Layer V Vermi-biofiltration bed mainly constructed using thick
bedding of soil mixed with small stones and pebbles along with
complex root-zone system of surface plant Cyprus rotundus. The
thickness of this layer was about 10in. — earthworm acts as biological
agent to remove solid fractions of wastewater and mineralization
of wastewater mainly driven by earthworm-microbe
interactions in root-zone system.
Layer VI Composed of surface vegetation stand of Cyprus. Itwas about
4 – 6 in. in length — wetland plant provides air in root-zone system
and removes nutrients fromwastewater through general absorption,
adsorption and translocation processes. Also provides shelters to
beneficial microbial communities responsible for N mineralization.
The detail of vermi-biofiltration/biofiltration unit is given in Fig. 1.
In the top layer of Reactor-I, i.e. Layer-V the fresh and viable specimens
of Cyprus were planted in top soil layers. The roots of plant were
planted deeply and surface layer was irrigated regularly (for one
week) by tap water in order to fix the planted Cyprus in top layer of vermireactor.
The mean density of Cyprus in vermireactor-I was about19
plants/in.2. The open space between plant stand was filled with a thin
layer of small stone to avoid direct hydraulic impact on the plant and
earthworm. In this vermi-biofiltration system efforts weremade to create
a kind of soil ecological system mainly comprised of thick soil layer
spiked with complex rooting system of Cyprus rotundus. The pieces of
stones and pebbles in this root-zone-filtration system create an appropriate
space for air and inoculated earthwormin sub-soil system. Nonetheless,
the root-zone system not only enhances the efficiency of
wastewater filtration but at the same time also provide shelters to bacterial
communities (e.g., N-fixers, ammonifying and denitrification bacteria)
responsible for nutrient removal from wastewater.
Reactor-II: Another unit of reactor, i.e. Reactor-II was introduced in
order to enhance the removal efficiency of the system. In Reactor-II
the biological component of the filtration unit was of more importance
therefore the majority of the reactor volume was filled with earthworm
and plant root zone layers. A rectangular plastic container of
size (23. 5-inch length×18-inch width×15-inch depth) was used to
construct the second unit (Reactor-II) of vermin-filtration system.
In Reactor-II there were two district layers: firstly, base layer (large
pebbles; 10–15 cm in diameter and height about 6-inches), and secondly,
top layer (small pebbles; 5–7 cm in diameter mixed with fine
sand and height up to 10-inches). The top layer acts as bedding substrate
for earthworms in Reactor-II. A thin plastic net sheet was placed
between the both layers to avoid movement of earthworms from top
layers to base layer of the vermireactor. Fresh and viable specimens
of plant: Cyprus rotundus were planted in top layer and thin patches
of small stones were placed over the open spaces around Cyprus
plant to avoid direct hydraulic impact of inflow water in Reactor-II
on plant stand and earthworms. The mean plant density in vermireactor
was 0.14 plants/in.−2 (calculated using values of total surface area
of Reactor-II and plant numbers in reactors). After plantation Cyprus
stand was allowed to grow for one week and during this period adequate
amount of tap water was supplied in vermireactor to facilitate
the fixing of roots of plant in top layers of Reactor-II. Initially, both
reactors were run for two–three days using fresh tap water to
wash and fix the layers of vermibeds in proper functioning forms.
After establishment of plant stands (after one week) the reactor
was run for wastewater treatment experimentations. In both experimental
vermi-biofiltration systems, i.e. Reactor-I and Reactor-II individuals
of earthworm P. sansibaricus were introduced over the
top layer the reactors. Small passages were made in the surface
layers of both reactors in order to facilitate worms to enter in the
top soil layers of the vermireactor. The initial earthworm density in
both vermi-biofiltration systems was measured in the ranges of
22.0–24.5 g/L. The earthworms were allowed to settle in vermireactors
for initial 2–3 days and thereafter, vermireactor was run for