Our results have proven, that although the system dynamics models, background data and results are interrelated and cannot be strictly categorized into boxes, for the integrity of the thesis the systemic discussion method was introduced. The summary of evidence will be discussed according to the scopes of the highlighted literature, with cross references included.

The methods by which the alternative fuel substitutes are implemented determine the level of applicability. Four studies in the literature were reviewed under the scope, which discuss the feasibility of biofuels in Ethiopia, Mexico, Colombia and Brazil. The level of bioethanol production in these countries diverges widely. Brazil is one of the top bioethanol producers, according to Balat et al. ^[1], while Ethiopia is behind, although it is growing rapidly.

The highlighted study published in 2016 by Demczuk and Padula ^[4] concluded that the feasibility of ethanol production could only be assured with a significant future increase in the pump price of gasoline. (Since the current government measures strongly assist the ethanol sector through incentives, there is no need for a price increase at this stage.).

The production of bioethanol has a long tradition in Brazil, enhanced by the support of the government in many ways, one being the PROALCOOL program ^[31].

One of Brazil’s approaches to increase the rate of development of biofuel production is the inclusion of family farmers in the production chain ^[31]. In order to make this feasible, an analysis of the role of stakeholders is required.

Despite (or perhaps because of) it being a rapidly developing country, Rendon-Sagardi et al. ^[12] describes the woeful results of Mexico which will bump into a fuel shortage in the future, in which domestic fuel demand will not be met even with the contribution of biofuels.

The Colombian study by Jiménez et al. ^[9] shows that the main commodity of the country’s bioethanol production is ground sugar. The study concluded that it is more profitable to use the sugar for ethanol production than to produce it for food. This might result in a shift of production that could have devastating effects on the food industry.

Ethiopia has not yet reached the potential critical thresholds of sugarcane and ethanol production and it was found that the increase in operations will have a harsh impact on the environment ^[32]. Nigatu ^[10] and Simionescu et al. ^[24] state in the highlighted literature that the quantity of ethanol consumption is highly dependent on its price difference with oil. Zenebe et al. ^[33] disputes that in the context of the existing competitive situation bioethanol production could overtake the country’s dependence on oil. Nigatu ^[10] suggests that a solution could be to find the best blending option. Patrascioiu et al. ^[34] introduces the Simplex algorithm which could be used as a validated software tool for the analysis of the optimum blending recipes.

To discuss some of the feasibility assessment opportunities, various examples are introduced to show the complexity of the system:

• In a study by Khoo ^[35], it was found that from among the bioethanol commodities of sugarcane bagasse, stover, switchgrass, rice husk and straw, the first commodity was proved to be the most sustainable because it had the smallest land footprint. erratic fluctuations in the oil

• West et al. ^[36] state that investment in cellulose-based ethanol production requires a lasting protection from erratic fluctuations in the oil and feedstock market. Investment in yield increases is the key field to sustain feasibility.

• Greenhouse gas savings seem not to have had any effect on changes in the development of the technologies ^[36].

Overall, alternative biofuel production (such as bioethanol) is a powerful tool for developing countries with available land resources to both develop agrobusiness and decrease their dependence on imports ^[37].

In the scope of food security, the main issue found among the discussions in the literature was the risk of food price rises because of increasing bioethanol production. Other worrisome factors were food supply and security, and the phenomenon of land use change ^[38].

Factors arising in the scope, which is currently extensively researched and will be more researched in the future, are sustainability and climate change ^[37].

For the worrying phenomenon of land use change, the solution of utilization of marginal or unproductive lands has been recommended by multiple studies ^[39]. Extensive farming methods and an increased use of land might result in the destruction of agricultural land, leading to wide-scale devastating consequences. The process of land use change is indicated under the scope of food security since changes in the availability of agricultural land directly influence the quality and quantity of food, as well as its price and safety for consumers.

As demand for biofuels is rising, producers are shifting towards the more productive commodities, resulting in increasing land use changes ^[40].

The highlighted study on the European Union by Papachristos and Adamides ^[15] found a scenario where increasing biofuel production has a negative effect on land availability for food crops. According to this scenario the promotion of incentives policies was discussed. This further emphasizes the interrelatedness of the scopes with each other.

In order to reduce the price of biofuels, as well as mitigating the effects changes in land use, the diversification of commodities would be helpful, since diversification reduces risk ^[41].

In the study of the system dynamics analysis of Ghana’s bioethanol market by Ansah ^[8], it was found that numerous investments were made in the field to improve its productivity. Political and economic decision makers have to pay special attention to the growth of the market to avoid any directly or indirectly caused alteration to the food market.

