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  • 1.
    Kyambadde, Joseph
    KTH, Skolan för bioteknologi (BIO).
    Optimizing processes for biological nitrogen removal in Nakivubo wetland, Uganda2005Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The ability of Nakivubo wetland (which has performed tertiary water treatment for Kampala city for the past 40 years) to respond to pollution and to protect the water quality of Inner Murchison Bay of Lake Victoria was investigated. The aim of this study was to assess the capacity of Nakivubo wetland to remove nitrogen from the wastewater after its recent encroachment and modification, in order to optimize biological nitrogen removal processes using constructed wetland technology.

    Field studies were performed to assess the hydraulic loading, stability and water quality of this wetland. The distribution and activity of ammonium-oxidizing bacteria (AOB) in Nakivubo channel and wetland were also investigated, and the significance of the different matrices in biological nitrogen transformations within the two systems elucidated. Studies to optimize nutrient removal processes were carried out at pilot scale level both in container experiments and in the field using substrate-free constructed wetlands (CWs) planted with Cyperus papyrus and Miscanthidium violaceum which were adapted to the local ecological conditions.

    Results showed that Nakivubo wetland performs tertiary treatment for a large volume of wastewater from Kampala city, which is characterised by large quantities of nutrients, organic matter and to a lesser extent metals. Mass pollutant loads showed that wastewater effluent from a sewage treatment plant constituted a larger proportion of nitrogen and phosphorus and biochemical oxygen demand (BOD) discharged into the wetland. The upper section of Nakivubo wetland exhibited high removal efficiencies for BOD, whereas little or no ammonium-nitrogen and metals except Lead were removed by wetland. Studies further showed that nitrifying bacteria existed in the wetland but their activity was limited by oxygen depletion due to the high BOD in the wastewater and heterotrophic bacteria from the sewage treatment plant. Distributional studies indicated the presence of more AOB in surface sediments than the water column of the lower section of Nakivubo channel, an indication that nitrifiers settled with particulate matter prior to discharge into the wetland, and thus did not represent seeding of the wetland. The significant reductions in concentrations of BOD compared to ammonium and total nitrogen in the channel and wetland wastewater confirmed this finding. Whereas suspended nitrifiers upstream of Nakivubo channel equally influenced total nitrogen balance as those in surface sediments, epiphytic nitrification was more important than that of sediment/peat compartments in the wetland, and thus highlighted the detrimental impacts of wetland modification on the water quality Inner Murchison Bay and Lake Victoria as a whole.

    Performance assessment of pilot-scale container experiments and field-based CWs indicated highly promising treatment efficiencies, notably in papyrus-based treatments. Plant biomass productivity, nutrient storage, and overall system treatment performance were higher in papyrusbased constructed wetlands, and resulted in effluent that met national discharge limits. Thus, papyrus-based CWs were found to be operationally efficient in removing pollutants from domestic wastewater.

