## 3 Results and Discussion
### Cassava Processing and the Utilization of Processing Residues for Biogas Production  
Figure 3 shows the environmental impacts of industrial and advanced cassava processing, including cassava cultivation and taking into consideration the credits from biogas production and utilization. Environmental impacts are expressed per kg of starch content to allow a comparison of the two main products from both production systems, i.e., cassava starch and cassava crisps. The following contribution groups are differentiated: (i) the processing of peeled cassava roots to starch and crisps, respectively, (ii) the washing and peeling of harvested cassava roots, (iii) cassava cultivation, and (iv) credits from the utilization of processing residues for biogas production and the utilization of the biogas for the generation of electricity and process heat. The total impacts of CED, DEF and GWP in the industrial scenario are 9.48 MJ/FU, 0.0001 m\({}^{2}\)/FU and 1.02 kg CO\({}_{2}\)-eq./FU, respectively. The results indicate that, in the industrial scenario, the utilization of cassava pulp and leaves for anaerobic digestion and the substitution of electricity and heat from conventional sources lead to environmental advantages in all impact categories The highest relative reductions of environmental impacts by the integration of biogas are achieved for CED, DEF and GWP with \(-\)28%, \(-\)15% and \(-\)21%, respectively. Figure 2: Environmental impacts of traditional (1) and modern (2) cassava cultivation per kg of harvested cassava root; cumulated energy demand (CED) in MJ, deforestation (DEF) in \(4\times 10^{-3}\) m\({}^{2}\), water stress index (WSI) in \(4\times 10^{-2}\) m\({}^{3}\), global warming potential (GWP) in \(4\times 10^{0}\) kg CO\({}_{2}\)-eq, ozone formation potential (OFP) in \(10^{-2}\) kg NMVOC-eq, acidification potential (AP) in \(2\times 10^{-1}\) mol H\({}^{+}\), human toxicity potential (HTP) in \(10^{-4}\) kg 1,4-DB-eq and ecotoxicity potential (ETP) in \(10^{-2}\) kg 1,4-DB-eq. In the advanced scenario, the total impacts of CED, DEF, GWP, OFP and WSI are 4.71 MJ/FU, 0.01 m\({}^{2}\)/FU, 2.6 kg CO\({}_{2}\)-eq./FU, 0.01 kg NMVOC-eq./FU and 0.01 m\({}^{3}\)/FU, respectively. The results indicate that the environmental impacts of cassava crisps can be reduced by the utilization of residues for biogas production. CED, GWP, OFP and WSI can be reduced by more than 10% with \(-\)74%, \(-\)27%, \(-\)14% and \(-\)12%, respectively. The credit for the substitution of conventional electricity and heat is the reason for these reductions of environmental impacts. The main contribution to the credit comes from electricity with 77% and 82% for CED and GWP, respectively. This is mainly due to the fact, that electricity production from hard coal has a share of 39% in the Malaysian electricity mix, while only LPG is substituted for heat. Figure 4 shows that most LCIA categories of the industrial production are dominated by the agricultural cultivation stage (72-100%). The exception is WSI, for which contributions of cultivation (27%), cassava root peeling (54%) and starch production (20%) are relevant. These results are different for the advanced production system. Here, CED, OFP, AP and ETP are also mostly driven by cultivation with 66%, 62%, 81% and 100%, respectively. On the contrary, for DEF, GWP, and HTP, crisp production has the biggest contribution to overall impacts with 98%, 65% and 94%, respectively. Especially for DEF, this result was unexpected as one would assume the cassava cultivation should be most relevant here. For all three impact categories, the high contribution to this impact is caused by a background process used in the processing, namely palm oil for frying. For DEF and GWP, deforestation and the related GHG emissions are responsible for this. In the case of HTP, it is pesticide application in palm oil production. Consequently, here, a processed agricultural product from the upstream chain has a significant influence on the overall impacts.