Cadmium Sorption by Moringa stenopetala and Moringa oleifera seed Powders: Batch, Time, Temperature, pH and Adsorption Isotherm Studies”.

There is a widespread recognition that the presence of heavy metals such as cadmium in water is hazardous to the environment and human health and their discharge into surface waters is of great concern world wide. The use of natural coagulants such as Moringa for heavy metal removal from water replacing expensive imported synthetic coagulants is particularly appropriate for agro-based developing countries such as Malawi. This study was aimed at investigating the potential of Moringa stenopetala and Moringa oleifera in the removal of cadmium(II) ions from water. The potential of M. stenopetala for cadmium removal was investigated by means of jar test beakers. With an initial cadmium concentration of 7 mg/l, M. stenopetala seed powder, at a dose of 2.50 g/100 ml, reduced the concentration of cadmium by 53.8%. Comparison of removal capacities between M. stenopetala and M. oleifera indicated that M. stenopetala was more effective than M. oleifera in removing cadmium from water (p < 0.05). Increasing initial cadmium concentration, agitation time and ionic strength reduced cadmium removal. Equilibrium sorption was attained at pH 5 where maximum cadmium removals were 82.7 and 70.7% using M. stenopetala and M. oleifera respectively. There was a reduction in cadmium removal between 0 to 60°C for M. stenopetala and 0 -40°C for M. oleifera before increasing with subsequent temperature increases. It was also shown that cadmium sorption at 30°C and pH 3 for the M. oleifera could best be modelled by the Freundlich isotherm whereas the Langmuir model is slightly better than the Freundlich isotherm in the case of the M. Stenopetala. The energies of adsorption from Dubinin-Radushkevich models have indicated that cadmium removal using both powders is based on physisorption. The results indicate that M. stenopetala and M. oleifera have potential in cadmium remediation of polluted waters

Soil Microbial Biomass Carbon, Nitrogen and Sulphur as Affected By Different Land Uses in Seronga, Okavango Delta, Botswana

Aim: The Okavango Delta at Seronga is fragmented into different land uses ranging from grasslands to woodland (Ximenia and mopane), often punctuated with cropped and fallow fields. The influence of land uses on surface (A1 horizon) soil physico-characteristics, nitrogen, sulphur, carbon, microbial population and biomass were studied to understand soil variability in order to devise conservation strategies for the area. Methodology: Total soil nitrogen (N) was analysed using a Leco N analyser, total carbon and sulphur by CS800 Carbon–Sulphur analyser. NH4+-N, NO3- and NO2- were extracted with KCl and determined using the indophenol blue method and by Griess-Ilosvay colorimetric method respectively. Microbial populations were determined by plate count method. Biomass carbon and flush of nitrogen were determined by fumigation and re- inoculation technique. Results: All the soils had a high sand content (> 85 %). Total soil N was generally very low, 0.017% in grasslands closest to the channel, 0.013% in cropped fields, 0.007% in fallow and lowest in woodlands (0.002%). Grasslands showed higher NH4+-N indicating low nitrification potential. Even if mopane woodlands had low total N, they had higher NH4+-N (0.067 ppm) and low NO2- compared to other land uses, this could be attributed to their inherent nitrification inhibition ability. No NO3--N was detected in these soils, probably due to the low nitrification ability and high leaching capacity of sandy soils. Microbial biomass C and population were highest in the grasslands and cultivated soils, while the woodlands had lower levels. Conclusion: Seronga soils have very low N, with the least in the woodlands furthest from floodplains. Grasslands closest to the channel basin had significantly higher total N, C and microbial biomass C but low S as opposed to the woodlands further from the channel. Cultivated areas had increased N and C levels and microbial biomass C compared to the woodland probably due to incorporation of crop residues and animal manure. The paucity of nitrifiers and undetectable NO3--N indicate a low nitrification potential and a high leaching ability of the soils. Fallowing of fields resulted in a decline in nutrient status