This is the first detailed report on the distribution of Ni, As, Sr and Ag in water, sediments and macrophytes from Lake Victoria, complemented with recent data on the heavy metals Cr, Cu, Zn, Cd and Pb. The study was conducted over an 11-month period at five sites in the Kenyan part of Lake Victoria: four sites in the Winam Gulf influenced by various anthropogenic pressures including a site near Kisumu City, and one in the main lake, perceived to have lesser direct anthropogenic influence. Compared with the main lake site, the water in Winam Gulf had significantly higher values for electrical conductivity and concentrations of dissolved components: organic carbon and bound nitrogen, as well as major and most trace elements. This contamination is also evident in surface sediments, which contained significantly higher levels of Cr, Zn, As, Ag, Cd and Pb compared with the main lake site. The mean levels of Cr, Cu, Zn, Ag and Pb exceeded probable effect levels at least at one of the gulf sites. The sediments at the Kisumu City site were classified as severely polluted with Cu (up to 259 mg/kg dw) and Pb (up to 1188 mg/kg dw). The sediment cores showed significantly higher levels of Cu, Zn, Ag, Cd and Pb in the surface (0-3 cm) versus subsurface (22-25 cm) layer at the Kisumu City site, indicating increasing pollution by these elements within the last 15 years. This is also the first report on trace elements in the emergent water plant Vossia cuspidata and submerged plant Ceratophyllum demersum from this lake. Even though the accumulation of most elements is comparable between C. demersum (whole plant) and V. cuspidata roots, the latter shows a better bioindicative potential. Contamination of the gulf with Ni, Cu, Zn, Ag, Cd and Pb is well mirrored in V. cuspidata roots. V. cuspidata strongly restricts the acropetal transport of trace elements, and hence using the shoots as fodder does not pose a risk to livestock.

The effects of metakaolinization and fused-metakaolinization on zeolites synthesized from quartz rich natural clays

Iron-modified raw kaolinite clay (Fe-MC) was synthesized by co-precipitation method, characterized, and then applied as a low-cost adsorbent to sequester sulfachloropyridazine (SCP) and sulfadimethoxine (SDM), emergent water contaminants, from aqueous media by batch equilibration at circumneutral pH. The adsorption rate was kinetically described by the pseudosecond-order model. Equilibrium monocomponent sorption data were fitted to three two-parameter linear and nonlinear isotherm models. The data were best described by Temkin and Langmuir nonlinear equations. Linearization of adsorption isotherms is demonstrated to be an unsuitable analytical tool for predicting adsorption isotherms. The Langmuir monolayer maximum adsorption capacities were 4.561 and 1.789 mg/g for SCP and SDM, respectively. The binary adsorption study showed an antagonistic adsorption process of SCP (R q, SCP = 0.625) in the presence of SDM (R q, SDM = 1.032). The thermodynamic parameters, namely enthalpy (ΔH), Gibbs free energy (ΔG), entropy (ΔS), Arrhenius activation energy (ΔE a), and sticking probability (S *), indicated that the processes are spontaneous, exothermic, and physical in nature. The adsorption process was attributed to hydrogen bonding and negative charge-assisted H-bonding (CAHB). Using the Langmuir isotherm, the amount of Fe-MC required for a given volume of effluent of known contaminant concentration could be predicted.

No abstract

The preparation and applications of Tilapia (Oreochromis niloticus) fish scale biochars (FSB) as an adsorbent in the removal of indigo carmine dye (ICD) from aqueous solutions is described. The biochars were prepared through pyrolysis over a temperature range of 200 °C–800 °C and characterized for surface charge, functional groups, thermal stability, particle size and morphology, elemental composition, crystallinity, and surface area by using pHpzc, Fourier transform infrared (FTIR) spectroscopy, thermo-gravimetric analysis (TGA), transmission electron microscopy/scanning electron microscopy (TEM/SEM), energy dispersive X-ray (EDX) spectroscopy, powder X-ray diffraction (PXRD) and Brunauer-Emmett-Teller (BET) techniques, respectively. Batch experiments were carried out to determine the variation of adsorption process with initial dye concentration, contact time, initial solution pH, adsorbent load, temperature and adsorbent pyrolysis temperature on the removal of the dye. The percentage removal increased with increase in initial dye concentration and adsorbent dosage. A pH of 2 was the most appropriate for the adsorption experiments. The equilibrium data fitted pseudo-first-order kinetics and Freundlich models, while the thermodynamic parameters confirmed that the adsorption process was endothermic.