4.2. Valorisation of by-products derived from slaughterhouse
Slaughtering activities involve not only the production of waste water but also an important amount of by-products (∼0.22 kg per kg carcass weight). The valorisation of this stream has not been considered within the system boundaries of the γ-Secretase inhibitor IX system (Base Scenario) since it is outside slaughterhouse-related activities (they do not receive any revenue for them).
However, this stream could be valorised in different applications: biogas, energy and animal feed production (Nguyen et al., 2011). For this reason, different alternative scenarios have been proposed where by-product valorisation has been considered within the system boundaries taking into account usual valorisation practices.
Moreover, it is common in Portugal for part of the animal by-product from slaughterhouses (category 2 material) to go through an incineration process in order to recover energy (electricity and heat). The remaining part (category 3 material) can be dedicated to animal fat and feed production. Thus, an alternative scenario has been proposed (Scenario B) taking into account the production of energy, animal fat and animal feed from that animal by-product from the slaughtering subsystem. In this scenario, 57% of animal by-product is sent for incineration and the remaining 43% to animal fat and feed production. Moreover, avoided processes with associated environmental loads have also been computed within this system boundary (electricity, heat and barley production). Inventory data concerning the incineration and fat and feed production processes as well as associated avoided processes have been taken from the Ecoinvent Database (Weidema et al., 2013).