Microalgal Bioeconomy: A Green Economy Approach Towards Achieving Sustainable Development Goals
School of Engineering and Built Environment, Griffith University, Nathan, QLD 4111, Australia
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Sustainability 2024, 16(24), 11218; https://doi.org/10.3390/su162411218
Submission received: 13 November 2024
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Revised: 16 December 2024
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Accepted: 18 December 2024
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Published: 20 December 2024
(This article belongs to the Special Issue Sustainable Energy: The Path to a Low-Carbon Economy)
Abstract
:This article delves into the role of microalgae in advancing a green economy, thereby contributing to the attainment of Sustainable Development Goals (SDGs). Microalgae, as sustainable resources, offer multifaceted benefits across various sectors, including aquaculture, agriculture, food and feed, pharmaceuticals, cosmetics, wastewater treatment, and carbon sequestration. This review highlights the versatility of microalgae in producing biofuels, high-value bioactive compounds, and bioremediation processes. It examines the technical viability and environmental sustainability of microalgae cultivation, emphasizing its low carbon footprint and resource efficiency. This article also explores the integration of microalgae into existing industrial processes, illustrating their potential to mitigate climate change, promote biodiversity, and enhance resource circularity. Challenges such as scalability, cost-effectiveness, and regulatory frameworks are discussed alongside the prospects for technological innovations and policy support to bolster the microalgae industry. By harnessing the potential of microalgae, this article underscores a pathway towards a more sustainable and greener future, aligning with the global agenda for sustainable development.
1. Introduction
Photosynthetic organisms known as algae thrive in various aquatic environments such as lakes, ponds, rivers, oceans, and wastewater. They exhibit resilience across diverse temperatures, salinity levels, pH ranges, and light conditions and can adapt to environments like reservoirs or deserts [1]. Algae exist either independently or in symbiotic relationships with other life forms. They are broadly categorized into three groups: Rhodophyta (red algae), Phaeophyta (brown algae), and Chlorophyta (green algae) [2]. Additionally, algae are divided based on size into macroalgae and microalgae. Macroalgae, also known as seaweed, are large, multicellular organisms visible to the naked eye. In contrast, microalgae consist of microscopic single cells that can be either prokaryotic, akin to cyanobacteria (Chloroxybacteria), or eukaryotic, resembling green algae (Chlorophyta) [2].
Microalgae, single-celled plants, grow by utilizing carbon, water, and other nutrients through photosynthesis. These cells lack roots, stems, or leaves and absorb nutrients more efficiently, growing faster than land-based plants. As microscopic entities, phytoplankton, which include microalgae, play a vital role in oceanic biodiversity and contribute approximately 50% to the planet’s primary production due to their rapid multiplication [3]. Algal biomass serves as a source of proteins, lipids, and carbohydrates. Depending on the species, it can be processed into food, animal feed, biofuels, bioplastics, cosmetics, and other high-value products [4,5].
Microalgae have been integral to human diets for centuries, with historical uses dating back to the Aztecs and populations in Chad. Notably, the cyanobacterium Spirulina was consumed as ’tecuitlatl’ by the Aztecs and as ’dihé’ in Chad [6]. Other species like Nostoc and Aphanotheca sacrum have been traditional foods in regions such as China, South America, and Japan [6]. The use of microalgae in modern biotechnology began in the 1940s, with significant advancements following the first Algal Mass Culture Symposium at Stanford University in 1952 [6]. Commercial cultivation started in Japan in the 1960s with Chlorella and expanded to large-scale Spirulina production in Mexico and Thailand in the 1970s [7]. By the 1990s, Japan alone traded around 2000 tons of Chlorella annually [8]. The production of Dunaliella salina for β-carotene started in Australia in 1986, later expanding to Israel and the USA [7]. This rapid development over 30 years highlights the significant growth and diversification of the microalgal biotechnology industry.
Contemporary microalgae production facilities primarily utilize two cultivation systems: open ponds and enclosed photobioreactors (PBRs) [9]. The open pond systems are simpler to manage and less costly to establish. However, they present challenges in regulating operational conditions. In contrast, enclosed PBRs offer enhanced control over these conditions, facilitating improved algal growth and the ability to alter the composition of algal biomass through the management of factors like temperature and lighting [10]. Nonetheless, this increased control of PBRs is associated with higher initial and ongoing maintenance costs. Consequently, the majority of microalgae production still predominantly occurs in open pond systems.
Various national and international entities, including the United States (US), the European Commission (EC), and the Organisation for Economic Co-operation and Development (OECD), have formulated official bioeconomy strategies, frequently incorporating algae and seaweeds. These strategies are designed to align with and contribute to several of the United Nations’ Sustainable Development Goals (SDGs) [11]. The 2030 Agenda for Sustainable Development frequently references the bioeconomy as a pathway to achieve objectives related to food security, nutrition, and the sustainable use of natural resources, thereby promoting sustainable economic, social, and environmental development [12]. In this article, we explore the potential role of the microalgal bioeconomy in advancing the concepts of the green economy as adopted by various regions and how it can directly support the attainment of sustainable development goals. Initially, this article discusses the interconnection between the bioeconomy, green economy, and sustainable development goals. Subsequently, it examines the potential avenues through which the microalgal bioeconomy can foster a green economy. Finally, this article delves into how this enhancement of the green economy can aid in achieving sustainable development goals.
2. Bioeconomy and Its Relation to SDGs
The bioeconomy refers to the use of renewable biological resources to produce food, feed, bio-based products, and bioenergy. It spans various sectors like agriculture, forestry, fisheries, and parts of the chemical and energy industries. It is notably innovative, integrating a wide array of sciences (like life sciences and social sciences), technologies (such as biotechnology and ICT), and local knowledge [13]. The Global Bioeconomy Summit describes it as the sustainable use and management of biological resources, encompassing science, technology, and innovation in all economic sectors [14]. While bioeconomy offers solutions to challenges like climate change, sustainable resource use, and rural income diversification, it does not automatically guarantee environmental and socioeconomic benefits. Recognizing and monitoring potential trade-offs is vital to prevent or reduce unintended negative impacts [14].
The sustainability of the bioeconomy hinges on the supply and consumption patterns of bio-based resources. Trees, especially for lignin–cellulosic applications like biofuels, are a key biomass resource. The bioeconomy’s focus on sustainably managed forests leads to increased afforestation in some areas and deforestation in others. This approach, along with the push to clear forests for biomass demand, challenges the bioeconomy’s alignment with Sustainable Development Goal (SDG) target 15.2 [15]. The sustainable bioeconomy, however, meets this target by encouraging global afforestation and reforestation, considering local and ecological factors. Increased biomass demand raises land value, potentially leading to new agricultural areas harming ecosystems and biodiversity [16]. This includes the risk of biodiversity loss due to invasive hybrid and genetically modified crops and land overuse leading to degradation or desertification. The bioeconomy’s impact on poverty mirrors that of industrial agriculture, with risks like land grabbing and increased dependence on global agricultural prices due to a shift from food to biomass crops [17].
According to FAO [18], the development of a sustainable bioeconomy should prioritize food security and nutrition across all levels. It must conserve, protect, and enhance natural resources, fuel competitive and inclusive economic growth, and contribute to healthier, more sustainable communities with heightened social and ecosystem resilience. Effective resource and biomass utilization is key, alongside leveraging existing knowledge, established technologies, and best practices. Encouraging research and innovation where necessary, it should also advocate for sustainable trade and market practices, address societal needs, foster sustainable consumption, and promote cooperation and knowledge-sharing among stakeholders in relevant fields and levels.
One study argued that the bioeconomy’s support of SDGs depends on how SDG targets are weighted and the concept of substitutability within the SDGs [15]. The bioeconomy marginally misses these targets, while the sustainable bioeconomy scenario achieves them, showing more progress. The sustainable bioeconomy’s benefits for land, oceans, water, and resource use outweigh its negatives, which are seen as inherent trade-offs within the SDGs [15]. Given the significance of sustainability in the bioeconomy, the EU revamped its Bioeconomy Strategy in 2018, focusing on sustainable, circular, and climate-friendly economic practices as central elements of its environmental policy [19]. Thus, effectively executing this strategy and managing biomass sustainably could both counteract climate change and help attain sustainability objectives.
3. Green Economy and Its Relationship to SDG
The UN Conference on Sustainable Development (Rio+20) in Rio de Janeiro in June 2012 marked a significant recognition that environmental and development issues cannot be separated [20]. The conference introduced the “green economy” concept, which is now widely adopted by organizations like the World Bank and the United Nations Environment Programme as a sustainability pathway [21]. This concept, pivotal in addressing financial and climate crises, plays a crucial role in meeting Paris Agreement climate targets. Encompassing various aspects of growth, well-being, and resource efficiency, the green economy integrates diverse economic and philosophical approaches to sustainable development. It is a framework for economic activities promoting long-term human well-being and social justice without compromising future generations’ environmental security. Operational goals of the green economy include reducing carbon emissions and pollution, enhancing energy and resource efficiency, fostering economic growth, and leveraging natural assets for sustainable and social development [20,21].
Numerous countries are formulating green economy strategies, policies, and programs at a national level. South Korea stands out as a leader in Asia in this regard. In 2009, the nation unveiled a five-year strategy committing to invest about 2 percent of its Gross Domestic Product (GDP) annually in green growth initiatives [21]. Green growth, a sustainability approach prioritizing environmental protection alongside economic growth, gained prominence in South Korea’s national policy in 2005 after being discussed in the 1990s [22]. This strategy redefines global warming prevention costs as investments in aligning economic development with environmental conservation. It encourages abandoning unsustainable practices for sustainable economic growth, emphasizing a shift from quantity-focused progress to quality, from physical product consumption to non-physical outputs, and from mere technological innovation to broader, socially embedded innovations, including organizational changes, social networks, and R&D specialization [22,23]. The East Asian model of green growth, noted for its emphasis on a green state with socially inclusive environmental policies, is particularly recognized [22].
China has also shown a keen interest in green economics. The country’s 12th Five-Year Plan (FYP) emphasizes the development of green industries [24]. The 12th FYP prioritized the promotion of seven emerging and strategic industries over the next five years, based on innovation and indigenous technological development, following the classic East Asian development model [25].
