1 Introduction

The global energy crisis, coupled with the environmental impact of fossil fuels, has necessitated the exploration of sustainable and renewable energy sources. Bioethanol, a type of biofuel, has emerged as a promising alternative due to its potential to reduce greenhouse gas emissions and reliance on fossil fuels (Maity et al., 2014; Kim et al., 2020). Bioethanol production from renewable biomass sources, such as microalgae, offers a sustainable solution to meet the increasing energy demands while mitigating environmental concerns (John et al., 2011; Ramachandra and Hebbale, 2020). The production of bioethanol from microalgae not only addresses the energy crisis but also contributes to waste remediation and the recovery of value-added co-products (Kumar et al., 2019).

Microalgae are microscopic, photosynthetic organisms that can grow in diverse aquatic environments, including freshwater and marine systems (Peng et al., 2019). They are considered an ideal feedstock for bioethanol production due to their high growth rates, ability to accumulate significant amounts of carbohydrates, and minimal land and water requirements compared to traditional crops (Khan et al., 2018; Pal et al., 2019). Certain species of microalgae can produce ethanol directly during dark-anaerobic fermentation, making them a direct source for bioethanol production (John et al., 2011). Additionally, microalgae can be cultivated using wastewater, which not only provides nutrients for their growth but also aids in wastewater treatment (Maity et al., 2014; Kumar et al., 2019). The co-production of bioethanol and other biofuels, such as biodiesel, from microalgae further enhances the economic viability of this renewable energy source (Dasan et al., 2019; Kim et al., 2020).

This study aims to evaluate the various species of microalgae for their suitability as feedstock for bioethanol production; optimize the cultivation conditions, including nutrient availability, light intensity, and temperature, to enhance the growth rate and carbohydrate accumulation in microalgae; develop efficient pretreatment and fermentation processes to convert microalgal biomass into bioethanol and assess the economic and environmental sustainability of microalgae-based bioethanol production systems. By addressing these objectives, this study hope to contribute to the advancement of bioethanol production technologies and promote the use of microalgae as a sustainable and renewable energy source.

2 Microalgae as a Bioethanol Feedstock

2.1 Characteristics and advantages of microalgae

Microalgae have garnered significant attention as a promising feedstock for bioethanol production due to their unique characteristics and numerous advantages. These microorganisms exhibit rapid growth rates and high photosynthetic efficiency, allowing them to convert atmospheric CO₂ into valuable biomass efficiently (Figure 1) (Lee et al., 2015; Khan et al., 2018; Arcigni et al., 2019). Microalgae can accumulate substantial amounts of carbohydrates and lipids, which are essential for bioethanol and biodiesel production, respectively (Lam and Lee, 2012; Kim et al., 2014; Li et al., 2015). Additionally, microalgae can be cultivated in diverse environments, including freshwater, seawater, and wastewater, reducing the competition for arable land and fresh water resources (Tan et al., 2015; Wang and Yin, 2018; Arcigni et al., 2019). This adaptability, coupled with their ability to sequester CO₂, positions microalgae as an environmentally sustainable and economically viable option for biofuel production (Lee et al., 2015; Simas-Rodrigues et al., 2015; Khan et al., 2018).

2.2 Comparison with traditional bioethanol feedstocks

When compared to traditional bioethanol feedstocks such as corn and sugarcane, microalgae offer several distinct advantages. Traditional feedstocks often require significant amounts of arable land, fresh water, and fertilizers, which can lead to food versus fuel conflicts and environmental degradation (Lam and Lee, 2012; Arcigni et al., 2019). In contrast, microalgae can be cultivated on non-arable land and utilize brackish or wastewater, thereby mitigating these issues (Wang and Yin, 2018; Arcigni et al., 2019). Furthermore, microalgae have higher biomass productivity and can be harvested multiple times throughout the year, unlike seasonal crops like corn and sugarcane (Lee et al., 2015; Tan et al., 2015; Khan et al., 2018). This continuous production capability enhances the overall yield and efficiency of bioethanol production from microalgae. Additionally, the lipid and carbohydrate content in microalgae can be optimized through various cultivation and pretreatment methods, further improving their suitability as a bioethanol feedstock (Kim et al., 2014; Simas-Rodrigues et al., 2015).