Warner et al. ^[42] found that for biofuels to serve approximately 25% of the global transportation demand by 2050 would require more than twice the land used to meet food demands per capita, even with the assumption of a 40% increase in food demand. These data should indicate to researchers the need to focus on research on the productivity of biofuel commodities.

Among many others, Musango ^[43] and Newes ^[44] advocate the utilization of a system dynamics approach for the application of the transition to a green economy because of the model’s transparency, its establishment of an optimization approach, the way it deals with complexity and its sectoral focus.

Shafiei et al. ^[6] states that the application of system dynamics to simulate the long-term and short-term effects of the transition to alternative fuels has the potential to provide vital policy measures. In line with the general purpose of greening of the economy, attention points need to be listed. These focus points, according to Musango ^[43], are achieving low carbon growth, developing resource efficiency and targeting pro-job development in developing countries.

By defining critical success factors, the model is guaranteed to fulfil the requirements set by Newes ^[44]. These critical success factors could include according to Newes ^[44] - the development of stakeholders’ thinking, the determining of the key leverage points and a provision of transparency in the model.

The two highlighted studies by Jonker et al. ^[7] and Jonker et al. ^[16] focused more on the land use aspect of the green economy transition. Jonker et al. ^[16] tested multiple scenarios and recommended one which described how an alternative solution for a green economy transition would be the utilization of a locally produced biomass-to-bioethanol process line. The studies emphasize the areas that need to be addressed. The first area is the improvement of feedstock availability, which could be achieved by using uncultivated marginal land as new land. This was followed by the reduction of capital costs, which means the introduction of alternative financial support. And finally, the studies introduced the factor of an incorporation of bioethanol production to invade ‘alien land’ ^[16].

Musango ^[43] concluded that the Western Cape Province of South Africa has great potential in transitioning to a green economy since several local sectors have proved that they are capable of utilizing alternatives. They focus on the fields of water management, agriculture, transportation systems, renewable energy sources, decreasing of carbon emission and other public goods and services.

The scope of incentives is in close contact with the scope of policy making, since policies enable the creation of financial support and the implementation of incentives.

Vimmerstedt and Newes ^[45] found that an increase in production of a set biofuel is more likely to be present when other incentives and economic conditions are moderately favourable for other biofuels. There are incentives present for biofuels in the USA, namely the Biomass crop assistance program, tax credits and loan guarantees ^[45]. These measures are worth considering in other countries.

The highlighted literature dealing with Colombia presents an as yet immature market. There is insufficient investment in the refining industry and in capacity building of crops, resulting in the appearance of difficulties in the transportation of the products. The model applied presented a promising future scenario if the right policies and incentives are implemented ^[17].

Not only under the scope of policy making, but regarding all aspects, the importance of policy making is ever more important in the sector, since more challenges have emerged for decision-makers in terms of biofuel production and transition, including ensuring the development of clean and safe energy sources, while equalizing the volatility effects of the market ^[40]. While the sector is continually growing in both size and complexity, according to Qudrat-Ullah ^[46] and Qudrat-Ullah ^[47] new or better tools of analysis are needed to enable decision-makers to acquire an appropriate system thinking approach.

Although it is not the task of policy makers, they have a moral obligation to take societal aspects into consideration, i.e., public opinion. The demographic data obviously need to be taken into account. A mathematical model (mixed integer linear programming) has been developed to model various aspects (including societal) within the bioethanol supply chain ^[48].

By the implementation of the right policy tools, the adoption of biofuels will give a lead in energy security, according to Papachristos and Adamides ^[15] and assist in the mitigation or even the reduction of CO₂ emissions ^[49]. Some of the models that utilize large-scale modelling have been implemented in the decision-making process debates at institutions such as the European Parliament, as noted by Fonseca et al. ^[50], which confirms the importance of model assessments.

Introduced by Bassi ^[51], a model was built to mimic the impacts of policies on the sector examined, including the factors of sustainability and other societal changes. The Threshold 21 model has an approach which includes three main factors (and their numerous sub-factors): society, economy and the environment. The model uses system dynamics methodology, using existing sector analyses and, contrary to other models, it can be calibrated to mimic each individual country’s sectoral particularities. This model is widely used around the globe, especially in countries with higher measures of bioethanol production.

Despite being top of the list for bioethanol production, according to Balat ^[3] Brazilian bioethanol production faces a rough road ahead ^[18]. As the results of Santos ^[18] and Kasperowicz et al. ^[52] regarding system dynamic modelling shows, the complexity of the system does not allow policy makers to rely on only single-factor decisions. As by Sterman ^[53] stated: ‘You can’t do just one thing’. The tools presented are worth considering to assess the decision-making processes to implement new policies.

