Environmental Engineering Reference
In-Depth Information
The study showed that floating mats of vegetation can be grown in lagoon
wastewater, and that the cattail was the best plant species for biomass production
and nutrient removal on this wastewater. At the wastewater strength used for this
study, both the maidencane and cattail survived and removed nutrients. The rush,
although initially showing promise, ultimately died and also showed growth prob-
lems with the inorganic control treatment. Total biomass produced on full-strength
wastewater during the study was 16,511 g m
-2
and 9751 g m
-1
for the cattail and
maidencane, respectively. Total N, P, and K removed on full-strength wastewater
were 534, 79, and 562 g m
-2
for the cattail and 323, 48, and 223 g m
-2
for the maid-
encane, respectively. Using an assumed root zone thickness of 30 cm for cattail
and 15 cm for maidencane, mass balance calculations showed that, on full-strength
wastewater, the cattail removed 43, 34, and 160% of the applied N, P, and K, respec-
tively, while the maidencane removed 52, 41, and 127%. More K was needed than
that calculated as being supplied by the wastewater in the root zone. This K clearly
came from mixing of wastewater within the tanks. The mass balance calculations
showed that N and P were in excess of plant needs for the full-strength wastewater
for the assumed root zone thickness. Since root zone thicknesses used for the mass
balance calculations were 15 or 30 cm, and lagoons are commonly in excess of 2
m deep, in most cases, lagoon nutrients will be greatly in excess of potential plant
uptake and removal.
9.3.5 Floating Vegetated Mat Study on a Single Anaerobic
Wastewater Lagoon at a Commercial Hog Farm
A floating vegetated mat study was conducted from 2005 to 2008 on a commer-
cial swine farm (Southern Select) located near Omega, GA. The producer flushed
all wastes from approximately 3000 hogs to a single anaerobic wastewater lagoon
adjacent to the swine houses. All wastes were flushed from the houses using fresh
water.
The floating platforms for this study were designed by Maryland Aquatic
Nurseries and Charleston Aquatic Nursery (Fig. 9.1). In our previous study [88]
we used PVC support frames covered with chicken wire and a coir mat. During
pre-study plant tests at the Southern Select lagoon in 2004 we determined that PVC
and chicken wire platforms (Fig. 9.2) were unsuitable for the highly concentrated
wastewater. The chicken wire rusted out in 2-3 months and the vegetation would
then fall through the platform into the lagoon. Maryland Aquatic Nurseries and
Charleston Aquatic Nursery designed a platform consisting of material cut in a
square with an inner hollow portion. The hollow portion was then covered with
fibrous coir materials and attached to the outer frame with plastic fasteners and a
stainless steel bar. These were tested in 2004 and found to work well on the lagoon
wastewater without deterioration due to poor water quality.
During summer-fall of 2004 through mid-summer 2005 a pre-study test was con-
ducted to determine which, if any, plant species could survive in this single stage
