The mixture of sewage sludge and biomass waste as solid biofuels: Process characteristic and environmental implication

Abstract

Oxy-fuel and air atmospheres were used to (co-)combust sewage sludge (SS) and biomass waste, coffee ground residues (CG) via thermogravimetric analysis (TGA). The combustion behavior of SS did not differ significantly in both atmospheres. The replacement of 79%N2 by 79%CO2 significantly influenced the char combustion of CG. Synergistic effect of the blends in the oxy-fuel was weaker than air condition. Activation energy of the co-combustion in the second stage was lower in the oxy-fuel than air atmosphere. The gaseous emissions during blend fuel combustion were investigated by online mass spectrometry (MS). Results show that the gas emissions of different fuels show different stage characteristics. CH3, H2O, C2H2 and NO emissions peaked from the volatiles combustion of CG, while the co-combustion led to SO2 increment. Besides, the composition of the solid residues was examined by X-ray fluorescence spectrometer (XRF), and their impact on environment was evaluated. The compositions of the solid residues pointed to the ability of SS to lower the fouling and slagging risks of CG. This investigation aimed to afford a fully understanding for the co-combustion progress of SS and CG under air and oxy-fuel environments and its implication for environment.