The scope of production includes the production of four different products along the biofuel production line: two commodities (beet sugar and corn) and two approaches to biofuel production.

The reviewed study by Rozman et al. ^[21] models the production of bioethanol in the European Union (focusing mainly on Germany, Austria and Croatia) from sugar beet. The reform of the sugar industry by the European Commission ^[54] shifted the EU’s status as a massive sugar exporter to a dependent importer. This drastically changed the EU’s sugar market ^[55]. The 2017 abolition of the sugar quota has balanced the market and opened up new opportunities for businesses ^[54]. Germany being the top bioethanol producer in the European Union, the examination and modelling of the trends of production is crucial for the sector. New coordinating behaviors are required between the commodity producers and their clients in order to increase efficiency and profitability ^[56]. The investments needed in agrobusiness (including biofuel production) to develop the sector are long-term investments, hence adequate policies and supporting materials are needed to support the industry ^[57]. The role of a country’s authorities is vital and is required to consider multiple influential aspects such as the economic and environmental factors. Given the complexity of the issue, a system dynamics model approach was advocated. This made possible a simulation of the effects of the investments in the sugar industry on both an environmental and an economical level ^[57].

This is a useful tool to be considered by many parties interested in the sector, such as farmers, policy makers and business owners.

The strength of the study by ^[57] lies in the accentuation of the level of complexity of the industry. It emphasizes the importance of the decision-making parties and their influence on the system.

Kibira et al. ^[23] state that the most eligible commodity for bioethanol production in the USA is corn. On the other hand, multiple papers discuss about the increasing market of cellulosic bioethanol production ^[22]. However, for cellulose-based biofuels it is a necessity the relatively low costs, to be competitive with gasoline, a combination of factors need to be present. The presence of an abundant amount of biomass as a commodity, capital expenditure and an increase in farmgate feedstock.

Kibira et al. ^[23] also raises the risk of food price increases as long as the commodities come from feedstock for food. Numerous studies have been made to investigate how to avoid these resources. The country has the possibility to produce annually approximately 1.3 billion tons of biomass which can be used for biofuel production. This amount enables the United States of America to replace almost two thirds of its gasoline consumption ^[58]. Sheenan ^[59] suggests that the 1–1.3 billion tons of biomass production (which is used for bioethanol production) will be achievable over the next 20 years, but this is a function of the price of oil and the policies regarding the sector.

To provide an outlook for a developing country, the study of Jonker et al. ^[7] was chosen for inclusion in the list of the highlighted literature. Developing countries are proving to have the potential to produce biofuel, thus reducing their dependence on crude oil exports ^[60]. According to Musango ^[43], a collective analysis of the three main factors is needed. These factors are the society, including the population, labor, health, education, poverty, infrastructure; the economy, including investment, production, technology, government and households; and the environment, including energy, land, water, minerals, sustainability and emissions. By promoting such a transdisciplinary approach, links between science, policy business and societal aspects can be made. Musango ^[43] further emphasizes the importance of system dynamics to capture system structures and uncertainties.

Before the discussion of the scope of sustainability, it needs to be stated that there are limits to the sustainable expansion of bioenergy both in terms of scale and the rate of expansion ^[61]. Although the innovation of technology drives the development of processes and products, according to Berawi ^[62], its sustainable introduction and maintenance is inevitable for our future.

Most of the literature on the sustainability of biofuels does not include the social aspect, according to Fontes and Freires ^[63], although this factor is worthy of inclusion, especially for the implementation of policies related to sustainability ^[20]. The importance and acknowledgement of sustainable supply change management is ever-increasing, and the integration of social objectives with environmental objectives is intensifying ^[64].

Brazil has multiple areas in which to achieve improvements, since it is one of the most developed bioethanol producers in the world. One of these aspects is enabling sustainability within development processes. Various modelling approaches have been conducted for the study of this sector, one being the system dynamics approach. The two studies highlighted target this method. The strength of the highlighted study by Guevara et al. ^[26] was the analysis of the environment and the scenarios required for the recognition of causes and effects. The main characteristic of the highlighted study by Silva et al. ^[28] compared to the other similar studies, is the provision of border values within which the model needs to operate, by using design science (survey methodology).

The scope of waste management highlights the managing processes of the generated by- products and residues.

The highlighted literature presents the waste management line of the two residues derived from the cane production process: bagasse and vinasse. According to Inman ^[65], aiming to achieve a more sustainable and environmental-friendly process line, the minimization or even the elimination of the negative effects is required.

