Microalga-Based Electricity Production: A Comprehensive Review

Abstract

This review evaluates the feasibility of using microalgal culture for sustainable energy production, emphasizing microbial fuel cells (MFCs) and biophotovoltaics (BPVs). This study’s uniqueness is rooted in its thorough examination of recent developments (2014–present) in microalgal strain selection, bioreactor design, and electrode materials. Furthermore, this review combines microalga cultivation with wastewater treatment, highlighting its importance. Notably, it examines advanced methodologies, such as the use of genetic engineering to enhance microalgal traits, nanotechnology to optimize electrode efficacy, and artificial intelligence (AI) to optimize bioelectrochemical systems. In addition, this study identifies possible future research avenues by examining microalga–bacterium consortia and cascaded biobattery systems. Consequently, the incorporation of case studies illustrating microalga biobatteries’ practical applications in low-power devices and wastewater treatment underscores the technology’s promise. Similarly, this study examines significant problems with enhancing farming methods, reconciling cost and yield, and integrating renewable energy sources with the grid, offering vital insights for academics and policymakers. Ultimately, this review emphasizes the need for economical cultivation methods, waste stream utilization, and scalable bioreactor designs, thereby considerably advancing sustainable energy options.

1. Introduction

1.1. The Imperative for Sustainable Energy Sources

The development of sustainable and renewable energy sources is a key priority in research, motivated by the pressing need to confront climate change and provide energy security. Renewable energy sources, such as solar, wind, hydropower, geothermal, and biomass, provide cleaner and more sustainable alternatives to finite fossil fuels, which greatly contribute to greenhouse gas emissions [1]. Moreover, increased use of renewable energy sources is an essential element for attaining the Paris Agreement’s objective of restricting the average global temperature increase to 1.5 °C compared to pre-industrial levels [2].

1.2. Economic and Social Benefits of Renewable Energy

The implementation of renewable energy sources offers significant economic and social benefits, in addition to environmental advantages. A collaborative assessment by the International Renewable Energy Agency (IRENA) and the International Energy Agency (IEA) forecast that increasing the proportion of renewable energy in the global electricity mix threefold by 2030 could generate as many as 24 million jobs globally [3]. This transformation could lower energy costs, improve energy stability, and foster sustainable development, especially in developing countries [4]. Furthermore, the transition to using renewable energy sources could enhance energy independence and security by diminishing dependency on imported fossil fuels, the supply of which is susceptible to geopolitical conflicts and price fluctuations [4]. The use of renewable energy sources could substantially enhance public health by reducing air pollution, which the World Health Organization predicts results in 4.2 million premature deaths globally each year. Moreover, a recent study showed a substantial decrease in the cost of electricity generated from renewable sources, such as solar and wind, in recent years. This downward trend is projected to persist, increasing the global economy’s reliance on renewable energy [5].

1.3. Microalgae as a Promising Renewable Energy Source

In renewable energy research, microalgae are being studied as a viable fuel for sustainable electricity production. This review seeks to deliver a thorough analysis of present microalga-based energy production, emphasizing recent progress, obstacles, and prospects in this developing domain. This study examines multiple facets of electricity generation using microalgae, such as cultivation and harvesting methodologies; biomass conversion techniques, including anaerobic digestion, fermentation, and gasification; and the incorporation of microalga-derived electricity production into current energy frameworks. This analysis examines the environmental and sociological impacts of microalga-based electricity generation, along with economic and policy frameworks that facilitate or obstruct its advancement.

1.4. Novelty and Future Directions

This review is novel due to its thorough analysis of existing knowledge and its recognition of the need to conduct significant research on microalga-based power production. This review integrates insights from recent studies and emphasizes innovative methodologies used for optimizing microalgal cultivation and biomass conversion processes, informing policymakers, industry stakeholders, and researchers about microalgal technology’s potential to foster a low-carbon and sustainable energy future. This review will also enhance scientific knowledge and offer actionable recommendations for future research directions to improve the practical application of microalgae in tackling global energy challenges, as economic viability improves with the declining costs of renewable technologies.

