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 extraction phases were mixed and dried with anhydrous sodium
sulphate. The extraction phases were concentrated to 0.2 ml under
a stream of high-purity nitrogen and analysed by GC–MS.
The chromatographic analysis used a DB–MS 30m×0.25mm
quartz capillary chromatographic column. The temperature programming
was held constant for 5 min at 40 ◦C and then increased
from 40 ◦C to 150◦C at a rate of 10 ◦Cmin−1. The temperature was
then held for 2min at 150 ◦C, followed by an increase from 150 ◦C
to 280 ◦C at a rate of 5 ◦C min−1. The GC–MS temperature was then
held for 3min at 280 ◦C. In addition, the sample size was 1L and
was not spitted. The introduction port temperature was 250 ◦C, and
the flow rate of the carrier gas was 1.0 ml min−1. Finally, the ion
source temperature was 200 ◦C, and the transmission line temperature
was 280 ◦C. The mass spectrum analysis conditions used EI as
the ionisationmethodat an electronic energy of 70 eV. The resulting
quality scanning area was from 40 to 500amu