Treatment efficiency of vertical flow constructed wetland systems operated under different recirculation rates

- Three pilot-scale VFCW systems (CW1, CW2 & CW3) with recirculation arrangements of 25, 50 and 75% were operated to treat dairy wastewater.
- The average concentration of pollutants in the influent was recorded as: BOD (323.0 ± 139.3 mg L−1); TP (37.6 ± 13.3 mg L−1); NH4-N (68.9 ± 13.5 mg L−1) and TN (114.9 ± 22.6 mg L−1) during the study period.
- Recirculation arrangement resulted in an increase of 10.0-19.3% TN removal from all CW systems.
- Maximum average purification rates of TSS (99.3%), BOD (97.8%), TP (97%), TN (50.5%) and NH4-N (50.7%) were achieved in CW3 with 75% recirculation.
- OTR value of all three CW systems ranged from 27.0 to 54.4 g O2 m−2 d−1 before recirculation showed an increase after recirculation and was found between 79.6 and 154.8 g O2 m−2 d−1.