The energy share of most islands is highly dependent on imported fossil fuels, which exposes them to volatile oil prices, limits economic development, and degrades local natural resources. On average, 88% of the total electricity demand in small island developing states (SIDS) is met by fossil fuels, while the remaining 12% is supplied primarily by hydropower, followed by wind energy and biomass in lower proportions [1
]. As an illustrative example, in the island countries of the Caribbean Community (CARICOM), 89.7% of the total installed electricity capacity corresponds to fossil fuel technologies and just 10.2% comes from renewables [2
]. Besides this, between the years 2000 and 2015, the average energy intensity (total energy consumption/GDP) in islands has increased by 23.4% with a corresponding emission intensity (total emissions/GDP) increase by 12.4% [3
]. This ongoing energy dependence fails to establish a precedent for global action to mitigate the long-term consequences of climate change, which pose a particularly acute threat to islands.
From 2010, the number of peer-reviewed publications about renewable energy in islands has nearly tripled, mainly because of the special attention that some intergovernmental organizations (like the Intergovernmental Panel on Climate Change) have given to island nations as they recognize islands’ vulnerability to climate change [4
Most studies have focused on variable rather than base renewable energy resources such as biomass. Surrop (2018) identified 41 studies published focused on wind, solar, and ocean-based technologies and just 12 studies about bioenergy in small island developing states (SIDS) during the 2010–2017 period [4
Studies regarding the potential use of alternative biomass feedstocks for energy production in islands are on topics as diverse as biodiesel production on Crete [5
], coconut oil electricity generation in the Pacific Islands [6
], biogas production from animal waste in Indonesia [7
], forest-waste-derived fuel with waste cooking oil in Taiwan [8
], biogas from animal manure in the Canary Islands [9
], biomass-fueled combined heat and power (CHP) in Åland Islands [10
], and perennial tree pruning biomass for electricity generation in Greece [11
]. Biomass research in Ecuador has addressed the energy potential of some residues from important agricultural commodities [12
]. In addition, liquid and gaseous biofuel potential generation has also being studied by some authors [16
There are some existing efforts in many SIDS to use biomass to contribute to the decarbonization of their energy matrixes and to reduce their dependence on imported fuels. The use of vegetable oil for electricity generation has been explored mainly by the Pacific Islands. Vanuatu has two 4 MW diesel engines on Efate (the capital) running on a mixture of 30% coconut oil and 70% petroleum, and 15% of the electricity generated comes from coconut oil [20
]. The island of Tokelau declared in 2011 its intention to become the world’s first 100% renewable country. This is to be achieved by a photovoltaic minigrid on each of the three islands which together would provide 90% of the electricity demand with the remaining 10% to come from coconut oil. Samoa also presents small-scale coconut oil utilization by its power utility [21
The feasibility of using waste cooking oil (WCO) as an alternative energy feedstock in islands has also been addressed in some research evaluating the potential of biodiesel (via recycled cooking oil) use in Singapore [22
] and feasibility of Langkawi waste cooking oil (WCO)-derived biodiesel [23
Life cycle assessment (LCA) is a quantitative methodological framework to assess the environmental performance of products and services throughout their life cycle. LCA has been used with success to assess the environmental sustainability of bioenergy systems [24
]. Existing environmental impact studies of biofuels derived from oleaginous feedstocks have mainly focused on biodiesel, such as life cycle analysis of biodiesel production [28
], comparative life cycle assessment of diesel production from crude palm oil and waste cooking oil via pyrolysis [29
], comparative life cycle assessment of alternative strategies for energy recovery from used cooking oil [30
], substitutable biodiesel feedstocks for the U.K. [31
], and the used-cooking-oil-to-biodiesel chain in Europe [32
Furthermore, some authors have studied the combustion emissions of transesterified WCO, mainly in automotive sources, such as the effects of fuel injection pressure on the performance and emissions of a diesel engine fueled with waste cooking oil biodiesel–diesel blends [33
], butyl-biodiesel production from waste cooking oil, and fuel properties and emission performance [34
], among others.
As shown, although some research has been conducted on the environmental impacts and emissions performance of oleaginous derived fuels, few authors have addressed these issues from the perspective of its straight use as a fuel (non-transesterified) in fixed sources for electricity production [35
In addition, converting waste streams such as waste edible oil into valuable resources represents a three-win solution, dealing simultaneously with human security, pollution, and energy recovery [37
]. Circular Economy (CE) is an emerging alternative concept to a traditional linear economy (make, use, dispose) in which resources are kept in use for as long as possible, extracting the maximum value from them whilst in use, and recovering and regenerating products and materials at the end of each service life [38
]. The use of waste flows as an energy source is complementary to CE principles [39
As in the case of most islands, electricity generation in the Galápagos Islands is heavily based on fossil fuels. According to its energy balance, 89% of the electricity produced in the islands comes from fossil fuels, 8.2% from wind, 2.5% from solar, and 0.1% from biofuels [40
]. According to Noboa et al. [41
], to progressively replace fossil-based energy in Ecuador, other types of non-conventional renewable technologies such as biomass (solid, liquid, and gas) must be developed.
