Behavior of heavy metals during fluidized bed combustion of poultry litter

In this study, we have examined the behavior of heavy metals during fluidized bed combustion of poultry litter. Heavy metals examined include As, Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni, Pb, V, and Zn. Solid and gaseous streams were analyzed and compared with relevant guidelines to determine the potential environmental impact of combustion and subsequent land spreading or landfill of the resulting ash. The majority of heavy metals were associated with the solid ash fraction, with low gaseous emissions. Pb and As were concentrated in the fine baghouse ash (160°C) due to their volatility. The remaining heavy metals, excluding Cd, were enriched in the heat exchangers and cyclone, where flue gas temperatures ranged from 580 to 220°C. Under the waste acceptance criteria, all samples of process ash, excluding bed ash, exceeded the limits for nonhazardous landfill waste, as a result of high levels of water-soluble Cr. Water-soluble Cr indicated the presence of Cr(VI), and its presence was confirmed using X-ray absorption near-edge structure spectroscopy (18.4% to 38.3%). The source of Cr was identified as the bedding material (wood shavings), and its conversion to Cr(VI) was temperature-dependent and could be facilitated by the high alkali content found in poultry litter.