## 4 Results and Discussion
### Role of AM in Reducing Green Wastes
The same also applies to metal powder, which is also prone to contamination, making it difficult to recycle [99]. Also, when printing metal powder, some of it is partially melted and oxidized, and its structure and composition is altered. This further complicates the recycling process. On the other hand, the usage of biodegradable materials such as PLA, PHAs and cellulose-based materials can address most of the concerns associated with conventional AM materials. However, the biodegradability of these materials depends on specific environmental conditions such as temperature and humidity. Also, the mechanical properties of these materials are limited [98]. Hence, there is need for further studies on improving the mechanical properties while maintaining their environmental benefits. Although the AM process is energy intensive, the careful selection of the suitable additive manufacturing process to be employed based on the requirements coupled with a proper product design may result in considerable energy savings at the preprocessing, processing or post-processing stages. Furthermore, effective process design and optimization as well as proper selection of the right material that suits an intended application are necessary to optimally harness the benefits of AM. Tables 4 and 5 present the impact of AM in green and lean manufacturing, respectively, while Table 6 presents the impact of LM, AM and GM on sustainable performance. The sustainable performance shown in Table 6 uses three key indicator metrics, namely economic, social and environmental performance. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Concept** & **Impact of AM in Green Manufacturing** & **Reference** \\ \hline \multirow{4}{*}{Use of biodegradable materials.} & Products manufactured with AM using & \\  & biodegradable raw materials can decompose & [PERSON] et al. [44], \\  & naturally without negatively impacting the & [PERSON] et al. [100]. \\  & environment. & \\ \hline \multirow{4}{*}{Remanufacturing.} & AM allows for remanufacturing of worn-out & \\  & metal-based parts so that they are restored to & \\  & their original state, thus reducing the & \\  & environmental burden associated with & \\  & manufacturing new parts. & \\ \hline \multirow{4}{*}{Recycling of polymer-based products.} & AM allows for the recycling of polymer-based & \\  & products, thus reducing the quantity of plastic & \\  & waste in landfills and the environment. & \\ \hline \multirow{4}{*}{Reduction in waste through optimized designs } & The design freedom offered by AM allows for & \\  & that use less material. & \\  & compared to conventional manufacturing & \\  & technologies. & \\ \hline \multirow{4}{*}{Producing lightweight parts with less  environmental impact.} & AM allows for the manufacture of &
\begin{tabular}{c} \text{[PERSON] et al. [105], \\ [PERSON] \\ and [PERSON] [106] \\ \end{tabular}} \\  & high-performance designs that result in reduced & \\  & carbon emissions. & \\ \hline \multirow{4}{*}{Elimination of assemblies through  consolidation of parts. This reduces the  environmental impact associated with  producing fasteners.} & AM allows for the manufacture of & \\  & high-performance products that use less energy. & \\ \hline \multirow{4}{*}{Producing parts from digital models, thus  eliminating production tools. This reduces the  environmental impact of manufacturing tools.} & AM eliminates the use of tools by producing & [PERSON] et al. [1], \\  & parts directly from CAD design models. & \\ \hline \multirow{4}{*}{Eliminating the environmental burden associated with  producing parts on demand and on site.} & Producing parts on site and on demand & \\  & eliminates the need for outsourcing and & [PERSON] et al. [1] \\ \cline{1-1}  & transportation. & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Role of AM in green manufacturing.