Galápagos has endured severe environmental and economic impacts from fossil fuel spills on its marine reserve. The most serious was caused by a spill from a tanker in 2001, at San Cristóbal Island. A total of 662,447 L of diesel and fuel oil was spilt into the sea. This disaster triggered the decision to foster renewable energy implementation in the islands. In this context, “The Zero Fossil Fuels” initiative was adopted [42
]. One component of this project is a biofuel program that aims to reduce the environmental footprint attributed to fossil fuel usage through partial replacement with vegetable oils. In addition, the risks associated with fossil fuel transportation from the mainland to the islands could also be addressed. The biodegradation rate of oleaginous biofuels is 80.4%–91.2% after 30 days, while fossil diesel only reaches 24.5% biodegradation during the same period [43
]. Floreana Island is the smallest (172.29 km2
) of the inhabited islands of the Galápagos archipelago. It is located 1000 km from Continental Ecuador [44
]. Since 2010, the biofuel pilot program has operated on the island using pure Jatropha curcas
oil as an energy source in three dual electricity generators which can work indiscriminately with 100% diesel, 100% pure vegetable oil, or any proportion of blends among those. The thermoelectrical group produces 256,713 kWh per year [40
]. The current electricity generation by source in Galápagos is shown in Table 1
The biofuel program also seeks to reach other islands in the future. The estimated biofuel demand for a B20 blend (20% biofuel/80% diesel) for the San Cristobal and Isabela islands is 585,964.4 and 268,003.2 L of biofuel per year, respectively [45
In terms of electricity generation, Floreana´s biofuel pilot project has tracked the efficiency of diesel and jatropha oil in terms of kWh produced per liter of fuel: 3.43 and 2.64, respectively [40
]. Although pure jatropha oil is the current sole biofuel source for electricity generation in Floreana, just 18.7% of the total electricity is produced on the island because of the absence of a robust supply chain. Jatropha curcas
production is exclusively based on the collection of mature fruits from plants used as living fences in Manabí province, located in the coastal region of continental Ecuador; agricultural production of the plant at commercial scale is nonexistent in the country. For this reason, it is important to identify environmentally friendly alternatives to permit the permanence of the biofuel project in the islands. As seen in Table 1
, the proportions of jatropha oil and diesel are 19.6% vs. 80.4%, respectively [40
In this context, the goal of this study is to evaluate from an environmental perspective two biomass alternatives for the generation of electricity on islands: refined palm oil (RPO) and waste cooking oil (WCO). The study was developed for the Galápagos Islands due to the singularity of its ecosystem and because of its proactive policy framework aimed to explore the integration of different renewable energy sources.
3. Emissions Testing Results
The results are shown in Table 2
. These figures are consistent with data registered by Souza (2012) [52
]. To estimate the use of the cogeneration unit, the average electricity production for 15 years of life expectancy was assumed from the Ecoinvent database.
CO emissions were in lower concentration in assays performed with diesel fuel. This fact can be related to the physical properties of the fuel that show their effect during its use in an internal combustion engine [53
]. In general terms, diesel fuel has been reported to contain a larger amount of energy per mass or volume unit than vegetable oils [54
]. In addition, WCO registered a lower CO emission factor than RPO. In such a context, this issue can be associated with the chemical modification that cooking oil may suffer during its use. These changes can affect its properties, such as viscosity or calorific value, which are also relevant for determining its performance in an internal combustion engine [54
The CO emission figures registered during the experimental test are concordant with the CO2 figures as well. This issue is highlighted by the fact that the diesel appears the most efficient choice in terms of energy and that WCO showed better performance when compared to RCO. In this context, it is affirmed that WCO is a better alternative as a fuel despite being considered a waste material.
Regarding the HC content, a trend like that for CO was found. Despite diesel fuel having no oxygen content in its composition, other properties such as its viscosity (determining fuel injection and air–fuel blending inside the engine) [55
] and calorific value caused the combustion efficiency to reach results better than those of the assayed oxygenated fuels. In addition, WCO appeared to be a better fuel when compared to RPO. This can be associated with the partial hydrogenation that oils suffer during the cooking process due to their contact with water at high temperatures [56
]. Saturation implies augmented hydrogen content in the oil composition; hence, its calorific value and viscosity increase at a similar rate [57
]. The electricity generation test results show fuel consumption levels of 0.216 L/kWh for WCO, 0.328 L/kWh for RPO, and 0.162 L /kWh for diesel.
