Abstract
The presence of toxic metals in municipal sewage sludge restricts the application of this biomass in agricultural area. A chemical leaching process using a combination of inorganic acid and two oxidants has been developed for sludge decontamination. The present study investigated the effects of the concentrations of sulphuric acid (H 2SO 4), hydrogen peroxide and ferric chloride on metal solubilization from sewage sludge, as well as preservation of fertilizing properties (nutrient content) and dewatering ability of the treated sludge. The analysis of the results from batch leaching tests has allowed to define the optimal conditions for the reagent concentrations, which are 56 kg Fe 3+ tonne −1 of dry sludge solids (tds), 8 kg H 2O 2 tds −1, and enough H 2SO 4 to reach a pH between 2.0 and 2.5 but less than 142 kg H 2SO 4 tds −1. Finally, under these conditions, oxidoreduction potential values are found to be between 450 and 475 mV.
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