Green growth is concerned with making growth processes more resource-efficient and stimulating demand for green technologies, goods, and services [26]. The adoption of green growth in the central policymaking of countries like South Korea and China has led to the formation of active groups interested in promoting green growth. The OECD has already proposed green growth as a policy pathway to achieve the targets of the SDGs, while the UN has included green growth as an important concept of resource efficiency. While few studies have examined the relationship between green growth and the SDGs, one study suggested a close relationship between green growth and SDG 8 (Decent work and Economic Growth) through green innovation (target 8.2 and target 8.4) [27]. For example, target 8.4 aims to improve global resource efficiency in consumption and production and endeavour to decouple economic growth from environmental degradation by 2030. Another study suggested that green growth is more or less related to the SDGs [28], while others have suggested that it is not sufficiently focused on social issues such as SDG 5 and SDG 10 [29,30].
The EU’s environmental policy has been revamped as the European Green Deal, aiming for a carbon-neutral EU by 2050 and encompassing initiatives in farming, biodiversity, circular economy, and building renovation [19]. This comprehensive strategy integrates with other environmental policies, including climate change and circular economy, and aligns significantly with the Sustainable Development Goals. It also focuses on enhancing the bioeconomy with specific strategies for forest management, soil, farmland, food production, and related green investments.
4. Role of Algal Bioeconomy to Promote Green Economy
The global algae industry is experiencing growth. Primarily, commercial algal cultivation is aimed at producing food and feed. A 2021 study identified 447 algal cultivation facilities in Europe, with the majority of the algal biomass (over 80%) being utilized for food, feed, and cosmetics [31]. The remainder is employed in the production of fertilizers, bio-stimulants, and pharmaceuticals, highlighting the algae industry’s future potential. The contribution of microalgae to the green economy is contingent on sustainable microalgal biomass production, environmental protection, resource conservation, and the application of green technologies in both upstream and downstream processing [32]. While renewable bioenergy is a critical aspect of Sustainable Development Goals (SDGs), the green economy, and sustainable bioeconomy, high production costs hinder the commercial viability of algal biofuel. It is notably more expensive than biofuel derived from soybeans, being ten times costlier [33]. Moreover, the energy return on investment for algal biofuel is significantly low. According to a 2015 report by the US Department of Energy, 87% of the total cost of algal biofuel production is attributed to algal cultivation [34]. As a result, the subsequent section will delve into the role of microalgae in promoting a green economy through sustainable approaches in wastewater treatment, carbon capture systems, and in the sectors of sustainable aquaculture, agriculture, food and feed, as well as in the pharmaceutical and cosmetics industries by safeguarding, restoring and investing in natural resources and supporting sustainable consumption and production. Information pertinent to this study on the green economy and bioeconomy principles of Korea, China, and Europe is organized in Table A1, Table A2 and Table A3, with the Sustainable Development Goals (SDG) goals and targets listed in Table A4 of the Appendix A. In the appendix, “GGn” denotes the Korean Green Growth Agendas, “An, Bn, Cn” refer to the Green Growth Index of China, and “BGn” and “GDn” correspond to the European Bioeconomy Strategy and Green Deal, respectively. The letter “n” signifies a numerical value. The SDG goals and targets are presented using their standard expressions.
4.1. Microalgae for Sustainable Carbon Capture System
The imperative to address climate change has necessitated a revaluation of our fuel utilization strategies. The challenge lies in reducing reliance on fossil fuels, a task complicated by the nascent commercial maturity of many renewable energy technologies. A prominent and extensively discussed solution is the adoption of carbon capture systems. Bioenergy with carbon capture and storage (BECCS) offers a potential for net negative carbon emissions and could significantly reduce carbon dioxide levels if implemented on a large scale. However, the economic impacts and feasibility of widespread BECCS deployment remain uncertain. As a negative-emissions technology in a carbon-taxed policy environment, BECCS would require substantial subsidies. Research indicates that in a scenario aiming to cap global warming at 2 °C, carbon tax revenues are diminishing, eventually posing a financial strain on general tax revenues [35]. Furthermore, the absence of carbon capture and storage (CCS) technologies disadvantages fossil fuel exporting regions, whereas their inclusion, especially BECCS, facilitates sustained fossil fuel use and exportation. The relationship between carbon pricing and the prices of biomass and food crops is direct; notably, BECCS helps moderate the rise in food crop prices by reducing carbon prices and overall biomass requirements in climate mitigation strategies [35].
Various carbon capture and utilization systems, including pre- and post-combustion carbon separation techniques, have been explored. Currently, post-combustion separation through carbon dioxide absorption using different amine solvents is deemed commercially feasible, albeit costly. For instance, South Korea has actively supported the development of domestic carbon capture, utilization, and storage (CCUS) technology as part of its strategy to diminish greenhouse gas emissions by 2030 [36]. However, they have recognized the significant time and financial investments required. Emissions from coal power plants, a major source of carbon dioxide, present an opportunity for effective carbon capture. Implementing carbon capture at coal-fired power plants can significantly reduce emissions, but it also leads to increased electricity costs compared to other emerging renewable sources. A study by the US Energy Information Administration revealed that a coal power plant equipped with 90% carbon capture and storage (CCS), commencing operations in 2023, would incur about 60% higher electricity prices compared to conventional rates [36]. The implementation of carbon capture facilities may lead to higher water usage and consumption due to increased cooling needs and CO2 separation in power plants. Recent studies indicate that expanding CCS could strain water resources, particularly in areas facing water scarcity [37].
Amine-based CO2 capture units impact the environment by using water chemicals and generating chemical waste. Degradation of alkanolamines leads to equipment corrosion, increasing operational costs. These by-products require treatment and disposal. Additionally, sulphur dioxide and nitrogen dioxide reactions with MEA (monoethanolamine) solvent form non-regenerable heat-stable salts, reducing solvent efficiency and causing solvent loss [38,39]. Other studies have explored the application of CCS systems using MEA or potassium carbonate in gas-fired combined power plants augmented with solar photovoltaic and wind turbine-generated electricity [40]. While renewable energy sources exhibit significantly lower environmental impacts than fossil fuel-based technologies, a discernible shift in environmental burdens was noted. This shift adversely affects human health and freshwater ecosystems. Additional research points to increased risks of acidification, eutrophication, and toxicity, primarily due to the use and degradation of MEA and related by-products [41].
The Gorgon Project in Australia exemplifies the environmental challenges linked with carbon sequestration [42]. This project aims to inject roughly 2 million tonnes of CO2 into a saline aquifer beneath Barrow Island, off Australia’s Northwest coast. The Environmental Protection Authority (EPA) raised several environmental concerns in their assessment, particularly regarding Barrow Island’s designation as a Class A nature reserve. Key issues highlighted include potential impacts on the local flatback turtle population, dredging activities, the introduction of non-native species, and threats to unique subterranean and local invertebrate species. The report expressed that a major concern with CCS is the risk of CO2 leakage from storage sites [42]. Although there is some experience in geologically storing CO2 and natural gas for about 10–20 years, the long-term effectiveness, spanning centuries or even millennia, remains unproven. Sudden or large-scale CO2 releases could lead to environmental disasters, posing grave risks, including potential fatalities in humans and animals [42].
A study reviewed the drawbacks of conventional carbon capture methods and compared them with microalgae and concluded that physical methods are costly, require specific geology, offer limited storage stability, and have significant ecological impacts; chemical methods suffer from inefficient CO2 capture, solvent evaporation, thermal instability, and equipment corrosion, besides requiring substantial reagents; and forest planting demands extensive land yet has low carbon absorption efficiency compared to microalgae [43]. Microalgae, known for their rapid growth and high CO2 fixation rate, present a solution to these issues. High concentrations of CO2 in flue gasses necessitate the use of CO2-tolerant, rather than CO2-sensitive, microalgae strains for effective CO2 capture. These tolerant strains can withstand high CO2 levels and temperatures and possess attributes like rapid CO2 fixation and growth in the presence of toxic substances like NOx, SOx, and H2S [44]. Microalgae such as Chlorella, Scenedesmus, and Chlorococcum have been successfully employed in capturing CO2 from effluents and industrial emissions [44]. A lab study using 10% (v/v) CO2 demonstrated that Scenedesmus obliquus, Chlorella pyrenoidosa, Scenedesmus dimorphus, and Chlorella vulgaris effectively eliminated about 95% of CO2 [45]. However, the primary obstacle in microalgal cultivation is creating an efficient, scalable, and economical system for carbonation that supports rapid microalgal growth to meet carbon capture demands. The primary methods for introducing CO2 into algal cultures include sparging, using bicarbonate solutions, and carbonation through membranes [46]. Key to enhancing microalgae’s CO2 absorption is selecting strains with fast growth, environmental resilience, and high CO2 fixation capabilities. Strategies to improve these traits include natural strain selection, random mutagenesis, Adaptive Laboratory Evolution (ALE), and genetic engineering to boost metabolic efficiency and environmental adaptability [47]. However, optimizing conditions for microalgae’s rapid growth and maximizing target compound productivity are often conflicting goals, addressable through methods like mutagenesis or genetic engineering [47]. Microalgae-based carbon capture systems fulfil the BG4 goal while also promoting circular economy and pollution reduction, addressing green economy goals such as GG1, GD2, GD4, GD8, A4, and B7.
4.2. Sustainable and Circular Use of Wastewater
Utilizing microalgae for bioremediation emerges as a promising approach, given their effectiveness in reducing biochemical oxygen demand (BOD), diminishing chemical oxygen demand (COD), remediating contaminants, neutralizing toxins, extracting nutrients, and producing eco-friendly effluent [48]. Microalgae can efficiently extract nutrients like nitrogen and phosphorus from wastewater, which serves as a valuable resource for biomass production. This approach reduces environmental pollution while generating safe biomass for applications in aquaculture and agriculture, including food and feed production. By utilizing non-toxic effluents from food industries, microalgae cultivation offers a cost-effective and eco-friendly alternative to traditional wastewater treatment methods. In contrast, traditional wastewater treatment systems often struggle to effectively eliminate numerous persistent pollutants, such as trace elements, toxins, and emerging contaminants [49].
