Harnessing waste materials and tidal flow in constructed wetlands: High-Performance treatment of dye and surfactant-contaminated wastewater

This study explores the effectiveness of sustainable substrates - seashells, ceramic brick fragments, and sand (mixed in a 3:1:1 ratio) - for treating synthetic wastewater contaminated with the azo dye Acid Red 18 and the surfactant Linear Alkylbenzene Sulfonate in a pilot-scale Constructed Wetland (CW) system. The CW, planted with Typha spp., was operated under a tidal flow regime, alternating between 96 h flooding and 72 h draining cycles. The system demonstrated exceptional performance, achieving (88.73 ± 5.81) % chemical oxygen demand reduction, (73.97 ± 9.69) % ammonium removal, and (74.78 ± 23.94) % total suspended soil removal. It also excelled in removing the dye (100 %) and the surfactant (90.62 ± 3.93) %. Over 133 days, the CW supported the growth of specialized microorganisms, including heterotrophic bacteria, ammonia-oxidizing bacteria, and denitrifiers. Although nitrite-oxidizing bacteria did not proliferate, potentially indicating a shift towards nitrite accumulation, the exact nitrogen removal pathway remains uncertain, particularly given the potential for conventional denitrification under high COD conditions. In situ monitoring revealed a gradual decline in dissolved oxygen and redox potential across different substrate layers. Despite rises in electrical conductivity and dissolved solids, the system maintained stable performance across all evaluated parameters, demonstrating the resilience of the CW system.