Characterization of Total Organic Carbon in Solid Residues Provides Insight into Sludge Incineration Processes

Abstract

In this paper, an analytical method is presented to determine the concentrations of elemental carbon (EC) and organic carbon (OC) in incinerator residues. This method is applied to sewage sludge incinerators with different combustion technologies. The results show that the OC concentrations are below the detection limit of 0.01 g/kg of dry matter (DM) and that the EC concentrations are lower than 0.3 g/kg of DM in the solid residues of the investigated stationary fluidized-bed furnace and of the multiple-hearth furnace. The OC concentrations in the investigated rotary kiln are lower than 2.5 g/kg of DM, and the EC concentrations are between 20 and 35 g/kg of DM in the rotary kiln bottom ash. Information on processes occurring in the rotary kiln are obtained by determining the EC and OC concentrations in different particle size classes of the bottom ash as well as by sampling the bottom ash during the turn-off of the rotary kiln and determining the EC and OC concentrations in these samples. By combining the results with the process parameters, it is concluded that the OC/EC ratio is a viable indicator for the temperatures within the furnace bed, while the EC concentration indicates the oxygen supply into the furnace bed.