## 4 Use of Pet Food Waste for Energy Production
### Greenhouse Gas Measurement Results and Mitigation Proposal  
As previously noted, GHG emission estimates focus exclusively on processes that use natural gas as a fuel, since the facility's electricity supply is certified as 100% renewable. As a result, there are no emissions attributed to the generation of electricity consumed by the company. The results of GHG emissions, based on the total natural gas consumption for the dryer and boiler systems, are shown in Figure 6. Greenhouse gas emissions, in CO\({}_{2}\)eq, were found to be directly proportional to production levels, reflecting the thermal energy demands of the manufacturing process. In 2020, the plant emitted a total of 2347.8 Mg of CO\({}_{2}\)eq from natural gas use, corresponding to 0.048 Mg of CO\({}_{2}\)eq per Mg of pet food produced. Figure 7 shows that the dryer is the largest contributor to GHG emissions, accounting for 68.76% of the total. This result is expected, as the dryer is the system with the highest natural gas consumption. The boiler contributes an additional 30.87% of the plant's GHG emissions. Accordingly, for every Mg of pet food produced, the dryer is responsible for 0.033 Mg of CO\({}_{2}\)eq, while the boiler accounts for 0.015 Mg. The proposed GHG mitigation strategy involves replacing natural gas with biomass as the fuel source for the boiler, as previously discussed. Biomass is considered carbon-neutral in terms of CO2 emission, thereby eliminating all GHG emissions currently attributed to the boiler's natural gas consumption. If biomass had been used in 2020, during the production of 48,319 Mg of pet food, the boiler's annual emissions would have been reduced by approximately 709.34 Mg of CO2 eq. This substitution would correspond to a reduction of 0.015 Mg of CO2 eq per Mg of pet food produced. Given the rapid growth of the pet food industry in Chile and worldwide, adopting biomass as a boiler fuel would have a significant long-term impact on the company under study. While this change alone would reduce the plant's current GHG emissions by 31%, the company's broader sustainability goals, together with increasingly stringent environmental regulations, are expected to drive the future adoption of technologies that could eventually decarbonize the drying process as well. Although Scope 3 GHG emissions were not assessed in this study, the proposed measure would likely contribute to additional emission reductions by lowering the frequency of natural gas deliveries to the facility and decreasing the volume of food waste transported for compostion. Figure 5: Photographs of carbon steel specimens before and after exposure to combustion gases. (**a**) Unevposed reference specimen; (**b**) exposed to combustion gases from cat food; (**c**) exposed to combustion gases from dog food; (**d**) exposed to propane–butane domestic gas; (**e**) exposed to combustion gases from residential pellets; (**f**) exposed to combustion gases from wood chips. The red rectangle represents the focus of corrosion and pitting on the sample. The results of this study provide valuable insights into the viability of using sustainable biomass to improve energy efficiency in boiler systems. From an energy perspective, both cat and dog food samples demonstrated potential as standalone fuels or co-firing alternatives, with higher heating values (HHVs) of 0.0185 GJ kg\({}^{-1}\) 0.0207 GJ kg\({}^{-1}\) for dog and cat food samples, which is comparable to other wastes researched as biocombustible  
Figure 6: Pet food production versus GHG emissions associated with thermal energy use. Figure 7: GHG emission distribution by equipment. in boiler systems, such as tea waste pellets (0.0182 GJ kg\({}^{-1}\)), shoe manufacturing waste (0.0235 GJ kg\({}^{-1}\)), rice husk (0.015 GJ kg\({}^{-1}\)), and Tobaco stalks (0.0174 GJ kg\({}^{-1}\)) [13; 14; 15]. In terms of greenhouse gas (GHG) emissions, substituting natural gas with pet food biomass could potentially reduce CO\({}_{2}\)eq emissions by 0.015 Mg GJ\({}^{-1}\) or, equivalently, 0.015 Mg per Mg of pet food produced.