Removal of phosphate ions from aqueous solutions using bauxite obtained from Mulanje, Malawi

Studies on stream water and effluent from selected wastewater treatment plants in Blantyre, Malawi, have reported phosphate concentrations above recommended levels. High phosphate levels in the effluent and streams pose a threat to aquatic life through the stimulation of excessive growth of plants and toxic cyanobacteria. Phosphate removal by bauxite was investigated as a function of pH, contact time, dosage, competing ions and initial phosphate concentration by means of jar tests. Phosphate removal increased with decreasing pH with maximum removal (99.75%) recorded at pH 2.40 ± 0.10. Phosphate removal was attributed to ligand exchange reactions with gibbsite and goethite minerals that are chemically and electrostatically favoured at low pH. Bauxite indicated a high phosphate removal capacity with 98.42% removal recorded for a dosage of 15 g/l. This was attributed to the presence of goethite and gibbsite minerals for which phosphate has a strong affinity. Kinetics studies revealed a fast adsorption reaction with 61 and 65% phosphate removal achieved after 30 min of contact at 20 and 40°C respectively. Phosphate removal was enhanced in the individual presence of calcium and magnesium ions whereas carbonate and sulphate ions reduced it by competing for active sites.Key words: Adsorption, bauxite, phosphate, gibbsite, goethite, eutrophication

Comparative Studies of the Speciation Patterns of Nickel and Chromium in Surface-, Ground- and Wastewater Systems in Botswana

Results of speciation stdies of nickel and chromium in wastewater, surface and groundwater systems using flame atomic absorption spectrometry (FAAS), graphite furnace atomic absorption spectrometry (GFAAS) and differential pulse adsorptive cathodic stripping voltammetry (DPAdCSV) are presented. Dimethylglyoxime (DMG) and diethylenetriaminepentaacetic acid (DTPA) were used as complexing agents forDPAdCSVdetermination of nickel and chromium, respectively, at a hanging mercury drop electrode (HMDE). Total nickel was in the range 3091–3201 mg L–1 in wastewater from an electroplating plant, 8.1–14.4 μg L–1 in surface water (freshwater) and 6.38–16.95 μg L–1 in groundwater. Total chromium was in the range 34.99–37.03 mg L–1 in electroplating wastewater and 15.8–571.0 mg L–1 in tannery effluents. Trace levels of chromium were detected in surface water (3.09–17.42 μg L–1) and groundwater (18.01–36.39 μg L–1). While most of the metal forms were found to be present in the CSV-labile fraction in the wastewater from the electroplating plant (mean of 67.9% for Ni and 79.8% for Cr), less than 5% of the total metal was present as CSV-labile fraction in tannery effluents, surface and groundwater samples. The tannery effluent was found to have very high complexation capacity (about 3 mg of Cr /L of effluent, i.e. 57.8 μM Cr). This complexing capacity of tannery effluent may have a potential application in environmental remediation.Keywords: Speciation, metals, complexation capacity, water systems, adsorptive cathodic stripping voltammetry

pH dependence of sorption of Cd2+, Zn2+, Cu2+ and Cr3+ on crude water and sodium chloride extracts of Moringa stenopetala and Moringa oleifera,/i>

The ability of crude water and sodium chloride extracts of partially defatted powder of Moringa stenopetala (MS) and Moringa oleifera (MO) to remove heavy metals (Cd2+, Zn2+, Cu2+ and Cr3+) fromsingle ion solution was investigated. At initial metal concentration of about 4 ppm, the extracts showed complete sorption for Cd2+, Zn2+ and Cr3+ ions at pH above 7.8, 4.0 and 4.0, respectively, at a dose of 1.0 ml of sorbent in 9.50 ml of metal solution. Cu2+ sorption increases slightly with pH to about 60% for MS at pH 6 and then becomes constant up to pH 8 when sorption rises to completion. Preliminarycharacterization of the actual powder by proton nuclear magnetic resonance showed clear presence of amide (-CO-N-H), benzenoid (Ar-H), saturated alkyl and unsaturated fragments in both MS and MO. The mass spectrum showed the presence of amino (R-NH2) fragments. The remarkable heavy metal sorption ability of M. stenopetala and M. oleifera could thus be attributable to, among other mechanisms,coordination or complex formation between the metal cations and pH dependent oxygen and nitrogen anionic sites of the Moringa proteins

Spatial and Seasonal Variability in Surface Water Chemistry in the Okavango Delta, Botswana: A Multivariate Approach