2.3 Specific strains of microalgae with high bioethanol potential

Several strains of microalgae have been identified as having high potential for bioethanol production. Chlorella vulgaris, for instance, is known for its rapid growth and high carbohydrate content, making it a suitable candidate for bioethanol feedstock (Kim et al., 2014). Under nutrient stress conditions, such as nitrogen limitation, the carbohydrate content of C. vulgaris can be significantly increased, enhancing its bioethanol yield (Kim et al., 2014). Other promising strains include those identified in China, which have shown potential for integrated biorefinery applications, producing both bioethanol and high-value co-products (Li et al., 2015). The optimization of cultivation conditions and genetic manipulation of these strains can further enhance their bioethanol production capabilities (Li et al., 2015; Simas-Rodrigues et al., 2015). The continuous research and development in this field aim to identify and optimize microalgal strains that can provide high bioethanol yields while maintaining economic and environmental sustainability (Lee et al., 2015; Simas-Rodrigues et al., 2015; Khan et al., 2018).

In summary, microalgae present a viable and sustainable alternative to traditional bioethanol feedstocks. Their rapid growth, high carbohydrate content, and adaptability to various cultivation conditions make them an attractive option for bioethanol production. By optimizing cultivation techniques and exploring specific high-potential strains, the bioethanol yield from microalgae can be significantly enhanced, contributing to the development of a sustainable biofuel industry.

3 Biochemical Pathways for Bioethanol Production

3.1 Overview of biochemical conversion processes

The production of bioethanol from microalgae involves several biochemical conversion processes, including pretreatment, enzymatic hydrolysis, and fermentation. These processes are designed to break down the complex carbohydrates in microalgal biomass into fermentable sugars, which are then converted into ethanol by microbial fermentation. The efficiency of these processes is crucial for maximizing bioethanol yield and making the production economically viable (Ho et al., 2013; Kim et al., 2014; Hernández et al., 2015).

3.2 Enzymatic hydrolysis of microalgal biomass

Enzymatic hydrolysis is a critical step in the conversion of microalgal biomass to bioethanol. This process involves the use of specific enzymes to break down the polysaccharides in the biomass into simple sugars. Various enzymes, such as cellulases and pectinases, have been studied for their effectiveness in hydrolyzing microalgal carbohydrates. For instance, pectinase from Aspergillus aculeatus has shown a high saccharification yield of 79% after 72 hours at 50 ℃ (Kim et al., 2014). Similarly, cellulase from Trichoderma reesei has been effective in hydrolyzing Chloroccum sp., achieving a glucose yield of 64.2% under optimal conditions (Harun and Danquah, 2011). The combination of physical, chemical, and enzymatic pretreatments can further enhance the hydrolysis efficiency, as demonstrated by the combination of acid hydrolysis followed by enzymatic hydrolysis, which produced high monosaccharide concentrations in various microalgal species (Hernández et al., 2015).

3.3 Fermentation processes: yeast and bacterial fermentation

Fermentation is the process by which the fermentable sugars obtained from hydrolysis are converted into ethanol by microorganisms. Yeast, particularly Saccharomyces cerevisiae, is commonly used for this purpose due to its high ethanol tolerance and efficiency. For example, continuous immobilized yeast fermentation of microalgal hydrolysate has achieved an ethanol yield of 89% (Kim et al., 2014). Additionally, the use of simultaneous saccharification and fermentation (SSF) processes has been shown to enhance ethanol yield, with repeated-batch SSF using immobilized yeast cells achieving a bioethanol yield of 88.2% of the theoretical yield (El-Dalatony et al., 2016). Bacterial fermentation, although less common, also holds potential for bioethanol production from microalgae, particularly when combined with yeast fermentation to optimize the overall process (Shokrkar et al., 2017).

3.4 Optimization of biochemical pathways for increased yield

Optimizing the biochemical pathways involved in bioethanol production from microalgae is essential for improving yield and process efficiency. This includes optimizing pretreatment methods, enzyme selection and conditions, and fermentation processes. For instance, nutrient stress cultivation, such as nitrogen limitation, can increase the carbohydrate content of microalgae, thereby enhancing the feedstock quality for bioethanol production (Kim et al., 2014). Additionally, the use of mixed microalgae cultures and the integration of various pretreatment strategies, such as acidic and enzymatic hydrolysis, can further improve sugar extraction and ethanol yield (Shokrkar et al., 2017). Post-treatment processes, such as neutralization and electrodialysis, can also play a significant role in enhancing bioethanol yield by removing inhibitory compounds and optimizing fermentation conditions (Seon et al., 2020). Overall, a comprehensive approach that combines these optimization strategies can significantly enhance the efficiency and yield of bioethanol production from microalgae (Ho et al., 2013; Hernández et al., 2015; Hemalatha et al., 2019).

