When it comes to designing effluent treatment plants, one crucial factor stands out: Biological Oxygen Demand (BOD). This value is the linchpin for balancing equations and determining flow rates between equipment. So, how do we get this vital number? Essentially, we measure the dissolved oxygen levels in a sample over a five-day period. It's a tried-and-true method that's still widely used today, even with fancy modern instruments available. Why? Because it's cost-effective and gets the job done!
Biological Oxygen Demand (BOD) Laboratory Procedure
Biological Oxygen Demand (BOD) is a crucial parameter in water quality assessment. It measures the amount of oxygen consumed by microorganisms in breaking down organic matter in water. In this post, we'll outline the laboratory procedure for determining BOD and provide a handy calculator to simplify the calculation process.
Analytical procedure: 5 days method
Testing Apparatus:1. Bottle with stopper (250ml)2. Incubator
Chemical Reagents for BOD Testing
To ensure accurate BOD results, you'll need the following chemical reagents:
1. NaOH Solution (1N)
2. HCl Solution (1N)
3. Sodium Sulphite Solution
Dissolve 1.5g of sodium sulphite in 1 liter of water. Important: Don't mix this solution with any previous test solutions.
4. Phosphate Buffer Solution
Dissolve the following in 500ml of water:
- 8.5g KH2PO4- 21.75g K2HPO4- 33.4g Na2HPO4.H2O- 1.7g NH4Cl
Then, make up the solution to 1 liter. Remember: Maintain a pH of 7.2.
5. MgSO4.7H2O Solution
Dissolve 22.5g of MgSO4.7H2O in water and make up to 1 liter in a volumetric flask.
6. CaCl2 Solution
Dissolve 27.5g of CaCl2 in water and add to a 1-liter volumetric flask.
7. FeCl3.6H2O Solution
Dissolve 0.25g of FeCl3.6H2O in water and make up to 1 liter.
8. Seeding Material
Use effluent water from the sample point as your seeding material.
By having these chemical reagents ready, you'll be all set to conduct your BOD testing accurately and efficiently.
Sample Preparation for BOD Testing Procedure:
To get accurate BOD results, we need to prepare our sample carefully. Here's a step-by-step guide:
Step 1: pH Adjustment
- Adjust the pH of your sample to 7 using acid and base solutions. This ensures that the microorganisms can thrive.
Step 2: Remove Residual Chlorine
- Add sodium sulphite solution to remove any residual chlorine, which can harm the microorganisms.
Step 3: Prepare Dilution Water
- Store your dilution water at 20°C and use it at approximately the same temperature.
Step 4: Add Nutrients
- For every liter of water, add:
- 1ml phosphate buffer solution- 1ml magnesium sulphate solution- 1ml calcium chloride solution- 1ml ferric chloride solution
Step 5: Add Seeding Material
- Add 0.1-1% seeding material to your dilution water. This helps microorganisms grow.
Step 6: Dilute the Sample
- Dilute your sample by 5%. For example, if you have 500ml of sample, add 500ml of dilution water.
Step 7: Prepare Bottles
- Pour the diluted sample into two glass-stoppered bottles. Repeat this process for lower-concentration samples.
Step 8: Measure Initial DO
- Test the initial DO concentration in one of the sample bottles and a blank one.
Step 9: Incubate
- Incubate the bottles at 20°C for 5 days.
Step 10: Measure Final DO
- After 5 days, measure the DO concentration in the diluted sample and the blank.
Calculate BOD
Now that you have your DO readings, you can calculate the BOD using the following formula:
BOD = (D1-D2)-(C1-C2) F/P
- D1 initial DO sample.
- D2 DO after incubation of sample.
- C1 Seeded dilution water initial DO
- C2 Seeded dilution water after incubation DO
- F =ratio of the seed in the sample to that in the control, that is percent seed in D1 divided by percent seed in C1 and
- P = decimal fraction of the sample used
By following these steps, you'll be able to accurately measure the BOD of your sample and gain valuable insights into its water quality.
BOD Calculator
Use our handy calculator to simplify the BOD calculation: