Sentence:  The maximum rate of oxygen transfer at 1.0 mg / l dissolved oxygen was calculated as 220 lb / day at a maximum rate of 9.3 mg / <WSD>l</WSD> / hr . 
Meaning of the word marked with <WSD> tags:  a metric unit of capacity, formerly defined as the volume of one kilogram of pure water under standard conditions; now equal to 1,000 cubic centimeters (or approximately 1.75 pints)