What kind of seed sources are available for BOD testing?
BOD seed sources
For testing Biochemical Oxygen Demand (BOD), there are a number of different reasonable sources for seed material. The following are some of the most commonly used:
- Plant Influent: If the plant has a stable influent, this is often the most successful seed source. For many plants, the primary influent is reliably a particular value. If the influent is stable and is mostly domestic in origin, consider this as the first seed source.
- It is recommended to settle the seed before use by placing the seed in a covered beaker in an incubator overnight.
- Decant off the particle free seed for use in samples that need seed.
- Primary Effluent: Effluent from the primary clarifier is another very good source for seed. It has an advantage over influent in that it is "settled" seed, so most particulates are not present in the seed. This eliminates the settling step.
- Final Effluent (prior to disinfection): If the effluent is sampled prior to disinfection, it may not be necessary to seed the effluent. Many facilities will still need to run Glucose and Glutamic Acid (GGA) standards, so the final effluent is a fine choice in this case.
- It is recommended to allow the seed to come to room temperature before use. Shake the effluent to get it to room temperature.
- Add 300 mL nutrient pillows to the bottle directly, since final effluent may be nutrient deficient.
- Artificial Seed: Artificial seed often does not work. If GGA values are low, the artificial seed is most likely the culprit (even if it's been used for years).
- It is recommended to use other types of seed.
- If one must use artificial seed, be sure to follow the vendor's recommendation.
- Seed as high as possible (for example, 1.2 mg/L of depletion).
- Allow as much time as possible for the seed to "wake up" from its freeze dried state prior to use (but after hydration).
- Add a small quantity of influent or primary effluent to the seed while hydrating it.
- Dirt: Often overlooked, soil is a good source of seed material. The bacteria that perform the BOD test are actually soil bacteria. If none of the other seed sources are adequate, consider experimenting with soil.
- Prepare 500 mL of dilution water (with buffers) in a 1000 mL beaker.
- Place a stir bar into the beaker and keep the water stirred actively.
- Obtain about 20 grams of soil from an actively growing lawn area.
- Place the 20 grams of soil into the 500 mL beaker.
- Allow approximately 1/2 hour of mixing.
- Filter and decant the water into a second 1000 mL beaker.
- Use the solution as a seeding solution.