The annual flood pulse in the Okavango Delta (Botswana), has a major influence on water chemistry and habitat. We explore spatial and temporal patterns in a suite of chemical variables, analysed from 98 sample points, across four regions, taken at different stages of the flood cycle. The major pattern in water chemistry is characterised by an increasing gradient in ionic concentration from deep-water sites in the Panhandle to more shallow, distal regions to the south. Concentrations of cations, anions, dissolved organic carbon, and SiO2 are significantly higher in the seasonally inundated floodplains than in permanently flooded regions. Several variables (including Na and total nitrogen) significantly increase from low flood to high flood, while others (including HCO3, SiO2, and Cl) increase in concentration, initially between low flood and flood expansion, before declining at maximum flood extent. Redundancy analysis (RDA) revealed that hydrological variables (water depth, flow velocity, flood frequency, and hydroperiod class) significantly explain 17% variation in surface water chemistry. Predictions of increasing flood volume in the near future may result in a decline in alkalinity and dilution of DOC. Our study provides an important baseline from which to monitor future change in the Delta

Assessing The Potability Of Water At Xhobe Watering Point In The Okavango Delta Ramsar Site Using Microbial And Chemical Indicators

Boteti River is one of the Okavango Delta outlets. Thamalakane River provides a major outflow from the Delta and its waters enter the Boteti River that flows through Xhobe settlement in the Okavango Delta Ramsar site. The river is used by local communities as a source of water for domestic consumption, fishing, irrigation and motorboat riding in some parts of it. In this study, the water quality of this river is assessed to determine whether it is potable. Temperature, turbidity, total suspended solutes (TSS), electro conductivity (EC), fecal coliforms (FC), fecal streptococci (FS), total coliforms (TC) and chemical indicators were measured at Xhobe watering point on June 2009 to check whether the water is safe for drinking. All the variables measured meet the Botswana Bureau of Standards (BOBS) specification for Class I drinking water except for FC at 5-20 CFU/100ml, FS at 18-128 CFU/100ml, and TC at 43-135 CFU/100ml. The results indicate that there is a possibility of pollution from fecal sources and organic matter because the microbiological content is beyond the BOBS specification for drinking water. The study is a baseline of the assessment of the potability of water used by people in settlements of the Okavango Delta Ramsar site. Therefore, it is important to monitor the quality of water using both microbial and chemical indicators especially in places where people directly use the river water for whole life consumption in order for them to have access to clean water and live a healthy life.Keywords: water quality, potability, microbiology, indicators, fecal pollutio

Mechanisms for biosorption of chromium(III), copper(II) and mercury(II) using water extracts of Moringa oleifera seed powder

In continuation of our work on heavy metal remediation using Moringa seed powder, this study examines the mechanisms of metal sorption on water extracts of Moringa oleifera (MO) seed powder using extended X-ray absorption fine structure (EXAFS). Chromium(III) is hydrolysed to form a mixture of [Cr3(OH)4(H2O)10]5+ and [Cr(OHx)2]nn(2x-3)+ complexes, x = 1 or 2. The chromium(III) complexesare octahedral with mean Cr-O bond distance of 1.97(2) Å. Copper (II) forms complexes with ligands with oxygen and/or nitrogen donor atoms, most likely amino and carboxylate groups. Copper(II) retainthe typical Jahn-Teller distortion with Cu-O/N bond distances of 1.97(2) and 2.21(4) Å. Furthermore, a CuC distance at 2.96 Å, and a corresponding Cu-O-C 3-leg scattering path at 3.10 Å are observed as well, strongly supporting that a large fraction of carboxylate groups are bound to the copper(II) ion on the equatorial plane. Mercury (II) forms mainly linear complexes with nitrogen donor ligands, d(Hg-N) =2.15(2) Å, most probably from amino groups in amino acids or proteins. This shows that the softer metal ions, copper(II) and mercury(II), form complexes with oxygen and/or nitrogen donor ligands in the MO extracts, while the harder and more highly charged chromium(III) ion becomes hydrolysed. The study therefore suggests that the successful biosorption of heavy metals by Moringa, a potential heavy metal removing agent, is attributable to its oxygen and nitrogen donating carboxylate and amino groups

Removal of Cd2+, Cr3+, Cu2+, Hg2+, Pb2+ and Zn2+ cations and AsO43- anions from aqueous solutions by mixed clay from Tundulu in Malawi and characterisation of the clay

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, Cd2+, Cr3+, Cu2+, Hg2+, Pb2+ and Zn2+ cations and AsO43- anions 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. pHpzc for the raw clay, as determined by potentiometric titrations, was 9.66 while pHpzc 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 Cr3+ 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. Zn2+ complete removal occurred at pH above 7 with 92% attributable to adsorption while the rest could be from both adsorption and hydroxide precipitation. Cu2+ was removed from pH 4 and completely above pH 6.8 with 50% due to adsorption. Cd2+ 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 Hg2+ at total Hg2+ concentration of 0.023 mM was pH independent fluctuating between 30 and 60%. No effective removal of AsO43- anion was observed. Water SA Vol.32 (4) 2006: pp.519-52

Bacteriological Contamination of Water in Urban Poor Areas: A Case Study of South Lunzu Township, Blantyre, Malawi

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