2. Microalgae as a Sustainable Energy Source

Microalgae have become a favorable source of bioenergy because of their distinct qualities, making them an appealing substitute for conventional fossil fuels. These microorganisms achieve rapid lipid accumulation, a crucial factor for biofuel production, and they release little carbon dioxide during their growth, rendering them a more ecologically sustainable energy source. Microalgae’s photosynthetic energy conversion can be harnessed to mitigate CO₂ emissions, produce valuable compounds, break down harmful substances, and extract heavy metals. For example, Cyanobacteria can annually convert around 25 gigatons of carbon dioxide into biomass globally [6]. Furthermore, microalgae can be grown with wastewater, minimizing the environmental consequences of their cultivation and improving wastewater treatment [7]. Microalgae can flourish under varied conditions, including in freshwater and saltwater, as well as under tropical conditions and at high temperatures. This adaptability makes them a versatile resource for the generation of bioenergy [8]. Photobioreactors can cultivate them, as these reactors are specifically engineered to maximize the availability of light and nutrients. This significantly increases biomass yields and rates of lipid buildup [9]. Genetic engineering has been employed to enhance the microalgal strains utilized in biofuel production, thereby increasing their capacity to synthesize lipids and other beneficial chemicals and compounds, such as carotenoids, astaxanthin, phycobiliproteins, vitamins, and phenolic acids [10,11]. Although microalgae offer numerous benefits for bioenergy production, several obstacles need to be overcome. These include the expensive nature of harvesting and processing microalgal biomass, as well as the development and enhancement of the efficiency and scalability of microalga cultivation and processing [7]. Nevertheless, microalgae possess substantial potential as a renewable source for producing bioenergy. Continuous research and development are needed address these obstacles and establish microalga-derived biofuels as a feasible substitute for conventional fossil fuels [12]. Exponential global population growth will perpetually amplify the global need for energy. The extensive utilization of fossil fuels on a global scale results in their gradual depletion owing to their unsustainable and non-renewable characteristics. Therefore, biofuels could provide a vital substitute for fossil fuels. Several developed nations are currently manufacturing biofuels on a commercial scale. Biofuels, including biodiesel and bioethanol, are highly effective alternative fuels derived from many biomass sources, such as food crops, crop residues, fruits, plant biomass, waste materials, and algae [13]. Biofuels derived from biomass have two favorable characteristics: renewability and markedly reduced environmental pollution and global warming. The combustion of fossil fuels is the primary source of greenhouse gas emissions, particularly carbon dioxide (CO₂), the primary driver of global warming. Fossil fuels emit 29 gigatons of CO₂ annually, with a cumulative total of 35.3 billion tons of CO₂ released to date. Biofuels, such as algal fuels, often have oxygen levels ranging from 10% to 45% and release less sulfur. In contrast, petroleum-based fuels lack oxygen and release high amounts of sulfur. Biofuels are environmentally friendly, readily accessible, sustainable, and dependable fuels derived from renewable sources. Microalga-based fuels are environmentally friendly, nontoxic, and have significant potential for mitigating global CO₂ emissions. According to Gendy’s study, 1 kg of algal biomass can sequester 1.83 kg of CO₂. Additionally, many species of algae utilize sulfur oxides (SOx) and nitric oxides (NOx) as nutrients in addition to CO₂ [14]. Microalgae are considered the most viable option for meeting the growing need for producing biofuels, food, animal feed, and important chemicals. Microalgae are very efficient photosynthetic organisms that can convert approximately 9–10% of solar energy (average sunlight irradiance) into biomass. The theoretical quantification of 8–10% energy conversion efficiency in microalgae suggests a maximum productivity of 280 tons of algal biomass per hectare (ha) per year, although outdoor mass culture has not yet achieved yields exceeding 100 tons per ha per year [15]. Microalgal feedstock is highly suitable for producing biofuels and can be cultivated without arable land or freshwater without impacting food chains for humans and animals. Additionally, microalgae can be grown in large quantities regardless of seasonal conditions, and they can reduce atmospheric CO₂ levels and treat wastewater. The lack of lignocellulosic components in the cell wall of microalgae simplifies the pretreatment process and reduces the overall manufacturing cost. Microalgae may utilize industrial waste for nutrition, and the energy required for their processing is lower than the energy generated by the algae [16].

3. Methods of Microalga-Based Electricity Production

According Lin et al., the production of microalga-based biobatteries is divided into two pathways: first, using live microalgae in MFCs and BPVs directly; and second, harvesting microalgal biomass for lipid extraction, as shown in Figure 1, which illustrates the biochemistry-directed synthesis process used for microalga-based biobatteries [17]. Recently, there have been notable improvements in techniques for generating energy from microalgae. These advancements include utilizing nano-additives, enzymatic hydrolysis, and anaerobic digestion. Nano-additives are particles introduced into microalgal cultures to augment their development and production. Recent research has demonstrated that using nano-additives can enhance microalgal biomass production by as much as 30% [18]. In addition, nano-additives can improve the efficiency of microalgal biofuel production by reducing the energy needed for lipid extraction and enhancing a biofuel’s overall quality [18]. Enzymatic hydrolysis utilizes enzymes to degrade microalgal biomass into its components, including lipids, proteins, and carbohydrates. This procedure can generate varied biofuels, such as biodiesel, bioethanol, and biogas. According to Shokrar et al.’s study, enzymatic hydrolysis is an energy-efficient method for producing biofuels from microalgae [19]. Another technique used for generating electricity from microalgae is anaerobic digestion, which utilizes microorganisms to decompose microalgal biomass without the presence of oxygen, producing biogas as a secondary product. Biogas can be utilized for energy generation by employing internal combustion engines or fuel cells. Çakmak and Ugurlu demonstrated that anaerobic digestion may efficiently produce biogas from microalgae with minimal energy [18]. Photovoltaic panels harness solar energy and transform it into electrical power, and microalgae can be utilized by photovoltaic panels to provide the organic matter required for fuel. A recent study demonstrated that combining microalgal cultivation with photovoltaic panels can generate power with high efficiency and minimal energy demands [20].

4. Efficiency and Environmental Impact

The effectiveness of microalga biobatteries relies on optimizing every stage of the process, ranging from the cultivation to the generation and storage of electricity.

4.1. Microalgal Cultivation Efficiency

The first stage is strain selection. Different species of microalgae display diverse growth rates, lipid contents, and electron transfer capacities. Choosing strains optimized for biofuel production is vital. Strains that produce large amounts of crops and have rapid growth rates, along with high lipid concentrations, are favored [21]. The second step involves cultivation systems: open pond systems are characterized by their simplicity and cost-effectiveness; however, they exhibit lower biomass yields and higher rates of evaporation. Enclosed photobioreactors (PBRs) enhance the regulation of environmental factors such as light, temperature, and CO₂, increasing biomass production [22]. Nevertheless, the energy expenditure required to uphold ideal conditions within PBRs can nullify the advantages. Current research is enhancing the effectiveness of PBRs by maximizing the utilization of light and ventilation systems [23]. The third stage is nutrient management. Microalgae need precise nutrients for maximum growth. Using wastewater streams as sources of nutrients can enhance sustainability and increase efficiency in resource utilization. Nevertheless, appropriate pretreatment of wastewater is vital to prevent contamination and the presence of undesirable nutrients that may impede microalgal growth [24]. The last stage is harvesting efficiency. Separating microalgal biomass from the growth medium is essential for subsequent processing. Utilizing inefficient harvesting techniques might result in substantial biomass loss, affecting overall efficiency [25]. Efforts are underway to investigate advanced harvesting methods, including flocculation, centrifugation, and filtration, to enhance efficiency and minimize energy usage in this phase.

