Heavy metal distribution and speciation during sludge reduction using aquatic worms

Abstract

Changes in heavy metal distribution and speciation during the reduction of sewage sludge with the worm, Limnodrilus hoffmeisteri were assessed. In sludge containing 108.3 ± 2.2, 455.5 ± 10.3, and 39.4 ± 1.8 mg/kg of Cu, Zn, and Pb, respectively, more than 81% of these metals remained in the sludge after predation by the worms, while 4.1-9.7% of these metals were released into the liquid. The maximum uptake values of Cu, Zn, and Pb by the worms reached 180.5, 587.4, and 55.8 mg/kg, respectively. The predation did not increase metal bioavailability in the final sludge as reflected by a 9.5-12.5% decrease in labile Cu and unchanged levels in labile Zn and Pb. The sewage sludge reduction efficiency of L. hoffmeisteri was 27.6-29.2%. These results indicated the relatively moderate changes in speciation and distribution of Cu, Zn, and Pb and the stable performance of worms in reducing sewage sludge.