Evolution of trace elements and polluting gases toward clean co-combustion of coal and sewage sludge

To promote the sustainable use of sewage sludge (SS), its mono-combustion and co-combustion with coal were characterized in this study. Co-combustion was performed with varying mass ratios, where the difference between co-combustion and the linear summation of their individual mono-combustion were mainly investigated. Here we systemically elucidated the evolutions of polluting materials including trace elements and polluting gases during co-combustion. We found that the substantial heat emitted by coal combustion can speed up sludge fixed carbon combustion at 400-600 degrees C. What's more, during co-combustion, the trace elements can be chemically bonded and fixed to the aluminosilicate structure of kaolinite. When the mixing mass ratio (sludge to coal) was 3:1, the presence of coal could not only reduce the emission of SO2, CH4S, COS and CS2 but also stabilize the trace elements in the bottom slags, especially for Cd, Pb and Ag. On the basis of the results, the principles for realizing a sustainable and clean co-combustion of sludge and coal were further identified from the respects of calorific value improvement, solid waste utilization and environmental pollution mitigation.