Table 2: Concentration of Cr(VI) in the four treatment stages measured by ion chromatography (Dionex ICS 2100 with column: Dionex IonPac CS5A, 4 × 250 mm; guard column: Dionex IonPac CG5A, 4 × 50 mm; eluent flow rate: 0.36 mL/min; injection volume: 1000 µL; temperature: 30°C; back pressure: 1700–2000 psi; postcolumn reagent system conditions: flow rate: 0.12 mL/min; detection: visible absorbance, 530 nm; noise: 6–8 µAU; runtime: 10 min).

Treatment stagesCr(VI) concentration, ppm
(mean ± standard deviation, )
% RSD

Aeration chamber0.0019 ± 0.0020105
Clarifier0.0006 ± 0.000233.3
Chlorination chamber0.0011 ± 0.000654.5
Sulfur dioxide chamber0.0010 ± 0.000660.0