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Title
Application of Municipal Wastewater Technology to Semiarid Regions: A Pilot Study using a Constructed Wetland in Toliara city, Madagascar”
Authors
Solphi Joli Hamelo
Research Topic
Abstract
The municipality of Toliara in South-west of Madagascar, having population of 203, 061,
generates approximately 8,250 m3/d of wastewater produced daily. At present, about 10 % of the total
wastewater is being collected by Toliara central and the remaining 90 % of the wastewater is being
disposed of into open drains or rejected anywhere. Under such conditions wastewater management is
difficult to realize in a city which such a poor sanitation infrastructure system. In this study, the
current situation for wastewater management has been investigated and possible solution discussed.
Application of a sewerage system and wastewater treatment has had particular focus. Included in this
has been collecting and characterizing wastewater from different areas of the city, application of
mathematical models for design of a constructed wetland for treatment of wastewater from the city
and a 14 months pilot experiment on wastewater treatment with a constructed wetland in Toliara city.
The Toliara wastewater composition included the analysis of oxygen, pH, temperature, BOD, TSS
and nutrients. Most of the wastewater was anaerobic or had low oxygen levels of 0.08 – 3.43 mg/L),
the pH value was in the range 7-7.5 and the wastewater temperature about 30-32 °C prevailed. The
BOD and TSS were ranged 179-220 mg/L and 51–159 mg/L. These results were applied to a model
developed for a constructed wetland, which was used for design of a constructed wetland for the city
of Toliara. The design was done at various temperatures experienced in Toliara, for different reactor
types and with and without pretreatment (septic tank). A pilot scale subsurface constructed wetland
system was designed to treat the septic tank effluent (public toilet used by 70-250 persons). The
wetland consists of two parallel modules for comparative studies and some of the cells were filled
with different media (with sand or gravel). The wetland systems were operated at three different
modifications in three phases (experimental phase I, II and III). The hydraulic loading rate applied
during the different experimental phases varied between the phases. The experimental results showed
higher removal efficiencies of BOD and TSS from phase I to phase II and to phase III. The main
reason for this was modifications to enhance the oxygen supply in the wetland. The maximum BOD
and TSS removal reached 62 and 45 %, respectively, in pond G, and 45 and 53 %; respectively, in the
reference pond D. As the removal efficiency for BOD and TSS increased, so did the removal of
nutrients; NH4-N(40-50%), NO3-N(25-50%) and PO4-P(30-40%).These results show potential for the
application of constructed wetlands for the treatment of wastewater in Toliara city. Further studies on
modification and optimizations are thus recommended.
Volume
1
Date of publication
December 1, 2011
Institution (University)
Institut Halieutique et des Sciences Marines Toliara
Page numbers (pp)
152