Elemental Composition of Suspended Particulate Matter Collected at Two Different Heights above the Ground in A Sub-Urban Site in Kenya

Suspended particulate matter samples were collected in a sub-urban area in Nairobi over a 12 month period at two different heights above ground using a “Gent” SFU sampler. A total of 126 sets of duplicate fine and coarse particulate matter samples were collected. The samples were analysed by energy dispersive x-ray fluorescence (EDXRF) and atomic absorption spectroscopy (AAS) for up to 10 elements. It was found that 66% of the samples collected at two metres and 50% of the samples collected at four metres height exceeded the WHO 24 guideline of 70μg m-3. Reduction in concentration of between 30 to 74 % for Ca, Ti, Zr and Fe were observed both in coarse and fine particulate matter fractions at the higher height. The elements Cu, Zn, Pb and Br represented 0.5 to 1.1 % of the total coarse particulate matter at both heights. Higher proportions of 1.5 to 3.5 % were observed at both heights in the fine particulate matter fraction. High enrichment factors were observed for Cu (10.8 - 228.3), Zn (12.4 - 124.6), Pb (59.4 - 1967) and Br (152.5 - 3038.7) at both heights suggesting anthropogenic activities such as industrial, urban refuse burning, residential and vehicular emissions could be the major contributors. Pb and Br were mainly from the vehicular emissions as indicated by the strong correlations (r > 0.593) and the Br/Pb ratios (0.307 to 0.339).Keywords: Sub-urban, EDXRF, AAS, Enrichment factors, Heavy metals, particulate matter

Laboratory study on the mobility of major species in fly ash–brine co-disposal systems: up-flow percolation test

Apart from the generation of fly ash, brine (hyper-saline wastewater) is also a waste material generated in South African power stations as a result of water re-use. These waste materials contain major species such as Al, Si, Na, K, Ca, Mg, Cl and SO4. The co-disposal of fly ash and brine has been practiced by some power stations in South Africa with the aim of utilizing the fly ash to capture the salts in brine. The effect of the chemical interaction of the species contained in both fly ash and brine, when co-disposed, on the mobility of species in the fly ash–brine systems is the focus of this study. The up-flow percolation test was employed to determine the mobility of some major species in the fly ash–brine systems. The results of the analysed eluates from the up-flow percolation tests revealed that some species such as Al, Ca and Na were leached from the fly ash into the brine solution while some species such as Mg, Cl and SO4 were removed to some extent from the brine solution during the interaction with fly ash. The pH of the up-flow percolation systems was observed to play a significant role on the mobility of major species from the fly ash–brine systems. The study showed that some major species such as Mg, Cl and SO4 could be removed from brine solution using fly ash when certain amount of brine percolates through the ash.Web of Scienc