Chemical toxicity and ecotoxicity evaluation of tannery sludge stabilized with ladle furnace slag

In this study, the stabilization of tannery sludge, which produced during the physico-chemical treatment of tannery wastewaters, was examined by the addition of ladle furnace slag. Moreover, the simultaneous addition of organoclay and ladle furnace slag for the stabilization of tannery sludge was also examined. Chromium and dissolved organic carbon in the leachate of raw tannery sludge, using the EN 12457-2 standard leaching test, were found to exceed the limit values for disposal in non-hazardous and even in hazardous waste landfills, according to the EU Decision 2003/33/EC. Tannery waste (air-dried sludge) was mixed with ladle furnace slag and water or ladle furnace slag, organoclay and water at different ratios, in order to study the stabilization of chromium and organic compounds. The mixtures were left for one week aging and then they were subjected to the standard leaching test EN 12457-2. The leachate of tannery waste stabilized with ladle furnace slag showed Cr concentrations below the respective regulation limit value for disposal in non-hazardous waste landfills; however, the dissolved organic carbon cannot meet the respective limit value. On the other hand, the leachate of tannery waste stabilized with a mixture of ladle furnace slag and organoclay, using 30:50:20 mass ratio, presented both Cr and dissolved organic carbon concentrations below the regulation limit values for disposal in non-hazardous waste landfills. Moreover, this leachate was further subjected to ecotoxicity test, using the Vibrio fischeri photo-bacterium. The leachate of stabilized tannery waste showed reduced ecotoxicity, in comparison with the toxicity effect of the leachate of the untreated tannery waste.