Performance of horizontal sub-surface flow constructed wetlands with different flow patterns using dual media for low-strength municipal wastewater: a case of pilot scale experiment in a tropical climate region

The work presented in this paper is based on the pilot study that was performed to investigate the role of flow pattern in the constructed wetlands (CWs) on the treatment performance of real low-strength municipal wastewater. Four identical pilot-scale horizontal sub-surface flow constructed wetlands (HSSF-CWs) were installed, out of which three beds were planted with a common macrophyte, whereas one was kept as a control. The distinction in the hydraulic design was baffles, vertical up-down (CW2) and side slits (CW3), and the third bed (CW1) was kept horizontal plain type (without baffles). The filter media used in all the beds was dual type, coarse and fine gravel. Monitoring was carried out to determine BOD5, COD, TSS, NH4+-N, TN, and TP concentrations at different sampling points. Results show that the baffled beds performed better compared to the non-baffled in the order of CW2 > CW3 > CW1 > Control. The highest removal efficiency was measured in the CW2 with a reduction in BOD5 (86%), COD (77%), TSS (80%), NH4+-N (59%), TN (66%), and TP (64%). The statistical method used also showed that the flow pattern has an impact on the treatment performances of the CWs.