ABSTRACT:The increasing influx of heavy metals into water bodies from industrial, agricultural, and domestic activities is of global concern because of their well documented negative effects on human and ecosystem health. A recent study of streams in Blantyre and Zomba, Malawi revealed lead levels of up 0.118 mg/L, exceeding the World Health Organisation acceptable level of 0.01 mg/L. Our ongoing study on low cost effective heavy metal remediation techniques in developing countries has already demonstrated that Moringa oleifera, the well known source of natural water clarifiers, is effective in heavy metal detoxification of water. This paper presents the first reported use of a related species, the African moringa, Moringa stenopetala for lead detoxification and preliminary investigation of the interaction of the metal with the polyelectrolytes of M. oleifera and stenopetala. The potential of M. stenopetala for lead removal was tested by means of jar tests. With an initial lead concentration of 7 ppm, M. stenopetala seed powder, at doses of 0.50, 1.00, 1.50, 2.00 and 2.50 g/100mL, reduced the concentration of lead by 20.00 ± 0.00, 46.19 ± 2.06, 71.19 ± 2.06 and 89.43 ± 0.60 and 96.23 ± 0.12 % respectively. M. stenopetala was more effective than M. oleifera in removing lead from water (p=0.001 at 95% confidence level). For oleifera, lead levels decreased exponentially during the first 5 h. of the reaction and then equilibrium was established; for stenopetala, a linear decrease was observed. The pH of the mixture rose from 2.30 to a maximum of 2.53 and 2.57 and then fell to an equilibrium value of 2.30 and 2.29 for oleifera and stenopetala respectively. Lead removal was also affected by pH, ionic strength, and water hardness. Our results show that M. stenopetala has potential in lead remediation of contaminated waters. Further studies are being carried out on remediation of other metals and the mechanism of the metal moringa interaction.

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Water and wastewater studies in Malawi have revealed very high levels of heavy metals in most streams and other water bodies particularly within urban areas. The metals are produced and released during industrial and agricultural activities, and also in vehicular emissions. These metals may pose serious threats to both human health and the environment. This study investigated the potential of mixed clay, obtained from the Tundulu area, in removing, Cd 2+ , Cr 3+ , Cu 2+ , Hg 2+ , Pb 2+ and Zn 2+ cations and AsO 4 3anions from aqueous solutions using batch equilibrium technique. Qualitative mineralogical characterisation of the clay revealed that the clay contains illite, distorted kaolinite, mixed layer minerals and non-clay mineral carbonate fluoroapatite. pH pzc for the raw clay, as determined by potentiometric titrations, was 9.66 while pH pzc of pretreated clay was 9.63. Pretreatment of the clay involved removal of carbonates, iron oxides and organic matter. Initial total metal concentrations ranged from 3 to 5 mg/ℓ. pH metal sorption dependence of the clay revealed Cr 3+ removal from pH of 3 to complete removal at pH 5 with over 90% of the removal attributable to adsorption on the clay while the remaining 10% attributable to both adsorption and Cr(OH) 3 precipitation. Zn 2+ complete removal occurred at pH above 7 with 92% attributable to adsorption while the rest could be from both adsorption and hydroxide precipitation. Cu 2+ was removed from pH 4 and completely above pH 6.8 with 50% due to adsorption. Cd 2+ removal was between pH of 6 and 9 with 85% due to adsorption to the clay. Lead was completely removed at pH greater than 7.67. Removal of Hg 2+ at total Hg 2+ concentration of 0.023 mM was pH independent fluctuating between 30 and 60%. No effective removal of AsO 4 3anion was observed.

ABSTRACT:This study assessed the ability of filamentous green algae; Spirogyra aequinoctialis to accumulate manganese, cadmium and lead from water. Water pH was also determined. Samples of S. aequinoctialis and their respective water environments were taken from designated sampling points in the city of Blantyre and Malawi during the rainy and dry season in order to capture seasonal variations. The concentration of metals in S. aequinoctialis were higher than in the corresponding water environment in both seasons, but lower in the rainy season than the dry season. In the rainy season the concentrations were (in S. aequinoctialis and (water) . This study has shown that S. aequinoctialis has the capability of accumulating manganese, cadmium and lead. Therefore it can be used as a biological indicator for long term heavy metal water pollution monitoring.

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