Bahareh Kokabian - Chemical Engineering Department, Amirkabir University of Technology,۴۲۴ Hafez Ave, Tehran, Iran
Babak Bonakdarpour - Chemical Engineering Department, Amirkabir University of Technology, ۴۲۴ Hafez Ave, Tehran, Iran Food Process Engineering and Biotechnology Research Centre, Amirkabir University of Technology, Tehran, Iran
Shahrzad Fazel - Chemical Engineering Department, Amirkabir University of Technology, ۴۲۴ Hafez Ave, Tehran, Iran Food Process Engineering and Biotechnology Research Centre, Amirkabir University of Technology, Tehran, Iran

Textile dyeing wastewaters usually contain a significant concentration of both reactive azo dyes and salts (mainly NaCl). Recently, sequential anaerobic-aerobic biological processes have been considered for the treatment of reactive azo dye containing wastewaters but little attention hasbeen paid to the effect of salt concentrations on the color removal performance of these processes.In the present study the effect of NaCl concentration in the range 0-100 g/l on the decolorizationand degradation of Reactive Black 5 – a common dye in textile dyeing – during a sequentialanaerobic–aerobic bacterial process at RB5 concentrations of 100 and 200 mg/l was studied. Statistical analysis showed that – for both dye concentrations - increase in salt concentration in the range 0-60 g/l lead to a statistically significant increase in anaerobic decolorization efficiencywhereas a further increases up to 100 g/l resulted in a statistically significant decrease. Kinetic analysis of the anaerobic decolorization data showed that for salt concentration in the range 0-80 g/l a second order model best describes the data whereas at 100 g/l the anaerobic decolorizationdata was best fitted using a first order model. UV-Vis spectral analysis indicated that aromatic amines formed as a result of anaerobic reduction of RB5 partly biodegraded in the subsequentaerobic phase. This analysis also showed that for NaCl concentrations up to 40 g/l the aromaticamines autoxidised whereas higher salt concentrations inhibited the autoxidation reaction. As a result – during the aerobic phase - at salt concentrations ≤ 40 g/l slight recoloration of the anaerobically decolorized wastewater occurred whereas at higher salt concentration there was no pronounced change in the color of the wastewater

anaerobic decolorization, Reactive black 5,aromatic amines