Comparative Analysis of Phytoremediation Performance in Horizontal Subsurface Flow Constructed Wetland Systems: Binary Plant Species Combinations for Leather Tannery Wastewater Treatment in South Bengal

Abstract

The sustainable wetland technology of treatment of leather tannery effluent needs optimization in the choice of the plant species to optimize contaminant removal and reduce the complexity of the system. The paper assessed the effectiveness of Horizontal subsurface flow constructed wetlands (HSF-CW) in phytoremediation using binary species combinations with two opposite combinations used in the evaluation of tannery wastewater of the Oxford tanners, Kolkata industrial cluster. The HSF-CW systems were piloted (60 days) in 5 systems, System 1 (unplanted control), System 2 (typha domingensis + Vetiveria zizanioides), and System 3 (phragmites australis + Salix alba). With an optimized hydraulic retention time (HRT) of 7.5 days, the Typha-Vetiveria binary system had the highest chemical oxygen demand (COD) removal of 82.4, total nitrogen (TN) removal of 68.9, and chromium (Cr) removal of 87.2, whereas the Phragmites-Salix system experiment did better in sulfide oxidation (81.6% S 2 - removal) and phosphorus uptake (73.2% TP removal). Analysis of plant tissues showed dissimilar patterns of metal accumulation as Typha-Vetiveria combination had 1247 ± 156 mg/m 2 of chromium accumulation and Phragmites-Salix maximum accumulation of sulfur bioaccumulation (7.8 ± 1.2 g/kg). Cost-benefit analysis showed that Typha-Vetiveria system was the most economical (USD 0.85/m 3) to be used on full scale in the tannery clusters of South Bengal. Findings indicate that binary species selection contributes to important treatmentPathway specialization, and complementary mechanisms can be used to optimize the treatment with contaminants.