4.2. Electricity Generation Efficiency

MFCs harness the inherent metabolic activities of microalgae. Microalgae in MFCs release electrons collected by anodes inserted into the culture medium, as they consume organic matter or utilize sunlight for photosynthesis. The electrons traverse an external circuit to move towards a cathode [25]. Nevertheless, MFCs have limited power generation capacity [26]. A recent study confirmed both that enhancing the performance of electrode materials increases the rate of electron transfer and that designing stacked MFCs increases efficiency [27]. Furthermore, direct electron transfer (DET) extracts electrons directly from microalgae during photosynthesis. By incorporating altered electrodes or conductive substances into microalgal growth, DET enables the direct transmission of electrons from the algae to the electrodes. This method could increase efficiency compared to MFCs [28]. However, the greatest obstacles lie in the development of biocompatible and efficient electrodes, as well as in achieving successful integration with microalgal cultures [29]. Recent progress in integrating biocompatible conducting polymer electrodes [30] with microfluidic chips [31] shows this approach’s potential for addressing these issues. Photosynthesis–bioelectrochemical systems (PBSs) integrate the fundamental concepts of photosynthesis with bioelectrodes. Microalgae gather light energy for photosynthesis and transmit the resulting electrons and protons to bioelectrodes, creating electricity. This strategy has potential efficiency benefits, but it requires intricate design optimization and additional development for practical implementation [32].

4.3. Biomass Conversion Efficiency

Ensuring conversion efficiency for converting microalgal biomass into a substrate that generates power is vital. Different methods, such as transesterification for biodiesel generation or thermochemical conversion for biofuel gas production, are used. Continuously researching ways to optimize conversion processes to decrease energy losses and enhance the amount of useful energy produced remains a key field of study [33].

4.4. Microalga Biobattery Integration Efficiency

Electrode design and materials like DET are crucial for the integration of biobatteries. It is essential to create electrodes that are both efficient and compatible with biological systems. To optimize electron transmission and energy storage capacity, it is essential to use advanced materials with both large surface areas and good conductivity [34]. Investigations into innovative electrode materials, such as composites made from graphene [35] and customized biocompatible polymers [36], show these materials’ potential for enhanced effectiveness and compatibility with living organisms.

4.5. Electrolyte Selection

The electrolyte used is vital in enabling the movement of ions within the biobattery. It is crucial to choose electrolytes compatible with both biological components (microalgae) and electrode materials. Research to optimize the composition of electrolytes aiming to balance ionic conductivity and biocompatibility is ongoing [34].

4.6. System Integration and Energy Management

It is essential to optimize the complete biobattery system to ensure optimal energy flow and minimize energy losses during charging and discharging cycles. This process involves the efficient control of power conversion stages and energy storage components [34].

4.7. Overall System Efficiency and Scalability

The overall efficiency of microalga-based biobatteries is determined by evaluating the energy input required at various stages (such as growing, harvesting, processing, electricity production, and biobattery operation) and comparing it to the ultimate energy output produced by the biobattery. Presently, the general efficiency is still low, impeding biobatteries’ widespread acceptance and use. One crucial factor affecting scalability is energy consumption in cultivation, as open pond systems exhibit reduced energy consumption, but have decreased biomass yields. PBRs, despite their increased yields, need substantial energy inputs to sustain optimal growing conditions. Additionally, researching energy-efficient PBR designs and alternative light sources, such as LEDs, enhances scalability [37]. Moreover, biomass processing efficiency can be greatly affected by energy-intensive processes such as lipid extraction via transesterification. Current research is developing new, more efficient ways for converting energy, as well as exploring the use of complete microalgal biomass sources for generating electricity. The intricacy of biobattery design, which encompasses the selection of electrode materials and the incorporation of microalgal cultures, can impede our ability to scale up the system. Further investigation into simpler and more economical biobattery designs is crucial.

4.8. Environmental Impact Considerations

Conducting a life-cycle assessment of the environmental impact of microalgae is essential, notwithstanding their potential as a renewable and sustainable biofuel source. Important factors include land and water use, greenhouse gas emissions, and nutrient management. Land and water resources can be affected by cultivation systems: open ponds require a substantial amount of land, whereas PBRs necessitate a smaller area, but consume a greater quantity of water. Implementing water conservation techniques, such as using wastewater treatment and closed-loop systems, can effectively reduce negative effects on the environment [24]. For greenhouse gas emissions, the cultivation of microalgae can reduce CO₂ levels by using atmospheric CO₂ for their growth, thereby contributing to CO₂ sequestration. Nevertheless, reduced carbon emissions from transportation may be nullified by the energy consumed during cultivation and processing. Maximizing energy efficiency and harnessing renewable energy sources for cultivation are crucial. Nutrient management is crucial to prevent environmental pollution caused by excessive nutrient leaching into nearby ecosystems. Implementing closed-loop systems and harnessing wastewater streams as a source of nutrients can effectively reduce the process’s environmental footprint [24].

