Azo dye containing wastewater treatment in earthen membrane based unplanted two chambered constructed wetlands-microbial fuel cells: A new design for enhanced performance

This investigation is the first of its kind to enhance detoxification of azo dye and other pollutants containing wastewater using an innovative earthen membrane-based two-chambered constructed wetland cum microbial fuel cell (CW-MFC). The present innovative design simulates the core of a shallow unplanted CW-MFC, which runs the sequential anaerobic and aerobic regimes without mixing of the cathodic and anodic wastewater. The obtained results revealed 94.04 ± 2.87% chemical oxygen demand (COD) and 94.22 ± 1.33% azo dye removal from the synthetic wastewater containing 550 mg/L initial COD and 50 mg/L Methyl orange (MO) azo dye, along with the current density and power density production of 544.6 mA/m3 and 148.29 mW/m3, respectively. The UV-visible spectrum demonstrated azo bond degradation in the anodic region, which was confirmed by the presence of sulphanilic acid as an intermediate of the azo dye degradation in the anodic effluent. The gas chromatography-mass spectrometry (GC-MS) analysis of anodic effluent proved the presence of an another intermediate, N.N-dimethyl-p-phenylenediamine (DMPD) and further confirms mineralization in the cathodic effluent with the elution of several mineralized polar compounds. Phytotoxicity study with Vigna radiata, Triticum aestivum, and Cicer arietinum indicated higher root growth rates (in comparison to control) of 30.72%, 13.53%, and 11.62% in the anodic effluent, whereas 69.70%, 60.28%, and 34.27% in the cathodic effluent, respectively, indicating decreased toxicity. The microbial analysis revealed a shift in microbial community of CW-MFC; the inoculum was abundant with Methanomicrobia class (18.55%), which shifted to class Bacteroidetes (13.99%) in the anodic region which was attributed to azo dye degrading bacteria. Whereas, cathodic microbial community consists of Alpha and Gamma Proteobacteria (59.50%), which are considered as the aromatic ring-degrading microbes.