PhD Theses

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Browsing PhD Theses by Subject "Aquaculture ponds"

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    Potential re-use of treated wastewater from a horizontal subsurface flow constructed wetland for aquaculture production: modeling of nitrogen dynamics and removal in aquaculture pond
    (University of Dar es Salaam, 2009) Yohana, Lawi
    The re-use of treated wastewater from a constructed wetland for aquaculture production has been investigated. Data were collected from an experimental fishpond constructed downstream the HSSFCW at UDSM-WSP system stocked with cichlid fish Oreochromis urolepis. Water quality from the treatment system, within fish pond and outlet of the fish pond were analyzed in accordance with the Standard Methods for the Examination of Water and Waste water (APHA, 1998) and included Nitrate, Turbidity, Organic nitrogen, pH Temperature, Dissolved oxygen, Biological oxygen demand, Total kjeldahl nitrogen, Ammonia, Nitrite and Total nitrogen. Furthermore, an ecological model to simulate nitrogen dynamics and removal in such a fish pond was developed. Results show that, constructed wetland can effectively polish waste water that can be re-used for fishpond culture and that fish can feed exclusively on phytoplankton and grow up to 200g in a period of 120 days. A dynamic and mechanistic mass balance model for nitrogen dynamics in fishpond was developed and simulated using STELLA modeling software and predicted the concentration of organic nitrogen (〖(r〗^2=0.99), nitrate (〖(r〗^2=0.65), and ammonia (〖(r〗^2=0.51). model output predicted that nitrate uptake, decaying and nitrification were the major pathways accounting for nitrogen transformation. They all together account for 62.15 of nitrogen transformation. Sensitivity of model parameters indicated that average nitrogen concentration was most sensitive to phytoplankton specific uptake rate. Further sensitivity analysis revealed that the concentration of nitrogen in any state variable is more affected bi changes in specific parameters included in the fishpond model than other forms of nitrogen in the pond. Model output and results of the processes affecting nitrogen transformations in fishponds and offer possibilities for the most effective management intervention. It is recommended from this study that a more complete integration of the model with respect to other nitrogen pool is required. Also other water quality with respect to fish production such as heavy metals and environmental estrogenicity be investigated.