4 Cultivation Conditions for Microalgae

4.1 Factors affecting microalgal growth

Microalgal growth is influenced by several key factors including light, temperature, pH, and nutrients. Light is essential for photosynthesis, and its intensity and wavelength can significantly impact growth rates. Optimal light conditions vary among species, but generally, higher light intensities promote faster growth up to a certain threshold beyond which photoinhibition can occur (Singh and Dhar, 2011; Hossain and Mahlia, 2019). Temperature also plays a crucial role, with most microalgae thriving in a range of 20 ℃~30 ℃. Deviations from this range can lead to reduced growth rates or even cell death (Hossain and Mahlia, 2019). The pH of the culture medium affects nutrient availability and cellular processes, with most microalgae preferring a pH range of 7~8 (Hossain and Mahlia, 2019). Nutrients such as nitrogen, phosphorus, and trace elements are vital for cellular functions and biomass production. Nutrient limitation, particularly nitrogen, can induce lipid accumulation, which is beneficial for biofuel production (Yang et al., 2016; Ho et al., 2017).

4.2 Photobioreactors vs. open pond systems

Photobioreactors (PBRs) and open pond systems are the two primary cultivation systems for microalgae. PBRs are closed systems that offer better control over environmental conditions, leading to higher biomass productivity and reduced contamination risks. They can be designed in various configurations such as tubular, flat-plate, and vertical columns (Muñoz and Guieysse, 2006; Yang et al., 2016; Hossain and Mahlia, 2019). However, PBRs are generally more expensive to construct and operate compared to open pond systems. Open ponds, including raceway ponds, are simpler and cheaper but are more susceptible to contamination and environmental fluctuations (Singh and Dhar, 2011; Arcigni et al., 2019). Hybrid systems combining the advantages of both PBRs and open ponds have been proposed to optimize productivity and cost-efficiency (Singh and Dhar, 2011).

4.3 Strategies for maximizing biomass production

Several strategies can be employed to maximize biomass production in microalgal cultivation. Optimizing light distribution and intensity is crucial, as it enhances photosynthetic efficiency. Techniques such as light dilution and the use of reflective surfaces can improve light penetration in dense cultures (Doucha and Lívanský, 2009; Liu et al., 2013). Temperature control is also important, and maintaining optimal temperatures can be achieved through the use of temperature-regulated systems or selecting strains adapted to local climatic conditions (Ho et al., 2017; Hossain and Mahlia, 2019). Nutrient optimization, including the use of wastewater as a nutrient source, can reduce costs and enhance growth rates (Muñoz and Guieysse, 2006; Yang et al., 2016). Additionally, employing genetic and metabolic engineering to develop high-yielding strains can significantly boost biomass production (Singh and Dhar, 2011).

4.4 Case studies of successful cultivation practices

Several case studies highlight successful microalgal cultivation practices. For instance, the cultivation of Chlorella vulgaris and Scenedesmus obliquus in a vertical flat-plate PBR using municipal wastewater demonstrated high growth rates and efficient nutrient removal, making it a cost-effective approach for biomass production (Yang et al., 2016). Another study on the outdoor cultivation of Scenedesmus obliquus in tubular PBRs in Taiwan showed high carbohydrate productivity and CO₂ fixation rates, particularly during the summer, indicating the feasibility of year-round cultivation (Figure 2) (Ho et al., 2017). The use of an attached cultivation method, where microalgae grow on vertical surfaces, has also shown promise in achieving high biomass productivity while saving water and reducing contamination risks (Liu et al., 2013). Lastly, the use of thin-layer photobioreactors in outdoor settings has demonstrated high photosynthetic efficiency and biomass yields, even under suboptimal climatic conditions, making it a viable option for large-scale bioethanol production (Doucha and Lívanský, 2009).

5 Harvesting and Pretreatment of Microalgal Biomass

5.1 Harvesting techniques: flocculation, centrifugation, filtration

Harvesting microalgal biomass is a critical step in the production of bioethanol, as it significantly impacts the overall efficiency and cost-effectiveness of the process. Various techniques are employed to harvest microalgae, including flocculation, centrifugation, and filtration.

