Phytoremediation of monoazo and diazo dyes in wastewater using up-fow constructed wetland

Abstract

Application of a sequential anaerobic and aerobic in a constructed wetland system can enhance the treatment performance of textile wastewater to efficiently remove color, organic compounds, and intermediate aromatic amines. Four laboratory-scale up-flow constructed wetland (UFCW) reactors planted with Phragmites australis were constructed to investigate the treatment performance between aerated and non-aerated reactors to treat methyl orange (MO) and reactive black 5 (RB5) containing synthetic wastewater. The treatment performances of UFCW reactors were greatly improved for 2 days hydraulic retention time (HRT) compared to 1 day HRT. The non-aerated reactors which demonstrated an almost entire anaerobic environment as evidenced by oxidation-reduction potential (ORP) profile yielded a better dyes removal efficiency with 93.12% (MO) and 89.49% (RB5) compared to the aerated reactor with only 75.48% (MO) and 81.29% (RB5) when the influent dyes concentration was 50 mg/L. Decolorization efficiency of monoazo dye MO was higher than diazo dye RB5. On the other hand, supplementary aeration created an almost wholly aerobic or anoxic environment in the aerated reactors proved that higher reduction on COD (~90%) was likely to achieve under aerobic condition than anaerobic condition with COD removal of only about ~85%. Other than COD reduction, the amounts of aromatic amines were also significantly reduced in the aerated reactors. As a result, a proper design ratio of anaerobic/aerobic region in UFCW is a key to accomplish not only color reduction but also COD and aromatic amines in textile wastewater treatment.