INDICATOR BACTERIA REDUCTION IN SEWAGE-SLUDGE BY A METAL BIOLEACHING PROCESS

The presence of a potentially toxic concentration of metals and the ineffective destruction of pathogenic microorganisms by conventional sludge stabilization processes limit sewage sludge utilization in agriculture. Therefore, we evaluate the metals bioleaching process potential for the elimination of indicator bacteria (total coliforms, fecal coliforms, fecal streptococci). Physico-chemical sludge characteristics (VS, VSS, soluble carbon and sulfate) as well as metals solubilization were also measured. The results obtained reveal that the high sulfuric acid production (pH < 2.5), as a result of sulfur oxidation by indigenous thiobacilli of sludge, allows a considerable reduction in bacterial indicators (3 log or under the limit detection of 10(3) cfu/100 ml) for sludges examined over a 5 day period. Heavy metals were solubilized to levels compatible with recommended norms for intensive sludge agricultural use. Moreover, this process allowed a VSS reduction, which varied according to the sludge used. These results indicate that this process can improve the stabilization of the digested sludge.