Analysing performance of real textile wastewater bio-decolourization under different reaction environments

The biological colour removal from textile wastewater is challenging because of the toxicity of dyes to microorganisms, and the need to test the process on real streams in order to ensure the reliability of the produced data. This present study has provided a comparative analysis of the bio-decolorization of a real wastewater containing a mixture of azo dyes under different environments: single aerobic and anaerobic, and sequential anaerobic-aerobic. Tests were performed in sequencing batch reactors operated at different exchange ratios and colour loads in the range of 0.1e0.3 and 0.002e0.1 kgCOD m3 d1, respectively. The work cycle lasted 24 h. With reference to the dominant wavelength, l ¼ 536 nm, resulting from the influent characterization, a maximum limit value of ~30% was observed for the colour removal in the aerobic system. Better performance has been achieved with the anaerobic (65% removal) and the sequential anaerobic-aerobic system, which reached efficiencies of 70e80%, for the range of applied colour loads. The sequential system exhibits the highest removal rate, which, for the highest colour load, is equal, in terms of absorbance units to 0.043 AU d1 L1. These values are even higher than the process rates obtained with more complex technologies, such as the granular sludge bioreactors. The demonstrated high performance of the sequential process with a real wastewater is a relevant step forward for promoting the application of the biological treatment (more sustainable than the generally employed chemical physical ones) to remediate highly polluted dye streams.