#### Literature Review  
Previous works indicated that to use torrefied lignocellulosic and non-lignocellulosic biomasses as fuel, the knowledge of physical, chemical, and structural changes caused by the torrefaction process must be studied [58; 59]. The properties of torrefied biomass material predominantly rely on the torrefaction severity (TS), which is calculated either by weight loss (WL), severity factor (SF), or torrefaction severity index (TSI). Energy yield, carbon content, and fixed carbon content are mostly shown by weight loss [39]. In addition to weight loss, mass yield and thermal degradation of biomasses are also used as indicators to show TS with an account of thermal degradation depending mostly on the type of feedstock [60]. Thus, to minimize the effect of the nature of the biomass, the researchers defined another index called the torrefaction severity index (TSI), which could be correlated with biomass loss during diverse torrefaction operations [39]. The TSI index under the most severe conditions was also defined [61; 62]. It indicated the quality of obtained torrefied biomass material from the lowest to the highest. TSI has been utilized to describe the thermal degradation degree of biomass, EF, energy yield, deoxygenation, dehydrogenation, decarburization, and upgrading energy index [58]. The severity factor (SF) was defined based on temperature and duration of torrefaction [63]. SF was initially conducted to evaluate steam, aqueous, and dilute acid pretreatment [47] but was later introduced to other processes as well. Past studies on the torrefaction process and TSI are summarized in Table 1.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Feedstock** & **Temperature (\({}^{\circ}\)C)** & **Duration (Time, min)** & **Main Finding** & **Reference** \\ \hline \multirow{6}{*}{Rubberwood, Gliricidia} & \multirow{6}{*}{250, 275, 300} & \multirow{6}{*}{30, 45, 60} & Calculated EMCI of & \multirow{6}{*}{[62]} \\  & & & Rubberwood at 275 \({}^{\circ}\)C and & \\ \cline{4-4} \cline{5-5} \multirow{6}{*}{Oak waste wood, mixed waste wood, sewage sludge} & \multirow{6}{*}{220, 240, 260, 280, 300, 320, 340, 400} & & 60 min or 300 \({}^{\circ}\)C and 45–60 min & \\ \cline{4-4} \cline{5-5} \multirow{6}{*}{Oak waste wood, mixed waste wood, sewage sludge} & \multirow{6}{*}{220, 240, 260, 280, 300, 320, 340, 400} & & 60 min or 300 \({}^{\circ}\)C and 45–60 min & \\ \cline{4-4} \cline{5-5} \multirow{6}{*}{Oak waste wood, mixed waste wood, sewage sludge} & \multirow{6}{*}{230, 340, 400} & & 60 min or 300 \({}^{\circ}\)C and 45–60 min & \\ \cline{4-4} \cline{5-5} \multirow{6}{*}{_Eucalyptus grandis_} & \multirow{6}{*}{210, 230, 250, 270, 290} & & 60 min or 300 \({}^{\circ}\)C and 45–60 min & \\ \cline{4-4} \cline{5-5} \multirow{6}{*}{Coffee grounds, Chinese medicine residue, algae residue (_Arthospira plantesis_)} & \multirow{6}{*}{200, 250, 275, 300} & & 60 min or 300 \({}^{\circ}\)C and 45–60 min \\ \cline{4-4} \cline{5-5} \multirow{6}{*}{Coffee grounds, Chinese medicine residue, algae residue (_In such context, the torrefaction properties of three different lignocellulosic and non-lignocellulosic biomasses and their mixtures were studied in this work under specific conditions (temperature, time, and atmosphere) with special attention to the physical, chemical, and structural changes (miscanthus, hops, sewage sludge, mixture of sewage sludge and miscanthus, and mixture of sewage sludge and hops). The torrefaction severity index (TSI) was calculated based on temperature and time concerning biomass weight loss. There have already been many studies on the torrefaction behavior of miscanthus and sewage sludge; however, minimal torrefaction studies are reported on the hops, and no torrefaction studies are reported on the mixtures of sewage sludge and miscanthus or hops. Sewage sludge is not directly suitable for usage as a solid fuel, mainly due to low calorific value and relatively poor carbon content. However, its mixing/combining with other raw lignocellulosic materials can significantly improve its fuel properties.