Thermodynamic modelling of the equilibria in lake Baringo, Kenya

The equilibria that control the composition of a lake is presented using lake Baringo, Kenya, as an example. Lake Baringo (0°37’N, 36°05’E) lies very close to the equator in the Baringo basin in the Eastern Rift Valley, Kenya. Water from the lake was analysed chemically using standard analytical techniques to obtain the stoichiometric concentrations of the major anions and cations. However, this does not indicate how the components are distributed amongst possible species. The speciation calculation was performed using the available equililbrium constants for all the metal – ligand and proton – ligand species identified. At pH 8 the composition of the water of lake Baringo was Ca2+ (58.88%); CaCO3 (41.12%); Mg2+ (97.33%); MgCO3 (2.88%); HCO3- (98.27%) and SO42- (99.88%). Sulphate forms very weak complexes of calcium and magnesium and was excluded from the model. MgHCO3+, CaHCO3+ and MgSO4 were found to be minor species.Key words: Speciation, thermodynamic modellin

A new spectrophotometric method for determination of residual polydiallyldimethylammonium chloride flocculant in treated water based on a diazotization-coupled ion pair

Polydiallyldimethylammonium chloride (polyDADMAC) is a water-soluble cationic polyelectrolyte used for water treatment. Its residues in treated water are contaminants as they react with chlorine to produce a carcinogenic compound. Commonly-used techniques for quantification of the polycation, such as colloidal and potentiometric titration as well as 1H NMR, have poor sensitivity and detection limits. This paper describes a more sensitive UV spectrophotometric method for quantitative determination of residual polyDADMAC in treated water, through formation of an ion pair with (4-hydroxy-1-napthylazo) benzene-sulphonic acid (dye). The ion pair, which is a colloidal solid material, was characterised by FTIR, 13C NMR and 1H NMR techniques. The colloid materials formed with different concentrations of polyDADMAC were dissolved in either N,N-dimethylformamide or 1,4-dioxane, followed by determination with UV spectrophotometry. The wavelength of maximum absorption (ëmax) was found to be dependent on the solvent used, with 1,4-dioxane showing a better linear range of 0.1–1.8 mg..-1 polyDADMAC. Varying the pH of the solutions had no significant effect on ëmax

Determination of levels of copper in Kamiti river along coffee farms in Kiambu, Kenya

Copper‐based fungicides are extensively used in the control of coffee pests and diseases because they are relatively cheap and effective. This practice presents serious environmental implications owing to the toxic nature of copper. We report here an assessment on the effects of the use of copper‐based fungicides on River Kamiti, which flows along coffee growing areas of Kiambu District, Kenya. The levels of copper in the river were determined using flame atomic absorption spectrophotometry (FAAS) and were found to range from 0.3 to 2.38 x 10‐2 mgL‐1. It was observed that high levels of copper coincided with coffee spraying seasons and a high amount rainfall, indicating that these contributed to increased seepage of copper in the river. Active pulping factories on both sides of the geographical regions were also found to be a source of the same. Statistical analysis on the experimental data of copper levels from the study sites showed that there was no significant difference between the regions implying that the sampling sites were not the source of variation. Although there is clear evidence that coffee farming introduces copper into the river, the levels of copper in Kamiti river were found to be within acceptable limits and this would be attributed to dilution effects. However, at specific points, the levels of copper were very high threatening the survival of aquatic animals, thus the use of copper compounds is of environmental concern.Key words: Copper, fungicides, river wate