Traditional wastewater treatment facilities necessitate the use of chemicals, energy, infrastructure, and a labour force for their operation, yielding treated water and sludge as outputs [50]. However, inefficient disposal of sludge can result in secondary pollution. Annually, the United States generates 6.5 million metric tons of dry municipal sludge as a byproduct of wastewater treatment. In comparison, microalgae-based wastewater treatment systems are more cost-effective than conventional treatment methods. They also have lower energy demands than the conventional activated sludge process, owing to the reduced oxygenation needs for bacterial metabolism [51]. Furthermore, microalgae can capture carbon from various sources, thereby reducing greenhouse gas emissions [51].
Traditional wastewater reclamation practices involve various organizations managing separate upstream and downstream processes, yet their effective collaboration is often lacking. This absence of teamwork presents a major obstacle in wastewater reclamation. However, integrating microalgae cultivation at the same location where wastewater collection, treatment, and recycling occur can effectively address this issue [52]. This study also evaluated numerous aspects of wastewater reclamation, including human contact levels, public health, environmental impact, water conservation, cost of treatment and distribution systems, perceptions of wastewater as a source of reclaimed water, community awareness of water supply issues, the role of reclaimed water in overall supply, perceptions of reclaimed water quality, and confidence in local public utility management and technologies. It concluded that incorporating microalgae cultivation in wastewater reclamation meets all these criteria effectively [52].
Research conducted in FCC Aqualia in Spain indicates that processing 500 million cubic meters of wastewater results in annual emissions of 1000 kilotons of CO2, 25 kilotons of nitrogen, and 5 kilotons of phosphorus. Alternatively, employing microalgae for processing the same amount can produce approximately 500 kilotons of microalgal biomass each year, effectively incorporating the nutrients into the biomass, which is consistent with the principles of a circular bioeconomy [53].
Various microalgal strains have shown the ability to remove different contaminants from wastewater. One study tabulated several examples [54]. For instance, C. vulgaris, Scenedesmus obliquus, Anabaena doliolum, Chlorella emersonii, Chlorella kessleri, and Chlamydomonas reinhardtii are effective in eliminating nitrogen and phosphorus. Coelastrum proboscideum and Cladophora glomerata specialize in extracting lead and cadmium. Dunaliella bioculata targets the pyrethroid insecticide Deltamethrin, while Micratinium reisseri can remove carbon, nitrogen, oxygen, calcium, and phosphorus. Coelastrella sp. is known for its ability to remove Rhodamine B. Oscillatoria sp., Scenedesmus incrassatulus, and Phormidium sp. are effective against Cr (VI). Phormidium tenue can extract naphthalene and anthracene. Additionally, Oscillatoria sp. and Phormidium sp. can remove Pb(ii), Nannochloropsis oculata can eliminate formaldehyde, and Gloeothece magna is efficient in removing Cd(II) and Mn(II) ions.
Microalgae derived from wastewater, though not fit for human consumption, present an eco-friendly alternative for feeding animals and aquaculture [55]. Due to their unique biochemical properties, they are also suitable for creating various types of biofuels. Furthermore, the remaining biomass after the extraction of proteins, lipids, or carbohydrates, referred to as spent microalgal biomass, can be repurposed for energy recovery or other uses [56]. Figure 1 depicts a schematic diagram of a circular wastewater treatment system incorporating microalgae.
The integration of wastewater-based algal cultivation systems for generating renewable biomass aligns with the European bioeconomy objectives BG2, BG3, and BG4, as it eliminates the need for chemical fertilizers. This approach significantly contributes to the circular economy and addresses multiple green economy goals, including GG1, GD1, GD2, GD4, A3, A4, A6, A14, B1, B17, B11, and C4, by reducing carbon emissions, conserving freshwater, diminishing water pollution, and facilitating clean energy production.
4.3. Microalgae for Sustainable Aquaculture
The demand for fish as a source of protein is increasing at a high rate. Considering the limitation of the availability of wildly caught fish and to avoid damage to marine aquaculture, reliance on aquaculture to meet market demand has increased. In 2011, fish farming surpassed beef production worldwide, and the growth rate of fish farming was five times faster than that of beef production [57]. The increased fish production also increased the price of fish feed. In the last decade, fish feed prices increased three times [57]. Considering the fact that fish feed accounts for 30% to 60% of the total operating cost, the industry is actively looking for alternate sources of fish feed. Land-based crops like grains and oilseeds are cost-effective and partially successful as fish meal substitutes, but they alter the nutritional quality of the resultant fish. In contrast, microalgae, being a stable protein source independent of fish captures, offer the aquaculture industry better cost control and reduced risk, encouraging future investment.
To reduce aquaculture costs, fishmeal is often partially replaced with protein-rich, low-cost feedstocks like soybean meal, which has proven effective for species like juvenile obscure puffer, white snook, and spotted seabass [58,59,60]. Microalgae, however, surpass soybeans in cultivation time, protein content, and resource recycling. Microalgae, with a higher protein content (about 60% in Chlorella sp. compared to 40% in soybeans), grow rapidly (5–20 days) and serve as a versatile nutrient source for aquaculture and agriculture by enhancing crop yield, acting as biostimulants, and recovering nutrients from wastewater [61,62]. Therefore, microalgae are a significant alternative feed source in aquaculture.
Microalgae are increasingly used in aquaculture for various purposes: as food additives, fish meal and oil substitutes, colour enhancers for salmonids, biological activity inducers, and nutritional value boosters for zooplankton fed to fish larvae and fry [63,64]. They enhance larval production through light attenuation, maintaining zooplankton’s nutritional quality, supplying growth-promoting vitamins, and exerting probiotic effects. Microalgae also stabilize and improve the culture medium quality. Their use in aquaculture is notable for benefits like increased weight gain, muscle protein and triglyceride deposition, disease resistance, improved flesh taste and texture, reduced environmental nitrogen output, enhanced omega-3 fatty acid content, improved physiological activity, starvation tolerance, carcass quality, and growth rate due to better digestibility [65,66]. Their role in aquaculture aligns with their natural function as food for aquatic organisms. Improved digestibility leads to accelerated growth, explaining the observed increase in aquaculture productivity following the transition from predominantly corn/soybean feeds to microalgal-based feeds [57].
Numerous studies have indicated that microalgae hold considerable promise for use in fish aquaculture. Choubert et al. (2006) discovered that Haematococcus pluvialis-fed rainbow trout (Oncorhynchus mykiss) had elevated astaxanthin levels [67]. Generally, consumers in the market favour rainbow trout with higher astaxanthin content and improved flesh colouration. Furthermore, research indicates a beneficial correlation between fish immunity and the consumption of the microalgae pigment astaxanthin [68]. Knutsen et al. (2019) discovered that spotted wolfish (Anarhichas minor) can effectively use up to 15% of the microalga Nannochloropsis oceanica in their diet. They also noted that microalgae, rich in lipids, polyunsaturated fatty acids, amino acids, antioxidants, and vitamins, offer benefits over fishmeal [69]. Therefore, substituting fishmeal with microalgae is becoming a growing practice in fish feed production.
Traditional aquaculture, where fish faeces and feed residue can lead to water eutrophication, is not considered environmentally friendly. The ammonia released from these sources into the water can hinder bream growth by affecting growth hormone/insulin-like growth factor and hypothalamic–pituitary–thyroid axes and also negatively impact the antioxidant capacity and survivability of aquatic animals [70,71]. According to Han et al. (2019) [72], integrating microalgae into fish farming not only provides technical advantages but also economic gains through circularity. Figure 2 presents a schematic diagram of an eco-friendly fish farming system integrated with microalgae. Microalgae contribute to oxygen production, reducing the need for traditional aeration methods and cutting energy costs. Their presence in fish habitats helps control harmful microorganisms, creating a healthier environment and reducing water replacement costs. The use of microalgae in feed enhances fish immunity, potentially reducing reliance on antibiotics and increasing product safety and market appeal. Additionally, treating aquaculture effluent with microalgae biotechnology offers a cost-effective alternative to conventional wastewater treatment, lessening the industry’s financial burden. Furthermore, substituting traditional feed with harvested microalgae biomass helps in managing the costs of fish rearing. CO2, a byproduct of fish metabolism, is expelled through their gills. Introducing microalgae into production ponds or tanks enables these algae to absorb CO2, simultaneously releasing oxygen back into the water. This process not only alleviates stress in fish but also boosts their metabolic growth rates. Additionally, green water systems offer the benefit of providing food for herbivorous filtering species like rotifers, copepods, artemia systems, tilapia, and oysters [57]. Therefore, effectively managing microalgae contributes to the removal of CO2 from ponds, reducing stress and mortality while enhancing the growth rate of aquatic species.
In the aquaculture sector, particularly in fish farming, microalgae play a pivotal role in enhancing food security and alleviating pressure on marine ecosystems, fulfilling BG1 and BG2 objectives. Furthermore, the application of microalgae in this domain directly supports circular economy principles and green industrialization, addressing goals such as GG1, GG3, GG9, GD2, GD4, GD5, GD7, A4, A6, B7, and B13.
4.4. Microalgae for Sustainable Agriculture
Population growth has led to higher food demand, placing a strain on crop production. To meet this demand on limited land, the predominant strategy involves intensifying fertilizer use. Inorganic fertilizers, recognized as carcinogens, often include harmful pesticides. Their misuse can lead to nutrient imbalances, affecting nutrient absorption and soil acidity, thereby lowering crop yields. These fertilizers also diminish soil organic matter and degrade soil structure, increasing soil acidity and erosion [73]. Additionally, they contribute to water contamination, harm wildlife and fish, and increase reliance on fossil fuels. Moreover, they are costly, less accessible in rural areas, and pose risks in areas with varying rainfall, requiring seasonal application [73]. Temperature and soil moisture affect the release of nutrients from organic fertilizers, often not aligning with plant needs. Their low nutrient content and limited availability make it challenging to meet crop nutrient demands solely through organic fertilizers. Additionally, they are needed in large quantities and may not be easily accessible to small-scale farmers [74].