  • 2.
    Kyambadde, Joseph
    et al.
    KTH, Tidigare Institutioner, Bioteknologi.
    Dalhammar, Gunnel
    KTH, Tidigare Institutioner, Bioteknologi.
    Kansiime, Frank
    Makerere University.
    Functional assessment of horizontal surface flow constructed wetlands receiving pre-treated domestic wastewater in Uganda.Inngår i: Water, Air and Soil Pollution, ISSN 0049-6979, E-ISSN 1573-2932Artikkel i tidsskrift (Annet vitenskapelig)
  • 3.
    Kyambadde, Joseph
    et al.
    KTH, Skolan för bioteknologi (BIO).
    Kansiime, F.
    Dalhammar, Gunnel
    KTH, Skolan för bioteknologi (BIO).
    Distribution and activity of ammonium-oxidizing bacteria in Nakivubo wastewater channel and wastewater treatment wetland,Uganda2006Inngår i: Acta Hydrochimica et Hydrobiologica, ISSN 0323-4320, E-ISSN 1521-401X, Vol. 34, nr 1-2, s. 137-145Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The pollution profiles of Nakivubo channel and wetland, and the spatial distribution of ammonium-oxidizing bacteria and the corresponding ammonium-oxidation activities along Nakivubo channel and wetland are presented. A set of physico-chemical and biochemical variables was monitored, and numbers and activity of ammonium-oxidizing bacteria in the water, sediment and epiphyton were quantified to estimate their influence on the nitrification and nitrogen bio-conversions in general, and to determine the factors influencing the distribution of ammonium-oxidizing bacteria in Nakivubo channel and wetland. Considerable numbers of ammonium-oxidizing bacteria and ammonium-oxidation activities were found upstream of Nakivubo channel suggesting that the physico-chemical conditions were suitable for the survival of nitrifying bacteria. However, the longitudinal decline in numbers and activity of ammonium-oxidizers was probably due to (1) high biodegradable organic matter input which supported proliferation of heterotrophs, consuming the little available oxygen, (2) hydro-sedimentary conditions of the channel, (3) die-off due to presence of toxic and inhibitory chemicals and metal compounds. The removal of biochemical oxygen demand was significantly higher than that of nitrogen indicating lower self-purification efficiency for nitrogen. A comparison of the ammonium-oxidation activity of the different phases indicated that epiphytic nitrification was more important than that of sediment and water compartments of the wetland, whereas sediment and suspended nitrifiers were equally important for nitrification upstream of Nakivubo channel.

  • 4.
    Kyambadde, Joseph
    et al.
    KTH, Skolan för bioteknologi (BIO).
    Kansiime, Frank
    Dalhammar, Gunnel
    KTH, Skolan för bioteknologi (BIO).
    Nitrogen and phosphorus removal in substrate-free pilot constructed wetlands with horizontal surface flow in Uganda2005Inngår i: Water, Air and Soil Pollution, ISSN 0049-6979, E-ISSN 1573-2932, Vol. 165, nr 1-4, s. 37-59Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In constructed wetlands (CWs) with horizontal sub-surface flow, nutrient removal, especially phosphorus, is limited because the root biomass fills the pore spaces of the substrate (usually gravel), directing wastewater flow to deeper wetland media; plants are not regularly harvested; the litter formed by decomposing vegetation remains on the surface of the substrate and thus does not interact with the wastewater; and the substrate media often used provide only limited adsorption. Effective nutrient removal including rootzone oxidation, adsorption and plant uptake therefore requires sufficient interaction of wastewater with the treatment media. We assessed the feasibility of biological nutrient removal from wastewater using substrate-free CWs with horizontal flow, planted with two tropical macrophytes namely, Cyperus papyrus and Miscanthidium violaceum. The objectives were to evaluate the system treatment efficiency under semi-natural conditions, and to assess microbial and plant biomass contributions to nutrient removal in the CWs. Results showed high removal efficiencies for biochemical oxygen demand, ammonium-nitrogen (NH4-N) and phosphorus (P) fractions in papyrus-based CWs (68.6-86.5%) compared to Miscanthidium (46.7-61.1%) and unplanted controls (31.6-54.3%). Ammonium oxidizing bacteria in CW root-mats (108-109 cells/gram dry weight) and residual nitrite and nitrate concentrations in the water phase indicated active system nitrification. Papyrus showed higher biomass production and nutrient uptake, contributing 28.5% and 11.2%, respectively, of the total N and P removed by the system compared to 15% N and 9.3% P removed by Miscanthidium plants. Compared to literature values, nitrification, plant uptake and the overall system treatment efficiency were high, indicating a high potential of this system for biological nutrient removal from wastewaters in the tropics.

