Higher COD mass loading rate beyond the removal capability of
the IVCWs was constrained by the available oxygen in the wetlands
beds, which was in agreement with other reports (Hiley, 1995;
Vymazal and Kröpfelová, 2009). The effluent organic matter could
be reduced further if IVCWs were fed with wastewaters with low
concentrations of organic matter as demonstrated in our previous
studies (Wu et al., 2008b).