5. Current Research and Innovations

Microalgae possess numerous advantages compared to conventional feedstocks for use in battery materials, such as their rapid growth rate, adaptability to diverse settings, and potential for biofuel generation. Research has demonstrated that microalgae can generate more energy per unit of land compared to conventional crops, rendering them a compelling choice for extensive energy production [20]. An important focus of research in microalga-based batteries is the advancement of electrode materials obtained from microalgal biomass. Figure 2 illustrates the key steps involved in producing a biobattery using microalgae as the source material. Scientists have investigated different methods for transforming microalgal biomass into electrode materials with excellent performance. These methods include pyrolysis, hydrothermal carbonization, and chemical activation [9]. These procedures can manufacture carbon materials with a porous structure, large surface area, and high conductivity. These materials are well suited to serving as electrode materials in batteries. For example, a recent investigation conducted by Wang et al. (2024) showcased the application of carbon generated from microalgae as an anode substance in lithium-ion batteries. They employed hydrothermal carbonization to transform microalgal biomass into porous carbon, which was subsequently utilized to produce lithium-ion battery anodes. The anodes demonstrated high capacity, favorable rate performance, and exceptional cycling stability, maintaining 91.4% of their capacity after 100 cycles [38]. Furthermore, researchers previously investigated the potential for utilizing materials obtained from microalgae as separators and electrolytes in batteries, in addition to electrode materials. They studied alga-derived biopolymers, specifically alginate and carrageenan, to determine their suitability as separator materials in lithium-ion batteries. These biopolymers can create flexible and porous membranes, while also exhibiting excellent ionic conductivity and strong mechanical characteristics [39]. Microalga-derived materials have previously been investigated as potential solid electrolytes for batteries. One example is the utilization of gellan gum, a biopolymer obtained from microalgae, as a solid electrolyte in sodium-ion and proton batteries. Gellan gum, when mixed with sodium perchlorate (NaClO₄) or ammonium thiocyanate (NH₄SCN), can create solid electrolytes with high ionic conductivity and excellent electrochemical stability [39]. Another field of study in microalga-based batteries combines microalgal cultivation with photovoltaic panels to store energy. This method uses photovoltaic panels to generate electricity for microalgal growth, which can then be utilized as a raw material to create battery materials or biofuels [20]. In a study conducted by Morales et al. (2019), the possible environmental consequences and energy equilibrium of combining microalgal cultivation with photovoltaic panels were examined. They discovered that employing this strategy can substantially decrease greenhouse gas emissions and energy usage when compared to conventional microalgal growth techniques [20]. They analyzed three specific factors related to microalga production: potential environmental effects, energy equilibrium, and carbon equilibrium. Combining microalga production with photovoltaic panels significantly decreased greenhouse gas emissions, achieving an 80% reduction compared to conventional microalgal cultivation techniques. Furthermore, the energy balance study demonstrated that this method can result in a surplus of energy, as the energy generated by the photovoltaic panels surpassed the energy needed for microalga growing and processing [20]. Although the results are promising, the researchers also discovered other problems that need to be resolved to apply this strategy, such as the exorbitant cost of solar panels and the requirement for additional investigations to enhance their effectiveness and expandability. In addition, the researchers observed that microalga-based batteries currently have poorer performance compared to typical lithium-ion batteries. Further investigation is required to enhance their energy density and cycle life [20].

