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This paper described the role of substrate (soil) with respect to the type of macrophytes
(plants) planted in the wastewater treatment in Horizontal Subsurface Flow (HSSF) Constructed
wetlands (CWs). Wastewater parameters investigated include Nutrients: Phosphorus (Total
Phosphorus, Ortho Phosphorus) and Nitrogen species (Total Kjeldahl Nitrogen (TKN Test)=(NH3-N +
organic-N) and NH
3
-N) from the Maturation Waste Stabilization Ponds (WSP) effluent, which
receives wastewater mainly of domestic nature from the University main Campus of Dar es Salaam,
aimed at removing these species. Others were: BOD, COD, TSS and heavy metals from industrial
effluents particularly from textile mills as well as physical parameters such as: EC, Temperature and
pH. The three substrates were used: murram, granite and limestone; all locally available and of size
range: 4-8mm and the two macrophytes used were: vetiver grass (vetiveria zizanioides) and common
reeds (Phragmites mauritianus). Six HSSF CW cells packed with different substrates each and planted
with different macrophytes, operated in parallel were used. Four cells received wastewater from the
Maturation Waste Stabilization Ponds: The first cell was filled with murram and planted with vetiver
grass (cell A). The remaining three cells were each filled with granite, murram and limestone
respectively and planted with Phragmites mauritianus plants (cells B, C and D). The two other cells
each of 1:0.6:0.3 m dimensions were used for industrial effluents treatment. One cell planted with
Vetiver grass and another one with Phragmites mauritianus, both packed with limestone soil. The field
experimental set-up was situated near the Waste Stabilization Ponds at the University of Dar es
Salaam.
The major findings of this study:
Vetiver grass performed better than Phragmites mauritianus in removing of pollutants. For
instance It was found from the treatment plant that: the organic removal (BOD) was on average
61.85% and 67.47% and COD of 37.9% and 46.2% for Phragmites mauritianus and Vetiver grass
respectively. Compared with various reporters it was concluded this removal to be good. |
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