Biofertilizers, especially those derived from microalgae, offer multiple advantages over chemical fertilizers. They effectively enhance the utilization of nitrogen, phosphorus, potassium, and other soil elements, increase crop stress tolerance, improve agricultural product quality and yield, and significantly reduce soil pathogen toxicity [74]. Microalgae affect soil microbial diversity, composition, and activity and produce bioactive metabolites beneficial for plant growth pest and pathogen control [75]. Notably, phenolic compounds, carotenoids, terpenoids, polysaccharides, free fatty acids, and phytohormones in microalgae are also recognized as plant growth promoters [76]. In tropical and subtropical regions, they are essential for replacing chemical fertilizers due to their ability to directly transfer nutrients to plants, thereby improving crop yield and reducing chemical runoff. Additionally, biofertilizers aid in nitrogen fixation, root growth promotion, and nutrient absorption in acidic soils and decrease the need for harmful pesticides and fungicides [77]. Polysaccharides of algal biomass aid in nutrient absorption, plant development, and stress resistance [78]. Additionally, microalgae serve as biopesticides, protecting plants from pathogens like fungi and bacteria [79].
Intensive use of chemical fertilizers, like superphosphate fertilizers, leads to the accumulation of heavy metals in agricultural soils. These fertilizers often contain contaminants such as cadmium, cobalt, copper, lead, zinc, chromium, mercury, and nickel [80]. A study revealed that soils treated with these fertilizers, as well as the plants grown in them, showed higher concentrations of zinc [81]. Microalgae demonstrate a high metal-binding capacity, attributed to their cell wall components like polysaccharides, proteins, and lipids, which contain metal-binding functional groups such as amino, hydroxyl, carboxyl, and sulphate [82]. This enables microalgae to effectively remove heavy metals from water, acting as a resource for complex polymers used in metal sequestration. Traditional heavy metal removal methods like reverse osmosis and ion exchange have limitations, including incomplete removal, high costs, and hazardous waste production. Microalgae offer an eco-friendly alternative by metabolizing, detoxifying, and volatilizing xenobiotic substances and heavy metals with no risk of environmental contamination due to their non-pathogenic nature. Additionally, microalgae can absorb and enzymatically degrade contaminants, making them a promising solution for water purification [73,82].
Using nitrogen fertilizers increases soil nitrogen and the release of nitrous oxides (N2O), significantly impacting global warming. Microalgae-based biofertilizers emit considerably less nitrogen oxides compared to urea, with soil nitric oxide (NO) and N2O emissions being 2–5 times and 2 times lower, respectively. This results in a 4–11-fold reduction in global warming impact compared to urea [83]. Cyanobacterial inoculation can fix about 10–40 kg/ha of atmospheric nitrogen annually, thereby reducing environmental pollution [84,85].
One review study identified different microalgal strains as promising elements of biofertilizers, such as Scenedesmus spp., Aulosira fertilissima, Dunaliella spp., Phaeodactylum spp., Spirulina spp., Chlorella spp. and Anthrospira are found effective for petunias, rice seedling, bell pepper, wheat, sugar beet, red beet and tomato [73]. Cyanobacteria inoculation can reduce the need for expensive chemical nitrogen fertilizers by 25–40%, and its use as a bio-fertilizer not only decreases chemical fertilizer consumption but also enhances rice and other crop yields [74]. Microalgae are considered organic fertilizers that minimize nutrient loss through the gradual release of nutrients like phosphorus, nitrogen, and potassium. They are more resistant to temperature and soil moisture variations than typical organic fertilizers [86,87]. Microalgal extracts can replace micronutrient foliar fertilizers, enhancing nutrient uptake and increasing nitrogen levels in plant shoots and root tissues [88]. Using algae biomass extracted oil as fertilizer in corn crops decreases the reliance on chemical fertilizers and enhances crop productivity. Additionally, the anaerobic digestion of algae waste to produce biomethane, and biohydrogen offers further benefits [89]. Solé-Bundó et al. (2017) discovered that digestate from untreated and anaerobically co-digested microalgae biomass, mixed with primary sludge, is nutrient-rich and can be used for improving agricultural soil [90].
Studies investigated the co-cultivation of microalgae and plants in hydroponic systems and found positive outcomes. Studies found that this approach benefits the growth of both microalgae and plants, enhancing crop biomass due to algal photosynthesis [91,92]. Barone et al. reported a significant increase in root length by approximately 130% when co-cultivating Chlorella vulgaris and Scenedesmus quadricauda with plants [91]. Similarly, Zhang et al. observed increased biomass productivity in both Chlorella infusionum and tomatoes in a co-cultivation hydroponic system [92]. They also noted that crop root respiration and exudation acted as carbon sources, fostering microalgal growth and increasing their biomass.
The employment of microalgae in agriculture not only bolsters food security and the use of renewable resources but also contributes to carbon emission reduction, aligning with BG1, BG3, and BG4 goals. This approach furthers the objectives of green consumption, pollution mitigation, and clean energy, meeting goals GG2, GG9, GD1, GD5, GD8, A7, B13, B14, and B15.
4.5. Microalgae for Sustainable Food and Feed
The rising global population has led to a surge in both food demand and production. This increase in food production is causing significant environmental impacts. Recent research shows that global food production contributes to one-third of worldwide greenhouse gas emissions [93]. While traditional agricultural intensification methods were effective during the green revolution, they are now deemed unsustainable. These methods involve considerable environmental trade-offs, such as habitat destruction, biodiversity loss, increased greenhouse gas emissions, deforestation, desertification due to livestock farming, and pollution from chemical fertilizers, adversely affecting both aquatic and terrestrial ecosystems [93].
Proteins from animal sources have historically played a vital role in ensuring human nutritional security, offering essential amino acids, calories, and important micronutrients like vitamins and minerals, which are often scarce in plant-based diets. However, many of the same food resources used for human consumption are also utilized in animal feed formulations. Most farm animals on land inefficiently convert these feedstuffs into edible products [94]. Consequently, the escalated production of land-based foods must be balanced against its environmental impact and nutrient transformation efficiency. Due to these factors, protein products from terrestrial animal farming are currently facing intense examination [95]. Research links diets high in red meat with increased mortality and various diseases like obesity, type 2 diabetes, cardiovascular issues, stroke, and colorectal cancer [96]. In contrast, replacing animal proteins with plant-based ones has been associated with lower mortality. Guaschferre et al. (2019) found that substituting red meat with plant proteins leads to improved blood lipid and lipoprotein profiles compared to fish or carbohydrates [97]. Consequently, a diet shift from meat to plant-based foods can reduce the risk of chronic diseases and overall mortality. Meat alternatives offer a healthier choice; they contain significantly less energy, saturated fat, and sodium, have no cholesterol, and double the fibre content compared to traditional meat burgers, promoting a healthier diet trend [98]. Regarding food safety, meat can be compromised by various hazards, with biological threats being the most concerning for meat safety [99]. In response, there is a growing trend towards high-quality plant-based proteins from innovative sources, such as legumes (including peas and lentils). These have gained popularity and are now considered a key solution to address the rapidly expanding demand for food proteins. However, the scarcity of arable land and fresh water has spurred a growing need for alternative sources of plant protein, leading to the enhanced development and utilization of proteins derived from algae [93]. The use of algae for protein extraction offers several advantages over traditional protein-rich crops in terms of yield and nutritional quality. Microalgae can produce more protein per area than land-based crops such as soybeans, pulses, and wheat [100].
Meat analogs are less risky regarding food safety issues since their raw materials are mainly plant sources of protein, which eliminates the risks of zoonosis. Furthermore, these plant-based ingredients will be subjected to multiple processing steps, including high-temperature cooking, to form a meat-like texture, where the contamination of microorganisms can be greatly reduced. Meat analogs thus present a greener, healthier, safer and more controllable food choice [101]. Meat alternatives, primarily derived from plant proteins, reduce the risk of zoonotic diseases. Their production involves multiple steps, including high-temperature cooking, which significantly lowers microbial contamination. Thus, meat alternatives are not only healthier but also safer and more environmentally sustainable food options [99]. However, the yield and protein content from these sources are insufficient to meet the growing demand for meat substitutes. Microalgae are now emerging as an innovative protein source for meat substitutes [99]. They offer various functional components such as peptides, carbohydrates, lipids, pigments, vitamins, and minerals, contributing to a range of health benefits for consumers. Additionally, microalgae exhibit a higher growth rate and are more adaptable to diverse growing conditions than terrestrial crops, making them a more efficient protein source [99]. Certain varieties of these marine organisms have protein content comparable to conventional sources like meat, eggs, soybeans, and dairy [102,103].
Harvesting protein from microalgae offers superior nutritional benefits and efficiency, showcasing a significant yield surpassing common crops like wheat, pulse legumes, and soybeans by several times per hectare, respectively [104]. Notably, agriculture for these terrestrial crops consumes about 75% of the world’s freshwater. In contrast, animal-based proteins require 100 times more water than plant-based sources for the same amount of protein. Microalgae cultivation, which does not need freshwater or farmland, presents a sustainable alternative, reducing the demand for resources needed for traditional crop farming [104]. However, the methods used to texture microalgal biomass into meat-like products are still in their infancy and need additional research. Recently, researchers at the University of Copenhagen have innovatively used blue–green algae to produce a novel protein in fibrous strands resembling meat fibres [105]. This development could pave the way for sustainable, minimally processed foods with desirable textures. By genetically modifying cyanobacteria to express a non-native protein, they achieved the formation of these protein strands. These could potentially be utilized in plant-based meats, cheeses, or other food products requiring specific textures. The protein self-assembles into nanofibers within the cyanobacteria, thanks to the insertion of foreign genes.
The application of microalgae in sustainable food and feed production addresses global challenges related to food security, resource efficiency, and environmental impact. Microalgae provide a renewable source of high-quality proteins, essential nutrients, and bioactive compounds that can serve as alternatives to conventional feedstocks, aligning with BG1, BG3, and BG4 goals. This approach supports the principles of circular bioeconomy and green consumption, contributing to pollution reduction, enhanced resource efficiency, and cleaner production processes. Furthermore, the integration of microalgae-based innovations into food systems promotes resilience to climate-related challenges, aligning with goals GG2, GG9, GD1, GD5, GD8, A7, B13, B14, and B15.
4.6. Microalgae for Sustainable Pharmaceutical Industry
Consumer preference for natural nutrients derived from whole foods is increasing, as opposed to synthetic nutrients produced in industrial settings. While chemically similar, natural and synthetic nutrients may differ in how the human body absorbs and responds to them. The digestion of synthetic nutrients in the human body is not yet fully understood. Nutrient absorption depends on bioavailability, potency, and formulation; bioavailability refers to the efficiency of nutrient absorption, potency to the impact on health, and formulation to the delivery method [106]. Synthetic nutrients generally have lower bioavailability, requiring higher quantities to achieve the same effects as natural nutrients because the synthetic nutrients may bind weakly to the receptors or enzymes [107,108].
