BOD calculation step by step
Biochemical Oxygen Demand calculation
BOD calculation method, BOD calculation formula
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1. STEP 1 : Gather data
2. STEP 2 : Calculate the BOD
3. Step by Step example : calculation of BOD5
4. BOD Calculator Excel
Environment protection is now a priority and water effluents form factories must be controlled to make sure they do not carry too much organic material. The BOD is one of the most common specification to make sure the effluents will not harm rivers. This page explains how to calculate the BOD from laboratory data.
1. STEP 1 : Gather data
In order to calculate the BOD, the laboratory is sampling some waste water, then is diluting it in a BOD incubation bottle. The lab must measure the following data :
D1 = oxygen
diluted level in the diluted sample at t=0 (mg/l)
D2 = oxygen diluted level in the diluted sample at t=5
days (mg/l)
B1 = oxygen diluted level in the dilution water at t=0
(mg/l)
B2 = oxygen diluted level in the dilution water at t=5
days (mg/l)
V1 = volume of wastewater sampled for dilution (ml)
V2 = volume of diluted sample (ml)
BOD calculation can then be performed.
2. STEP 2 : Calculate the BOD
The BOD at 5 days can be calculated with the following BOD calculation formula :
BOD5 = [(D1-D2)-(B1-B2)f]/P
With :
f = (V2-V1)/V2
P = V1/V2
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3. Step by Step example : calculation of BOD5
A factory has taken a sample of its effluents and sent it to the lab. The lab takes 10 ml of waterwater and dilute it in a BOD incubation bottle of 250 ml. The lab measures the oxygen level in the diluted water and gets 10 mg/l at t=0 and 2 mg/l at t=5 days, it takes also the same measures on the dilution water and gets 9.5 mg/l at t=0 and 8 mg/l at t=5 days. The lab wishes to calculate the BOD5 of the effluent.
Step 1 : collect the data
D1 = oxygen diluted level in the diluted sample at t=0 =
10 mg/l
D2 = oxygen diluted level in the diluted sample at t=5
days = 2 mg/l
B1 = oxygen diluted level in the dilution water at t=0 =
9.5 mg/l
B2 = oxygen diluted level in the dilution water at t=5
days = 8 mg/l
V1 = volume of wastewater sampled for dilution = 10 ml
V2 = volume of diluted sample = 250 ml
Step 2 : Calculate the BOD5
f = (V2-V1)/V2 = (250-10)/250 = 0.96
P = V1/V2 = 10/250 = 0.04
BOD5 = [(D1-D2)-(B1-B2)f]/P = [(10-2)-(9.5-8)*0.96]/0.04 = 164.4 mg/l
4. BOD calculator Excel
MyEngineeringTools.com has developed a free Excel calculator that allows you to calculate the BOD5 from the experimental data defined above : BOD calculator Excel
Warning : this calculator is provided to illustrate the concepts mentioned in this webpage, it is not intended for detail design. It is not a commercial product, no guarantee is given on the results. Please consult a reputable designer for all detail design you may need.
