Potential of Vetiver Grass (Chrysopogon zizanioides) in Phytoremediation of Kipevu Wastewaters

Abstract

Wastewater treatment worldwide has mainly been done using physical, chemical and biological treatment systems such as activated sludge and biological nutrient removal technologies. Mombasa produces large amounts of pollutant-laden effluent water that is collected and primarily treated and discharged into the Indian Ocean. Various pollutants such as nitrates, phosphates, zinc and cadmium in water bodies pose a threat to the aquatic species. The aim of this study was to explore the potential of vetiver grass as a phytoremediation technology to minimise pollutants in water bodies. Field experiments were carried out using plastic containers of five litres which were set-up simultaneously with planted grass hydroponically. Wastewater was characterized for physicochemical parameters before and after treatment with the grass. The parameters studied were: effects of vetiver on reduction of pollutants with time and effect of biomass (number of Vetiver plants) on treatment efficiency. Wastewater had high levels of Chemical Oxygen Demand (1440 mg/L), Biological Oxygen Demand (75 mg/L) nitrates (775 mg/L), phosphates (25 mg/L) and Total Dissolved Solids (1432 mg/L) , which were beyond the maximum contaminable levels. A drastic increase in the pollutants uptake with time was observed. The levels of nitrates, phosphates, chemical oxygen demand, biological oxygen demand and total dissolved oxygen reduced by 89.76%, 85.6%, 84.51%, 69.33% and 16.76% respectively over 28 days. During the same period, a direct correlation in the reduction of Chemical Oxygen Demand and nitrates with increased number of plants was observed. The potential of vetiver grass after four weeks hydroponic treatment was found to be efficient in the reduction of pH, nitrates, phosphates, total nitrogen, total phosphorous, total dissolved solids, chemical oxygen demand and biological oxygen demand. The study recommends that vetiver grass be introduced in the aeration tanks to improve the efficiency of Kipevu waste water treatment plant.