calibration set and 16 samples for validation set. The COD range in
calibration set was 112 mg L1 to 1872 mg L1
, whereas in validation
set, COD values were from 130 mg L1 to 1792 mg L1
.
UV–vis spectra were measured by HACH DR/5000 spectrophotometer
with wavelength range from 200 to 650 nm
(Δ¼2 nm). A home-made sample cell (Fig. 1) was designed and
fabricated to adjust pathlength (0.5–18 mm). The adjustment of
pathlength, defined by the distance of two quartz windows, was
subjected to the movement of a threaded cylindrical tube sealed
with O-ring. One revolution of the cylindrical tube equals to 1 mm
adjustment. Each wastewater sample was subjected to UV–vis
spectroscopic measurements at 19 different pathlengths (0.5 mm
and 1–18 mm with 1 mm increment). The pathlength accuracy
was checked by comparing with standard cuvettes of 1 mm, 5 mm
and 10 mm. The differences of absorbance values were found to be
negligible. Absorbance values of different pathlengths were set to
zero according to MilliQ deionized water (18.2 MΩ cm at 25 1C)
at the corresponding pathlength. Triplicate measurements for each
wastewater sample at each pathlength were taken and the average
spectrum was generated for further data processing.
COD measurements were conducted according to standard
methods using COD digestion reaction and direct reading spectrophotometer
(DR/5000, Hach Company, USA).
2.