Constructed wetland is an effective wastewater treatment technology which is used
in worldwide. Nevertheless, the effectiveness of using this wastewater treatment is
depending on the selection of the type of design used and other factors. This research
was conduced to test the influence of media and vegetation subsurface flow
constructed wetlands, designed based on the first-order plug flow kinetics. In this
study, four horizontal subsurface flow wetlands (HSSF), each with dimensions of 1.3
m (L) × 0.5 m (W) ×0.4 m (D), were constructed at the Research Station of Tehran
University, located in Karaj, Iran. The study was carried out from April to
September, 2007. Gravel and zeoilte were used in this study as substrate. Gravelbeds
with and without plants, and gravel-beds mixed with 10% zeolite, with and
without plants were examined to investigate the feasibility of treating synthetic
wastewater which was specially produced and modified to imitate agricultural
wastewater. The average synthetic influent wastewater contained approximately 100 mg l-1 Nitrate (NO3-N), 10 mg l-1 total Phosphorous, 10 mg l-1 Zn (II), 2 mg l-1 Pb (II)
and 1 mg l-1 Cd (II), while the macrophytes selected were Phragmites Australis and
Juncus Inflexus in combine with each other. Water discharge was 65 l / day for each
cell, and retention time (HRT) was 1.4 d. The influent and effluent Zn, Pb, Cd, P and
NO3-N concentrations were monitored and analyzed every 15 days to assess the
performance of the wetland units for removal efficiencies based on the statistical
analyses. Two intermediate samples were also collected from each cell to evaluate
the values of pollutant concentrations, the parameters along the units, and the effect
of the HRT. At the end of the study, plants were harvested and analyzed for the
same factors (NO3, P, Zn, Pb and Cd).
The results derived indicated that the system had acceptable and optimal pollutant
removal efficiency, and that both plants were found tolerant under the tested
conditions. The wetland system could achieve the NO3-N removal of 79.19% in
vegetated cell with gravel and 10% zeolite as substrate, and 86.58% in an
unvegetated cell with gravel and 10% zeolite as substrate, and 82.39% in vegetated
cell with gravel as substrate, and finally 87.94% in unvegetated cell with gravel as
substrate. As for the P removal, the efficiencies of 93.12%, 89.47%, 81.76% and
76.65% were respectively achieved for the vegetated cell with gravel and zeolite as
substrate, the vegetated cell with gravel as substrate, unvegetated cell with gravel and
zeolite as substrate, and unvegetated cell with gravel as substrate. The outflow
concentrations of Pb and Cd were found to be under the detection limit; however, as
for Zn, the removal efficiencies of 99.9%, 99.76%, 99.71% and 99.52% were
concluded for the vegetated cell with gravel and zeolite, unvegetated cell with gravel
and zeolite, vegetated cell with gravel, and unvegetated cell with gravel, respectively
