Dear Sanjay,

Please read the following text:

PREPARATION OF SEED MATERIAL

Select a material to be used for seeding which will have a BOD of at least 180 mg/L.  This will help ensure that the seed correction meets the 0.6 mg/L minimum specified in “Standard Methods”, current Edition.  Place the material in a suitable container and incubate at 20°C for 24‑36 hours. Usually, settled raw domestic sewage prepared in the manner above will have sufficient BOD for use as a seed material.  If not, small quantities of digester supernatant, return activated sludge, or an acclimated seed material can be used to increase the potency of the seed material used for the test.  As an alternative, commercially available seed material may be used. The seed correction should not exceed 1.0 mg/L BOD, therefore care should be taken not to use too strong a seed material for the test.  The key to a good seed correction is a relatively stable seed material which produces a good seed correction in every test situation.

SEED BOD DETERMINATION

This step requires preparation of a dilution series using the seed material and unseeded dilution water.  Prepare two bottles of each dilution for the seed control series.  If the meter method is used for DO measurements, only one bottle for each dilution needs to be prepared.  The percentage of seed used in each dilution and the number of dilutions is optional, but sufficient dilutions should be used to ensure that at least one dilution gives a depletion of 2.0 mg/L with at least 1.0 mg/L DO residual.

Determine the initial DO of each dilution, then incubate the dilutions for five days at 20°C.  At the end of the incubation period, determine the final DO of the dilutions.  Calculate the depletion of each seed dilution using formula #1 below.

#1  DO depletion = Initial DO ‑ Final DO

Select the seed dilution(s) which meet the required criteria and calculate the BOD of the seed material using formula #2 below.  (If more than one dilution meets the criteria, calculate the BOD of each such dilution and average the results for the seed material BOD.)

#2  Seed BOD = (DO depletion x 300)/Seed dilution, mL

The calculated seed BOD represents the BOD exerted by 300 mL of undiluted seed material.  The ratio of the seed BOD to 300 mL will be used to calculate the seed correction for seeded samples.

DETERMINATION OF SEED VOLUME

The most common methods for introducing the seed material into the sample dilutions are (a) addition of the seed to the dilution water and (b) addition of the seed directly to the sample BOD bottles.  Method (a) requires a calculation to determine the volume of seed for each dilution since the amount of seed will vary with the volume dilution water used for each sample dilution.  Method (b) is somewhat easier to use as the volume of seed for each dilution is constant.

When Method (a) is used to introduce the seed material, calculate the volume of seed in each sample dilution using formula #3 below.

#3  Volume of seed in sample dilution = (Volume of seed in dilution water x dilution water in sample, mL)/Total volume of dilution water.

SEED CORRECTION

The calculation of the seed correction is based on the BOD of the seed material and the volume of seed used in each dilution.  The seed correction is actually the oxygen demand exerted by the oxidation of the small amount of organic matter in the seed material in the sample dilutions.  If the BOD exerted by 300 mL of seed material and the volume of seed material in each sample dilution are known, the seed correction can be calculated using formula #4 below.

#4  Seed Correction = (Seed BOD x mL seed in sample dilution)/300

It should be noted that the seed correction for each sample dilution must be calculated when the seed is added to the dilution water.  When the seed is added directly to each BOD bottle, the seed correction is the same for all seeded dilutions using the same seed volume and material.

DETERMINATION OF SAMPLE BOD

The calculated seed correction is subtracted from the DO depletion in the determination of the BOD for each valid sample dilution.  It should be noted that there are two criteria specified in “Standard Methods” which should be checked before the seed correction is used to determine the sample BOD.  Those sample dilutions meeting these criteria should yield the most valid results.  These criteria are as follows:

1.     The sample dilutions should deplete at least 2.0 mg/L DO after five days incubation at 20°C.

2.     The sample dilutions should have a final DO of at least 1.0 mg/L after five days incubation at 20°C.

The BOD, using the seed correction, should be calculated for the sample dilutions which meet both criteria.  If more than one sample dilution meets the criteria, the final BOD should be an average of the individual BOD results for the sample dilutions.  If none of the sample dilutions meet both of the criteria, the one dilution which comes closest should be used to calculate the final BOD of the sample.

NOTE:  If this is the case, a notation should be made on the sample bench sheet that potentially invalid data has been used to determine the noted value.  Sample dilution volumes should be carefully selected to ensure that at least one dilution meets both criteria.

Calculate the seeded sample BOD using formula #5 below.

#5  BOD mg/L = (DO depletion ‑ Seed correction) x 300/mL of sample

EXAMPLE BOD DETERMINATION

Seed Material Data:

A series of dilutions were prepared in 300 mL BOD bottles using settled raw sewage and unseeded dilution water.  The dilution range, initial DO, final DO, and depletions (using formula #1) are given in Table 2.

Table 2

                  Bottle #           mL Seed          Initial DO          Final DO          Depletion

                      1                       3                     7.95                  5.20                  2.75

                      2                       6                     7.95                  3.85                  4.10

                      3                       9                     7.90                  2.40                  5.50

                      4                     12                     7.85                  1.35                  6.50

Since all of the dilutions meet the desired criteria, the seed BOD should be the average of all the calculated BOD values for the dilutions.  Use formula #2 to determine the BOD of each seed dilution, then calculate the average seed BOD.