Natural products present distinct advantages and pose challenges in the realm of drug discovery when compared to synthetic molecules, owing to their extensive structural diversity and intricacy. Natural products are generally characterized by a larger molecular mass, an abundance of sp3 carbon and oxygen atoms, and fewer nitrogen and halogen atoms. They also have more hydrogen bond acceptors and donors, lower octanol–water partition coefficients, and enhanced molecular rigidity [109]. This increased rigidity makes them particularly effective in addressing protein–protein interactions during drug development [110]. Natural products, having evolved to fulfil specific biological roles, are especially pertinent for the treatment of infectious diseases and cancer. Their long-standing application in traditional medicine also provides critical insights into their effectiveness and safety [111].
Natural products, shaped by evolution, confer advantages to their producing organisms through effective interaction with biological receptors. Their distinct physical and chemical traits, such as increased sp3-hybridized carbons, chiral centres, and complex three-dimensional structures, enable them to effectively engage biological targets [112]. These traits differ from the simpler, planar structures of synthetic molecules. In the lab, natural products can be modified to enhance drug-like properties, including stability and receptor range [112]. Historically fundamental to drug development, these specialized metabolites from microbes and plants remain underutilized in pharmaceuticals, with a preference for synthetic compounds. Although over half of the approved drugs from 1981 to 2019 were synthetic, a third of clinically used drugs in 2014 were based on natural products [113,114]. Microalgae, yet to be fully explored, present a significant opportunity for discovering novel chemical structures and mechanisms for drug development.
Microalgae have garnered interest in the medical research community due to their diverse range of potent active metabolites, including fatty acids, polysaccharides, phenolic compounds, and carotenoids, among others. Current research in the pharmaceutical use of algae is primarily concentrated on applications such as anti-cancer, antibacterial, anti-viral, anti-hypertensive, and antihyperglycemic treatments [115].
Research on algae’s pharmaceutical potential in cancer treatment has shown promising results. Studies indicate that Sargassum fusiforme polysaccharides exhibit anti-tumour and immune-boosting effects in treating nasopharyngeal carcinoma in mice [116]. Additionally, Monostroma latissimum polysaccharides have been effective against enterovirus 71, enhancing survival rates and reducing viral loads in infected mice [117]. Spirulina extract-embedded nanofibers used in artificial skin scaffolds have demonstrated beneficial effects on mouse fibroblast health and proliferation without any toxic impact [118]. Furthermore, a lectin from the red algae Alsidium seaforthii has shown potential in lowering blood sugar and lipid levels, improving insulin resistance, and enhancing pancreatic function in diabetic rats [119]. In another case, Sargassum fusiforme fucoidan significantly alleviated diabetes symptoms in diabetic mice by altering the gut bacteria associated with the disease [120].
Once a drug successfully completes preclinical animal testing, it becomes eligible for human trials upon approval from drug regulatory authorities. Studies on algae’s clinical applications have been conducted, though they are fewer compared to animal studies. In human trials, Spirulina has demonstrated significant antioxidant and anti-inflammatory benefits, effectively treating chronic obstructive pulmonary disease (COPD) [121] and oral health issues [122]. Additionally, a protein from red algae, griffithsin (GRFT), has shown excellent potential as a pioneering topical protein-based anti-HIV prophylactic in clinical settings [123]. However, as of now, there are no commercial pharmaceutical products directly sourced from microalgae. In the pharmaceutical industry, the utilization of microalgae can promote the use of renewable resources in drug production, satisfying BG3 while also supporting green consumption and lifestyles, which is in line with GG9.
4.7. Microalgae for Sustainable Cosmetics Industry
Conventional skincare cosmetics often contain harmful, non-biodegradable petroleum-based ingredients. The average cosmetic product contains 15–20 chemicals, leading to potential exposure to 75–100 chemicals daily through cosmetic use [124]. This raises concerns about exposure to hazardous substances, prompting a shift towards biological or naturally derived cosmetics. The Australian Government’s AICIS (former name NICNAS) regulates cosmetic chemical use to ensure safety, while the EU has banned 1328 harmful chemicals in cosmetics. Other nations like Canada, Japan, and India are also addressing these safety concerns [124].
The paramount consideration in the commercialization of cosmetic products is their safety for human use [125]. This necessitates conducting various tests before these products reach the market, including assessments for genetic toxicity, phototoxicity, photogenotoxicity, toxicokinetics, and carcinogenicity [126]. Despite these extensive testing procedures, recent studies have raised concerns about potential health risks associated with the use of cosmetics. Safety data may be insufficient for synthetic ingredients in certain instances, potentially leading to hypersensitivity reactions, anaphylactic responses, lethal poisonings, or long-term effects for users [127]. The continuous exposure of various chemicals may lead to synergistic interactions and additive effects due to shared ingredients across different products [128]. Consequently, the imperative to substitute chemicals drives ongoing innovation in the cosmetic industry. A current challenge is meeting customer demands for natural ingredients driven by heightened awareness of the importance of using quality and environmentally sustainable products [129]. The rise in natural ingredients’ popularity can be attributed to their high antioxidant content. Antioxidants counteract oxidative stress, a key contributor to aging, by neutralizing free radicals. These radicals, which can damage biomolecules like lipids, proteins, and DNA, are produced during normal metabolism and are increased by environmental factors like sunlight and cigarette smoke [130]. Humans have developed an antioxidant defence system, but it requires continuous replenishment, making natural ingredients a valuable source of antioxidants. Factors such as environmental impact, sustainability, and health risks are driving the transition from traditional to bio-based cosmetics. The demand for natural products is growing due to the decline in non-renewable resources and environmental regulations. Bio-based cosmetics offer benefits like waste reduction and low-energy consumption, leading to a robust market for natural, sustainable products [131]. Companies like Estée Lauder and L’Oreal are increasingly focusing on biocosmetics, which currently hold a 10% market share with a rising total market value [124,132,133].
Various plant-based substitutes are currently being explored to supplant synthetic chemicals. Using vegetable oils instead of synthetic chemical Cosmetics vegetable oils is not economically competitive. Marine sources, particularly algae, serve as viable alternatives for new raw materials. Algae-based cosmetic products are increasingly replacing synthetic equivalents on the market, featuring extracts with various bioactive compounds (polysaccharides, proteins, peptides, amino acids, fatty acids, sterols, glycolipids, phospholipids, pigments, phenolic compounds, vitamins) or their purified forms, although until now this market is dominated by macroalgae [127].
Studies indicate that compounds derived from microalgae serve as key active ingredients in cosmetics, and their properties also make them suitable as excipients like stabilizers, dyes, or thickening agents [129,134,135]. These extracts and bioactive molecules are commonly utilized in personal care products such as face lotions, creams, shampoos, body soaps, and cosmetic colourants in products like eye shadow, lipstick, and face makeup [136,137,138]. Their sterols are used in moisturizing creams [139]. Pigments from microalgae, including chlorophyll, keto carotenoid astaxanthin, and β-carotene, are incorporated in anti-aging creams, anti-irritant peelers, and skincare products. Keto carotenoid astaxanthin and β-carotene also act as precursors to vitamin A [136]. Furthermore, their secondary metabolites, including proteins, carotenoids, pigments, and fatty acids, are known for preventing blemishes, repairing damaged skin, and maintaining skin moisture [138].
Bioactive compounds from microalgae offer various cosmetic applications, such as Chlorella polysaccharides for moisturizing and thickening [140], Haematococcus pluvialis-derived Astaxanthin for sunscreen protection [141,142], and Spirulina and Porphyridium’s Phycocyanobilin and phycoerythrobilin as pigments in eyeliners and lipsticks [141]. Chlorophyll from Chlorella sp. is used to mask odours in dentifrices and deodorants [143]. Nannochloropsis’s Canthaxanthin is utilized in tanning cosmetics and cosmeceuticals [142], while Porphyridium cruentum and Spirulina platensis’s Phycocyanin are used in eyeshadows [144,145]. Anabaena vaginicola’s Lycopene serves as an anti-aging and sunscreen product [146]. Ectoine from various microalgal strains is known for its immune, UV, stress protection, and moisturizing properties [147,148]. Phytohormones from Nannochloropsis oceanica are employed in anti-aging products [147,149], and Chlorella vulgaris extracts are also used for their anti-aging effects [150,151].
In the cosmetics industry, the use of microalgae encourages the adoption of renewable resources for product development, fulfilling BG3 and advancing green consumption and lifestyles, as outlined in GG9.
4.8. Technological Innovations in Microalgae
Microalgae face several challenges related to scalability, productivity, and cost-efficiency. However, recent advancements in technology have opened new pathways for addressing these limitations. Genetic engineering has been instrumental in optimizing microalgae strains for enhanced productivity and resource efficiency. For example, targeted modifications in Chlorella and Nannochloropsis strains have resulted in increased lipid accumulation, making them more viable for biofuel production. Synthetic biology enables the design of custom metabolic pathways to improve yields of high-value metabolites such as carotenoids, omega-3 fatty acids, and proteins [6].
The biorefinery model maximizes the use of microalgal biomass by integrating multiple production streams. This approach allows for the simultaneous extraction of biofuels, animal feed, bioplastics, and pigments, reducing waste and improving economic feasibility. Utilizing wastewater and industrial CO2 as feedstocks further reduces operational costs while enhancing environmental benefits [152].
Innovative photobioreactor designs, such as vertical tubular reactors and flat panel PBRs, have significantly improved light utilization and biomass productivity. These reactors minimize contamination risks and are scalable for industrial applications. Adaptive laboratory evolution (ALE) techniques have also been used to develop robust microalgal strains capable of thriving under industrial conditions [44].
4.9. Regulatory Frameworks for Microalgal Applications
- Current Challenges
The scaling and commercialization of microalgal applications face regulatory hurdles, including a lack of standardized policies for production, quality control, and environmental safety. Variability in regulations across regions complicates the global adoption of microalgae-based products. Furthermore, emerging technologies, such as genetically engineered strains, are often not addressed within existing frameworks, leading to uncertainty for industry stakeholders [153].