6. Case Studies and Applications

Based on current policy and market conditions, it is projected that worldwide renewable energy capacity will reach 7300 GW by 2028 and increase to 2.5 times its current level by 2030. However, the G20 countries currently have about 90% of the world’s renewable power capacity. In an expedited scenario, assuming that the G20 countries implement existing policies and ambitions more effectively, their combined installed capacity may triple by 2030 [3]. According to a report issued by the International Energy Agency in 2023, spot prices for solar PV modules experienced an almost 50% decrease compared to the previous year, while manufacturing capacity increased to three times the levels seen in 2021. Based on the present building of production facilities, the global supply of solar PV will reach 1100 GW by the end of 2024. This potential output is estimated to be three times higher than the currently forecast demand. In 2023, the increase in renewable electricity capacity was around 507 GW, nearly 50% greater than in the previous year. This growth was facilitated by ongoing policy support in over 130 nations. Causing a substantial shift in the worldwide growth trajectory, global growth in 2023 was mostly fueled by significant growth in the solar PV (+116%) and wind (+66%) markets in the People’s Republic of China. The next five years will see a significant increase in renewable power capacity, mostly driven by solar photovoltaic (PV) and wind energy [3]. These two sources will account for an unprecedented 96% of total energy capacity added due to their lower generation costs compared to both fossil fuel and non-fossil fuel alternatives in most countries. Furthermore, supportive policies are expected to continue promoting the growth of solar PV and wind energy. By 2028, the capacity for generating renewable power will reach around 40,400 TWh, representing a growth rate of nearly 70% compared to 2022. Over the following five years, several significant milestones in renewable energy could be reached [3]. Figure 3 differentiates renewable electricity capacity additions by technology and segment. A review reported that many studies have investigated the capacity of microalga biobatteries [38]. Microalga-based biobatteries show great potential for use in wearable devices. Scientists have created flexible solid electrolytes using κ-carrageenan and NH₄Cl, which exhibit excellent ionic conductivity and electrochemical stability [38]. These electrolytes have been utilized to fabricate biobatteries for providing prolonged power to wearable devices, such as smartwatches and fitness trackers. In 2020, Perumal and Selvin successfully created flexible solid electrolytes using κ-carrageenan and NH₄COOH [40]. These electrolytes exhibited excellent ionic conductivity and electrochemical stability. The electrolytes were utilized to develop biobatteries for providing long-lasting power to wearable devices, such as smartwatches and fitness trackers. The utilization of these electrolytes in wearable devices represents a viable and ecologically conscious substitute for conventional battery technology [38]. Microalga-based biobatteries have demonstrated substantial promise in medical devices. Researchers have created alginate hydrogels and carrageenan-based wound dressings that may provide bioactive molecules and enhance wound healing [38]. Microalgae can power these biobatteries, which offer a sustainable energy solution for medical devices. Furthermore, research has been conducted on the utilization of microalga-based biobatteries in biofuel manufacturing, where scientists have created microalgal biofuels utilized to fuel automobiles and various other applications. These biofuels are generated by fermenting microalgae, which may be cultivated on ground not suitable for farming and have low requirements for water and nutrients [41]. Moreover, researchers have devised novel techniques that use nanotechnology for cultivating microalgae, enhancing their growth rates and biomass generation and creating novel materials and designs for biobatteries, resulting in enhanced performance and longevity [42]. Nanotechnology has been utilized to improve the performance of microalga-based biobatteries, which is a notable advancement. Scientists have created nanoparticles that enhance the conductivity and stability of biobatteries. Nanomaterials can produce biobatteries that exhibit superior efficiency and sustainability compared to conventional batteries [43]. Scientists at the University of California, Riverside, USA, employed the green alga Chlamydomonas reinhardtii in a biobattery configuration that produced enough electricity to operate low-power devices such as environmental sensors [44]. The study utilized a dual-chambered system, as follows. (A) Anode chamber. The chamber in an electrochemical cell where oxidation occurs at the anode, releasing electrons. The C. reinhardtii culture was stored in this compartment. In this scenario, the algae performed photosynthesis and sent electrons to the anode using a mediator called 2,6-dichloro-3-phenoxyacetic acid (DCP). (B) Cathode chamber. Within this chamber, there was a potassium ferricyanide solution that served as the electron acceptor at the cathode, thereby allowing the circuit to be completed. The study successfully attained a maximum power density of 23 mW/m², thereby confirming the viability of utilizing microalga biobatteries to supply energy for small electronic devices [44]. A study conducted in 2021 and published in the Journal of Water Process Engineering examined the application of a diverse microalgal community for both wastewater treatment and power production [45]. The consortium comprised a diverse array of microalgal species, in addition to exoelectrogenic bacteria. The experiment employed a single-chamber MFC design that included mixed-culture consortia, as well as anode and cathode electrodes. The microalgae were cultivated using wastewater as the growth medium, while the organic matter in the wastewater served as the substrate for generating energy [45]. The consortium of exoelectrogenic bacteria allowed for the decomposition of organic debris and the transport of electrons to the anode. The case study yielded favorable outcomes, as the mixed-culture consortium efficiently eliminated organic contaminants, such as chemical oxygen demand (COD), from the effluent. Furthermore, the biobattery exhibited a peak power density of 115 mW/m³, indicating its capability to treat wastewater while simultaneously generating electricity [45]. In another study, researchers investigated the application of the marine microalga Tetraselmis suecica for bioremediation and power production in a two-chambered MFC system. The study examined T. suecica’s capacity to eliminate contaminants such as nitrate and phosphate from saltwater while concurrently producing energy. The MFC attained a peak power density of 27 mW/m³, indicating the possibility of combining bioremediation with power generation in maritime environments [46]. Another study conducted in the last 5 years introduced an innovative air–cathode MFC design that utilizes C. reinhardtii. This design obviates the need for a distinct oxygen supply in the cathode chamber, thereby diminishing complexity and costs. The MFC attained a peak power density of 54 mW/m³ while concurrently generating hydrogen gas via a biological process incorporated into the system. This case study demonstrates biobatteries’ capacity to integrate energy generation with the creation of valuable biofuels such as hydrogen [47]. The utilization of microalga–bacterium consortia in the creation of biobatteries was investigated for its potential to harness the combined benefits of microalgae and bacteria through synergistic actions [48]. Microalgae supply the organic material necessary for bacterial respiration via photosynthesis or by releasing exudates. Bacteria, specifically exoelectrogenic species, promote effective electron transport to the anode, improving biobattery performance. In 2021, a study introduced a new model called a microalga–bacterium consortium (ABACO), consisting of microalgae and bacteria working together. This model improves the performances of biobatteries by optimizing the interaction between microalgae and bacteria. The study illustrated that ABACO can increase biobattery systems’ efficiency by up to 30% in comparison to conventional single-culture systems [48]. In 2021, Fallahi et al. conducted a study that explored the use of microalga–bacterium consortia to improve the performances of biobatteries [49]. The authors provided evidence that the utilization of consortia can enhance biobattery efficiency by up to 25% in comparison to conventional single-culture systems. Additionally, they explored the possible uses of microalga–bacterium consortia in biobattery systems [49]. The study showcased the capability of microalga–bacterium consortia to improve biobattery performance and emphasized the need for additional research to address the obstacles and restrictions of existing biobattery systems.

6.1. Bioelectricity Investments: Global Examples

Investment is necessary at different stages for the development and commercialization of microalga biobatteries. Stakeholders can greatly support the development of this technology by focusing on early-stage development and research and development (R&D) [50]. This sector revolves around ongoing R&D endeavors for enhancing microalgal strains to generate electricity focusing on strain selection and engineering. The aim of this R&D is to identify and characterize microalgal strains that exhibit high electron transfer efficiency and strong growth properties under regulated conditions. Genetic engineering methods can be used to further improve these characteristics [51]. One such method is bioreactor design and optimization, used for creating effective and scalable bioreactor systems that enhance microalgal growth, optimize light utilization, and enable efficient metabolite extraction [52]. Another method is electrode material development, used for the investigation of innovative electrode materials for efficiently capturing electrons from microalgae and enhancing the overall performance of biobatteries. Universities that have robust biotechnology or bioengineering programs, in addition to receiving research grants from government entities such as the US Department of Energy or the European Union Horizon 2020 program, are significant funders of these initial research and development projects [53]. Beyond the laboratory, pilot projects are crucial for evaluating the practicality and expandability of microalga biobatteries in real-life environments. This type of project necessitates financial investment in pilot plant construction and involves the construction of facilities used to demonstrate the technological feasibility of cultivating microalgae, extracting biofuel, and fabricating biobatteries on a larger scale. Another method is process optimization, used to enhance and streamline the complete process sequence, starting from cultivation and extending to biobattery assembly, by utilizing data gathered from pilot projects. Thorough cost analyses and life-cycle assessments (LCAs) are conducted to examine the economic feasibility and environmental consequences of producing microalga biobatteries [54]. Cleantech businesses that specialize in microalga biofuels and venture capital firms focusing on sustainable technologies can play significant roles in assisting the development of pilot projects [55].

Table 1. Potential investment areas in global bioelectricity generation (microalga-powered biobatteries).

