2. Materials and methods
Six beds at the campus of Nanyang Technological University
(Latitude 1 180 N, Longitude 103 500 E) were installed. The location
is a typical tropical environment and is generally hot and humid
year round. The average temperature ranges from 23 C to 32 C
(74 Fe86 F). There is no distinct wet/dry season and most rainfall
occurs during the northeast monsoon (November to January) when
the rainfalls are usually sudden and heavy.
Fig. 1 shows the layout of the horizontal subsurface flow constructed
wetland (HSSF CW). The wetland beds were 120 cm long,
60 cm wide and 60 cm deep. Thickness of gravel bed was 0.30 m
with 4e10 mm gravel (D60 ¼ 3.5 mm). The porosity was 0.45. Three
HSSF CWs were planted with cattail (Typha Angustifolia) at
a density of approximately 14e15 plant/m2
, and 3 beds without
plant. The latter were used as “unplanted” control beds. The
emergent macrophyte, Typha Angustifolia, had been cultivated for 3
years earlier and then established in the tanks for 2 months before
the experiment. All the containers had a flat bottom and a horizontal
drainage pipe 0.4 m long and 50 mm in diameter located at
the lower edge of the containers. Before the experiment data was
collected, all the beds were irrigated with wastewater from
secondary treatment process in wastewater treatment plants for
two weeks, and operated with synthetic wastewater for four weeks
before experimental data was collected.