Phytoremediation of textile effluents containing azo dye by using Phragmites australis in a vertical flow intermittent feeding constructed wetland

Abstract

An azo dye, acid orange 7 (AO7), was selected to study the role of Phragmites australis ( P. australis) peroxidases (POD) activity in its degradation in a vertical flow constructed wetland (VFCW). Crude plant extract was found to degrade AO7 and its aromatic amines, after 120 h in contact with H 2O 2, and removals of 3.2 – 5.7 m g AO 7 g P . a u s t r a l i s − 1 were obtained for 40 mg AO7 l −1 ( 8 m g AO 7 g P . a u s t r a l i s − 1 ). The VFCW was found to be suitable to treat an effluent containing an azo dye. For influent concentrations of 130 mg AO7 l −1 POD activity increased 2.1-, 4.3- and 12.9-fold for leaves, stems and roots, respectively. At 700 mg AO7 l −1, inhibition of POD activity occurred immediately, but it returned to the previous levels after only 2 days. An AO7 organic load of 21 up to 105 g COD m 2 day −1, revealed non-toxicity, being expectable to achieve removals of 11 up to 67 g COD m 2 day −1. Both [AO7] and TOC removal efficiencies were found to be similar (approximately 70%), which is indicative of AO7 mineralization. A 3 h cycle was found to be sufficient to degrade AO7 and a system buffering capacity from 5 to 25 min cycle −1 was demonstrated by flooding level control.