Why determination of cod of an unknown wastewater sample is necessary prior to its bod measurement in the laboratory?
Answers
Answer:
Dilution is needed to prevent the depletion of entire oxygen present in in BOD bottle in less than incubation period of 5 days. For a valid BOD test APHA manual specifies some min DO of 1 mg/L to be present in the bottle after end of 5 days and DO consumed should be at least 2mg/L during incubation. Suppose saturation DO is 8 mg/l and expected BOD is 400 mg/L then, volume of sample to be added in 300 ml BOD Bottle has the following range:
minimum ml sample = [(8 mg/L 6 mg/L) x 300 mL]/400 mg/L=1.5 ml
maximum ml sample = [(8 mg/L 1 mg/L) x 300 mL]/400 mg/L=5.25 ml
Also, excess dilution reduces precision.
Answer:
Dilution is needed to prevent the depletion of entire oxygen present in in BOD bottle in less than incubation period of 5 days. For a valid BOD test APHA manual specifies some min DO of 1 mg/L to be present in the bottle after end of 5 days and DO consumed should be at least 2mg/L during incubation. Suppose saturation DO is 8 mg/l and expected BOD is 400 mg/L then, volume of sample to be added in 300 ml BOD Bottle has the following range:
minimum ml sample = [(8 mg/L 6 mg/L) x 300 mL]/400 mg/L=1.5 ml
maximum ml sample = [(8 mg/L 1 mg/L) x 300 mL]/400 mg/L=5.25 ml
Also, excess dilution reduces precision.