  • 5.
    Kyambadde, Joseph
    et al.
    KTH, Tidigare Institutioner, Bioteknologi.
    Kansiime, Frank
    Makerere University .
    Gumaelius, Lena
    KTH, Tidigare Institutioner, Bioteknologi.
    Dalhammar, Gunnel
    KTH, Tidigare Institutioner, Bioteknologi.
    A comparative study of Cyperus papyrus and Miscanthidium violaceum-based constructed wetlands for wastewater treatment in a tropical climate2004Inngår i: Water Research, ISSN 0043-1354, E-ISSN 1879-2448, Vol. 38, nr 2, s. 475-485Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The treatment efficiencies of constructed wetlands containing Cyperus papyrus L. (papyrus) and Miscanthidium violaceum (K. Schum.) Robyns (synonymous with Miscanthus violaceum (K. Schum) Pilg.) were investigated in a tropical climate (Kampala, Uganda). Papyrus showed higher ammonium-nitrogen and total reactive phosphorus (TRP) removal (75.3% and 83.2%) than Miscanthidium (61.5% and 48.4%) and unplanted controls (27.9% ammonium-nitrogen). No TRP removal was detected in control effluent. Nutrients (N and P) were significantly higher (p < 0.015) in papyrus than Miscanthidium plant tissues. Plant uptake and storage was the major factor responsible for N and P removal in treatment line 2 (papyrus) where it contributed 69.5% N and 88.8% P of the total N and P removed. It however accounted for only 15.8% N and 30.7% P of the total N and P removed by treatment line 3 (Miscanthidium violaceum). In addition, papyrus exhibited a significantly larger (p = 0.000) number of adventitious roots than Miscanthidium. Nitrifying bacteria attached to papyrus (2.15 x 10(6) +/- 1.53 x 10(5) MPN/g DW) and Miscanthidium roots (1.30 x 10(4) +/- 8.83 x 10(2) MPN/g DW) and the corresponding nitrification activities were consistent with this finding. Epiphytic nitrifiers appeared more important for total nitrification than those in peat or suspended in water. Papyrus root structures provided more microbial attachment sites, sufficient wastewater residence time, trapping and settlement of suspended particles, surface area for pollutant adsorption, uptake, assimilation in plant tissues and oxygen for organic and inorganic matter oxidation in the rhizosphere, accounting for its high treatment efficiency.

  • 6.
    Kyambadde, Joseph
    et al.
    KTH, Tidigare Institutioner, Bioteknologi.
    Kansiime, Frank
    Makerere University.
    Gumaelius, Lena
    KTH, Tidigare Institutioner, Bioteknologi.
    Dalhammar, Gunnel
    KTH, Tidigare Institutioner, Bioteknologi.
    Hydraulic loading, stability and water quality of Nakivubo wetland, Uganda2004Inngår i: African Journal of Aquatic Science, ISSN 1608-5914, E-ISSN 1727-9364, Vol. 29, nr 2, s. 213-220Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nakivubo wetland, which has performed tertiary water treatment for Kampala city for the past 40 years, is ecologically stressed by agricultural and infrastructural developments. Field studies were carried out to assess the hydraulic loading, pollution profile, stability and water quality of this wetland. The upper and lower Nakivubo wetland receive 4.13-7.66 x 104 and 3.50-10.32 X 104m3/day of water respectively, of which 48.3-57.9% of total hydraulic loading to the upper wetland was carried by sampling station S1. The influent water to the upper wetland had a total BOD5 and NH4-N loading ranging from 2.6-4.4 x 103kg BOD/day and 0.79-1.68 x 103kg NH4-N/day respectively. The National Water and Sewerage Corporation's effluent constituted a large proportion of BOD and NH4-N loading into Nakivubo wetland. Zinc, copper and chromium were detected in trace amounts at most sampling stations. However, lead was occasionally detected at Kibira channel (station S5) at a concentration of 0.4mg/l, which is higher than the permitted Ugandan discharge limit of 0.1mg/l (NEMA 1999). The wetland showed a very high removal efficiency for BOD, ranging from 77.4%-86.3%, compared to ammonium-N which ranged from -66.1% to 33.1% indicating limitations with the nitrification process. A low self-purification for zinc, copper and chromium was also observed in the upper Nakivubo wetland, possibly due to poor plant-wastewater interaction resulting from wetland drainage. In the lower Nakivubo wetland conductivity and dissolved oxygen were generally higher in papyrus- than in Miscanthidium-vegetated zones. However, the BOD and ammonium-N loadings did not vary significantly (P = 0.217 and P = 0.359 respectively) between the two vegetated zones.

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