Sentence:  Research at Fayette , Missouri on <WSD>oxidation</WSD> ponds has shown that the BOD in the treated effluent varied from 30 to 53 mg / l with loadings from 8 to 120 lb BOD / day / acre . 
Meaning of the word marked with <WSD> tags:  the process of oxidizing; the addition of oxygen to a compound with a loss of electrons; always occurs accompanied by reduction