Table 1: UV-Vis absorbance and concentrations of wastewater samples spiked with different volumes of a 0.5 ppm Cr+6 standard at 540 nm using standard addition method; .

NWWTP
treatment stages
Concentration (ppm) of Cr(VI) spikedAbsorbance (mean ± SD)Determined Cr(VI) concentration (ppm) % RSD

Aeration chamber0.10.024 ± 0.0020.009 ± 0.00667
0.20.045 ± 0.001
0.30.068 ± 0.001

Clarifier0.10.023 ± 0.0010.007 ± 0.00571
0.20.045 ± 0.001
0.30.066 ± 0.001

Chlorination chamber0.10.024 ± 0.0010.008 ± 0.00675
0.20.045 ± 0.001
0.30.068 ± 0.002

Sulfur dioxide chamber0.10.022 ± 0.0010.004 ± 0.006150
0.20.043 ± 0.001
0.30.067 ± 0.001