BOD5 is depend not only on amounts of pollutants but characteristics of the pollutants. If pollutants are easily degradable oxygen consumption is high during initial stage, but refrectory matters will not biodegraded within short term and BOD5 could be estimated low. Hence, basically not possible to calculate only with provided information.

BOD represents the amount of oxygen consumed by bacteria and other microorganisms, so the rate of oxygen consumption is affected by a numbers of variables such as:pH,the type of organic and inorganic material in the water,therefore it is complex and impossible to give a unique way without considered all of parameters

There is a standard water and wastewater test for BOD5, with results in mg/l oxygen demand. The value essentially assumes the wastewater is aerated, so oxygen is available. If for example, all of the pollution at 5g/person/day was biodegradable by aerobic bacteria - oxygen in 5 days, that’s 5g in 100 liters, or 50 mg/l. But not necessarily all aerated pollution is going to breakdown in 5 days, so that is why Standard testing is run. (See reference book - Standard Methods for Testing Water and Wastewater)

Doing this is quite simple. Just measure the O2 at the time and after 5 days and then calculate the difference (values in mg/L). Sample incubation conditions: 20°C in a closed, dark incubator. There are some devices that do the work themselves and generate the result, reducing human error. But, the gain in analysis quality doesn't seem to be important. It is worth buying these devices if there is a lot of demand and for the long term. For a one-off project it's not worth it.

thanks you for your responses

I think it is 5000mg/100 L so the BOD is 50 mg/L.

For this you may also require dilution water, ie. diluting the sample with a mixture of aerated dilution water to 25%, and then finding the initial DO and incubating it for 5 days and finding the final DO, as mentioned by other experts. this dilution is required as the waste water will have nil initial DO when we directly measure the DO. how to prepare the dilution water, you may please refer:

Kaladharan, P and Prema, D and Nandakumar, A and Leelabhai, K S (2001) Manual of Analytical Methods for Seawater and Sediment. Manual. Central Marine Fisheries Research Institute, Kochi.

Dilution scale depends on the type of waste and waste load. Hope this is useful@