In attempt to understand the synergistic mechanisms controlling the co-combustion processes of blended fuels, two medicinal biowastes (lignocellulose and non-lignocellulose) and three different-rank coals (lignite, bituminite and anthracite) were employed in this work. Intrinsic characteristics of parent materials were firstly measured with the help of C-13 NMR, FTIR and XRD technologies, followed by the thermogravimetric analysis of mono- and co-combustion behaviors. The results suggested that synergistic processes depended on the amount and properties of light volatiles in biowastes, but both lignocellulose and non-lignocellulose biowastes had positive effects on co-combustion with coals to some extent. Among them, the blends with low-rank coal showed the highest combustion efficiency. The actual HHV of blends with coal A (low-rank coal) exceeded their theoretical one, reaching the increases of 3.1-4.5%, 6.9-7.0% and 11.5-11.6% for 30%, 50% and 70% addition of coal A, respectively. Additionally, the introduction of biowastes also lowered the activation energy to initiate main decomposition of coals, increased the co-combustion reactivity, as well as altered the main combustion profiles to different extends. In general, co-combustion with low-rank coal achieved the best combustion efficiency among the blends. These findings would be beneficial for efficient utilization of organic biowastes as solid fuels in existing co-firing equipment. (C) 2019 Elsevier Ltd. All rights reserved.