- Successful Regional Examples
European Union (EU): The EU has established a robust framework for promoting sustainable bioeconomy strategies, including microalgae. The Renewable Energy Directive (RED) mandates renewable energy incorporation into transportation fuels, providing a significant opportunity for microalgal biofuels. Research funding programs like Horizon Europe further encourage advancements in algal biotechnology, supporting large-scale integration of algae into bioeconomy practices [153].
South Korea: South Korea has incorporated microalgae into its Green Growth Strategy, focusing on CO2 sequestration and bioeconomy development. Policies incentivize partnerships between industry and research institutions to enhance the scalability and adoption of microalgae cultivation technologies. Large-scale projects integrate algal systems with industrial CO2 emissions, demonstrating their role in mitigating climate change [153].
India: India’s National Bio-Energy Mission supports the inclusion of microalgae as a renewable energy source. Pilot projects, particularly those focused on algal biofuel production and wastewater treatment, highlight the nation’s commitment to integrating algae into its renewable energy goals. Government incentives further encourage rural adoption of algal technologies, especially in agricultural regions [153].
- Recommendations for Future Policies
To unlock the full potential of microalgae, global and regional regulatory frameworks must:
- Establish consistent quality standards for microalgal products to ease commercialization.
- Facilitate public–private collaborations to mitigate investment risks and enhance technological advancements.
- Introduce carbon credit systems and subsidies to promote microalgae adoption in biofuels and wastewater treatment sectors [153].
- Integration into the Circular Economy
- Regulatory frameworks must align with the principles of the circular bioeconomy, emphasizing resource efficiency and waste valorisation. By incorporating microalgal systems into global sustainability goals, such as the Sustainable Development Goals (SDGs), regulators can ensure environmental and economic benefits on a broader scale [153].
4.10. Successful Policy Examples for Microalgal Applications
European Union (EU): The European Union has taken significant strides in fostering the adoption of microalgae through its Green Deal and bioeconomy strategies. The Renewable Energy Directive (RED) mandates that at least 14% of transportation fuels come from renewable sources, creating opportunities for microalgal biofuels to compete with traditional options. Additionally, Horizon Europe funding allocates billions of euros to research and innovation in sustainable technologies, including microalgae-based products [154].
Specific projects, such as the ALGATEC initiative, aim to integrate microalgae cultivation with wastewater treatment systems, promoting nutrient recovery and CO2 sequestration. EU-wide certification programs are also being developed to ensure consistent quality and safety standards for microalgae-based foods and feeds [155].
South Korea: South Korea’s Green Growth Strategy incorporates microalgae cultivation as a tool for addressing climate change and resource sustainability. The government has invested heavily in CO2 sequestration projects, with microalgae playing a pivotal role in industrial carbon capture initiatives. Collaborative efforts between academic institutions and industries and leading algae companies have led to advancements in algal biotechnology [156].
For example, large-scale algae farms have been established to capture CO2 emissions from power plants and use the biomass for biofuels and animal feed. These projects demonstrate how targeted government support can accelerate the commercialization of innovative technologies [157].
United States: The United States has prioritized microalgae through the U.S. Department of Energy’s (DOE) Algae Program, which funds research to reduce the costs of algal biofuels. The DOE’s initiatives aim to achieve a cost target of USD 2.50 per gallon for algal biofuels by 2030 [158]. Additionally, state-level programs in California and Arizona provide subsidies and tax credits for industries incorporating algal solutions into carbon capture and wastewater treatment systems [158,159].
One notable project is the Algae Biomass Organization (ABO), which advocates for streamlined federal policies and funding to support algae-based technologies. Collaborations with the Environmental Protection Agency (EPA) ensure that algal systems meet environmental safety standards while providing economic incentives for adoption [160].
India: India has initiated programs like the National Bio-Energy Mission to promote algal biofuels as part of its renewable energy goals. Research centres are working on pilot-scale algae farms for biofuel production and wastewater treatment. State governments provide financial incentives for farmers adopting algal cultivation, particularly in rural areas [161,162,163].
Global Integration: While these regions offer compelling examples of microalgal policy integration, a global framework for standardizing regulations would benefit the industry. The United Nations Food and Agriculture Organization (FAO) has begun initiatives to develop global standards for algae-based products, ensuring safety, quality, and sustainability across international markets [153].
5. Discussion
The growth of the microalgal bioeconomy offers an avenue for job creation, aligning with sustainable bioeconomy objective BG5 and green economy ambitions A15, A16, GG4, and GG5. By integrating into various industries, microalgae can spur technological advancement and enhance economic productivity, particularly in high-value-added sectors. Developing the microalgal industry can modernize industrial infrastructure and foster sustainable consumption and production practices that are both resource-efficient and environmentally friendly. This development necessitates bolstering scientific research and technological expertise at both national and international levels. It also involves supporting developing countries to fortify their scientific and technological capacities through global cooperation, knowledge exchange, and the dissemination of green technologies.
The advancement of microalgal industries, coupled with technological progression and market growth, supports the achievement of sustainable development goals (SDGs) 8.2, 8.4, 9.4, 9.5, 9.b, 12.1, 12.a, 17.6, and 17.7. Utilization of microalgae in sectors like aquaculture, agriculture, food and feed production, and wastewater treatment can facilitate access to plant proteins and sustainable crop production, thereby contributing to SDGs 2.1, 2.3, and 2.4. Investments in these areas can foster technological innovation and agricultural research, benefiting developing and least-developed countries, particularly by financially empowering rural farmers through well-coordinated international cooperation. This aligns with SDG 2.a.
In the pharmaceutical sector, microalgae can enhance access to safe, effective, and quality medicines and vaccines, supporting SDGs 3.8 and 3.b through research and development. Moreover, their use in agriculture, aquaculture, food and feed production, wastewater management, and carbon capture can reduce reliance on harmful chemicals, mitigate water, land, and forest usage, and improve municipal waste and wastewater management. These contributions are in line with SDGs 3.9, 6.3, 6.4, 11.6, 12.2, 12.4, 12.5, 15.1, and 15.2. Additionally, microalgae’s role in the agriculture, food and feed, and carbon capture sectors aids in reducing greenhouse gas emissions, addressing SDG 13.1.
The sustainable cultivation of microalgae in aquaculture promotes responsible fish farming, helping to avoid detrimental fishing practices and supporting SDGs 14.4 and 14.7. Lastly, the potential of microalgae for bioenergy production, especially from biomass unsuitable for higher value purposes, contributes to achieving SDG 7.2. Table 1 demonstrates the contributions of microalgal applications across various industries to achieving different SDG goals and targets.
The growth of the microalgae market is hindered by several key challenges [164,165]. Firstly, the undesirable sensory qualities of microalgae, such as taste, odour, and colour, deter consumer acceptance. Secondly, the extraction and processing of microalgae are costly. Thirdly, there are regulatory hurdles in incorporating new species of microalgae into food products. Despite its higher protein content compared to conventional sources like meat and dairy, microalgae-based functional foods have not gained significant market traction. This is largely attributed to low public awareness of its benefits, limited research incentives, and insufficient funding for microalgae technology [165]. Furthermore, conservative eating habits and reluctance to try new foods with unusual flavours contribute to the limited popularity of microalgae superfoods [165].
Currently, targeting high-value products like food additives and cosmetics or employing a biorefinery strategy is profitable for businesses. Although there is revenue potential in natural pigments, the market for these is limited [166]. Commercializing bulk commodities from microalgae is not profitable yet due to low market prices and high production costs [166]. However, future R&D advancements could improve this situation. Algae-based biofuels, a hot topic, could mitigate issues associated with the oil palm industry, such as food competition and wastewater pollution. Yet, with current fuel prices, producing microalgae for energy is not economically viable, and short-term projections do not show a change in this trend [166]. A biorefinery approach, however, could be viable by focusing on high-value products and using algal residue for biofuel. For instance, the residual biomass of Haematococcus, known for astaxanthin used in medicines and supplements, has the potential for energy production [167].
5.1. Cost Analysis of Microalgal Cultivation
The economic feasibility of microalgae cultivation is significantly influenced by key cost drivers such as energy consumption, nutrient supply, and harvesting processes. These components collectively account for the majority of operational expenses in both small-scale and industrial systems. Energy consumption, particularly for mixing, aeration, and lighting, is one of the largest contributors, representing approximately 30–50% of the total production cost. For example, traditional open-pond systems rely on paddle wheels for mixing, which, while energy-intensive, are less costly compared to photobioreactors (PBRs) that require controlled lighting and CO2 delivery systems to optimize productivity [168]. Advances in LED technology and solar-powered operations have recently been introduced to mitigate these costs, offering promising solutions for reducing energy input in PBR systems [169].
Nutrient supply is another major expense, particularly the provision of nitrogen, phosphorus, and carbon dioxide required for algal growth. Fertilizers used in traditional cultivation processes can be expensive, often limiting scalability. However, integrating nutrient-rich wastewater streams into microalgal systems has proven to be a cost-effective alternative. For instance, wastewater sourced from agricultural or industrial operations can reduce nutrient costs by up to 70% while also addressing environmental issues associated with nutrient runoff [170]. Additionally, utilizing CO2 emissions from industrial flue gasses as a carbon source not only lowers costs but also contributes to greenhouse gas mitigation efforts, creating a dual benefit for the industry.
Harvesting and biomass dewatering represent another significant cost driver, accounting for 20–30% of the total operational expenses. The high-water content in algal biomass necessitates energy-intensive processes such as centrifugation, filtration, or flocculation to achieve acceptable dry weight percentages. Innovations in harvesting technologies, such as electrocoagulation and membrane-based systems, have shown the potential to reduce costs significantly, particularly for large-scale operations [171]. For example, large-scale systems using electrocoagulation have demonstrated energy savings of up to 50% compared to conventional centrifugation methods, making them viable for industrial adoption [169].
The integration of circular economy principles, such as co-locating microalgal facilities with wastewater treatment plants or industrial CO2 emitters, has been a pivotal strategy for reducing overall costs. Companies like A4F in Portugal have successfully implemented these approaches, leveraging low-cost wastewater and CO2 sources to reduce nutrient and energy expenses while producing high-value co-products such as biofertilizers and bioplastics. These examples underscore the importance of combining innovative technologies with resource-efficient practices to improve the economic feasibility of microalgal cultivation [172].
