Evaluating the performance of horizontal sub-surface flow constructed wetlands: A case study from southern India

Constructed wetlands are a nature-based engineering solution enabling polishing of septic tank effluents at low-cost. However to date, the influence planting on treatment efficiency remains little understood. Here we report case study evaluating performance two near-identical Horizontal Sub-Surface Flow Wetlands (HSSF-CW) deployed school in southern India. The HSSF-CWs were similar size and construction with exception that one system was planted (Canna indica) whilst other operated without plants. Both systems hydraulic loading rate (HLR) retention time (HRT) 84 mm day?1 3.7 days, respectively treat effluent from tanks. monitored fortnightly for year kinetics, nutrient organics removal efficiencies evaluated. Significant reduction biochemical oxygen demand (BOD5) chemical (COD) (p < 0.05) observed both BOD5 67% 61% unplanted systems, respectively. Whilst met environmental discharge standards set by Central Pollution Control Board (CPCB), India, total phosphorus (TP) suspended solids (TSS) significantly greater than system. first-order decay constants (K) obtained TN (KTN) (KBOD5) (0.16 0.30 day?1) higher (0.09 0.27 day?1). Greater R2 values (~ 0.90) suggests applicability model assess contaminant degradation. Plants contributed 7% (0.3 g/m2/day) BOD5, 18% (1.9 COD 5% load removal. Our data demonstrates is effective improving constructed wetlands, improvement marginal here, it noted rust infection could have limited effectiveness plants this case.