Ash-to-emission pollution controls on co-combustion of textile dyeing sludge and waste tea

Abstract

Given the globally increased waste stream of textile dyeing sludge (TDS), its co-combustion with agricultural residues appears as an environmentally and economically viable solution in a circular economy. This study aimed to quantify the migrations and chemical speciations of heavy metals in the bottom ashes and gas emissions of the co-combustion of TDS and waste tea (WT). The addition of WT increased the fixation rate of As from 66.70 to 83.33% and promoted the chemical speciation of As and Cd from the acid extractable state to the residue one. With the temperature rise to 1000 °C, the fixation rates of As, Cd, and Pb in the bottom ashes fell to 27.73, 8.38, and 15.40%, respectively. The chemical speciation perniciousness of Zn, Cu, Ni, Mn, Cr, Cd, and Pb declined with the increased temperature. The ash composition changed with the new appearances of NaAlSi3O8, CaFe2O4, NaFe(SO4)2, and MgCrO4 at 1000 °C. The addition of WT increased CO2 and NOx but decreased SO2 emissions in the range of 680–1000 °C. ANN-based joint optimization indicated that the co-combustion emitted SO2 slightly less than did the TDS combustion. These results contribute to a better understanding of ash-to-emission pollution control for the co-combustion of TDS and WT.