Hydraulic behaviour of vertical-flow constructed wetland under different operating conditions

Five vertical-flow constructed wetland (VFCW) units planted with cattail (Typha augustifolia) were used to study the effects of feeding (continuous and batch), hydraulic loading rates (HLR) and drainage patterns (free drainage and percolate impounding) on hydraulic behaviour. The tracer studies were divided into two parts: (i) continuous feeding at an HLR of 0.005, 0.025, 0.05, 0.075, 0.1 and 0.3 m3 m(-2) d(-1) operating at different drainage patterns (i.e. free drainage and percolate impounding) and (ii) batch feeding at different water levels of percolate impounding (20, 30 and 40 cm). The results revealed that although the hydraulic behaviour of VFCW systems was strongly dependent on the operating pattern (feeding and drainage), it was not significantly affected by the hydraulic loading rate. The results of continuous feeding study concluded that (a) percolate impounding achieved an increase in HRT that was 1.6 times the HRT with free drainage, (b) the dispersion in both drainage patterns were moderate, and (c) the results from the tank-in-series (TIS) model correlated more closely with the data observed than with the dispersion plug flow (DPF) model. For batch feeding and percolate impounding, a uniform flow distribution of the tracer occurred in the water column after 2.1, 3.1 and 4.4 days for 20, 30 and 40 cm, respectively.