POLLUTION HAZARDS OF HEAVY METALS IN SEWAGE SLUDGE ASH FROM THE WASTEWATER TREATMENT PLANTS IN CAMBERENE, SENEGAL

Solid wastes and their by-products are gaining interest worldwide given their high environmental impact. Fly ash and Bottom ash from Camberene sludge waste center  (Senegal) were characterized to assess the heavy metal contamination (using XRF and the Toxicological Risk) that is very important in type 1 unlike in type 2. The Index of geo-accumulation (I_geo), the Pollution load index (PLI), the Enrichment factor (EF) and Contamination factor (CF) have been computed to evaluate the contamination rate. These show that the fly ash has aI_geo value of 3.57 for Pb and 3.04 for As which means they are very polluted. For Cu we have an I_geo value of 4.23 and for Zn it is 4.67 so these ashes are strongly to extremely polluted by Cu and Zn but unpolluted to moderately polluted by Cr. For the bottom ashes we have I_geo values of 3.03 for Cu and 3.02 for Zn, to say they are also strongly polluted. However, they are not polluted by Cr and are only moderately polluted by Pb and As results confirmed by the EF calculation. Fine and dirty ashes have significantly been enriched by the metal As with an EF of 13.71 while for Pb its EF is 19.10 for the fine ash. As for the bottom ash we have respectively 7.26 and 5.19 for the EF of As and Pb. From the values of PLI these ashes are very highly polluted. Their possible dangerousness depends essentially on their heavy metal contents (criterion H14 of Directive 91 / 689 / EEC). In this Directive the material is toxic if its content in heavy metal is higher to some thresholds (see Annex III, Table 6). Most of their heavy metal contents are below the threshold in Annex III, indicating their harmlessness. This analysis highlighted the principal characteristics to be taken into account before using the SSA properly.