## 2 Materials and Methods
### Environmental Conditions
The entry feeding hopper (1) for the wet material (alperujo and orujo) had a height of 50 cm, the diameter in the upper part was 50 cm and the diameter in the lower part was 20 cm. The concentric drum (10) had a length of 2500 cm and 80 cm in diameter. In addition, paddles were built inside the drum to allow samples to be homogenized. Finally, the trommel had two orifices, one for the exit of the dry biomass (11) and the other for the exit of the exhaust gases and particulate matter (8). The exhaust gases and particulate matter passed through a separation cyclone (7) to extract fine particles, while the hot gases were released through an outlet pipe where gas samples were taken for Volatile Organic Compounds (VOCs) analysis. The working conditions of the drying trommel were selected based on those normally used in the olive oil production industry. A working temperature in the concentric drum of 420 \(\pm\) 10 \({}^{\circ}\)C was selected and controlled using two thermocouples (PT100), one for the entry of hot gases into the system and the other inside the drum of the drying trommel. The drum rotation speed of the system was programmed at 5.0 RPM and an inclination of 15\({}^{\circ}\) in order to achieve a better displacement of the material inside the drum and achieve a homogeneous drying in a total time of approximately 15 min. The final outlet moisture of the alperujo and orujo was between 10-15\(\%\)\(w/w\) on dry basis. For each sample of alperujo and orujo, three tests per sample were carried out allowing to evaluate the outlet emissions and waste characteristics after the drying process (Table S2, supplementary material). In all cases, the average humidity of the material after the tests fluctuated between 11-13% \(w/w\) on dry basis, while the average for ash content and the measuring heating value were 1.5-3.0% \(w/w\) and 22.3 MJ kg\({}^{-1}\), respectively, for both alperujo and orujo. Sampling of VOCs and Conditions of Thermal Desorption-Gas Chromatography/Mass Spectrometry (TD-GC/MS)  
At a distance of 50 cm from the outlet pipe of the exhaust gases of the drying trommel, three samples were taken for each test at different times (5 min, 10 min and 15 min) at an average outlet temperature of 150 \({}^{\circ}\)C. In order to extract the gas samples, a suction pump (Markes Easy VOC model LP-1200, Germany) was used, extracting an amount of 100 mL through an absorbent tube (Markes C2-BAXX-5315 odor/sulfur. C6/7-C30, thiols and mercaptans, Germany). Once the gases were adsorbed, VOCs desorption was carried out using a cold trap of thermal desorption (Markes model Unity-xr, Germany). The gases were extracted in Split mode, driven with helium for 1 min to the hot trap programmed at 300 \({}^{\circ}\)C and then cooled to 20 \({}^{\circ}\)C in the cold trap to finally be  
Figure 1: Biomass drying trommel. (1) hopper; (2) thermal power; (3) roller guide; (4) motor; (5) gear systems; (6) induced fan; (7) cyclone discharger; (8) exhaust gas; (9) thermocouple; (10) drying drum; (11) dry biomass output. heated to 300 \({}^{\circ}\)C for 5 min. VOCs were transferred by means of a transfer line heated at 200 \({}^{\circ}\)C to one column (RESTE-Rtx-5 MS, PA, USA. w/integrin-guard Crossbond 5% diphenyl-95% dimethyl polysaccharide. 30 m, 0.25 mmID, 0.25 \(\upmu\)m df) installed in a GC/MS (Thermo Fisher Scientific, model Trace 1300/ISQELTL, MA, USA). The working conditions of the GC for the oven were in Split mode with a working temperature between 40 \({}^{\circ}\)C and 220 \({}^{\circ}\)C. Flow: 1.2 mL/min; Split Ratio: 10 \({}^{\circ}\)C/min, the transfer line temperature of the MS detector was 200 \({}^{\circ}\)C while the ion source temperature was set at 250 \({}^{\circ}\)C. The qualitative identification of VOCs was carried out using the Chromeleon 7.2 software package, which is compatible with the NIST library [14], using retention times observed in the chromatograms.