## 1 Introduction
### FW Characterisation  
Characteristics and composition of FW strongly depends on where in the process the non-edible and non-usable materials are generated. FW generated in the first part (agriculture and livestock) are mainly composed of non-edible materials, separated from feedstocks. They are completely different in composition from FW generated in the final step of food supply chain (markets), where other material fractions are included, such as glass, metals, paper, plastics, and so forth, which stem from packaging. In the case of FW generated by the consumers, its composition depends strongly on different eating and cooking habits [34]. For those reasons, many researchers had characterised FW, each one with its own compositions and characteristics, depending on its origin, geographical location, social behaviours, habits, and local products... [35]. From the point of view of AD and waste reuse, it is important to thresh the composition regarding organic components like lipids, proteins, and carbohydrates (LPCH) and volatile fatty acids (VFA), content of total solids (TS) and volatile solids (VS), nitrogen content (N), carbon content (C), and its ratio (N/C). A review of FW characteristics and composition is provided in Table 1.  
Figure 1: Waste management hierarchy according to Council Directive 1999/33/CE [17]. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Food Waste Composition**} \\ \hline
**FW Type and Origin** & **TS [\%]** & **VS [\%]** & **Proteins [\%]** & **Lipids [\%]** & **Carbohydrates [\%]** & **VFA [\%]** & **C [\%]** & **N [\%]** & **C/N Ratio** & **Reference** \\ \hline Household individual sorted materials & & & & & & & & & [36] \\ \hline Meat and bone & & 70-75 & 23-30 & 1 & & & & & [37] \\ Fish and fishbone & & 75.6 & 20.2 & & & & & [38] \\ Egg and shell & & 35 & 32 & 2 & & & & [39] \\ Diary products & & 25-35 & 20-45 & 53 & & & & [39] \\ Fruit & & 4 & 2 & 83 & & & [40] \\ Vegetable & 27 & 1.4 & 27 & & & & & [41] \\ \hline Individual fractions from OFMSC & & & & & & & & \\ Animal kitchen waste & 33.3 & 54.4 & 35.7 & 9.9 & & & & & [42] \\ Vegetable kitchen waste & 13.4 & 21.6 & 19.4 & 57.6 & & & & & \\ Raw animal waste & 38.6 & 99.8 & 27.2 & 13 & & & & & \\ Raw vegetable waste & 10.8 & 19.4 & 11.1 & 69.4 & & & & & \\ \hline OFMSC in Sweden & & 90.8 & 18.2 & 20 & 29.4 & 0.35 & 50 & 2.8 & 17.85 & [43] \\ \hline Fractions of OFMSC in Denmark & & & & & & & & & [44] \\ \hline Animal food waste & 41 & 84 & 12 & 25 & 52 \({}^{\ast}\) & & & & & [44] \\ Vegetable food waste & 24 & 93 & 5 & 14 & 53 \({}^{\ast}\) & & & & & \\ \hline Food waste & & 29.3 & 26.6 & 35 & 32.5 & 48.4 & 3.8 & 12.7 & [45] \\ \hline Food waste & 18.1 & 17.1 & & 23.3 & 61.9 & & & & [46] \\ \hline Food waste & 23.1 & 21.0 & & & & & 56.1 & 2.3 & 24.5 & [47] \\ \hline Food waste for AD & 30.9 & 26.35 & & & & & 46.8 & 3.54 & 13.2 & [48] \\ \hline Kitchen waste & 24 & 23.2 & 15 & 23.9 & 55.2 & 54 & 2.4 & 22.5 & [49] \\ \hline Food waste & 23.2 & 21.7 & 2.9 & 6.5 & 13.7 & & & & [50] \\ \hline OFMSC from municipal biovaste & 20 & 18 & 30 & 4.4 & 10.7 & & & 17 & [51] \\ \hline Food waste & 16.7 & 15.3 & 2.4 & 1.4 & & & & 11.5 & [52] \\ \hline Notes \({}^{\ast}\): Only easily-degradable carbohydrates & & & & & & & & & \\ \hline \multicolumn{10}{c}{**Metal Elements in FW [3/3/3-TS]**} \\ \hline
**S** & **Ca** & **Mg** & **K** & **Na** & **Fe** & **Zn** & **Cu** & **Mn** & **Mo** & **Reference** \\ \hline Food waste & 3.4 & 1.7 & 0.7 & 9.6 & 10.1 & 0.041 & 0.032 & 0.005 & 0.008 & 0.00003 & [45] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Food waste composition reported by various authors. Whilst the composition in terms of carbohydrates, lipids and proteins gives an overall idea of the composition, together with the solids content, a more extensive characterisation in terms of carbon content or nitrogen is necessary to finally differentiate them.