Hybrid chemical and biological process for decontaminating sludge from municipal sewage

A hybrid chemical and biological process for decontamination of sewage sludge containing heavy metals and pathogenic microorganisms, consisting essentially of:

• a) mixing the sludge with an acidic leaching solution to acidify the sludge to a pH sufficiently low to dissolve the majority of the heavy metals and to destroy the majority of the pathogenic microorganisms;
• b) maintaining an oxidation reduction potential higher than +400 mV;
• c) effecting a solid-liquid separation to provide a solid fraction comprising decontaminated acid sludge and a liquid fraction containing the heavy metals dissolved in the leaching solution;
• d) neutralizing the sludge;
• and
• e) recovering the decontaminated neutralized sludge, the recovered sludge having a fertilizing element content which is defined as Ntotal and Ptotal and which is not reduced in comparison to the initial contaminated sludge.

A hybrid chemical and biological process for decontaminating sewage sludge containing heavy metals and pathogenic microorganisms, comprising:

• a) treating the sludge, in a reactor, with an acidic leaching solution to acidify the sludge to a pH between 2.0 and 3.0 so as to dissolve the majority of the heavy metals and to destroy the majority of the pathogenic microorganisms, without dissolving significant quantities of carbon, the leaching solution containing an oxidizing agent in a quantity sufficient to maintain an oxidation reduction potential higher than +400 mV, without aerating the sludge;
• b) maintaining the reactor at ambient temperature during step (a);
• c) flocculating the sludge treated in step (a);
• d) effecting a solid-liquid separation to provide a solid fraction comprising decontaminated and dehydrated acid sludge, and a liquid fraction containing the heavy metals;
• e) neutralizing the decontaminated acid sludge, and
• f) recovering the decontaminated and neutralized sludge, the recovered sludge having a fertilizing element content which is defined as Ntotal and Ptotal and which is not reduced in comparison to the initial contaminated sludge.

A hybrid chemical and biological process for decontaminating sewage sludge containing heavy metals and pathogenic microorganisms, comprising:

• a) treating the sludge with an acidic leaching solution to acidify the sludge to a pH between 2.0 and 3.0 so as to dissolve the majority of the heavy metals and to destroy the majority of the pathogenic microorganisms, without dissolving significant quantities of carbon, the leaching solution containing an oxidizing agent in a quantity sufficient to maintain an oxidation reduction potential higher than +400 mV, without aerating or heating the sludge;
• b) flocculating the sludge treated in step (a);
• c) effecting a solid-liquid separation to provide a solid fraction comprising decontaminated and dehydrated acid sludge, and a liquid fraction containing the heavy metals;
• d) neutralizing the decontaminated acid sludge, and
• e) recovering the decontaminated and neutralized sludge, the recovered sludge having a fertilizing element content which is defined as Ntotal and Ptotal and which is not reduced in comparison to the initial contaminated sludge.