Spectrometric evidences to resolve the debate on direct role of macrophyte in organic pollutant removal and degradation in constructed wetlands

Abstract

Direct role of macrophyte (aquatic plant) in constructed wetlands has been an issue of serious debate in organic pollutant treatment for last many decades. The present study was performed to investigate the direct role of plants using azo dye methyl red (MR) as a model organic pollutant in constructed wetlands. The study was performed using widely used wetland macrophyte Canna indica L. (Cannaceae) in constructed wetlands with multiple controls experiments. Dye decolourization and ultraviolet-visible spectroscopy (UV-Vis) study revealed that about 99.0 % removal of MR occurred in presence of plants. Results show that C. indica based CW system was able to remove 99.0 % of colour and 75.0 % of COD while the system without C. indica was able to remove 73.6 % of colour and 42.0 % of COD. Simultaneously, accumulation of MR was also observed in the cells of C. indica stem at the end of experimental period. Gas chromatography-mass spectrometry (GC-MS) analysis established that the cleavage of mutagenic azo bond occurred due to the presence of plants. Instead, in absence of plants though discolouration took place, but breakdown of azo bond was not found. Kinetic models depict that plants perform chemisorption mechanism for degradation of MR. Negligible reduction in plant growth and regulatory functions stated that the wetland plants can phyto-remediate and withstand such concentration of MR (50 mg/L) provided during the study. The study affirms that wetland plants can play a direct role in degradation and detoxification of organics pollutant. Results from the experiment revealed that plants play a direct role for the treatment of organic pollutants in constructed wetland treatment system.