The fate of metals in sewage sludge incinerators

The fate of heavy metals in multiple hearth sewage sludge incinerators was examined using mass balance techniques. All major process streams into and out of the incinerators were sampled in order to characterize the partitioning of Cu, Ni, Pb, and Cd into the major effluent streams, and to calculate a metals mass balance around the incinerators. The results indicate that the residual particulate matter from the incineration process becomes progressively more enriched in the more-volatile metals (Cd and Pb) with decreasing particulate size, in the order bottom ash < cyclone ash < scrubber water particulate < stack particulate. The less-volatile metals Cu and Ni are not similarly enriched. The mass balance indicates that approximately two-thirds of the Cd mass entering the incinerators is partitioned to the scrubber water stream, while the bottom ash stream receives most of the Cu, Ni, and Pb.