The last scope of the literature highlighted is the scope of the water footprint. The scope discusses the magnitude of the water footprint for various stations of the bioethanol process line by measuring direct and indirect water use ^[65]. With rapid population growth and the appearance of the negative effects of climate change, water supply changes are an ever-present source of stress for regions with water scarcity ^[66].

The study highlighted examines water consumption by integrating Bioethanol supply chain analysis with the Water footprint assessment ^[29]. The study used the combination of supply chain evaluation and system dynamics to be able to establish the water consumption trends of Mexico. Emergent countries (like Mexico) are expected to increase natural resource consumption in the future ^[29].

To measure the water footprint of a process line, multiple models have been made, but Inman et al. ^[65] created a model (BioSpatial H₂O) that is able to analyze water consumption by building on previous results and providing a platform for a scenario based assessment. Models like this enable researchers to provide well-founded, more secure measurement to application calculations.

Aivazidou et al. ^[67] found that it is less economically and environmentally sustainable to reuse and recycle industrial water than to utilize technological innovations in agriculture such as the precision agriculture. The changes in water consumption behaviour cause stress, since, according to a 2005 estimate, 35% of the world’s population is experiencing long-term water shortages ^[68].

To be able to provide a comprehensive answer, the complexity of the sector needs to be understood. Which bioethanol commodity is the most ideal, and how much it is worth producing or using it differs from country to country. It is desirable to develop a model (or apply existing ones, possibly by further developing them) in order for the country or region to find the appropriate base material, its cultivation parameters and the feasibility of consumption. Forrester ^[69] confirms the disappointing findings of this paper: the number of authors using system dynamics is growing more rapidly than the number of professionals who are able to use it. Since system dynamics is a useful tool in order to understand complex systems, not using it would not solve the current problems. A more thorough education system and a consistent reporting method is required. Such education could be achieved by providing training sessions on how to use the available tools. Numerous approaches have emerged in the field, and two projects about the bio-economy ‘BIOECONOMY’ and ‘BIO-CLIMATE’ have been established. Initiatives like this enable the scientific community to deepen their knowledge and help them to acquire the most up-to-date research methods. Musango ^[43] mentions that these partially conducted studies might even be more restrictive for a deeper understanding of the technologies analyzed than properly conducted ones due to their lack of integrity. Learning to apply the model in one field, leads to the discovery of new aspects in another ^[69].

Ghaderi et al. ^[70] have analysed the relation of bioethanol and biodiesel by system dynamic modelling. They advocate that the total market share of biofuels could be increased by the enhancement of oil plant production and a reduction in bioethanol production.

Kuo et al. ^[71] have analysed the role of state subsidies in the conversion to the application of a bioethanol-gasoline blend. Their results highlight the importance of the world crude oil price in the competitiveness of bioethanol. The role of bioethanol in the international CO₂ trade is relatively limited.

In our opinion, based on the literature review, a more comprehensive system for the bioethanol model could be formulated. The basic building blocks of this model can be summarised in Figure 3.

In our opinion, the models should better integrate the short- and long-term consequences of changing air quality. The model-calibrations and optimisation should take into consideration the results of dynamic system optimisation e.g., Kalman-filtering Sinopoli et al. ^[72] or Powel optimization ^[73].

The PRISMA statement appears to be a useful method to drive consistency into the systematic reporting discipline. A constructed, pre-established structure enables scientists and researchers from all fields to be able to publish without compromising through omission, or overpacking their papers. On the other hand, no structural instruction should come at the expense of elasticity; authors need to be able to appropriately express their thinking. A balance between a structural spine and a flexible scientific outlook should be established.

These measures thus have a great latent potential to offer vital policy insights ^[6]. Fritz et al. ^[37] concludes that the most powerful tool to use is case studies, especially if they are paired with a rationale and a model. These findings all have implications for future research. Research into the implementation of the combination of system dynamics and a reviewing mechanism (such as the PRISMA statement) in other fields is recommended.

Multiple preventive factors were present in the creation of this study, although there is no evidence that any of them have modified the assessment negatively. These limitations include but are not restricted to: the conscious restriction of only using literature in English, the use of a large number of references even though they might not cover the topic adequately, the fact that retrieval of the research identified was incomplete, the fact that other possible aspects of the bioethanol sector were not entirely addressed, a lack of consideration of societal aspects and the possibility of bias within and across studies.

Despite these limitations, the study seems to address a satisfactory area of the sector, allowing it to be used a springboard for further studies.