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A comparative study of Cyperus papyrus and Miscanthidium violaceum-based constructed wetlands for wastewater treatment in a tropical climate
KTH, Superseded Departments, Biotechnology.
Makerere University .
KTH, Superseded Departments, Biotechnology.
KTH, Superseded Departments, Biotechnology.
2004 (English)In: Water Research, ISSN 0043-1354, E-ISSN 1879-2448, Vol. 38, no 2, 475-485 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
2004. Vol. 38, no 2, 475-485 p.
Keyword [en]
constructed wetlands, Cyperus papyrus, Miscanthidium violaceum, nutrients, tropical wetlands, wastewater treatment
National Category
Other Environmental Engineering
Identifiers
URN: urn:nbn:se:kth:diva-24141DOI: 10.1016/j.watres.2003.10.008ISI: 000188061900024Scopus ID: 2-s2.0-1542752357OAI: oai:DiVA.org:kth-24141DiVA: diva2:344102
Note
QC 20101028Available from: 2010-08-17 Created: 2010-08-17 Last updated: 2011-11-01Bibliographically approved
In thesis
1. Optimizing processes for biological nitrogen removal in Nakivubo wetland, Uganda
Open this publication in new window or tab >>Optimizing processes for biological nitrogen removal in Nakivubo wetland, Uganda
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
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.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. viii, 62 p.
Keyword
Environmental technology, Ammonium-oxidizing bacteria, Biological nitrogen removal, Coliform retention, Constructed wetlands, Cyperus papyrus, Miljöteknik
National Category
Other Environmental Engineering
Identifiers
urn:nbn:se:kth:diva-134 (URN)91-7283-962-7 (ISBN)
Public defence
2005-02-25, Kollegiesalen, Valhallavägen 79, Stokcholm, 14:00
Opponent
Supervisors
Note
QC 20101028Available from: 2005-02-20 Created: 2005-02-20 Last updated: 2010-10-28Bibliographically approved

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