5.2. Economic Feasibility
Economic viability remains a significant barrier for microalgal applications. The commercialization of microalgal products is constrained by high operational and production costs, particularly in bulk applications like biofuels. As highlighted in Table 2, key economic factors such as energy consumption, nutrient supply, and harvesting methods substantially influence overall costs. Strategies to reduce these costs include leveraging circular economy principles, such as integrating wastewater as a nutrient source and utilizing industrial CO2 emissions for cultivation. These approaches not only lower production expenses but also align with sustainability goals, creating dual economic and environmental benefits. Further advancements in cost-effective production methods are essential for enhancing market competitiveness.
5.3. Toxin Production in Microalgal Cultivation and Mitigation Methods
Toxin production is a critical concern in microalgal cultivation, especially when scaling up for commercial applications. Certain species, such as Microcystis aeruginosa, Alexandrium tamarense, and Prymnesium parvum, are known to produce harmful toxins under specific environmental conditions, including high nutrient availability, light stress, and temperature fluctuations. These toxins pose significant risks to the safety and quality of products derived from microalgae, particularly in food, feed, and nutraceutical applications. Effective mitigation strategies are essential to address these challenges. Selecting non-toxin-producing or genetically stable strains, such as Chlorella vulgaris and Spirulina platensis, is a primary preventive measure [173]. Additionally, real-time monitoring systems equipped with biosensors can detect environmental shifts that may trigger toxin production, enabling timely corrective actions. Cultivation in controlled environments, such as photobioreactors, further minimizes the influence of external stressors and contamination risks. Moreover, post-harvest testing for toxin residues using techniques like chromatography or immunoassays ensures that the biomass meets safety standards [174]. Implementing these approaches not only reduces the risks associated with toxin production but also enhances the reliability and marketability of microalgal products.
5.4. Best Practices for Limiting Contamination in Outdoor Cultivation Systems
Contamination is a pervasive challenge in outdoor microalgal cultivation systems due to exposure to environmental factors such as competing microorganisms, predators, and airborne debris. Effective contamination control is crucial for maintaining productivity and quality while ensuring economic feasibility. One effective strategy involves the use of physical barriers, such as transparent covers or protective nets, which shield cultures from external contaminants like insects and birds [170]. Pretreatment of input water through UV sterilization or chemical disinfectants further reduces the introduction of unwanted microorganisms, while low-cost methods like solar pasteurization have shown promise in resource-limited settings. Cultivating robust and fast-growing strains, such as Spirulina and Dunaliella, which thrive in extreme salinity or alkalinity, can also help outcompete contaminants [171]. Frequent harvesting of biomass and routine cleaning of cultivation equipment minimize biofouling and contamination buildup. To maintain economic viability, adopting low-cost measures like solar-powered aeration systems or using locally sourced nutrients can significantly reduce operational expenses. By integrating these best practices, outdoor cultivation systems can achieve a balance between productivity, quality, and cost-effectiveness.
5.5. Technological Advancements
Technological innovations have driven significant progress in microalgal applications, particularly in biorefinery processes and cultivation systems. Table 3 illustrates the quantitative evidence of how advancements in photobioreactor designs, genetic engineering, and AI-powered monitoring systems have improved productivity, reduced costs, and enhanced product quality. For example, supercritical CO2 extraction techniques, as explored by companies like Algatechnologies Ltd., Kibbutz Ketura, Israel, and Cyanotech Corporation, Kailua-Kona, Hawaii, USA, have optimized pigment and bioactive compound recovery. However, further innovation is needed in areas such as mild protein and carbohydrate extraction, the development of low-fouling membranes, and the use of sustainable solvents. These advancements will help bridge the gap between experimental successes and industrial scalability.
5.6. Application-Specific Insights
Microalgae demonstrate immense potential in diverse applications, particularly in aquaculture and agriculture. Table 4 highlights the economic and functional benefits of algae-based products in these sectors. In aquaculture, replacing fishmeal with microalgal alternatives reduces feed costs while improving fish health and sustainability. Similarly, in agriculture, algae-derived biofertilizers enhance soil fertility and reduce dependency on chemical inputs, offering a sustainable alternative. Despite these advantages, further research is needed to optimize production systems and reduce the costs of these applications to enable wider adoption.
In biorefinery processes, lipid extraction technology is established and robust. However, advancements are needed for efficient and mild extraction and separation of proteins and carbohydrates from lipids. Research should focus on two areas: enhancing aqueous extraction efficiency with novel solvents like ionic liquids or surfactants and developing cost-effective filtration systems, such as membranes, for protein–carbohydrate fractionation [166]. Improvements should aim at increasing membrane lifespan through low-fouling systems, reducing transmembrane pressure, and enhancing selective permeation. Additionally, sustainable and recoverable solvents for protein and lipid extraction are necessary. Companies like Algatechnologies Ltd. and Cyanotech Corporation are exploring supercritical CO2 for pigment extraction from algae [166]. The use of ionic liquids and surfactants must be validated for toxicity and food-grade quality.
Significant advancements in biomass production costs have been achieved through a better understanding of processes and operational strategies. However, the industry still grapples with immature production technologies and those not tailored for algae biorefinery. This evolving field anticipates further cost reductions in the future [166]. Progress in cultivation is crucial as it enhances productivity, quality, and composition of biomass, impacting both upstream processing and market prices.
5.7. Case Studies in Large-Scale Microalgal Cultivation
One notable example of successful large-scale microalgal cultivation is Algenol Biotech, Fort Myers, Florida, a U.S.-based company pioneering the production of sustainable ethanol and bio-based products. Algenol employs its proprietary Direct-to-Ethanol® Technology, which integrates CO2 utilization, algae cultivation, and ethanol production into an efficient process. Utilizing photobioreactors (PBRs), Algenol optimizes light and CO2 distribution while mitigating contamination risks, making the technology suitable for large-scale deployment. The company captures industrial CO2 emissions from nearby facilities to feed into its PBRs, achieving a significant reduction in greenhouse gas emissions while enhancing algal growth. This process has demonstrated the potential to produce over 10,000 gallons of ethanol per acre per year, positioning Algenol as a leader in algae-based biofuel production. The company’s approach not only addresses environmental challenges but also ensures economic feasibility by producing co-products such as bioplastics and animal feed from algal biomass residuals [175].
In Portugal, A4F Algae Solutions (located in Lisbon) exemplifies how microalgae can be integrated into circular economy models. Specializing in the design and operation of large-scale algae cultivation systems, A4F employs outdoor raceway ponds for biomass production, particularly in wastewater treatment applications. These systems are both cost-effective and energy-efficient, leveraging natural sunlight to sustain algal growth. By incorporating microalgae into wastewater treatment plants, A4F removes excess nutrients like nitrogen and phosphorus while simultaneously producing valuable products such as biofertilizers and biofuels. The company’s Allmicroalgae facility is a flagship example, supplying global markets with omega-3 fatty acids and natural pigments derived from algae. A4F’s dual-purpose approach addresses environmental challenges, such as water pollution, while demonstrating economic viability in diverse markets [172].
Another successful case is Qualitas Health, based in Houston, Texas, USA, which focuses on producing algae-based omega-3 fatty acids under the brand name iWi®. Unlike traditional cultivation systems, Qualitas utilizes saltwater algae grown in open ponds located in arid regions, which makes use of non-arable land and saline water. This innovative approach minimizes freshwater use and relies on solar energy, ensuring sustainable operations. The company’s algae cultivation process has been shown to produce omega-3 with a lower carbon footprint compared to fish-based alternatives, making it a key player in the global nutraceutical market. By transforming barren landscapes into productive sites for sustainable algae cultivation, Qualitas Health addresses the growing demand for environmentally friendly nutritional products [176].
These examples demonstrate the scalability, economic feasibility, and environmental benefits of large-scale microalgal cultivation projects, highlighting the potential for microalgae to contribute significantly to global sustainability goals.
5.8. Future Perspectives
The discussion underscores the need for coordinated efforts to address economic and technological challenges. Standardizing regulations and fostering international collaboration will further accelerate the adoption of microalgal technologies. Continued investments in R&D and policy frameworks tailored to the unique challenges of the microalgal industry are imperative for achieving global sustainability goals.
Table 1.
Contributions of Algal Industries to Sustainable Development Goals (SDGs).
