Environmental Engineering Reference
In-Depth Information
(96.9%), SS (78.1%), total alkalinity (74.6%), PO
4
-P (89.2%), NO
3
-N (81.7%),
acidity (73.3%), NH
4
-N (95.1%), COD (77.9%), hardness (68.6%) and coliform
bacteria (70%). An increase in the concentration of dissolved O
2
was also observed.
9.3 Floating Vegetated Mats
9.3.1 Concept
Additional methods for utilizing and removing the nutrients contained within animal
wastewater lagoons and other contaminated water bodies are needed. One poten-
tial method for removing nutrients is to have floating vegetation growing in the
lagoon, farm pond, canal, stream, or river which is periodically harvested. With the
removal of biomass from the mats, nutrients taken up by the plants are then removed
from the water body. Successful implementation of this concept may provide water
managers with an additional tool for treating or utilizing the nutrients contained in
contaminated waters.
A number of different species of plants commonly grow in water bod-
ies. Examples include water lilies (
Nymphaeaceae
), water hyacinth, duckweed
(
Lemnaceae
), and many different species of algae. Although these take up nutri-
ents from the water, if not harvested they fall to the bottom of the water body after
death. There is no removal of nutrients from the system, only cycling. Although it
is possible to harvest free floating species, it may not be economically feasible on
large water bodies due to the need for specialized harvesting equipment. Also, algae
generally are considered undesireable in water bodies because they lower dissolved
O
2
levels causing a negative effect on fish populations.
A different concept for growing vegetation in water bodies for the purpose of uti-
lizing nutrients and improving water quality is to have floating islands from which
the vegetation can be harvested. While most naturally floating vegetation is at or
slightly above the water surface, use of a floating platform to support the plants
allows for growth of relatively tall vegetation. Tall vegetation can produce consider-
able amounts of biomass which thus removes significant amounts of nutrients from
the water body.
Floating islands of vegetation are known to occur naturally. Van Duzer [84]
reported on lush floating vegetated islands found in the sinkholes on El Rancho
Azufrosa near the small town of Aldama in the state of Tamaulipas in northeast-
ern Mexico. The water in the sinkholes was highly mineralized, smelling strongly
of sulfur, and was also quite warm, with average temperatures ranging from 28.3
to 33.8
◦
C. The flora of the floating islands was dominated by a grass known as
“zacate,” and in fact it is the distinctive islands of zacate that give the sinkhole its
name “Zacaton.” The names “zacate” and “zacaton” are applied to several differ-
ent species, including
Muhlenbergia robusta, Festuca amplissima,
and
Sporobolus
wrightii,
as well as other species in these genera. A small number of shrubs and
cacti also grow on these islands.
