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Speciation of heavy metals in sewage sludge after mesophilic and thermophilic anaerobic digestion

Lidia Dąbrowska

Department of Chemistry, Water, and Wastewater Technology, Faculty of Environmental Protection and Engineering, Czestochowa University of Technology, Dąbrowskiego 69, 42200 Częstochowa, Poland



Abstract: Two types of sewage sludge anaerobic digestion were carried out: mesophilic and thermophilic. Metal speciation analysis was performed revealing some changes in the chemical form of the metals during the stabilization process of sludge. After both methane fermentation processes, a comparable level of organic matter distribution was obtained (≈ 40 %). The amount of produced methane during thermophilic and mesophilic digestion was 560 mL of CH4 and 580 mL of CH4 from 1 g of removed organic matter, respectively. Low concentration of heavy metal ions in the liquid phase of sludge was observed. Metal ions precipitated and remained bound throughout the stabilization process. No accumulation of heavy metals in the mobile fractions of sludge (exchangeable and carbonate) was observed for either digestion process. The highest increase of zinc, copper, nickel, cadmium, and chromium concentration was observed in the organic-sulfide fraction, whereas the highest increase of lead was found in the residual fraction.

Keywords: heavy metals – sewage sludge – mesophilic digestion – thermophilic digestion

Full paper is available at

DOI: 10.2478/s11696-011-0128-9


Chemical Papers 66 (6) 598–606 (2012)

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