Biochemical Oxygen Demand (BOD) Flashcards
What is BOD?
A measure of the relative strength of waste via its ability to consume oxygen
What is the standard test length for BOD?
5 days
What is the most common alternate test length for BOD?
20 days; also known as ultimate BOD
How with post-chlorination samples impact testing?
The sample will need to be neutralized and reseeded to allow biological activity
How long may a BOD sample be held prior to analysis?
48 hours from time of sampling
Procedure for preparation of dilution water
1) For each liter of distilled water add 1mL of each of the four nutrients (Calcium chloride; Ferric Chloride; Magnesium Sulfate; Phosphate Buffer)
2) Saturate the dilution water at 20C by aerating with filtered air or shaking a partially filled bottle
3) DO should be approximately 7.5-8.5 mg/L, but never over 9
How do you prepare a dilution of a sample?
Dilution selections are made based on the anticipated strength of the wastes.
Three separate dilutions will be made by adding the proper amount of waste to the graduated cylinder and filling with dilution water
For example, a 50% dilution would be 50% dilution water and 50% sample (150 mL each).
What extra steps are taken with samples prepared above a 10% dilution?
The must be warmed to above 20C and shakn vigorously before analysis or bubbling may occur during incubation which invalidates the test.
How do you fill BOD bottles?
Begin by wasting a minimum of 950mL of distilled water from the siphon to clear it. Then siphon the sample dilution directly into the BOD bottle slowly without introducing bubbles. Fill all three bottles of a given dilution, measure DO, and place in incubator prior to moving on to the next set.
How long are BOD bottles incubated and at what temperature?
5 days + or - 3 hours at 20C +or- 1
BOD test procedure
1) Prepare dilution water and dilution water blanks
2) Run DO on bottle 1; this is the initial DO.
3) Incubate dilution blank bottle 2 and 3 for 5 days at 20C. Run DO on these bottles and record as final DO.
3) For each sample, make up duplicates of three dilutions
4) Run a DO on one of the duplicates for each sample dilution.
5) Incubate the other duplicates for the dilutions for 5 days at 20C
6) Run DO’s on the incubated sample dilutions and record the final DO.
7) Calculate
How do you perform chlorine neutralization on a BOD sample?
1) Make up 0.025N Na2SO3.
2) Place 200 mL of sample into 500mL Erlenmeyer flask
3) Add 10mL of 1:50 H2SO4 and 10 mL of 10% KI solutions. Add 1 mL of starch. The solution will turn blue if chlorine is present.
4) Titrate immediately with the sulfite until the blue disappears.
5) Divide the amount of sample left by 200 and multiply by amount of sulfite used.
6) Add this amount of sulfite [plus .2mL to the sample container and shake well.
7) Let stand for 15 minutes then retest for chlorine.
8) Repeat until the solution does not return to blue.
What do you do if the chlorine test sample goes colorless then returns as a very deep blue?
Perform a DPD chlorine residual and dope the sample by 5x that amount per liter.
What pH should the sample be for a BOD test?
Between 6.0 and 8.0. If not, you need to adjust a portion of the sample to 7.0 to allow for seeding.
Seeding procedure
1) Allow the sample to settle for at least 1 hour, preferably overnight.
2) Add to each graduated cylinder an amount of seed material sufficient to cause a 0.6 to 1.0 mg/L depletion by itself. (divide 0.8 by the seed BOD and multiply by 1000)
3) Run a BOD on the seed material to allow for correction of the BOD test. The dilution of the seed material is 2, 5, and 10% for settled influents.