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
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
]; nevertheless, we observed some contradicting conclusions reported in other studies [108
]. 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
]. According to our results, RPO is the main contributor to GWP with 305 kg CO2
eq, from which around 40% is CH4
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. Promising research has addressed the potential of POME to generate biohydrogen and biomethane (or a mixture of these: biohythane) for energy purposes [111
]. These alternative POME utilizations could dramatically reduce the GHG footprint during the production phase. The second-largest GHG emission source identified in this study is transport (marine and road), accounting for 61 kg CO2
eq; it is important to mention that this footprint could be reduced if agricultural production areas are located closer to refining facilities and to marine ports.
In addition, N2
O contributes 42 kg CO2
eq; this GHG is commonly derived from the use of nitrogen-based fertilization and was estimated as a function of applied N, as mentioned. It is important to mention that by-products of palm oil production can also be used for fertilization: the use of 300 kg of empty FFB could be equivalent to 4.8 kg of potassium chloride (KCL), 0.25 kg diammonium hydrogen phosphate (DAP), and 10 g of borate per plant [112
In the case of WCO, the higher contributor to GWP (91% of the total) is the use of electricity from the Galápagos electricity grid which, as mentioned, is heavily reliant on fossil fuels. This footprint could be reduced if more renewable energy is integrated into the system. The second GHG source is road and marine transportation.
Regarding RPO-based electricity acidification potential, the main contributor with 1.6 kg SO2
eq is ammonia emissions derived from N fertilizer application during the agricultural production of FFB. Thus, it is important to stress the environmental benefits related to the reduction of chemical nitrogenated fertilization. The second contributor, with 20%, is NOx emission derived from the use of fossil fuels in transport and energy generation during the production process. Regarding WCO-based electricity, the main source of acidification in this study came from SO2
and NOx from the combustion of fossil fuels during electricity generation in the Galápagos grid; these impacts are relevant in sensible ecosystems such as islands. According to Glynn (2018) [113
], if CO2
emissions are not reduced, ocean warming and acidification are projected to drastically reduce or eliminate coral reefs from the Galápagos between the years of 2026 and 2035.
In RPO electricity production, chemical oxygen demand (COD) contributes 62% of the total eutrophication potential (PO4 eq); this process is linked to the high amount of oxidizable pollutants found in the wastewater from the extraction phase. In terms of abiotic depletion (ADP), 56% of the total antimony (Sb) equivalent is attributed to the use of fossil fuels in RPO production, including fuels used for input production and materials.
Considering the rich and sensible marine ecosystem of the Galápagos, the main contributor to marine ecotoxicity is wastewater from WCO cleaning with 80.6 1,4 Dichlorobenzene equivalent (1,4–DB eq). In this regard, adequate final disposal of the wastewater in this process is crucial to reducing this environmental impact.
Some of the unanswered questions and future research derived from this study are to (i) study the willingness of business owners to provide WCO in Galápagos or other islands; (ii) conduct emissions testing in conditions similar to those of the electric group located on Floreana Island; (iii) analyze the environmental impacts of WCO disposed in the sewage system in Galápagos; (iv) determine the impact of the potential energy usage of other by-products not exploited in the production cycle, such as palm kernel residues and sludges from the extraction phase; and (v) analyze the land-use change impact of productive zones with high carbon content, such as the Amazonian region.
The results of this study indicate that a system based on locally generated waste such as WCO is a superior alternative to continental RPO in environmental terms. This is mostly associated with the fact that WCO is a waste material which does not have environmental or resource impacts associated with its production and processing. The life cycle of RPO includes agricultural production, industrial processing, and transport. In addition, fewer resources are used in the in situ processing and transport of WCO compared to RPO.
Both feedstocks, RPO and WCO, independent of their production impacts, meet the conditions for being used as an energy source for non-variable electricity generation on islands. The experience of Galápagos with the direct use of vegetable oils provides valid evidence for the use of non-transesterified oleaginous feedstocks for electricity generation which can be extrapolated to other islands.
Nevertheless, further analysis should be performed to understand the flows and the current and future availability of WCO on any island that considers this as an option. It is also important to study in more detail the impacts of incorrect WCO disposal in fragile ecosystems such as islands.
Regarding RPO, it is important to include impacts related to land-use change in agricultural productive zones where deforestation is an issue.
Finally, the electricity production test shows that WCO has higher electricity yield when compared to RPO. This can be associated with the partial hydrogenation that oils suffer during the cooking process due to their contact with water at high temperatures.