Integrating the flooded time, multiple tides, and effluent recirculation to intensify nutrients, 17α-ethinylestradiol, and triclosan removal in a tidal flow constructed wetland treating urban stream water

A vertical subsurface tidal flow constructed wetland (TFCW, 117 L) was evaluated at pilot-scale under controlled conditions to investigate the effects of reduced flooded time, multiple tides, effluent recirculation, and supplemental aeration on the removal of nutrients, 17α-ethinylestradiol (EE2), and triclosan (TCS) from contaminated urban stream water. The downflow TFCW, planted with Alt hernanthera philoxeroides (Mart.) Griseb (32 plants m -2 ) onto fragments of red clay bricks (44% porosity) and light-expanded clay aggregates (33% porosity), was operated in four stages: one tide with flooded:rest times of 48:12 h (Stage I) and 36:12 h (Stage II); and two tides with 100% effluent recirculation and flooded:rest times of 6:6 h (Stages III and IV). In Stage IV, the effluent was additionally aerated in an external reservoir before recirculation, and the system remained drained for 6 h before the subsequent cycle. The applied strategies did not significantly influence BOD 5,20 (up to 98%) and COD removal (up to 90%), but the combination of multiple tides, effluent recirculation, and aeration increased the removal of TP (78%), TN (75%), and TAN (89%), indicating enhanced nitrification under higher oxygen availability. This stage resulted in the highest removal of EE2 (85%) and TCS (97%). Effluent recirculation and aeration promoted marked shifts in the microbial community, increasing the abundance of microorganisms involved in nitrification and simultaneous nitrification-denitrification. Overall, multiple tides combined with effluent recirculation were effective to intensify nutrient and emerging contaminant removal in TFCWs under the evaluated conditions, while effluent aeration should be carefully evaluated due to its energy demand.