Effect of Typha angustifolia, feeding modes and intermittent aeration on the performance of hybrid constructed wetland systems treating Reactive Black 5 diazo dye wastewater

The current research assessed the effectiveness of four hybrid constructed wetland (HCW) systems for the remediation of synthetic dye wastewater with Reactive Black 5 (RB5) azo dye. All HCW systems had identical configurations, consisting of a horizontal CW followed by a vertical CW, and operated under diverse conditions such as the presence of plants (Typha angustifolia), feeding modes (batch and continuous) and intermittent aeration (4 h day^-1). Anaerobic-aerobic conditions simulated within the HCW systems were crucial in removing the pollutants from synthetic dye wastewater. The planted HCW system operating in continuous-continuous feeding mode exhibited better colour reduction (91%). The planted HCW system with continuous-continuous feeding mode and intermittent aeration achieved better COD (90%) and BOD₅ (99%) removals, and a significant reduction in dye degradation intermediates generated from RB5 reduction. Typha angustifolia had a beneficial effect on pollutant removals, attributed to the enhanced microbial density and biomass activity in the plant rhizosphere. The microbial density and biomass activity in the rhizosphere region of the planted system were (116 ± 28) × 10⁴ CFU mL^-1 and 1074 mg COD g VSS^-1 day^-1, respectively, notably higher than those in the non-rhizosphere region of the planted system ((186 ± 97) × 10² CFU mL^-1 and 794 mg COD g VSS^-1 day^-1) and the unplanted system ((91 ± 35) × 10² CFU mL^-1 and 772 mg COD g VSS^-1 day^-1). The introduction of continuous feeding mode and intermittent aeration in vertical units further improved pollutant removals in the HCW system. This improvement could be attributed to the steady feeding approach inherent in continuous mode operation, which may result in less toxicity to the system and the degradation of organic compounds under more favourable aerobic conditions.