Investment Focus	Description	Example Companies/Institutions	Citations
Early-Stage Research and Development	Funding research into the optimization of microalgal strains for electricity generation, improving bioreactor design for efficient growth, and developing novel electrode materials from microalgal extracts.	Universities (e.g., Wageningen University, Arizona State University) and government research grants (e.g., US Department of Energy, European Union Horizon 2020 program).	[56,57]
Pilot Project Development	Supporting pilot projects testing the feasibility and scalability of microalga-powered biobatteries in real-world settings.	Cleantech startups (e.g., JouleBug(Raleigh, US), PhycoBloom (London, UK)) and venture capital firms (e.g., SOSV Chinaccelerator (Shanghai, China)).	[58,59]
Strategic Partnerships	Collaboration between energy companies, biotechnology firms, and research institutions to accelerate technology development and commercialization.	Established energy companies (e.g., Shell (Coventry, UK), Enel Green Power (Rome, Italy)), biorefinery companies (e.g., Green Plains Inc. (Omaha, NE, USA), Neste (Espoo, Finland)), and national laboratories (e.g., National Renewable Energy Laboratory (Denver, CO, USA), Forschungszentrum Jülich (Jülich, Germany)).	[60,61]
Technology Acquisition and Integration	Investments in companies developing microalga processing technologies or biobattery components that can be integrated with microalga-derived materials.	Material science companies (e.g., Covion (Newcastle, UK), BASF (Ludwigshafen, Germany)) and battery technology companies (e.g., Samsung SDI (Yongin-si, South Korea), LG Chem (Seoul, South Korea)).	[62,63]
Manufacturing and Supply Chain Development	Investments in building infrastructure and establishing robust supply chains for the large-scale production of microalga-based biobatteries.	Engineering firms specializing in biorefinery design, logistics companies, and government incentives for sustainable manufacturing.	[64,65]
Market Development and Consumer Awareness	Funding initiatives to raise awareness of microalga biobatteries and promote consumer adoption.	Sustainability advocacy groups, clean energy marketing agencies, and government subsidies for renewable-energy solutions.	[66,67]

presents a thorough summary of prospective investment prospects at different phases of development in the microalga-powered biobattery industry. It identifies crucial areas in need of financial support, providing specific instances of corporations and institutions engaged in each phase.

6.2. Local Approaches for Bioelectricity Production: Saudi Arabia

Saudi Arabia, a country abundant in petroleum reserves, is actively diversifying its energy portfolio and transitioning towards a more sustainable future. Generating bioelectricity by utilizing renewable resources to produce electricity shows great potential. Microalga-powered biobatteries have significant potential in this field because they can efficiently generate clean energy while also capturing carbon. Nevertheless, there are a lack of detailed data regarding specific local investments made in this technology in Saudi Arabia. Although there are difficulties, Saudi Arabia offers a favorable setting for microalga biobatteries. This technology benefits from the nation’s ample sunlight and its emphasis on diversifying its energy sources, making it an advantageous choice. Government efforts that support and encourage research and development in renewable energy could be significant in attracting investments and facilitating cooperation between local universities and foreign research groups. King Abdullah University of Science and Technology (KAUST), an esteemed institution renowned for its emphasis on cutting-edge technologies, could make significant contributions to the development of microalga biofuels and bioelectrochemical systems. Moreover, it is worth exploring the ongoing projects or plans of the Saudi Arabian National Centre for Biotechnology (SANCEST) in the field of microalga biofuels.

Table 2. Local investments in bioelectricity generation in Saudi Arabia.

Year	Investment	Description	Citation
2020	Eco-tourism camps with solar energy systems	A proposed design for an eco-tourism camp in Taif, Saudi Arabia, with solar energy systems used for lighting and power generation.	[68]
2023	Wind resource assessment	A wind resources assessment of Jubail Industrial City, Saudi Arabia, for industrial and commercial applications.	[69]
2023	Renewable energy development strategies	A study on selecting appropriate renewable-energy development strategies for Saudi Arabia, including solar, wind, biomass, hydroelectric, and geothermal energy.	[70]
2016	Distributed photovoltaic generation	A study on making distributed photovoltaic generation attractive for households in Saudi Arabia, including grid-connected PV systems.	[71]
2023	Optimizing residential solar PV systems	A study on optimizing residential solar PV systems via net-metering approaches, including energy storage and microgrid applications.	[72]
2016	Alga biorefinery	The development of an alga biorefinery in Saudi Arabia to produce bioenergy and bioproducts via wastewater treatment.	[73]
2024	Renewable energy integration	Optimizing renewable energy integration through innovative hybrid microgrid design, including solar photovoltaic (PV) panels, a battery storage system (BSS), and a diesel generator (DG).	[74]

provides a concise overview of the investments made in bioelectricity generation in Saudi Arabia, with a specific focus on microalga-powered biobattery utilization. The table provides the year of investment, the type of investment, a concise description, and a citation for each entry.

