Three concrete ponds, each with a dimension
of 0.6 m width, 1.8 m length and 1.2 m depth,
were constructed at the Hatyai Municipality Central
Wastewater Treatment Plant, Southern Thailand,
under the realistic conditions as shown in Figure 1.
Lotus and hydrilla were planted along with one
control unit without plant (Figure 2). Wastewater
from the second constructed wetland of the Hat Yai
Municipality Central Wastewater Treatment Plant
was introduced to the experiment using peristaltic
pumps to operate and maintain a fixed flow rate.
The experiment was divided into two schemes
which are summarized as shown in Table 1.
RUN No.1 was operated at a hydraulic retention
time (HRT) of 5.4 days in order to simulate
the maximum receiving flow of the treatment plant
from the Hatyai Municipality. This run was conducted
from July 6, 2003 till September 11, 2003.
RUN No.2 examined the performance of lotus
and hydrilla systems when operated at an organic
loading rate the same as the design criteria for nonaerated
water hyacinth system (USEPA, 1991). This
run was conducted at HRT of 10.5 days starting on
September 19, 2003 till November 21, 2003. The
influent and effluent of each unit was analyzed for
pH, 5-day biochemical oxygen demand (BOD5),
suspended solids (SS), total kjeldahl nitrogen