Sentence:  The high cost of land and a few operational problems resulting from excessive loadings have created the need for a wastewater treatment system with the operational characteristics of the <WSD>oxidation</WSD> pond but with the ability to treat more organic matter per unit volume . 
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