Article ID: Q13064 Created Date: 6/22/2010 9:48 AM Last Modified: 6/22/2010 9:48 AM Author: Scott Dorner Original URL: http://www.opssys.com/instantkb/article.aspx?id=13064 BOD Example Calculations The method consists of filling an airtight bottle with a sample. The bottle is a specified size and filled to overflowing. The sample is incubated at constant temperature for five days. Dissolved oxygen (D.O.) is measured by probe before and after incubation. BOD is computed based on the difference between initial and final D.O. The test uses dilution water and a known amount of sample in a 250-300 ml incubation bottle. A small amount of seed is added to samples where microbial activity may not be present. The initial D.O. is measured by probe and the bottle is stored at 20 °C. After five days, final D.O. is measured. If no seed is used, the BOD of the bottle is computed using Equation 1. BOD = IDO - FDO (Eq. 1) VS / VB where: IDO = initial D.O. of diluted sample, mg/L FDO = final D.O. of diluted sample, mg/L VS = volume of sample, ml VB = volume of bottle, ml BOD = biochemical oxygen demand, mg/L When seed is added, seed control tests must be done to determine the amount of oxygen depleted by the seed. Calculation of BOD includes a correction factor for seed as expressed by Equation 2. BOD = (IDO - FDO) - (Cavg * SV) (Eq. 2) VS / VB where: IDO = initial D.O. of diluted sample, mg/L FDO = final D.O. of diluted sample, 0 mg/L VS = volume of sample, ml VB = volume of bottle, ml Cavg = correction factor for oxygen depletion resulting from presence of seed SV = Volume of Seed added to Sample in ml. Q13064 - INFO: BOD Manager Example Calculations Close Window Page 1 of 4 Print Article 3/16/2011 http://www.opssys.com/instantkb/print.aspx?id=13064 BOD = biochemical oxygen demand, mg/L The correction factor for a bottle of Seed is derived using Equation 3. C = ( ISDO - FSDO) (Eq. 3) VN where: C = correction factor for oxygen depletion resulting from presence of seed ISDO = initial D.O. for seed control test N FSDO = final D.O. for seed control test N VN = volume of seed used in control test N The Seed Corrections (mg/L) per ml of seed added is then calculated: Cavg = Sum(C) Count of non-marked Seed bottles Seed Correction (mg/L) per ml of seed added is the average of all non-marked correction factors for the Seed Sample. The Final BOD is calculated by averaging all non-marked (i.e. bottles that pass the criteria) bottles for the sample. The Final BOD is stored in the associated OPS variable (see BOD Manager Sample Setup) Final BOD = SUM(BODs) Count(Bottles) Example 1: Unseeded BOD 300 ml bottles are used Bottle #10 BOD = (8.6 - 5.2) / (6/300) = 3.4/ 0.02 = 170 The Final BOD = (170 + 142.50 + 129) / 3 = 147.17 Example 2: Seeded BOD Calculate the Effluent BOD which is seeded with the Sample named "Seed". Page 2 of 4 Print Article 3/16/2011 http://www.opssys.com/instantkb/print.aspx?id=13064 The first step is to calculated the Seed Correction per ml of seed added. Therefore we need to calculated the Seed bottles first: Seed Correction per ml using equation 3: Bottle 110: (8.9 - 5.8) / 10 = 3.1 / 10 = 0.31 Bottle 111: (8.94 - 5.7) / 12 = 3.24 / 12 = 0.27 Therefore the Seed Corrections (mg/L) per ml of Seed added = (0.31 + 0.27) / 2 = 0.29 To calculate the BOD for Effluent bottle 210 using equation 2: ((8.7 - 5.3) - (3 * 0.29)) / (200 / 300) = (3.4 - 0.87) / .6667 = 2.53 / .6667 = 3.8 Final BOD for the Effluent Sample is the average of valid (unmaked) BOD's for bottles 210, 211, 212 : Therefore it is (3.8 + 3.64) / 2 = 7.44/2 = 3.72 ===> 4 when rounded to zero decimal places as specified for Effluent BOD in Edit/View Variables. Note: Bottle 212 was NOT used in the average because it was marked due to invalid Final DO (Final DO must be 1.0 or greater as specified in Criteria Setup ). Page 3 of 4 Print Article 3/16/2011 http://www.opssys.com/instantkb/print.aspx?id=13064 Close Window Page 4 of 4 Print Article 3/16/2011 http://www.opssys.com/instantkb/print.aspx?id=13064 . to Sample in ml. Q13064 - INFO: BOD Manager Example Calculations Close Window Page 1 of 4 Print Article 3/16/2011 http://www.opssys.com/instantkb/print.aspx?id=13064 BOD = biochemical. Final BOD is stored in the associated OPS variable (see BOD Manager Sample Setup) Final BOD = SUM(BODs) Count(Bottles) Example 1: Unseeded BOD 300 ml bottles are used Bottle #10 BOD =. used Bottle #10 BOD = (8.6 - 5.2) / (6/300) = 3.4/ 0.02 = 170 The Final BOD = (170 + 142.50 + 129) / 3 = 147.17 Example 2: Seeded BOD Calculate the Effluent BOD which is seeded with the