Performance comparison of stacked constructed wetlands under varying dye-rich wastewater

The applicability of constructed wetlands (CWs) at the pilot scale is mainly limited by the large land area requirement and long retention time. Subsequently, its wider application in industrial wastewater treatment is limited by low removal efficiency for high strength wastewater. Hence, here we investigate novel vertically stacked constructed wetlands (S-CWs: ((a) planted stacked wetlands (A-S-CW), (b) partially planted stacked wetlands (B-S-CW), and (c) unplanted control systems (C-S-CW)) for the treatment of dye wastewater under varying concentration, focusing on key drivers of textile effluent chemical oxygen demand (COD) and colour. The lab-scale trials conducted with vertical stacking, shorter HRT (1d), daily fresh feeding, and varying influent loads with each dosing replicated over 20 consecutive cycles. The results revealed vertical stacking as a promising strategy for pilot-scale application with reduced land area requirements. The results revealed that the planted A-S-CW system achieved superior treatment efficiency, achieving up to 94% COD, 94% NH 4 + –N, 47% nitrate, and > 98% color removal compared with other systems. Moreover, one-way ANOVA confirmed statistically significant differences ( p < 0.01) among wetland configurations in COD and NH 4 + –N removal (R 2 > 0.98), suggesting that removal is driven by biological processes, which was also confirmed by principal component analysis (PCA). These finding indicates vertical stacking could provide sustainable and low cost textile wastewater treatment with low land foot print.