Fate of aromatic amines through decolorization of real textile wastewater under anoxic-aerobic membrane bioreactor

The presence of residual dyes and their biotransformation products in textile wastewater is considered the main challenge of wastewater treatment plants. Many biological treatment methods have been used for treatment of textile wastewater. However, incomplete dye mineralization produces colorless Aromatic Amines (AAs) which are considered carcinogenic and highly toxic to aquatic organisms. This study assessed the removal efficiency and the fate of AAs in the treatment of real textile wastewater by anoxic-aerobic MBR. The fate of 22 AAs in both aqueous and sludge phases was investigated under different Internal Recycle ratio (IR). Most AAs possessing one aromatic ring and an Electron Donating Group (EDG) such as (-NH2) and (-CH3) are highly biodegradable under aerobic condition (above 80%), whereas AAs with 2 aromatic rings and strong Electron Withdrawal Group (EWG), such as azo bond and (-Cl) exhibited low to moderate removal efficiency (below 75%). The AAs increased by 91% (from 205.1 to 393.7 ng/L) in the anoxic tank (IR = 2.0), owing to the unique bacterial diversity under high IR operation scheme. On the other hand, AAs in the anaerobic tank (IR = 0.0) increased by 6.1% (from 489.26 to 519.1 ng/L), whereas, the AAs in the aerobic tank remained constant at 50 ng/L in both cases. Most of AAs accumulated in sludge under reducing condition due to the refractory behavior of AAs in this environment, whereas hydrophobic AAs were slightly accumulated in aerobic sludge.