Análisis de variables: Determinación de demanda bioquímica de oxígeno DBO5 en aguas marinas-costeras

Scientific Concepts / Nature Phenomena

• Biochemical Oxygen Demand (BOD5 / DBO5): A measure of the amount of dissolved oxygen that microorganisms require to degrade organic matter in a water sample over a 5-day incubation period.

• Microbial degradation at controlled temperature: Tests are conducted at 20 ± 1 °C to standardize oxygen consumption by microorganisms.

• Marine vs. non-marine inoculation limitations:

  • Some samples may contain materials not readily biodegradable under typical microbial activity.
  • In such cases, the method may require inoculation with an adapted microbial population.
  • For this lab, marine-water samples are not inoculated, because a standardized marine inoculum is not available.

• Use of standard reagents and nutrients: Nutrient additions support and standardize microbial activity, including:

  • phosphate buffer
  • magnesium sulfate
  • calcium chloride
  • iron chloride

• Dissolved oxygen verification: Dilution water must have adequate initial dissolved oxygen: minimum 75 mg O₂/L.

Method / Procedure (Outlined)

Test Duration and Conditions

• Incubate for 5 days at 20 ± 1 °C.
• Measure initial dissolved oxygen and final dissolved oxygen after incubation.

Core Materials / Equipment

• Incubator capable of maintaining 20 ± 1 °C for 5 days
• Dissolved oxygen measurement equipment (using a standardized luminescence or membrane probe)
• Stirring and aeration setup (for adjusting/mixing dilution water)
• Winkler bottles (300 mL) with ground-glass stoppers (with sealing film)
• Volumetric/transfer tools (pipettes, cylinders, volumetric flasks), thermometers, magnetic stir bars
• Reagents including nutrient solutions, buffers, salts, and standard substances (e.g., glucose, glutamic acid)

Preparation of Dilution Water

1. Add the required dilution water to a container.
2. Check dissolved oxygen. If < 75 mg O₂/L, stir/aerate until the requirement is met.
3. For each liter of dilution water, add 1 mL each of:
   • phosphate buffer solution
   • magnesium sulfate solution
   • calcium chloride solution
   • iron chloride solution

Inoculum Preparation (Commercial Seed)

• Prepare inoculum using a commercial seed/tablet:
  1. Place the seed tablet in 500 mL dilution water.
  2. Stir and aerate for 1 hour.
  3. Rest 5–15 minutes.
  4. Transfer the supernatant to a clean beaker.

Standard Preparation

1. Partially fill a bottle with water.
2. Add:
   • 6 mL glucose–glutamic acid solution
   • 4 mL inoculum solution
3. Fill to the bottle neck with water.
4. Insert the probe and measure initial oxygen.
5. Remove the magnet; stopper and seal using a water seal + film.
6. Incubate 5 days at 20 ± 1 °C.

Processing Marine Samples

• Stabilize samples by bringing them to 20 ± 3 °C (room temperature stabilization).
• Mix to distribute solids.
• Fill a Winkler bottle about two-thirds full, avoiding bubbling.
• Measure initial oxygen while the sample is under gentle magnetic stirring.
• After incubation:
  1. Remove seals
  2. Determine final oxygen
  3. Compute BOD5/DBO5 using initial and final oxygen values (explicit “formula with initial and final oxygen measurements” referenced).

Researchers or Sources Featured

• INVEMAR (Instituto de Investigaciones Marinas): Named as the institution validating the working range.

• Standard Methods 52 10 b: Explicitly referenced as the source for method-related reagent/pretreatment guidance.

• PolySer seeds: Mentioned as an adapted microorganism seed type used elsewhere, but stated as not applicable to marine water in this context.