Fractionation and leachability of Cu in lime-treated sewage sludge

Lime-treated sewage sludge was produced using a bench process to study the leachability and fractionation of Cu, which has a great affinity for organics in sewage sludges. The amount of Cu fractionated to the organically-bound form in sewage sludge was 73.7% by weight, while the lime treatment resulted in a decrease to 55.6%. The addition of lime to lime-treated sludge mainly led to an increased shift in Cu from the organically-bound fraction to exchangeable and acid-soluble fractions, indicating that the lime treatment caused Cu in sewage sludge to become unstable. The instability resulted from the affinity of Cu for organics, which irreversibly dissolve with Cu at very high pH during processing and natural drying of sludge. Semi-dynamic extraction revealed that the lime treatment also increased percent cumulative leaching of Cu from sewage sludge after the extraction period of 12 days.