Browsing by Author "Senzia, M. A."

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    Modelling Nitrogen Transformation and Removal in Primary Facultative Ponds
    (Elsevier, 2002) Senzia, M. A.; Mayo, Aloyce W.; Mbwette, T. S. A.; Katima, Jamidu; Jørgensen, S. E.
    This paper presents a dynamic rational model for nitrogen transformation in primary facultative ponds. The results show that, the dominant mechanism for nitrogen removal was sedimentation of organic nitrogen (9.7%). The major nitrogen transformation route was through mineralization (19.2%) followed by ammonia uptake by microorganisms (17.4%) and nitrification (2.4%). Denitrification process was another possible route for removal of nitrogen (4.1%), but volatilisation played a negligible role (0.1%). Approximately 38.8% of nitrogen flowing to primary facultative pond did not undergo any transformation. It was further found out that 8.3% of influent nitrogen was unaccounted for, which might be lost through seepage to the ground or evaporation. Nitrogen contained in microorganisms accounted for 50% of the total nitrogen in the final effluent.
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    Modelling Nitrogen Transformation in Horizontal Subsurface Flow Constructed Wetlands Planted with Phragmites Mauritianus
    (2004) Senzia, M. A.; Mashauri, Damas A.; Mayo, Aloyce W.
    A mathematical model was developed to permit dynamic simulation of nitrogen interaction in a pilot horizontal subsurface flow constructed wetland receiving effluents from primary facultative pond. The system was planted with Phragmites mauritianus, which was provided with root zone depth of 75 cm. The root zone was packed with gravel of 6 to 25 mm diameter in uniform proportions. Stella II software was used to simulate nitrogen transformation processes. The results show that the most influential nitrogen transformation processes were nitrification, denitrification, plant uptake, decomposition and accretion of organic nitrogen. Volatilisation played a negligible role in reducing nitrogen at the typically neutral pH levels found in subsurface wetland systems. Denitrification process, which ensures the permanent removal of nitrogen, accounted for 0.219 g/m2.d, which was only 15.0% of incoming nitrogen load (1.458 gN/m2.d). Harvesting of plants removed 0.195 gN/m2.d (13.4%) from the system. Accretion of organic nitrogen was a major pathway accounting for 0.279 g/m2.d, which is 19.2% of all the influent nitrogen. The accumulation of ammonia nitrogen was found to be high compared to other water phase state variables (organic nitrogen and nitrate nitrogen).
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    Suitability of Constructed Wetlands and Waste Stabilisation Ponds in Wastewater Treatment: Nitrogen Transformation and Removal
    (2003) Senzia, M. A.; Mashauri, Damas A.; Mayo, Aloyce W.
    It is estimated that 90% of sewage in cities in developing countries are today discharged untreated into water bodies. In Tanzania, pollution of rivers such as Karanga, Njoro and Rao in Moshi; Mirongo in Mwanza and Themi in Arusha is the cause of frequent disease outbreaks in communities downstreams. Solutions to effluent crisis can be found by its proper treatment and disposal. The principal objective of wastewater treatment is to allow effluents to be disposed without danger to human health or unacceptable damage to the ecology of receiving water bodies. Field investigations were made on pilot scale horizontal subsurface flow constructed wetlands (CW) units located downstream of waste stabilisation ponds (WSP). Six units filled with gravel of 6–25 mm diameters in equal proportion, which gave an initial hydraulic conductivity of 86 m/d were used. While four units covering surface area of 40.7 m2 each, were located downstream of primary facultative pond, the other two units with surface area 15.9 m2 each were located downstream of maturation pond. An attempt was made to compare the output of mathematical models for Phragmites and Typha macrophytes located downstream of primary facultative pond. Based on total inflow nitrogen of 1.457 gN/m2 d, while Phragmites has shown a removal of 54%, Typha had a removal of 44.2%. Furthermore, while the system downstream of primary facultative pond has accretion as a major pathway, accounting for 19.1% of inflow nitrogen, the system downstream of maturation pond has denitrification as its major removal mechanism accounting for 20.5%. In this paper, a comparison of land required by CW and WSP based on the amount of water to be treated is made.