Flocculation is widely regarded as a cost-effective and efficient method for harvesting microalgae. It involves the aggregation of microalgal cells into larger flocs, which can then be easily separated from the culture medium. Chemical flocculants, such as chitosan, have been shown to achieve high clarification efficiency, reducing the volume to be processed by subsequent dewatering steps (Xu et al., 2013). Bioflocculation, which uses natural compounds or microorganisms to induce floc formation, is also a promising approach due to its environmental friendliness and potential for large-scale application (Wan et al., 2015; Ummalyma et al., 2017; Nguyen et al., 2019).

Centrifugation is another common method used for harvesting microalgae. It involves the use of centrifugal force to separate microalgal cells from the culture medium. While centrifugation is effective, it is often associated with high energy consumption, making it less economically viable for large-scale operations compared to flocculation (Matter et al., 2019; Wang et al., 2019).

Filtration techniques, including microfiltration and ultrafiltration, are also employed to harvest microalgae. These methods rely on the use of membranes to separate microalgal cells from the culture medium. Filtration can be effective, but it may require significant energy input and maintenance of the filtration systems, which can increase operational costs (Matter et al., 2019).

5.2 Pretreatment methods to enhance bioethanol yield

Pretreatment of microalgal biomass is essential to enhance the yield of bioethanol by breaking down the complex cell wall structures and increasing the accessibility of fermentable sugars. Various pretreatment methods have been investigated, including thermal, mechanical, chemical, and biological techniques.

Thermal pretreatment involves the application of heat to disrupt the cell walls of microalgae. Studies have shown that thermal pretreatment at relatively low temperatures (75 ℃~95 ℃) can significantly enhance the anaerobic biodegradability of microalgae, increasing methane yield by up to 70% compared to non-pretreated biomass (Passos and Ferrer, 2014).

Mechanical pretreatment methods, such as bead milling and ultrasonication, physically break down the cell walls of microalgae, improving the release of intracellular components. These methods can be effective but may require substantial energy input (Passos et al., 2014).

Chemical pretreatment involves the use of acids, alkalis, or other chemicals to solubilize the cell walls of microalgae. This method can be highly effective at increasing biomass solubilization and subsequent bioethanol yield, but it may also introduce additional costs and environmental concerns (Passos et al., 2014).

Biological pretreatment uses enzymes or microorganisms to degrade the cell walls of microalgae. This method is environmentally friendly and can be highly specific, but it may require longer processing times and careful control of conditions (Passos et al., 2014).

5.3 Comparison of pretreatment effectiveness

The effectiveness of different pretreatment methods varies depending on the specific microalgal species and the desired outcomes. Thermal pretreatment has been shown to be effective at enhancing methane yield and energy balance, making it a promising option for bioethanol production (Passos and Ferrer, 2014). Mechanical pretreatment methods, while effective, may be less economically viable due to high energy requirements (Passos et al., 2014). Chemical pretreatment can achieve high solubilization rates but may introduce additional costs and environmental concerns (Passos et al., 2014). Biological pretreatment offers an environmentally friendly alternative but may require longer processing times and careful control of conditions (Passos et al., 2014).

In conclusion, the choice of harvesting and pretreatment methods for microalgal biomass significantly impacts the efficiency and cost-effectiveness of bioethanol production. Flocculation stands out as a cost-effective and scalable harvesting technique, while thermal pretreatment shows promise for enhancing bioethanol yield. Further research and optimization of these methods are essential to realize the full potential of microalgae in bioethanol production.

6 Technological Advances in Bioethanol Production

6.1 Innovations in cultivation technologies

Recent advancements in microalgae cultivation technologies have significantly enhanced the efficiency and sustainability of bioethanol production. Heterotrophic cultivation systems, which allow for high cell densities and substantial lipid accumulation, have been identified as particularly effective for large-scale production. These systems also facilitate simultaneous wastewater treatment, making them a dual-purpose solution for biofuel production and environmental remediation (Mohan et al., 2015; Kumar et al., 2019). Additionally, the use of treated municipal wastewater as a growth medium has shown promising results, with certain microalgae strains demonstrating high growth rates and effective nutrient utilization, further reducing the costs associated with cultivation (Reyimu and Özçimen, 2017).

6.2 Advances in genetic engineering of microalgae

Genetic engineering has emerged as a powerful tool to enhance the bioethanol production capabilities of microalgae. By manipulating environmental stress responses and stress tolerance, researchers have been able to increase lipid and carbohydrate production, which are critical for bioethanol synthesis. Omics-based technologies have provided deeper insights into gene regulation under stress conditions, enabling targeted genetic modifications to improve production efficiency (Chen et al., 2017). Furthermore, synthetic biology and multi-omics integration have opened new avenues for optimizing metabolic pathways, thereby enhancing the overall yield of bioethanol and other valuable bioproducts (Chen et al., 2017).