Bottle #1 BOD = [(7.95 ‑ 5.20) x 300]/3 = (2.75 x 300)/3 = 275

Bottle #2 BOD = [(7.95 ‑ 3.85) x 300]/6 = (4.10 x 300)/6 = 205

Bottle #3 BOD = [(7.90 ‑ 2.40) x 300]/9 = (5.50 x 300)/9 = 183

Bottle #4 BOD = [(7.85 ‑ 1.35) x 300]/12 = (6.50 x 300)/12 = 162

Average seed BOD = (275 + 205 + 183 + 162)/4 = 825/4 = 206 mg/L

This value represents 206 mg/L BOD exerted by 300 mL of the seed material.  In other words, a 300 mL sample of the undiluted seed material would use 206 mg/L DO if incubated at 20°C for five days (assuming that oxygen was available to the sample).

Sample Data

Two series of sample dilutions were prepared at the same time as the seed control series.  Sample series “A” was prepared by adding 1 mL of the seed material directly to each 300 mL sample BOD bottle.  Series “B” was prepared by adding 4 mL of the seed material to each liter of dilution water.  An unseeded dilution water blank was also run with the series (depletion = 0.2 mg/L DO).

Series “A”

                  Bottle #           mL Seed          Initial DO          Final DO          Depletion

                      5                     10                     8.00                  6.30                  1.70

                      6                     50                     7.95                  4.60                  3.35

                      7                     75                     7.70                  3.90                  3.80

                      8                   100                     7.55                  0.90                  6.65

Examination of the data reveals that bottle #5 can be discarded because it does not meet the 2.0 mg/L depletion criteria, and bottle #8 can be discarded because it does not meet the minimum final DO criteria.  The seed correction then will only be applied to bottles #6 and #7.

Using formula #4, the seed correction (S.C.) is determined:

S.C. = (Seed BOD x mL seed in sample dilutions)/300

S.C. = (206 x 1)/300 = 0.69 mg/L

Using formula #5, the BOD for each valid sample dilution can be calculated:

BOD for bottle #6 = [(3.35 ‑ 0.69) x 300]/50 = (2.66 x 300)/50 = 15.96 mg/L

BOD for bottle #7 = [(3.80 ‑ 0.69) x 300]/75 = (3.11 x 300)/75 = 12.44 mg/L

The average BOD for two valid dilutions representing the sample BOD is 14.2 mg/L BOD.

Series “B”

                  Bottle #           mL Seed          Initial DO          Final DO          Depletion

                      9                     10                     8.10                  6.30                  1.80

                     10                    50                     7.95                  4.50                  3.45

                     11                    75                     7.65                  3.85                  3.80

                     12                   100                     7.15                  0.70                  6.45

As in series “A”, examination of the data reveals that bottles #9 and #12 can be discarded because they do not meet both of the criteria for most valid results.  Since the dilution water for these samples was seeded, individual seed corrections must be determined for bottles #10 and #11.

Using formula #3, the volume (mL) of seed material in each valid dilution is determined:

mL seed in bottle #10 = (4 x 250)/1000 = 1.0 mL

mL seed in bottle #11 = (4 x 225)/1000 = 0.9 mL

Using formula #4, the seed correction (S.C.) for each valid dilution is determined:

S.C. for bottle #10 = (206 x 1)/300 = 0.69

S.C. for bottle #11 = (206 x 0.9)/300 = 0.62

Using formula #5, the BOD for each valid dilution can be determined:

BOD for bottle #10 = [(3.45 ‑ 0.69) x 300]/50 = (2.76 x 300)/50 = 16.56 mg/L

BOD for bottle #11 = [(3.80 ‑ 0.62) x 300]/75 = (3.18 x 300)/75 = 12.72 mg/L

The average BOD for the two valid dilutions representing the sample BOD is 14.64 mg/L.

Quiz 5.5

1.     Why must samples which have been dechlorinated or adjusted for pH variations be seeded?

2.     What materials can be used to seed a BOD sample?

3.     What is the acceptable range for seed correction factors in the BOD test?

 For more details, please see attached file.

Hoping this will be helpful,

Rafik

Thank you very much Prof. RafiK, much appreciated.

Regards

Sanjay

May be it will help

http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Environmental/BOD/procedur.htm

Thanks Prof. Sera. Appreciated

I think there may be some miscommunication with regard to the question and the meaning of the word "seed". Rafik uses the word seed in the meaning of a sample (of e.g. sludge) that can be seeded to introduce biological activity to be able to measure BOD of a sample. Sanjay probably means seeds as the embryo containing structure for plant propagation (as he chooses the Key word "Seeds". In that case the method needs to be different. Please make clear what is asked.

Generally  "filtered and 24 hour incubated domestic wastewater/Sewage is used as seed in the BOD experiment. My question was for that seed instead of "plant seed".

Okay, that is clear!