Accumulation Of Nitrogen And Phosphorous By Vetiver Grass (Chrysopogon Zizanioides) In A Model Constructed Wetland Treatment System For Polishing Municipal Wastewater

Abstract

Kenya is classified as water scarce country yet the existing fresh water resources are under constant threat of pollution resulting from wastewater inflows. Wastewater contains nitrates and phosphates that stimulate excessive plant growth when released into water bodies thus deteriorating their quality. The purpose of the study was to evaluate the performance of Vetiver grass in the uptake of Nitrogen and Phosphorous from the three (horizontal, vertical and hybrid subsurface flow wetland systems) model constructed wetland units for treating municipal wastewater. Nitrogen and phosphorous accumulation in the roots and shoots of the Vetiver grass was determined and the data subjected to ANOVA at 5% confidence level. Vetiver grass accumulated 18,100 mg and 35.3 mg/kg Nitrogen and Phosphorous, respectively in the hybrid system compared to 9,400 mg Nitrogen and 19 mg/kg Phosphorous, in the horizontal subsurface flow system and 10,400 Nitrogen and 18.3mg/kg Phosphorous in the vertical subsurface flow system. Accumulation of nitrogen and phosphorous by Vetiver grass in all the wetland systems were significantly different (P≤0.05). There was also significant (P≤0.05) difference of N and P accumulation in the shoots and the roots with N accumulating more in the shoots while P in the roots.