Influence of operating parameters on arsenic transformation during municipal sewage sludge incineration with cotton stalk.

Addition of cotton stalk (CS) has been proved to promote dramatically the transformation of toxic As to less toxic As in the fly ash during municipal sewage sludge (MSS) incineration. However, the fate of arsenic during co-firing of MSS and CS in different operating parameters was still unclear. In the present study, the effects of incineration temperatures and O content in the flue gas on speciation transformation of arsenic during MSS and 70% MSS/30% CS incineration were investigated in a bubbling fluidized bed. The results show that less arsenic is distributed in bottom ash whereas more arsenic is migrated to the fly ash and flue gas, with the temperature increasing from 800 °C to 950 °C. The arsenic capture in fly ash is facilitated predominantly by the condensation and/or physical adsorption of AsO(g) at the temperatures from 800 °C to 900 °C. The chemical oxidation of AsO(g) is favored by forming various arsenates (As) at 950 °C. At low O content from 1% to 5%, some arsenic compounds in MSS such as AsS can react with O to produce AsO(g), and then more AsO(g) is captured in the fly ash by the inherent mineral compounds like CaO through the condensation and/or physical adsorption. Further increasing O content especially to 9% stimulates significantly the oxidation of As to As in the fly ash, which is mainly attributed to the chemical reactions between AsO(g), various mineral compounds and sufficient O.