## 2 Materials and Methods
### System Boundaries and Scenarios  
The scope of the research includes the complete process of the products' life cycles from the raw material extraction, to the final products, ready to be marketed, as in the cradle-to-gate perspective. The system boundaries of the two different scenarios considered for corn cob valorization have been presented in Figure 1. The life cycle scenarios consider three phases:  
* raw materials production (corn cob);
* transportation to the processing site;
* processing of the raw materials for the production of the new product.  
The raw materials are obtained from a background system, common to both Scenario 1 and Scenario 2, and aimed to provide as a main product the maize grains. The background system consists of cultivation, harvesting, and preparation of the maize grains and, in this background system, the corn cob has been considered a co-product. The collecting phase of the corn cob can be considered a phase of the cultivation process, carried out in parallel to the maize grain separation. Indeed, external machines implementable on the harvesters for the separate collection of grains and chopped cobs are available today. The two scenarios system considers the transportation to the processing factory and the commuting steps, as shown in Figure 1, obtaining the products ready to be sold. A transport distance of 100 km between the farm and the processing plant has been hypothesized in both scenarios, as representative average distance between the farm and processing plant (feed and organic litter production) in the area under study. The two scenarios have been analyzed in the hypothesis of considering a small-scale proximity production (i.e., a local scale system), which would make the exploitation of these residues advantageous [37]. The packaging phase is excluded from the boundary system defined for the investigation, considering the fact that the packaging type, size, and material are heterogeneous and depend on the factory policies and choices.  
Concerning the comparative products, on one hand, the manufacture of silicon carbide consists of the reaction of silicon dioxide and carbon, yielding silicon carbide and carbon monoxide [38]. The system boundaries are included from the silica sand mining operation to the production of silicon carbide. The process also considers electricity consumption and transports, keeping constant the distances between production factory and raw materials extraction site, as previously defined from farm to factory. On the other hand, the production system of wood pellets considers wood residue from sawmills and woodchips as raw materials. In particular, the raw materials primarily are pre-treated and dried, then comminuted and mixed, then pelletized and cooled [39]. The database system also involvesthe packaging processes for the 20% of the total product, while the 80% of the product is considered to be sold unpacked. In this case, the system boundaries for the wood pellets neglecting this process consider the whole product sold unpacked.  
Figure 1: Boundaries of the two systems for the valorization of the corn cob: (**a**) Scenario 1 for the production of corn cob pellet; (**b**) Scenario 2 for the production of corn cob grits.