6.3 Integrated systems for bioethanol production and wastewater treatment

The integration of bioethanol production with wastewater treatment presents a sustainable approach to resource utilization. Microalgae-based systems have been successfully employed to treat various types of wastewater, including dairy and food processing wastewater, while simultaneously producing bioethanol. These integrated systems not only reduce the environmental impact of wastewater but also provide a cost-effective medium for microalgae cultivation (Hemalatha et al., 2019; Chong et al., 2021). Membrane-integrated systems have been particularly effective, offering low-cost and eco-friendly solutions for the separation, purification, and concentration of bioethanol and other valuable by-products (Kumar et al., 2019). This approach aligns with the principles of green chemistry, promoting both high productivity and environmental sustainability (Reyimu and Özçimen, 2017). By leveraging these technological advances, the potential of microalgae in bioethanol production can be fully realized, contributing to a greener and more sustainable future.

7 Economic and Environmental Impact

7.1 Cost analysis of microalgae-based bioethanol production

The cost analysis of microalgae-based bioethanol production involves evaluating the expenses associated with the cultivation, harvesting, and processing of microalgae into bioethanol. Studies have shown that the production cost can be significantly reduced by optimizing cultivation methods, selecting appropriate algal species, and utilizing renewable energy sources. For instance, the use of autotrophic cultivated microalgae and the integration of renewable energy sources can lower production costs and environmental impacts (Zhang et al., 2022). Additionally, the use of wastewater for microalgae growth can replace synthetic cultivation mediums, further reducing costs and environmental pressures (Marangon et al., 2021).

7.2 Life cycle assessment (LCA) of microalgal bioethanol

Life cycle assessment (LCA) is a crucial tool for evaluating the environmental sustainability of microalgal bioethanol production. Several studies have conducted LCA to assess the energy balance, CO₂ emissions, and overall environmental impact of the process. For example, an LCA study in Brunei Darussalam demonstrated a favorable net energy ratio and low CO₂ emissions for industrial-scale bioethanol production from microalgae (Hossain et al., 2019). Another study highlighted the environmental benefits of using anaerobic digested wastewater for microalgae cultivation, which resulted in a positive energy conversion efficiency and reduced environmental impact (Li et al., 2020). These assessments underscore the potential of microalgal bioethanol as a sustainable alternative to fossil fuels.

7.3 Environmental benefits and challenges

Microalgae-based bioethanol production offers several environmental benefits, including the reduction of greenhouse gas emissions and the utilization of non-arable land and wastewater for cultivation. Microalgae can sequester CO₂ and produce valuable bioactive compounds, contributing to a circular bioeconomy (Porcelli et al., 2020). However, challenges remain, such as the high energy consumption during the cultivation and processing stages. For instance, the drying process of microalgae biomass can significantly impact the life cycle and environmental sustainability of the production process (Marangon et al., 2021). Addressing these challenges through technological advancements and process optimization is essential for realizing the full environmental benefits of microalgal bioethanol.

7.4 Comparison with fossil fuels and other biofuels

Microalgal bioethanol has been compared to fossil fuels and other biofuels in terms of environmental impact and sustainability. Studies have shown that microalgal bioethanol can achieve significant reductions in global warming potential and fossil energy requirements compared to conventional diesel (Adesanya et al., 2014). Additionally, the use of microalgae for bioethanol production can mitigate the environmental impacts associated with first-generation biofuels, such as land use change and food competition (Lardon et al., 2009). The integration of advanced cultivation and processing methods, such as hybrid systems and the use of renewable energy, can further enhance the sustainability of microalgal bioethanol (Aitken et al., 2014; Arcigni et al., 2019).

In conclusion, the economic and environmental impact of microalgae-based bioethanol production is promising, with potential cost reductions and significant environmental benefits. However, addressing the challenges related to energy consumption and process optimization is crucial for the sustainable development of this biofuel.

