## 6 Discussion  
As mentioned in the introduction, there is increasing interest in the research of non-variable energy sources on islands to reduce their dependency on imported fossil fuels. Some studies have been conducted regarding the use of alternative oleaginous sources for energy generation on islands; nevertheless, most of them have focused on biofuels produced through transesterification processes. Few studies have analyzed the use of alternative energy sources such as WCO in island systems. Moreover, there is a lack of research regarding the environmental impacts of electricity generation from biomass feedstocks in this type of ecosystem. In this context, our study aimed to evaluate the environmental impact of the direct use of non-transesterified feedstock options for electricity generation on islands--imported RPO vs. locally produced WCO--in addition to providing direct data on the emissions from the combustion of these two materials. According to the results, straight RPO-based electricity production accounts for a higher environmental footprint when compared to WCO in all impact categories, as presented in Figure 7.  
The impact category results presented in Table 11 are coherent in magnitude with similar studies developed for _Jatropha curcas_-based electricity generation [27]. Figure 7: Comparison of the characterization results of WCO- vs. RPO-based electricity generation in Galápagos. Abbreviations are presented in Table 11.  
As mentioned, the main strength of this study is the presentation of a full-chain LCA for both feedstocks to provide inputs to decision-makers when analyzing bioenergy options for islands, and the provision of firsthand measurement data from combustion emissions. In terms of limitations, we must mention that although the selected agricultural production area represents the average production conditions of palm oil in Ecuador, a bigger sample including other producer provinces and other land-use changes could increase the representativeness of the FFB production system in the country. Regarding emissions testing and electricity generation yield, our results are in good agreement with the literature [36; 97; 107]; nevertheless, we observed some contradicting conclusions reported in other studies [108; 109]. It is possible to get contradicting results in emissions studies because they are dependent on many variables, such as different physical conditions, experimental atmospheres, test equipment, and, especially, the combustion chamber. In this regard, one of the main weaknesses of this study is that the emissions test was performed in a 10 kW-200 rpm engine; this could result in lower efficiency and higher emissions. In addition, it is very difficult to predict the chemical composition of WCO as it is dependent on many factors like temperature, exposure to air, and cooked food composition, among others [110]. These variables can impact the performance of the final material when combusted. Another important limitation of the study is the limited number of emission measurements performed in conditions other than those of Floreana Island's electricity generation group. Regarding the LCA data and results, as mentioned, most of the existing studies analyzed transesterified fuels, which made result comparisons difficult as our study relied on straight use. Nevertheless, the calculated environmental burden reduction from WCO usage is still consistent with the literature [37; 48]. According to our results, RPO is the main contributor to GWP with 305 kg CO\({}_{2}\) eq, from which around 40% is CH\({}_{4}\) derived from wastewater produced during the production of crude palm oil. Palm Oil Mill Effluent (POME) is an underutilized liquid waste stream from palm oil mills which is generated during the palm oil extraction/decanting process and is often seen as a serious environmental issue. Nevertheless, POME could be used as a good biomethane source, which can also be used for energy production.