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Water Quality Index Research Methodologies: BOD
[BOD Research Background]

HOW TO DO A FIVE-DAY BOD TEST

  1. Begin by determining the amount of dissolved oxygen in the stream water by using a Hach Dissolved Oxygen (DO) test kit as described on the "How to do a Dissolved Oxygen Test" page. Record this amount.

  2. Clean and rinse the 60ml D.O. sample bottle. Carefully. refill the sample bottle with stream water. Stopper the bottle. Be sure there are no air bubbles in the sample.

  3. Wrap the bottle completely with aluminum foil.

  4. Place the bottle in a dark room at about 20oC or 68oF (room temperature) for five days (120 hours).

  5. At the end of the five day period, measure the amount of dissolved oxygen left in the water by using the Hach DO test kit.

  6. Subtract the DO value obtained on day five from that obtained on day one. The difference is the five-day BOD.


EXAMPLE:

                Day one DO level equals        14 mg/l
                Day five DO levels equal    -   6 mg/l
                5-day BOD equals                8 mg/l*
*Report this number as your five-day BOD.

Use the rough standards below too begin interpret your findings.

    1-2 mg/l BOD

    Very clean water, little biodegradable waste
    3-5 mg/l BODModerately clean water, some biodegradable waste
    6-9 mg/l BODMany bacteria, much biodegradable matter
    10 or more mg/l BODVery bad; someone may be dumping biodegradable wastes into the water.

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