The Influence of Lime and Hydroxyapatite Addition on Metal Partitioning and Stabilisation in Sewage Sludge

Ksenija Cer Kerčmar, Marija Zupančič* and Peter Bukovec

Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, SI-1000 Ljubljana, Slovenia
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The influence of lime addition on metal mobility in sewage sludge was studied. The sequential extraction procedure by Tessier was used to evaluate metal mobility in dehydrated sewage sludge with and without lime addition. Data from the partitioning study indicate that As is the most mobile metal in sewage sludge sample, while Ni and Cd are slightly less mobile. Addition of lime in general decreased the mobility of metals. Exceptions are Ni and Cu. The mobility of Ni slightly increased after lime addition, while a great increase in mobility of Cu was observed. The phosphate stabilisation agent hydroxyapatite was added to sewage sludge to evaluate its stabilisation efficiency for metals and to determine its influence on metal mobility in lime-treated sewage sludge. Water and acetic acid extractions were used for determination of water soluble and potentially bioavailable metal fractions. Results showed a decrease in the mobility of all metals after hydroxyapatite addition, especially Pb and Zn. Concentrations of water soluble metals in lime-treated sewage sludge also decreased after hydroxyapatite addition, but less than in sewage sludge without added lime. In general, lime had a higher stabilization efficiency than hydroxyapatite, but special attention should be given to sewage sludges containing high concentrations of Cu.

Keywords: Hydroxyapatite, immobilization, lime, metals, sewage sludge