Nitrate is an important indicator of water pollution and its high
concentration in freshwater bodies leads to eutrophication problem.
In this study there was significant impact on nitrate concentration
in effluents after treatment in both experimental reactors. But NO3
−
reduction arte was prominent in vermi-biofiltration unit than biofiltration
system (Table 3). The level of NO3
− in effluent after final treatment
cycle was 27.9 mg/L for vermi-biofiltration unit and 186.9 mg/L
for biofiltration unit. There was about 92.7% total removal of NO3
−–N
in vermi-biofiltration unit that was significantly higher than total removal
in biofiltration unit (51.3% removal) (t-test: pb0.001). In traditional
wetland biofiltration system the nutrients and metals may be
removed from the polluted water and retained in the sediment and
taken up by the plants and by microorganisms associated on the surface
of the roots and sediments, by immobilization in sediments via.,
mechanism such as adsorption on ion exchange sites binding to organic
matter, incorporation into lattice structure and precipitates
into insoluble compounds [37]. The results of removal efficacy of biofiltration
system were similar to those observed in constructed wetlands
by other researchers [28, 32] and were moderately higher
than those detected in horizontal flow constructed wetlands planted