It depends on the own characteristics of the specific wastewater.
COD values are generally higher than BOD, however, there is no real ratio. It depends on the treatment process i.e if the same process is used all the time under the same conditions. Other factors can affect both factors such as composition of the waste being treated.
Dear Dr. Udaya Bhanu
Do you have some references "BOD/COD relationship for assessing toxicity" can you please share with me
The ratio BOD: COD is a characteristic of a particular wastewater and is a simple and direct measure related to its biodegradability. That is, there is no absolute value for any residual water, but will directly depend on its composition. It is usual to consider a wastewater that has a BOD ratio: COD with a value greater than 0.4 indicates that you can apply a biological treatment if necessary. However, as this relationship will depend on the data quality of BOD and COD, analytical quality assurance should be applied, so that the data are sufficiently reliable. In the case of the BOD, as this method is made applying an inoculum of microorganisms, among other things, you must ensure that toxic compounds are not present, in order to guarantee the correct grow of such microorganisms.
Thanks Dr. Maria Del Carmen Espinosa Lloréns for sharing your views with us
Is there any possibility for getting higher COD value than BOD value..?? whether it depends on the source of samples??
Thanks Munavar Iqbal and friends here...
I have a lot of unpublished work carried out in this area. However this para is intended for a better understanding of the concept.
BOD is based on activity of microbes. COD is based on chemical reaction (oxidation). If microbial seed we use for BOD is not active then it results in Higher BOD. It is as good as no microbe is added. Even if the same microbial seed is more active or more in volume, then also it results in lower BOD. It takes a lot of time and expertize to carry out BOD for 100% accuracy. Hence I believe in standardized BOD namely using a seed of uniform composition tested with glucose as standard.
To avoid all confusions Take it granted that COD of filtered samples free from inorganic compounds (mostly anions) alone is reliable.
Regarding using BOD5:CODCr ratio as an indicator of Toxicity, We need a lot of work to be carried out with different standard solutions, standardized microbes, toxicity tests etc.
Unfortunately I never had an oppurtunity to work on this demanding topic after my PhD days.
The relation between COD and BOD depends on the characteristics of water sample and the ratio between them is changeable with regard to treatment time
Chemical Oxygen Demand (COD) is the total size of all chemicals (organic, with some exceptions , es. benzene et...and in-organic) in water or wastewater;
BOD5 measures the amount of oxygen that the bacteria consume to degrade the organic matter present in the water or wastewater. The value of COD is greater than BOD5; usually a maximum of up to 4 times in the industries of medium size; but it varies greatly depending on the industrial process and especially on the nature of the substances discharged in the effluent.
One of the answer mentioned the toxicity based on the ratio of BOD to COD, why if the ratio is too low, it indicates that that the sample is toxic?
I think is not necessary to explain about BOD or COD you know this. Here the important thing is that you must obtain your ratio by your own. Then, the most important thing is that you have to standardize your method for your own samples to obtain the values of COD and BOD after your repeated many times your analysis. When you do so, then you will have a better knowledge of your samples then you can apply the necessary treatment if required. The only true thing is that you have to follow the international standards for the methods. Then, in the description of your methods you have to explain how you did, especially if you did some modifications. As many colleagues already wrote here, there is not an accurate ratio, because the wastes are different and how you treat your samples.
what is the usual BOD range for pond waters ?? I am getting 12 -132 ppm. Is this ok or I should get below 10?
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