Comparative Study on the Migration of Heavy Metals in the Sewage Sludge Treated by Supercritical/Subcritical Water Oxidation Process

Abstract

Abstract. Super/sub-critical water oxidation technology has been utilized to treat sewage sludge in the study. Heavy metal content and characteristics of leaching toxicity in the reaction effluent have been investigated in detail, and then the relationship between the microstructure of sludge residue and immobilization of heavy metals is analyzed systematically. The obtained results show that the enrichment ratios of heavy metals in the sludge residue are above 68%, except As; Super/sub-critical water oxidation process has good immobilization effects on the heavy metals in sewage sludge residue, except Cd and Cu; Compared with subcritical state, supercritical water oxidation process has more obvious immobilization effects on the heavy metals in sewage sludge residue. The heavy metals in sewage sludge residue exist in the form of complex compounds, presenting obviou s crystalline state, with part of crystal structures being similar. The formation of crystal microstructures contribute to the enrichment and immobilization of heavy metals in sewage sludge.