Environmental Engineering Reference
In-Depth Information
The aquaculture wastewater is quite different from the swine lagoon wastewater in
that it is relatively low in N and P, although algae will grow profusely.
The test during 2008 showed that many of the species which grew well in mod-
erately or severely contaminated swine lagoon wastewater could not survive in the
aquaculture wastewater. Three species which did grow well in 2008 were iris, cat-
tail, and soft rush. This study will measure both the nutrient uptake by the plants
and the quality of the water in the tanks. The ultimate objective is to see if float-
ing vegetated mat systems can be used to improve aquaculture wastewater quality
sufficiently so that the treated water can be recycled back to the aquaculture ponds.
9.3.7 Research Needs
Considerable research is needed on floating mat technology. Research needs include
studies to determine relationships between water quality and specific plant species
to find ones which will thrive on a given water body, studies which will determine
the potential for production of biomass, studies to develop engineering technologies
for handling the platforms and vegetation, studies of how best to utilize the plant
materials (either living or harvested), and economic feasibility studies. Our work at
Tifton, GA has shown that plant species are very sensitive to water quality. Grasses
that grew well in severely contaminated low O
2
swine lagoon wastewater at a com-
mercial farm died when placed on wastewater from aquaculture ponds. We also
found that there were local adaptations among the same species according to avail-
able nutrient levels. We successfully grew cattail in our first study with moderately
contaminated swine lagoon wastewater. The cattail we used were found growing
naturally along the sides of ponds on the University of Georgia Animal Science
Farm. When we used cattail from the same source for our studies with aquaculture
wastewater, they died. However, we found native cattail growing on the sides of
the aquaculture ponds (low nutrient level water) which worked well on the floating
platforms in tanks containing aquaculture wastewater. Also, different plant species
produce different amounts of biomass and have different overwintering patterns, so
determination of best species to produce biomass is needed.
Engineering research needs to be done to develop methods for handling vege-
tated mat systems. Methods need to be developed for completely mechanizing mat
systems. At the research scale we have been moving mats and harvesting vegeta-
tion mostly by hand. This is labor intensive and not very economical. If a system of
sprigging, moving the mats on and off of a water body, and then harvesting and
transporting the vegetation can be developed then floating mat systems become
much more economically viable.
Research is also needed to study alternate platforms for floating mats. Our
research to date has been with platforms built from PVC, chicken wire, and a fiber
mat, or from polypropylene with a hollowed out area covered with coir fiber blan-
ket as supplied by Maryland Aquatic Nurseries and Charleston Aquatic Nursery.
Another platform type for floating mats which has been developed and is being
marketed comes from Floating Island International (Fig. 9.9). The platforms from