7. Challenges and Limitations

A major obstacle to the production of electrical energy using microalgae is the exorbitant cost associated with cultivating and processing microalgae. The cost of cultivating microalgae is determined by several factors, such as the specific microalgal species employed, the cultivation technique used, and the scale of production. Chisti (2007) conducted a study that revealed that the cost of cultivating microalgae might vary between USD 0.50 and USD 5.00 per kilogram depending on the specific species and cultivation technique employed. Microalga-based electrical energy production is hindered by the restricted capacity to scale up microalgal growth [22]. Microalgae can be grown under several conditions, such as wastewater and brackish water. However, the expansion of microalga farming is restricted by the lack of ideal places for cultivation and the high cost of large-scale growth. Furthermore, the efficiency of microalga-based fuel cells limits the production of electrical energy from microalgae. The electrical energy generation capacity of microalga-based fuel cells is constrained by the microalga-based biofuel production process’s efficiency. Another significant obstacle lies is the high cost of cultivating and processing microalgae, rendering the manufacturing of battery components from microalgal biomass commercially impractical. To resolve this issue, scientists are investigating many approaches to enhance the effectiveness and expand the capacity of microalga production. These approaches include utilizing sophisticated bioreactor designs, optimizing growing conditions, and genetically modifying microalgal strains. In addition, scientists are investigating the utilization of other industries’ waste streams and byproducts as raw materials for microalgal growth. This approach could lower manufacturing costs [12]. The use of microalgal photosynthetic CO₂ fixation is constrained by the cells’ stability and reusability. Su and his colleagues initially encapsulated cyanobacterial cells within a porous silica framework to improve the cells’ long-term viability, creating a photosynthetic biosystem for effectively fixing and assimilating CO₂ [75]. The immobilization process uses acidifying aqueous colloidal silica precursors. The immobilization of cyanobacteria formed substantial cavities surrounding the cells, potentially facilitating cell division. Therefore, the presence of microvoids within the mesoporous material makes it highly suitable for cell retention. The immobilized cyanobacterial cells were capable of autofluorescence for 12 weeks, suggesting that chlorophyll A within the immobilized cells remained stable for a long period and that the cells could still undergo photosynthesis [75]. Moreover, the utilization of radio-labeled NaH₁₄CO₃ demonstrated that the cyanobacterial cells consistently converted CO₂ into organic compounds within the silica gel. The use of silica gel to immobilize cyanobacteria was an innovative approach for creating microalga–material hybrids for converting photosynthetic energy. This breakthrough enhanced photosynthetic CO₂ fixation. Cell immobilization using porous silica gel is a viable technique for storing microalgae cells. This is because silica material is both compatible with cells and transparent, enhancing photosynthetic CO₂ fixation by increasing cell stability and lifespan. Nevertheless, the photosynthetic activities and proliferation capability are inherently constrained when compared to the cells’ natural form [75]. Ultraviolet (UV) radiation is a major factor that hinders the growth of microalgae when exposed to sunlight. Its biological effects mostly produce reactive oxygen species (ROS) [76]. Silica hydrogels containing CeO₂ nanoparticles were utilized as UV-shielding structures to immobilize Chlorella vulgaris cells for extended periods [77]. In addition, a simplified method was created to create a protective CeO₂ outer layer for Chlorella cells. This was achieved by directly attaching CeO₂ nanoparticles to the cells, effectively shielding them against oxidative stress caused by UV radiation. Furthermore, the incorporation of a SiO₂–TiO₂ composite shell enhanced photosynthetic activity by alleviating thermal stress [78]. At present, microalga–material hybrids (MMHs) primarily enhance photosynthetic carbon fixation by increasing resilience to environmental challenges. Due to its exceptional biocompatibility and clarity, silica is most frequently utilized. Nevertheless, more verification is required to determine the applicability of the silica-based cell immobilization approach to all microalgal species. It is important to mention that using silica-based cell immobilization or shellization can improve the activity and stability of microalgae. However, it is challenging to give microalgae functions that they do not naturally possess. A hybrid of microalgae and silica can expand the habitat of algae from lakes and oceans to terrestrial environments. This hybrid shows potential for controlling desertification and exploring remote wilderness areas in the future. While the current construction methods are not appropriate for large-scale use in achieving carbon neutrality, microalga–material interface technology can be valuable in certain specific situations where cost is not the primary concern [75].

8. Future Perspectives and Recommendations

8.1. Emerging Trends in Microalga-Based Biobatteries

The increasing need for environmentally friendly and renewable energy sources requires a transition away from conventional fossil fuels. Biobatteries, which harness biological mechanisms to produce electrical energy, represent a promising future pathway. Microalga-based biobatteries are particularly promising due to their distinct characteristics. Microalgae are small photosynthetic organisms that transform sunlight and carbon dioxide into biomass. Biomass can be utilized to develop bioelectrochemical systems that produce electricity via diverse biological mechanisms. Various trends and advancements are influencing the future development of microalga biobatteries. Genetic engineering methods offer the potential for developing microalgal strains that have increased photosynthetic efficiency, stronger electron transfer capacities, and greater resistance to environmental factors [79]. As a result, a variant with an enhanced ability to convert sunlight into energy through photosynthesis and higher production of organic matter can be obtained. This can substantially enhance the power generation and overall performance of a biobattery. Recent research has shown the capacity of genetic engineering to be utilized in microalga biobatteries. An example of this is a research article published in Frontiers in Bioengineering and Biotechnology in 2024, where CRISPR/Cas9 technology was employed to modify the genetic material of the microalga C. reinhardtii [80]. This modification generated a strain that exhibited higher biomass productivity and enhanced photosynthetic efficiency. In 2024, in a study published in Microalgae Biofuels, researchers employed genetic engineering techniques to augment the light-absorbing ability of Picochlorum celeri [9].

