## 4 Use of Pet Food Waste for Energy Production
\begin{table}
\begin{tabular}{l c c} \hline \hline
**Sample Type** & **Dog Food** & **Cat Food** \\ \hline Average high calorific (HHV) & 0.01846 GJ kg\({}^{-1}\) & 0.02071 GJ kg\({}^{-1}\) \\ Average low calorific (HHV) & 0.01678 GJ kg\({}^{-1}\) & 0.01882 GJ kg\({}^{-1}\) \\ Ashes & 0.42 wt \% & 0.27 wt \% \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Calorific value and ash content of analyzed pet food samples. Figure 3: Monthly distribution of thermal energy consumption (GJ) by the two main systems of the plant. However, copper (Cu), nickel (Ni), thallium (TI), and antimony (Sb) were not detected by any of the analytical methods. Although some of the metals identified may be toxic to pets, their mere presence does not necessarily indicate a health hazard. Heavy metals occur naturally in many ecosystems and can be absorbed by plants during growth, which explains their trace presence in raw materials used for pet food production, even at extremely low concentrations [36]. The plant enforces strict quality control procedures upon the arrival of raw materials to ensure compliance with established safety thresholds for animal health. Sulfur was also detected in the analyzed pet food samples. According to the literature, biomass typically contains low levels of sulfur, with 40-90% retained in the ash after combustion. However, the presence of volatile sulfur released during combustion is particularly relevant for estimating corrosion potential, as it serves as a precursor to hydrogen sulfide (H\({}_{2}\)S) and sulfuric acid (H\({}_{2}\)SO\({}_{4}\)) through direct or sequential reactions with emitted steam. These compounds are highly corrosive and can significantly damage machinery and infrastructure [37]. Therefore, quantifying sulfur content is essential for predicting corrosion risk and informing the implementation of gas cleaning systems. These may include filtration using quicklime or slaked lime or the injection of pure oxygen or air (2-6 % vol) at the reactor outlet to reduce H\({}_{2}\)S formation [38]. Future studies should quantify sulfur (S) concentrations more precisely to support these assessments. The results obtained from the TD-GC/MS analysis of VOCs were categorized by compound families and compared with literature data, as shown in Figure 4. The exhaust gases from the combustion of cat food samples had higher concentrations of alcohols and aldehydes, while those from dog food contained more hydrocarbons, as illustrated in Figure 4. Among the hazardous VOCs, due to their potential to form ozone and secondary particulate matter, benzene and toluene were detected in dog food samples. In contrast, only benzene was found in cat food [39]. \begin{table}
\begin{tabular}{l c c c} \hline
**Metals** & **Method** & **Cat Food** & **Dog Food** & **Unit** \\ \hline Cr & AAS & \textless{}0.50 & \textless{}0.50 & mg kg\({}^{-1}\) \\ Hg & AAS & \textless{}0.50 & \textless{}0.50 & mg kg\({}^{-1}\) \\ Pb & AAS & \textless{}0.50 & \textless{}0.50 & mg kg\({}^{-1}\) \\ As & AAS & \textless{}0.50 & \textless{}0.50 & mg kg\({}^{-1}\) \\ Se & AAS & \textless{}0.50 & \textless{}0.50 & mg kg\({}^{-1}\) \\ Cd & AAS & \textless{}0.50 & \textless{}0.50 & mg kg\({}^{-1}\) \\ Sn & AAS & 0.02 & 0.02 & mg kg\({}^{-1}\) \\ Zn & AAS & 0.20 & 0.30 & mg kg\({}^{-1}\) \\ Fe & AAS & 0.36 & 0.48 & mg kg\({}^{-1}\) \\ Cr & AAS & 0.04 & 0.04 & mg kg\({}^{-1}\) \\ Ca & AAS & 16.86 & 19.01 & mg kg\({}^{-1}\) \\ K & AAS & 9.41 & 9.56 & mg kg\({}^{-1}\) \\ Al & AAS & 1.37 & 1.28 & mg kg\({}^{-1}\) \\ Si & AAS & 7.50 & 7.20 & mg kg\({}^{-1}\) \\ S & XRF & 5.23 & 4.35 & wt \% \\ P & XRF & 7.50 & 7.90 & wt \% \\ Cl & XRF & 6.47 & 6.22 & wt \% \\ N & KJELDAHL & 5.12 & 4.16 & wt \% \\ \hline \end{tabular}
\end{table} 
Table 2: Relevant chemical elements. Measurements were performed by two methods. AAS: Atomic Absorption Spectrophotometry (measured in mg kg\({}^{-1}\)). XRF: X-Ray Fluorescence (measured in wt %).