Question

A BOD test was conducted on the unchlorinated effluent of a municipal wastewater treatment plant at 20°C. The wastewater portion added to a 300-mL BOD bottle was 30 mL, and the dissolved oxygen (DO) values listed below were measured using a dissolved-oxygen probe. No seed was added to the bottles. What is the BOD value for each “valid” sample? Valid samples are ones that do not violate the following two rules:

1. DOf is less than 1.0 mg/L (unclear if still an aerobic bottle) and

2. DOi-DOf < 2.0 mg/L (imprecise measurement).

Time (days), DO (mg/L): 0.01,8.7 1.0,7.8 4.0,5.7 6.0,4.9 10.0,3.9 14.0,0.5

1 - sampled just after preparation of sample bottles.

Answer 1