameters in reference are most important, when we apply remedial practices to treat waste water in a WWT plant . TSS- Suspended solids are of 3 forms, floaters, in suspension and sinkers. Depending on their proportion, treatment for process is applied, When it is easier to create sinkers, it is best done by a settler and adequate HRT,     Next physical process will be to make them as floaters to duly skim/ scum them out. BOD and COD is best done by chemical process to be followed. Can we have comments to provide views on the above, with well wishes,      

please give me your email address

 Yes, certainly there is a relation between them as the suspended solids comprises  ( volatile + ash ).Now the volatile portion contributes to BOD5. On the other hand BOD5 correlates with COD as the latter contributes to the oxidation of organic and inorganic matter while BOD5 contributes to organic matter  (bacteria ).Refer to  (Metcalf & Eddy Inc )(Wastewater Engineering treatment, Disposal and Reuse ) chapters 9,10. Thanks dear 

Total Suspended Solid is inversely proportion to Dissolve Oxygen

COD:BOD Ratio = 1.9:1

In case of municipal sewage, Ratio between COD and BOD would be in the range of 1.6 to 2.0.

Dear Researchers.

@ Muhammad Shoukat has aptly indicated the basis of sewage effluent, however if the flush water is less then COD will be proprtionately more.

Waste water from chemical factories will have COD higher than 3 to 4 times

Well wishes.

Hi all, I have a doubt. Are COD and VSS(Volatile suspended solids) related?