Environmental Engineering Reference
In-Depth Information
is the removal of nutrients from the system through constant cutting and removal
of the biomass from the floating mat system. In contrast, most constructed wetland
systems have permanent vegetation which means that plant tissue ultimately falls to
the bottom of the wetland as it senesces.
9.3.4 Small Scale Study Using Secondary Stage Swine
Lagoon Wastewater
A study was designed in late 2000 to test the hypothesis that plant species commonly
found in ponds or wetlands could produce biomass and remove nutrients from swine
lagoon wastewater. The idea for the study was a follow-up from a presentation
made by Mr Chris Hoag of USDA-NRCS Plant Materials Laboratory, Aberdeen,
ID, showing a study to improve farm pond water quality using vegetation growing
on platforms constructed of PVC pipe and chicken wire. The scientific question that
came from that presentation was whether or not there were any plant species which
would grow on a floating platform in swine lagoon wastewater.
A replicated study was conducted by USDA-ARS and the University of Georgia
from 2001 to 2002 using aquaculture tanks at a field site approximately 760 m from
the University of Georgia Coastal Plain Experiment Station main swine research
facility at Tifton, GA [88]. The floating platforms were built using 0.64 cm diame-
ter PVC pipe, chicken wire, and fibrous matting material. Each frame had an outer
square and an inner cross constructed of PVC pipe. Attached to the sides and sup-
ported by the middle T-cross were chicken wire and fibrous matting. Each individual
platform was 1 m
2
and was built to float inside of a tank capable of holding 1285 L
of wastewater.
There were three different nutrient treatments, three different plant species,
and four replicates of each combination, for a total of 36 floating mats each
contained within an individual tank. The three different nutrient treatments were
full-strength wastewater,
1
/
2
-strength wastewater (swine lagoon wastewater mixed
with well water), and inorganic nutrients (1/4-strength Hoaglund solution) [89].
The full-strength wastewater contained on average total nutrient concentrations of
160 mg L
-1
N, 30 mg L
-1
P, and 45 mg L
-1
K, while the
1
/
2
strength wastewater con-
tained half this amount. Total nutrient concentrations for the
1
/
4
- strength Hoaglund
solutionwere53mgL
-1
N,8mgL
-1
P, and 59 mg L
-1
K. The
1
/
4
-strength Hoaglund
solution was designed to provide sufficient N and P for the plants so that they would
not die, but insufficient for rapid growth. Every two weeks, half of the liquid in each
tank was replaced with new liquid of the appropriate nutrient level (full-strength
wastewater,
1
/
2
-strength wastewater, or
1
/
4
-strength Hoaglund solution), except dur-
ing the winter months when the nutrient replacement interval was spread out to
every three weeks, since the plants were either dormant or very slow growing.
Three different wetland plant species were selected for the study: cattail (
Typha
latifolia L.
), soft rush (
Juncus effuses
), and maidencane. The cattail and rush species
were selected for the test because of published information concerning their use in
constructed wetlands [90-99] while the maidencane was selected because it had
