15, Dec 2020
BOD test
  1. A five day seeded BOD test has been conducted on a wastewater
    sample at 20°C. A volume of 4 mL of the waste sample was added to a
    300 mL BOD bottle along with 3 mL of microbial seed and the bottle
    was then filled with dilution water. The initial dissolved oxygen (DO) of
    the bottle was 8.8 mg/L and the final DO after 5 days was 5.7 mg/L. A
    control seed-only bottle of 300 mL contained 30 mL of seed in dilution
    water. The initial DO of this bottle was 8.8 mg/L and the final DO was
    6.4 mg/L.
    (i) What is the 5-day BOD of the wastewater sample?
    (ii) If the reaction rate constant is 0.23 d-1 what is the ultimate BOD?
  2. A town generates a combined industrial and domestic wastewater of
    4400 m3/d and an average BOD5 of 500 mg/L. The industrial waste
    content of the industrial wastewater amounts to 500 m3/d with an average BOD5 of 2000 mg/L.
    (i) What is the percentage of total BOD5 load contributed by the
    Industrial waste?
    (ii) What is the BOD5 of the domestic wastewater only?