In this work, three hybrid vertical down-flow constructed wetland (HVDF-CW) systems with different
compound substrates were fed with domestic sewage and their pollutants removal performance under
different hydraulic loading and step-feeding ratio was investigated. The results showed that the hydraulic
loading and step-feeding ratio were two crucial factors determining the removal efficiency of
most pollutants, while substrate types only significantly affected the removal of COD and NH4
þ-N.
Generally, the lower the hydraulic loading, the better removal efficiency of all contaminants, except for
TN. By contrast, the increase of step-feeding ratio would slightly reduce the removal rate of ammonium
and TP but obviously promoted the TN removal. Therefore, the optimal operation of this CWs could be
achieved with low hydraulic loading combined with 50% of step-feeding ratio when TN removal is the
priority, whereas medium or low hydraulic loading without step-feeding would be suitable when TN
removal is not taken into consideration. The obtained results in this study can provide us with a guideline
for design and optimization of hybrid vertical flow constructed wetland systems to improve the pollutants
removal from domestic sewage