8 Challenges and Future Prospects

8.1 Technical and economic challenges in large-scale production

The large-scale production of bioethanol from microalgae faces several technical and economic challenges. One of the primary technical hurdles is optimizing the growth rate and product synthesis of microalgae. Enhancing these parameters is crucial for making the process economically viable (Khan et al., 2018; Subhash et al., 2021). Additionally, the dewatering of algae culture for biomass production and the pretreatment of biomass are significant challenges that need to be addressed to improve the efficiency of bioethanol production (Khan et al., 2018). The high energy costs associated with algae cultivation, harvesting, and processing further complicate the economic feasibility of large-scale production (Li et al., 2015). Moreover, the development of effective and economical microalgae cultivation systems, as well as efficient biomass harvesting methods, are critical for the commercial viability of microalgal biofuels (Chen et al., 2011).

8.2 Policy and regulatory considerations

Policy and regulatory frameworks play a crucial role in the development and commercialization of microalgae-based bioethanol. Government support through subsidies, tax incentives, and funding for research and development can significantly impact the growth of this industry (Tan et al., 2015). Additionally, regulations that promote the use of renewable energy sources and reduce greenhouse gas emissions can create a favorable environment for the adoption of microalgae-based biofuels (Ramachandra and Hebbale, 2020). However, stringent environmental regulations and the need for compliance with safety standards can pose challenges for the large-scale implementation of microalgae cultivation and bioethanol production (Mohan et al., 2015). Therefore, a balanced approach that encourages innovation while ensuring environmental and safety standards is essential for the sustainable development of this sector.

8.3 Future research directions and potential breakthroughs

Future research in the field of microalgae-based bioethanol production should focus on several key areas to overcome existing challenges and achieve potential breakthroughs. One promising direction is the development of two-stage cultivation strategies, which involve high biomass production under optimized conditions followed by the accumulation of biofuel compounds under stress conditions (Nagappan et al., 2019). This approach can enhance the overall productivity and economic viability of the process. Additionally, exploring heterotrophic cultivation systems that can produce high cell densities and large quantities of lipids for biodiesel production can also be beneficial (Mohan et al., 2015).

Another important area of research is the integration of biorefinery concepts, which can valorize by-products and co-products in microalgae production, thereby improving the techno-economic feasibility of the process (Markou and Nerantzis, 2013; Subhash et al., 2021). The simultaneous production of high-value compounds along with biofuels can make the overall process more economically attractive (Markou and Nerantzis, 2013; Li et al., 2015). Furthermore, advancements in photobioreactor design and the development of efficient hydrolysis and fermentation processes can significantly enhance the yield and efficiency of bioethanol production from microalgae (Chen et al., 2011; Ho et al., 2013).

In conclusion, addressing the technical and economic challenges, aligning policy and regulatory frameworks, and focusing on innovative research directions are essential for realizing the full potential of microalgae in bioethanol production. With continued efforts and advancements in these areas, microalgae-based bioethanol can become a viable and sustainable alternative to fossil fuels.

9 Concluding Remarks

Microalgae have demonstrated significant potential as a sustainable source for bioethanol production. Various studies have highlighted the advantages of microalgae, including their high photosynthetic efficiency, rapid growth rates, and ability to grow in non-arable land using brackish water, which reduces competition with food crops. The integration of microalgae cultivation with biorefinery approaches has been shown to enhance the economic viability of biofuel production by enabling the extraction of valuable co-products such as lipids, proteins, and other bioactive compounds. Additionally, stress-induced cultivation strategies and two-stage cultivation methods have been identified as effective means to boost the production of biofuel compounds, although these methods may impact overall biomass yield.

The findings from these studies suggest that microalgae could play a crucial role in the future of the bioethanol industry. The ability of microalgae to capture carbon dioxide during cultivation and convert it into biofuels and other valuable products presents a dual benefit of reducing greenhouse gas emissions and providing a renewable energy source. The co-production of bioethanol and biodiesel from microalgae, as demonstrated in studies using psychrophilic microalgae, further underscores the potential for microalgae to contribute to a diversified biofuel portfolio. However, challenges such as high energy costs associated with cultivation, harvesting, and processing need to be addressed to achieve commercial viability.

Microalgae offer a promising and sustainable alternative to traditional biofuel sources. Their ability to grow in diverse environments, coupled with the potential for high-value co-product extraction, makes them an attractive option for bioethanol production. The development of optimized cultivation and processing techniques, along with integrated biorefinery approaches, will be essential to overcoming current economic and technical barriers. As research continues to advance, microalgae could become a cornerstone of sustainable biofuel production, contributing to energy security and environmental sustainability.

Acknowledgments

We appreciate the feedback from two anonymous peer reviewers on the manuscript of this study.

Conflict of Interest Disclosure

The authors affirm that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest.

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