Aromatic Amine Degradation in a UASB/CSTR Sequential System Treating Congo Red Dye

Abstract

In this study an anaerobic (upflow anaerobic sludge blanket reactor)/aerobic (completely stirred tank reactor) sequential system was used to treat a synthetic wastewater with minerals and co-substrate together with 100–4000 mg L⁻¹ of Congo Red dye (Direct red 28) (CR), which is a banned azo dye in Turkey. The effect of hydraulic retention time (HRT) on the decolorization and the COD removal efficiency was investigated at constant 100 mg L⁻¹ Congo Red concentration. 77% of COD and 95% of color was removed at a HRT of 0.486 days and a maximum organic loading rate of 6.656 kg COD m⁻³ day⁻¹ in the anaerobic/aerobic stage. In the continuous operations, 88% of COD, 99% of color and 91% of total aromatic amine (TAA) were removed at a HRT of 3.60 days and at a CR concentration of 4000 mg L⁻¹. This corresponds to an organic loading rate of 1.81 kg COD m⁻³ day⁻¹, and a CR dye loading rate of 46.37 g dye m⁻³ h⁻¹, respectively, in the whole system. The TAA produced under anaerobic conditions was ultimately removed in the aerobic stage, resulting in very low aromatic amine recoveries (5–18%) in the last one. Therefore the aerobic effluents exhibited higher IC₅₀ and specific methanogenic activities (SMA) compared to anaerobic and dye containing samples, indicating the reduced toxicity.

Keywords:

• Anaerobic/aerobic system
• Aromatic amine
• Azo dye
• Congo red

Acknowledgments

This project was funded by the Turkish Scientific and Technical Research Council (TUBITAK) and Turkish Government Planning Institution (DPT) via Dokuz Eylul University Research Foundation. The authors would like to thank for the financial support to project with grant numbers 199 Y 110 and 0 908 20 0001.