## 2 Materials and Methods
### Characteristics of the Initial Materials and Composting Procedure  
Four composting sets were prepared by mixing food waste (FW), coming from the central canteen building located at the Arrosadia campus of the UPNA (Pamplona, Navarre, Spain), with the campus pruning waste (CPW). The amounts of each type of waste used in each of the composting sets are shown in Table 1.  
Timing differences between the different sets and canteen service days resulted in small variations in the amount of waste managed. The principal properties of the biowastes used in each composting set are shown in Tables 2 and 3. The composting sets were formed inside the compost modules at the UPNA community compo \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Amount** & **Set 1** & **Set 2** & **Set 3** & **Set 4** & **Average** & **SD** \\ \hline FW & 838 & 794 & 784 & 542 & 740 & 134 \\ CPW & 230 & 236 & 155 & 132 & 188 & 52 \\ FW:CPW & 4:1 & 3:1 & 5:1 & 4:1 & & \\ Total & 1068 & 1030 & 939 & 674 & 928 & 177 \\ \hline \end{tabular}
\end{table} 
Table 1: Amount of food waste and campus pruning waste managed in each composting set (kg on a fresh weight basis). was carried out with each addition of new material, as well as with transfers to another composting module, as the various sets were completed to a height of approximately 80 cm, filling the composting module. The end of the bio-oxidation was considered reached when the temperature in the sets fell to the temperature of the environment and the difference between the set material temperature and environment temperature was \(\leq\) 10 \({}^{\circ}\)C for at least 10 consecutive days [21]. The bio-oxidative phase lasted 162, 137, 170, and 89 days for sets 1 to 4, respectively. After this, the compots were maintained for maturation during 67, 80, 64, and 76 days for sets 1 to 4, respectively. The sets were sampled at four different times: the initial phase (M1), the thermophilic stage (M2), the end of the bio-oxidation stage (M3), and the maturity phase (M4). Composite samples were obtained by collecting, mixing, and homogenizing seven subsamples from seven different places of the sets, considering the whole profile \begin{table}
\begin{tabular}{l c c c c} \hline  & **FW1** & **CPW1** & **FW2** & **CPW2** \\ \hline Dry weight (\%) & 82.4 \(\pm\) 1.1 & 34.1 \(\pm\) 0.3 & 60.7 \(\pm\) 2.0 & 8.8 \(\pm\) 0.1 \\ pH & 6.1 \(\pm\) 0.04 & 6.3 \(\pm\) 0.05 & 4.3 \(\pm\) 0.05 & 6.2 \(\pm\) 0.04 \\ EC (dS m\({}^{-1}\)) & 6.37 \(\pm\) 0.05 & 1.09 \(\pm\) 0.08 & 5.14 \(\pm\) 0.06 & 1.38 \(\pm\) 0.01 \\ OM (\%) & 90.5 \(\pm\) 0.6 & 95.8 \(\pm\) 0.8 & 95.8 \(\pm\) 0.7 & 92.0 \(\pm\) 0.7 \\ TOC (\%) & 43.8 \(\pm\) 0.3 & 50.0 \(\pm\) 0.4 & 49.2 \(\pm\) 0.4 & 44.5 \(\pm\) 0.3 \\ TN (\%) & 2.23 \(\pm\) 0.02 & 0.83 \(\pm\) 0.01 & 2.32 \(\pm\) 0.14 & 0.83 \(\pm\) 0.01 \\ TOC/TN ratio & 19.7 \(\pm\) 0.1 & 60.4 \(\pm\) 0.7 & 21.5 \(\pm\) 1.3 & 53.7 \(\pm\) 0.4 \\ P (g kg\({}^{-1}\)) & 2.76 \(\pm\) 0.04 & 0.46 \(\pm\) 0.01 & 3.41 \(\pm\) 0.03 & 1.87 \(\pm\) 0.06 \\ Fe (mg kg\({}^{-1}\)) & 662 \(\pm\) 10 & 249 \(\pm\) 33 & 64.5 \(\pm\) 3.0 & 533 \(\pm\) 11 \\ Cu (mg kg\({}^{-1}\)) & 7.91 \(\pm\) 0.10 & 3.59 \(\pm\) 0.03 & 3.82 \(\pm\) 0.16 & 9.36 \(\pm\) 0.18 \\ Mn (mg kg\({}^{-1}\)) & 46.4 \(\pm\) 0.7 & 12.8 \(\pm\) 0.1 & 14.1 \(\pm\) 0.1 & 34.6 \(\pm\) 0.8 \\ Zn (mg kg\({}^{-1}\)) & 39.6 \(\pm\) 0.6 & 18.6 \(\pm\) 0.2 & 20.74 \(\pm\) 0.1 & 42.0 \(\pm\) 1.0 \\ Cd (mg kg\({}^{-1}\)) & 0.13 \(\pm\) 0.01 & 0.04 \(\pm\) 0.00 & 0.02 \(\pm\) 0.01 & 0.03 \(\pm\) 0.00 \\ Cr (mg kg\({}^{-1}\)) & 7.91 \(\pm\) 0.35 & 3.59 \(\pm\) 0.10 & 3.82 \(\pm\) 0.00 & 9.36 \(\pm\) 0.2 \\ \hline \end{tabular} FW1 and FW2: food waste used in the composting sets 1 and 2; CPW1 and CPW2: campus pruning waste used in the sets 1 and 2. EC: electrical conductivity; OM: total organic matter; TOC: total organic carbon: TN: total nitrogen.  
\end{table} 
Table 2: Characteristics of the biowastes used in the composting processes (sets 1 and 2). Data expressed on a dry weight basis.