Wastewater Treatment and other Research Initiatives with Vetiver Grass

Abstract

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.