2.3. Experimental methods
Determination of wastewater COD was done using the potassium
dichromate oxidation method [19]. The wastewater organic
composition analysis was done using the GC–MSmethod. For sample
pretreatment, 25 ml of coking wastewater was adjusted to
pH 11 and extracted twice with 5ml methylene dichloride. The
wastewater samples were then adjusted to pH 2 and extracted
twice again with 5mlmethylene dichloride. The alkaline and acidic