## 3 Results and Discussion  
### Chemical Characterization of the Residues  
The first phase of the work focused on characterizing the chemical composition of the four residues and the wheat bran (WB) used in some solid-state cultures as the additive. The choice of WB was made due to the inclusion, in this investigation, of spent coffee grounds (SCG), a matrix that, owing to its constituent particles' fine granulometry, has low porosity, making gas exchanges problematic. Due to its coarse texture, wheat bran is well-suited to act as a bulking agent capable of increasing the material's overall porosity. Added to this is the fact that the bran has a relatively high nitrogen content (30.1 g kg\({}^{-1}\)) (Table 1), being mainly composed of protein and amino acids [34]. Furthermore, WB contains microelements and cofactors which are essential for growth, such as B vitamins and folates [35]. Consequently, this study set up and analyzed solid-state cultures on both non-amended and WB-amended residues to make the experimental design homogeneous. Table 1 shows that the holocellulosic component, determined by the cellulose and hemicellulose contents' aggregation, constituted a significant fraction of the residues under study, since its mass fraction (\(w_{HC}\)) reached values equal to or well above 0.50 of the dry weight. In particular, the highest \(w_{HC}\) was found in barley straw, where the aggregate sum of the cellulose and hemicellulose concentrations gave a value equal to about 0.70, followed by RTB, in which the value of this parameter was slightly less than 0.60. Cellulose was the dominant polysaccharide in RTB, barley straw and DSF (405.9 \(\pm\) 12.3, 420.6 \(\pm\) 2.2 and 395.4 \(\pm\) 24 g kg\({}^{-1}\), respectively). Conversely, SCG exhibited the lowest content of this \begin{table}
\begin{tabular}{c c c c c c} \hline
**Parameter (g kg\({}^{-1}\))** & **RTB** & **SGC** & **DSF** & **Barley Straw** & **WB \(\dagger\)** \\ \hline Hemicellulose & 189.2 \(\pm\) 3.2 a & 375.2 \(\pm\) 16.8 c & 172.2 \(\pm\) 14.9 a & 279.3 \(\pm\) 3.0 b & 187.6 \(\pm\) 12.2 c \\ Cellulose & 405.9 \(\pm\) 12.1 c & 120.2 \(\pm\) 3.2 a & 393.4 \(\pm\) 24.4 c & 420.6 \(\pm\) 2.2 c & 201.1 \(\pm\) 24.3 b \\ Klason lignin & 204.2 \(\pm\) 4.6 c & 201.7 \(\pm\) 7.2 c & 257.4 \(\pm\) 14.2 d & 165.2 \(\pm\) 4.6 b & 73.2 \(\pm\) 3.9 a \\ Crude lipids & 20.8 \(\pm\) 14.4 a & 139.8 \(\pm\) 5.4 c & 19.3 \(\pm\) 2.7 a & 16.2 \(\pm\) 1.8 a & 45.4 \(\pm\) 4.3 b \\ Reducing sugars & 3.6 \(\pm\) 0.4 a & 4.1 \(\pm\) 0.2 a & 9.2 \(\pm\) 0.4 b & 41.8 \(\pm\) 2.7 c & 49.3 \(\pm\) 3.2 d \\ Phenols & 17.2 \(\pm\) 15.5 b & 49.2 \(\pm\) 2.4 d & 15.3 \(\pm\) 2.4 b & 21.4 \(\pm\) 1.6 c & 9.2 \(\pm\) 1.7 a \\ Ash & 85.3 \(\pm\) 7.0 d & 20.4 \(\pm\) 2.5 a & 82.1 \(\pm\) 3.6 d & 70.1 \(\pm\) 5.3 c & 43.6 \(\pm\) 2.1 b \\ Nitrogen & 5.9 \(\pm\) 0.3 a & 22.8 \(\pm\) 1.6 c & 19.8 \(\pm\) 1.1 b & 5.4 \(\pm\) 0.4 a & 30.1 \(\pm\) 1 d \\ Carbon & 423.4 \(\pm\) 8.0 ab & 508.9 \(\pm\) 11.1 d & 415.3 \(\pm\) 8.2 a & 467.4 \(\pm\) 5.4 c & 441.2 \(\pm\) 4.2 b \\ Hydrogen & 62.1 \(\pm\) 2.0 b & 75.6 \(\pm\) 1.8 c & 59.4 \(\pm\) 2.1 a & 55.2 \(\pm\) 4.1 a & 69.3 \(\pm\) 4.2 c \\ Sulphur & 1.7 \(\pm\) 0 b & 1.0 \(\pm\) 0 a & 2.2 \(\pm\) 0.1 b & 0.1 \(\pm\) 0.0 a & 1.8 \(\pm\) 0.0 b \\ \hline \end{tabular} \(\dagger\) Starch, the content of which was 175.4 g kg\({}^{-1}\) in WB, was omitted in this table since this parameter was not detected in the other waste.  
\end{table} 
Table 1: Chemical composition of residual thistle biomass (RTB), spent coffee grounds (SCG), digestate solid fraction (DSF), barley straw and wheat bran (WB). The data, expressed as g kg\({}^{-1}\) of the dry weight, are the mean \(\pm\) standard deviation of 3 determinations. Multiple pair-wise comparisons were made between the row means using the Tukey test; identical letters denote that row means were not significantly different (\(p\) > 0.05). parameter (120.2 \(\pm\) 3.2 g kg\({}^{-1}\)), and hemicelluloses were the most abundant polysaccharide fraction (375 \(\pm\) 16.8 g kg\({}^{-1}\)).