8.2. Nanotechnology and AI Applications

Nanotechnology applications such as the incorporation of nanoparticles into biobattery designs can provide several advantages, including greater electrode performance, improved light absorption by microalgae, and heightened biocompatibility [81]. Recent studies have shown that nanoparticles can significantly improve the power output and efficiency of biobatteries. An example of this is a study published in Bioresource Technology in 2024, which utilized nanoparticles to improve microalgae’s ability to absorb light in a biobattery design that notably increased the amount of power produced [82]. A separate study conducted in 2021 and published in Biomass and Bioenergy employed gold nanoparticle-laced carbon fiber electrodes to significantly improve the bioelectrocatalytic activity and power generation ability of compost-based microbial fuel cells [83]. Nanoparticles can improve the biocompatibility of biobatteries, which is essential for their safe and efficient application in biological systems. An example of this is a research report published in Batteries in 2023, where nanoparticles were employed to augment the ability of a biobattery to interact with living organisms, notably decreasing harmful effects [84]. Furthermore, the utilization of nanoparticles in biobatteries offers improved scalability and manufacturability, in addition to the benefits. An example of this method is mentioned in a research article published in Molecules in 2023, where nanoparticles were employed to augment the scalability of a biobattery, notably increasing manufacturing capacity [85]. The use of artificial intelligence (AI) and machine learning (ML) algorithms has fundamentally transformed microalga production and enhanced the efficiency of biobattery performance. By utilizing AI and ML techniques, it is feasible to improve the conditions for growing microalgae, predict the efficiency of biobatteries, and accelerate the development of self-regulating bioelectrochemical systems [86]. A recent study has shown the capacity of AI and ML to support the growth of microalgae, as published in Bioresource Technology in 2024, where machine learning algorithms were employed to forecast the growth rate of microalgae, achieving a correlation coefficient of 88% [87]. In 2024, a study utilized AI to enhance the growth environment for microalgae, notably increasing biomass production [88]. Furthermore, AI and ML have been employed to predict the efficiency of biobatteries, in addition to their application in microalgal culture. An example of this is a research article published in 2023, stating that the use of a dual-polarization (DP) or Thevenin ECM for thermal modeling of lithium-ion batteries, considering all parameter dependencies except for charge/discharge current dependency, improved heat generation predictions by up to 9% (current) or 22% (hysteresis) [89]. Furthermore, another study utilized AI to enhance the design of biobatteries, notably increasing energy density [90]. AI and ML have been utilized to accelerate the advancement of self-regulating bioelectrochemical systems, as mentioned in a study published in Current Opinion in Electrochemistry in 2024. The study utilized machine learning algorithms to enhance the performances of bioelectrochemical systems, notably improving efficiency [91]. In 2024, a study used AI to forecast the effectiveness of bioelectrochemical systems, achieving a correlation coefficient of 92% [92].

8.3. Future Directions and Challenges

Microbial consortia are being studied to investigate the possible improvement of biobattery efficiency, employing a combination of microalgae and bacteria, where the bacteria help to move electrons from the microalgae to the electrodes. Cascaded biobattery systems are a potential future development connecting numerous bioreactors containing different microalgal strains in series or parallel to increase power outputs [93]. Recent research, which was mentioned in Front. Bioeng. Biotechnology in 2024, has shown that microbial consortia can improve the efficiency of biobatteries by utilizing a combination of microalgae and bacteria to enhance the power output of a biobattery, resulting in a substantial improvement in efficiency [94]. Cascaded biobattery systems are a prospective advancement linking multiple bioreactors holding diverse microalgal strains in a series or parallel arrangement to provide enhanced power outputs. This technique has demonstrated efficacy in augmenting biobattery efficiency. A study published in 2024 employed a cascaded biobattery system to notably increase power production, resulting in a power density of 1.2 W/m² [95]. To address the obstacles and constraints hindering the advancement of microalga-based biobatteries and electricity generation, numerous suggestions might be put forward. First, we could allocate funds towards research and development; therefore, additional investigation and advancement are required to enhance the scalability and efficiency of microalga production and conversion procedures. This could be accomplished by using novel culture techniques, such as photobioreactors and open pond systems, and investigating innovative conversion methods, such as biochemical conversion and thermochemical conversion. Second, we could advance technological innovations: the enhancement of efficiency and sustainability in microalga-based biobatteries and power production requires the development of novel technologies, such as enhanced bioreactors and biofuels. These technologies may encompass sophisticated bioreactors for enhancing the productivity and effectiveness of microalga production and biofuels that can augment the energy density and sustainability of microalga-derived biofuels. Third, we could enhance the conversion process: this is a crucial stage in the manufacturing of biofuels derived from microalgae. To enhance the conversion process, researchers could investigate novel conversion techniques, such as biochemical and thermochemical conversion, which can potentially enhance processes’ efficiency and sustainability. Fourth, we could expand market reach: the commercialization of microalga-based biobatteries and electricity production requires the development of new markets. This could be accomplished by creating innovative uses, such as biofuels for transportation and electricity generation, and by exploring emerging markets, such as aerospace and defense. Finally, we could tackle the difficulties associated with scalability: the ability to scale up microalgal growth is a crucial obstacle that needs to be overcome to advance microalga-based biobatteries and electricity production. To tackle this difficulty, researchers could investigate novel growing techniques, such as photobioreactors and open pond systems, which could enhance the productivity and effectiveness of microalga production.

9. Conclusions

This comprehensive review assessed the viability of using microalgae as a sustainable source for power production. This investigation analyzed different bioelectrochemical systems, including microbial fuel cells (MFCs) and biophotovoltaics (BPVs), emphasizing their distinct benefits and existing constraints. Notable advancements in improving efficiency and minimizing environmental effect were achieved, focusing on the optimization of microalgal strain selection, bioreactor design, and electrode materials. Combining microalga production with wastewater treatment emerged as a viable technique for achieving sustainability and resource optimization. Recent breakthroughs in genetic engineering, nanotechnology, and artificial intelligence applications have the potential for enhancing system performance. Case studies illustrated the practical utilization of microalga biobatteries for energizing low-power devices and facilitating wastewater treatment.

Nonetheless, there are still obstacles to enhancing agricultural methods, reconciling electricity generation with production expenses, guaranteeing sustained stability, and assimilating renewable energy sources with current grid infrastructures. Future studies must create resource-efficient growing methods, investigate waste streams as nutrient sources, and enhance bioreactor designs for light utilization. Moreover, the advancement of economical electrode materials and scalable bioreactor configurations is essential for practical use. In conclusion, microalga-derived energy production has considerable potential for creating a more sustainable energy framework. Confronting present difficulties and utilizing existing scientific technologies may establish microalga biobatteries as feasible contributors to cleaner energy generation and reduced reliance on fossil fuels.