KINETICS OF METAL POLLUTANTS BIOSORPTION IN LAKE VICTORIA AND ITS ENVIRONS USING MORINGA OLEIFERA SEED POWDER

Abstract

In the last three decades attention has been paid to environmental management caused by hazardous materials such as heavy metals whose levels have risen due to increased anthropogenic activities. One of the techniques used to remove heavy metals is biosorption. The kinetics of biosorption of metal pollutants in Lake Victoria and its environs using Moringa oleifera seed powder was investigated with a view of using it as a low cost biosorbent for the removal of toxic heavy metals from waste water. FT-IR analysis was done for identifying the functional groups of moringa oleifera seeds powder. The FT-IR spectrum indicated the presence of –NH, -OH, -COOH in the biomass. Samples from eight sites on Winam Gulf were taken and analyzed for heavy metals (Cu, Cd, Cr, Mn, Pb and Zn) using AAS prior to digestion using HNO3 and HCl. Measurements of electrical conductivity, salinity, dissolved oxygen and total dissolved solids were done at the sampling sites. Model polluted water sample was prepared for use in the batch biosorption experiments with respect to parameters such as contact time, pH, particle size, adsorbent dosage, presence of other metal ions, effect of adsorbent pretreatment, isotherms, kinetics and adsorbate concentration. The levels of trace heavy metals in most of the samples were above WHO standard; Cd (range; 0.013 - 0.037 mg/l) mean value 0.0263 mg/l ± 0.005, Pb (range; ND- 1.13 mg/1) mean value 0.545 mg/l ± 0.013, Zn (range; 0.3005- 3.467 mg/L) mean value 3.011 mg/l ± 0.0311, Cr (ND-0.459 mg/l) mean value 0.317 mg/l ± 0.0113, Mn (0.153-4.967 mg/l) mean 2.312 mg/l ± 0.0281, Cu (range ND- 1.543 mg/l) mean value 0.05 mg/l ± 0.005 was the only heavy metal below WHO standard of 1.0 mg/L The maximum biosorption capacity was observed at pH 5 for all six metals, particle size of 0.250 mm, and adsorbent dosage of 0.6 g. Increased initial metal concentration led to increase in the rate of biosorption. Biosorption was higher in single systems and lower in binary systems. The data fitted into both the Langmuir and Freundlich adsorption isotherms with coefficient of determination values ranging between 0.958 and 0.999. However, the data fitted better into the Langmuir isotherm for most of the experiments with ccoefficient of determination between 0.986 and 0.999. Pseudo second order kinetics fitted best into the experimental data with coorelation coefficient ranging between 0.913 and 0.999. The results suggest that Moringa oleifera seeds have the potential application in heavy metal ions decontamination from aqueous effluents. The results also demonstrated that pretreatments influenced the biosorption capacity of the biomass for most of the metals significantly, and the order of modification efficiency was NaOH > CaCl2 > KMnO4 > HCl. Hence pretreatment of Moringa oleifera further enhances biosorption.