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How are plants being used to treat effluents from fish-farms?


Thors Hammer 5 / 60  
Apr 8, 2012   #1
Unit Two Assignment
Thesis:

Plants are being used to treat wastewater produced from fish farms by up-taking contaminants and turning them into harvestable energy.

Analysis:

It starts by understanding that plants can treat different media like air, soil, and water while removing unwanted contaminants like organic nutrients, metal compounds, ammonias, and turn them into energy for growth. These processes are refered to as Phytoremediation. There are several methods of Phytoremediation including: Phytoaccumulation, Phytostabalization, Phytodegradation, Rhizodegradation, Phytovolitization and Rhizofiltration (arabidopsis).

Fish-farms produce effluent water containing fish excrement and leftover food particles. Plants that have various nutrient requirements similar to those found in the wastewater remove those contaminants effectively and store them in their roots and leaves throughout their lifecycle. This process is known as Rhizofiltration. Other phytoremediation processes such as Hydraulic control involves the plants removing groundwater and diffusing it into the atmosphere to control water levels (arabidopsis).

A good example of Rhizofiltration being used for fish-farming would be where plants are grown hydroponically using raceway wastewater as a source of nutrients while removing contaminants from the water in an environmentally conscious way. Larger facilities can provide controlled environments where they can manipulate artificial lighting, humidity, CO2, and provide plants various substrates for rooting while feeding them the rich wastewater. The plants mature using the nitrogen, phosphorous and potassium along with other macro/micro and trace nutrients effectively depleting the water of those nutrients. Certain plants may be harvested for aesthetical purposes, or processed back into fish-feed forming a symbiotic relation by promoting operational self-sustainability. By facilitating the need for large volumes of nutrients enables the farmer to clean larger volumes of effluent water and sustain an abundance of perpetually grown vegetation. By recycling the water through a closed circuit before releasing it back into the environment, allows control over how many times the wastewater may be treated and therefore how contaminant free the final product will be. This also allows the farmer to use various concentrate levels of nutrients for more sensitive plants. In some cases after water treatment, the plants may be too contaminated for use, or may have been used to absorb dangerous contaminates which now necessitate for reasonable or safe disposal. For example: Sunflowers were used to uptake Radionuclides in contaminated water pools in Chernobyl. In addition, Alfalfa, poplar, juniper and fescue have been used in Phytoextraction treating soil and groundwater of petroleum and hydrocarbons in Ogden, UT.

Case Study One:

In an experiment (Ghaly et al., 2005) conducted with Tilapia wastewater from a fish-farm located in Chezzacook, Halifax County, Nova Scotia. Five plants were selected for growth, and each characterized for their required Nitrogen, Phosphorous, and Potassium: Alfalfa 113/59/180 - White Clover 170/59/180 - Fall Rye 50/22/17 - Barley 56/28/17 - Oat 56/22/22. The chemical analysis of the effluent water for those nutrients was averaged at 115/50/230. The Clover and Alfalfa had growth problems from the start and died off. The Oat, Rye and Barley had the best results which showed the "total reductions in solids of Nitrogen, Phosphorous, and Potassium ranged from 54.7% to 91% (Ghaly et al., 2005). The study revealed "the plants were able to remove all the pollutants in the wastewater and significant portions of those released substances."(Ghaly et al., 2005)

Case Study Two:

A study conducted to determine the Efficiency of aquatic macrophytes to treat Nile tilapia pond effluents (Henry-SilvaI; Monteiro CamargoII, 2006) was conducted in Brazil. They used the water containing 2000 juvenile tilapia and released it into large concrete tanks for treatment every twenty-four hours. The test showed that over the course of the season, concentration levels of Nitrogen and Phosphorous increased compared with the water source (Henry-Silva et al,. 2008). This was due to the increased feed being used to feed the growing fish (three times more at the end than at the start) as well as accumulation of nutrient levels within the plants. The tests conclude by saying that "after macrophyte treatment, it is possible reusing effluent treated in fish farms and to release it into the aquatic ecosystem avoiding artificial eutrophication." (Henry-SilvaI; Monteiro CamargoII, 2006)

Conclusion:

Although macrophytes can be used to treat effluent water sources from fish farms, limitations as to the efficiency of treating large volumes are numerous. However, by balancing sufficient need for nutrients in ratio with the effluent needed to be treated, along with selection the appropriate plants and growing techniques, would allow for great potential when raising fish inland.

References:

Ghaly A.E., Kamal M. and Mahmoud N.S. "Phytoremediation of aquaculture wastewater for water recycling and production of fish feed." Elsevier.2004.Web. 28 March 2012.

"Arabidopsis.info" What is Phytoremediation. March 28. 2012.

Hegedus, Reka et al,."Potential phtroremediation function of plants in effluent treatment of an intensive fish-farming system using geothermal water"Sapientia.2009. March 28. 2012.

Gustavo Gonzaga Henry-SilvaI; Antonio Fernando Monteiro CamargoII, 2006. Science Agricola. Efficiency of aquatic macrophytes to treat Nile tilapia pond effluents, Oct 2006. Web. 28 March. 2012.

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