## 3 Results and Discussion
### Framing within ENplus(r) Parameters  
ENplus(r) is an independent certification scheme for wood pellets that ensures their quality and performance for heating purposes [47]. It sets stringent standards for the production, logistics, and trading of wood pellets, helping to guarantee their reliability and efficiency as a renewable energy source. To evaluate the potential of wine pomace and distillation stillage as alternative sources for pellet production, it is essential to compare their properties against the ENplus(r) standards. This comparison helps determine whether these biomasses can meet the quality requirements for commercially viable wood pellets, ensuring their reliability and efficiency as renewable energy sources. The ENplus(r) pellet classes are divided into 3 groups: A1, A2, and B (Table 6) [47].  
Both samples have moisture contents well below the ENplus(r) thresholds, indicating suitability for energy recovery in terms of moisture. However, their ash contents significantly exceed the maximum limits set by all ENplus(r) classifications, which could pose challenges for their use as fuel according to these standards. Therefore, incorporating a pre-treatment step, such as leaching, is necessary to enhance the efficiency and effectiveness of the energy recovery process [48].  
The nitrogen content in both samples is also higher than the ENplus(r) limits, raising concerns about potential NOx emissions during combustion [49].  
Distillation stillage has a sulfur content that exceeds all ENplus(r) classification limits, which could lead to higher SOx emissions, while wine pomace meets the A2 and B standards but not the A1 limit [47; 49]. Despite these challenges, both samples exceed the minimum LHV requirement set by ENplus(r), indicating their high energy recovery potential [47].  
In summary, while distillation stillage and wine pomace exhibit favorable moisture content and high LHV for energy recovery, their high ash, nitrogen, and sulfur contents may limit their suitability under ENplus(r) standards, particularly for the higher quality classifications. In order to make these materials viable for production, it is recommended to mix them with sawdust from a suitable type of wood [50]. This combination enhances their suitability for combustion by improving their heating value and reducing the high concentrations of nitrogen, sulfur, and ash found in both wine pomace and distillation  
\begin{table}
\begin{tabular}{c c c c c c} \hline  & **Moisture (\%)** & **Ash (\%)** & **N (\%)** & **S (\%)** & **LHV (MJ/kg)** \\ \hline ENplus® A1 & \(\leq\)10.0 & \(\leq\)0.70 & \(\leq\)0.3 & \(\leq\)0.04 & \(\geq\)16.5 \\ ENplus® A2 & \(\leq\)10.0 & \(\leq\)1.20 & \(\leq\)0.5 & \(\leq\)0.05 & \(\geq\)16.5 \\ ENplus® B & \(\leq\)10.0 & \(\leq\)2.00 & \(\leq\)1.0 & \(\leq\)0.05 & \(\geq\)16.5 \\ Distillation stillage & 5.454 \(\pm\) 0.118 & 3.762 \(\pm\) 0.129 & 2.57 \(\pm\) 0.301 & 0.153 \(\pm\) 0.032 & 19.109 \(\pm\) 0.024 \\ Wine pomace & 5.268 \(\pm\) 0.027 & 6.359 \(\pm\) 0.038 & 2.494 \(\pm\) 0.055 & 0.043 \(\pm\) 0.012 & 18.514 \(\pm\) 0.032 \\ \hline \end{tabular}
\end{table}
Table 6: Threshold values of parameters in accordance with ENplus® system [47].  
stillage. For example, spruce sawdust could be used in the mixing process. From the [51] results it is possible to estimate the amount of sawdust needed for the mixture to meet ENplus(r) certification standards. For distillation stillage pellets, the mixture should contain approximately 8.38% of the sample for an A1 classification, 21.74% for an A2 classification, and around 31.85% for a B classification. For wine pomace, the mixture should have about 4.95% or less sample for an A1 classification, 22.28% for an A2 classification, and approximately 36.24% for a B classification.