| Goal/Target | Focus Points | Aquaculture | Agriculture | Food and Feed | Wastewater | Carbon Capture | Pharmaceutical | Cosmetics |
|---|---|---|---|---|---|---|---|---|
| 2 | ||||||||
| 2.1 | “Access to safe, nutritious and sufficient food all year round.” | √ | √ | √ | ||||
| 2.3 | “Double the agricultural productivity and incomes of women, indigenous peoples, family farmers.” | √ | √ | √ | ||||
| 2.4 | “To ensure sustainable food production systems and implement resilient agricultural practices that increase productivity and production, that help maintain ecosystems, that strengthen capacity for adaptation to climate change and that progressively improve land and soil quality.” | √ | √ | √ | ||||
| 2.a | “Increase investment, including through enhanced international cooperation, in rural infrastructure, agricultural research and extension services, technology development in order to enhance agricultural productive capacity in developing countries, in particular least developed countries.” | √ | √ | √ | ||||
| 3 | ||||||||
| 3.8 | “Access to safe, effective, quality and affordable essential medicines and vaccines.” | √ | ||||||
| 3.9 | “Reduce the number of deaths and illnesses from hazardous chemicals and air, water and soil pollution and contamination.” | √ | √ | √ | √ | √ | ||
| 3.b | “Research and development of vaccines and medicines.” | √ | ||||||
| 6 | ||||||||
| 6.3 | “Improve water quality by reducing pollution, eliminating dumping and minimizing release of hazardous chemicals and materials, halving the proportion of untreated wastewater and substantially increasing recycling and safe reuse globally.” | √ | ||||||
| 6.4 | “Substantially increase water-use efficiency across all sectors and ensure sustainable withdrawals and supply of freshwater.” | √ | √ | |||||
| 7 | ||||||||
| 7.2 | “Increase substantially the share of renewable energy in the global energy mix.” | √ | √ | |||||
| 8 | ||||||||
| 8.2 | “Achieve higher levels of economic productivity through diversification, technological upgrading and innovation, including through a focus on high-value added sectors.” | √ | √ | √ | √ | √ | √ | √ |
| 8.4 | “Improve progressively, through 2030, global resource efficiency in consumption and production and endeavour to decouple economic growth from environmental degradation.” | √ | √ | √ | √ | √ | √ | √ |
| 9 | ||||||||
| 9.4 | “To upgrade infrastructure of industries to make them sustainable, with increased resource-use efficiency and greater adoption of clean and environmentally sound technologies and industrial processes.” | √ | √ | √ | √ | √ | √ | √ |
| 9.5 | “To enhance scientific research, upgrade the technological capabilities of industrial sectors in all countries.” | √ | √ | √ | √ | √ | √ | √ |
| 9.b | “To provide support domestic technology development, research and innovation in developing countries, including by ensuring a conducive policy environment for, inter alia, industrial diversification and value addition to commodities.” | √ | √ | √ | √ | √ | √ | √ |
| 11 | ||||||||
| 11.6 | “To reduce the adverse per capita environmental impact of cities by paying special attention to municipal and other waste management.” | √ | ||||||
| 12 | ||||||||
| 12.1 | “To implement Sustainable Consumption and Production Patterns.” | √ | √ | √ | √ | √ | √ | √ |
| 12.2 | “To achieve the sustainable management and efficient use of natural resources.” | √ | √ | √ | √ | |||
| 12.4 | “To achieve the environmentally sound management of chemicals and all wastes throughout their life cycle, and significantly reduce their release to air, water and soil in order to minimize their adverse impacts on human health and the environment.” | √ | √ | √ | √ | √ | ||
| 12.5 | “To reduce waste generation through prevention, reduction, recycling and reuse.” | √ | √ | √ | ||||
| 12.a | “To provide support developing countries to strengthen their scientific and technological capacity to move towards more sustainable patterns of consumption and production.” | √ | √ | √ | √ | √ | √ | √ |
| 13 | ||||||||
| 13.1 | “Strengthen resilience to climate-related hazards and natural disasters in all countries”. | √ | √ | √ | ||||
| 14 | ||||||||
| 14.4 | “To regulate harvesting and end overfishing, illegal, unreported and unregulated fishing and destructive fishing practices.” | √ | ||||||
| 14.7 | “To increase the economic benefits to small island developing States and least developed countries from the sustainable use of aquaculture.” | √ | ||||||
| 15 | ||||||||
| 15.1 | “To ensure the conservation, restoration and sustainable use of terrestrial and inland freshwater ecosystems.” | √ | √ | |||||
| 15.2 | “To promote the implementation of sustainable management of all types of forests, halt deforestation, restore degraded forests.” | √ | ||||||
| 17 | ||||||||
| 17.6 | “To enhance international cooperation on and access to science, technology and innovation and enhance knowledge-sharing on mutually agreed terms.” | √ | √ | √ | √ | √ | √ | √ |
| 17.7 | “To promote the development, transfer, dissemination and diffusion of environmentally sound technologies to developing countries.” | √ | √ | √ | √ | √ | √ | √ |
Table 2.
Economic Aspects of Microalgae Applications.
| Application | Current Cost Challenges | Quantitative Data | Cost Reduction Strategies | Timeline for Competitiveness | Potential Benefits |
|---|---|---|---|---|---|
| Biofuels | High production costs, 10× soybean biofuel costs ([177]) | Production cost: 2.50 USD/L vs. 0.25 USD/L for soybean biofuel ([177]) | Improved photobioreactor designs, biorefinery approaches ([4]) | 5–10 years with sustained R&D investment in photobioreactors and biorefinery integration ([177]) | Reduction in greenhouse gas emissions; circular economy enhancement |
| Pharmaceuticals | Expensive extraction and processing of metabolites ([6]) | Metabolite extraction costs up to 500 USD/kg ([178]) | Genetic engineering for higher metabolite yield ([15]) | 3–7 years with advancements in genetic engineering and scalable extraction technologies ([178]). | Improved access to affordable medicines; enhanced drug efficacy |
| Aquaculture | Costly fish feed substitutes; scaling issues ([69]) | Microalgae fish feed costs 1000 USD/ton vs. 600 USD/ton for soybean ([171]) | Integrating wastewater treatment with feed production ([179]) | 2–5 years; already competitive for high-value aquaculture species ([170]). | Reduced pressure on wild fisheries; improved food security |
| Wastewater Treatment | Low-cost effective scalability ([180]) | Operational cost savings of up to 30% in integrated systems ([169]) | Using industrial effluents for algal growth ([11]) | 3–8 years; reliant on supportive policies and incentives for widespread adoption ([180]). | Reduced water pollution; enhanced nutrient recovery |
| Cosmetics | Expensive purification of bioactive compounds ([7]) | Pigment extraction costs 400 USD/kg, depending on purity and methods used [178] | Using advanced solvents and bioreactor systems ([7]) | 5–7 years with the adoption of advanced bioreactor systems and sustainable solvent technologies ([178]). | Increased consumer safety; reduced environmental impact |
Table 3.
Cost Analysis of Microalgal Applications.
| Application | Current Cost Challenges | Quantitative Data | Cost Breakdown (with Examples) | Cost Reduction Strategies | Timeline for Competitiveness | Potential Benefits |
|---|---|---|---|---|---|---|
| Biofuels | High production costs approximately 10 times higher than soybean biofuels ([177]). | Production cost: 0.66 USD/L compared to 0.25 USD/L for soybean biofuel ([177]). | Energy (40–60%): Powering paddle wheels in raceway ponds or lights in photobioreactors. Example: LED lighting can save 20–30% on energy ([169]). Harvesting (20–30%): Centrifugation or flocculation to concentrate biomass. Example: Electrocoagulation reduces energy use by up to 50%. - Nutrients (10–20%): Sourcing nitrogen and phosphorus. Example: Wastewater integration saves up to 70% on nutrient costs ([177]). | Improved photobioreactor designs and biorefinery approaches ([169]). | 5–10 years with sustained R&D investment ([177]). | Reduction in greenhouse gas emissions; enhancement of the circular economy ([177]). |
| Pharmaceuticals | Expensive extraction and processing of metabolites ([178]). | Metabolite extraction costs up to 500 USD/kg ([178]). | - Extraction and Purification (50–70%): Supercritical CO2 extraction for carotenoids or metabolites. Example: Supercritical CO2 extraction for astaxanthin costs 200–300 USD/kg. - Cultivation (10–20%): Optimized media costs for high-value strains. Example: High-cell density cultivation of Haematococcus pluvialis reduces media usage ([178]). | Genetic engineering for higher metabolite yield ([178]). | 3–7 years with advancements in scalable extraction technologies ([178]). | Improved access to affordable medicines; enhanced drug efficacy ([178]). |
| Aquaculture | Costly fish feed substitutes; scaling issues ([170]). | Microalgae fish feed costs approximately 1000 USD/ton vs. 600 USD/ton for soybean feed ([170]). | - Cultivation (30–50%): Raceway ponds for algal biomass. Example: Using sunlight reduces energy costs by 40%. - Harvesting (30–40%): Flocculation or filtration for feed-grade biomass. Example: Chitosan-based flocculants reduce costs by 20%. - Downstream Processing (10–20%): Drying or pelletizing algal feed. Example: Spray-drying algae for aquafeed costs ~200 USD/ton ([171]). | Integrating wastewater treatment with feed production ([171]). | 2–5 years; already competitive for high-value aquaculture species ([170]). | Reduced pressure on wild fisheries; improved food security ([170]). |
| Wastewater Treatment | Challenges in low-cost scalability ([169]). | Operational cost savings of up to 30% in integrated systems ([169]). | - Nutrient Recovery (30–50%): Removing nitrogen and phosphorus. Example: Algae in municipal wastewater can remove up to 90% of nitrogen and 80% of phosphorus. - Energy Use (20–30%): Aeration for algal ponds. Example: Solar aeration reduces energy costs by 15–25% ([169]). - Harvesting (10–20%): Sedimentation or membrane separation. Example: Sedimentation reduces harvesting costs by 30% compared to centrifugation. | Utilizing industrial effluents for algal growth ([169]). | 3–8 years; relies on supportive policies and incentives ([180]). | Reduced water pollution; enhanced nutrient recovery ([169]). |
| Cosmetics | Expensive purification of bioactive compounds ([178]). | Pigment extraction costs approximately 400 USD/kg, depending on purity [178]). | - Purification (50–70%): Solvent-based extraction of pigments like β-carotene or lutein. Example: Using ionic liquids reduces extraction costs by 20% ([178]). - Cultivation (10–20%): High-density culture systems for pigment-rich strains. Example: LED-optimized cultivation of Dunaliella salina reduces energy use by 30%. | Using advanced solvents and bioreactor systems ([178]). | 5–7 years with the adoption of sustainable alternatives ([178]). | Increased consumer safety; reduced environmental impact ([178]). |
Table 4.
Quantitative Evidence of benefits of microalgae.
| Application | Comparative Metrics | Quantitative Data | Environmental Benefits | Case Studies |
|---|---|---|---|---|
| Biofuels | Production cost: Algae 0.66–11.57 USD/L vs. Soybean 0.25 USD/L ([169,177]). | Yield: 20–30 tons/ha/year; CO2 capture: 1.6–1.8 tons/ton algae ([168,169]). | Reduction in GHG emissions by 50–70% compared to fossil fuels ([169,177]). | DOE-funded algae farm integrating biorefinery in Arizona ([177]). |
| Pharmaceuticals | Yield: 4–10% astaxanthin content in Haematococcus pluvialis vs. 0.1–0.3% in synthetic chemical production ([178,181,182]). | Extraction cost: 300–500 USD/kg for purified astaxanthin ([178]). | Reduced reliance on synthetic chemicals; low-energy purification ([171]). | Cyanotech’s supercritical CO2 extraction for carotenoids ([170]). |
| Aquaculture | Nutritional profile: Higher omega-3 content in algae feed (10–25% EPA/DHA) vs. fishmeal (5–15% EPA/DHA) ([170]). | Microalgae fish feed costs 800–1200 USD/ton vs. 500–600 USD/ton for soybean feed ([170]). | Reduced reliance on wild fish stocks; improved aquatic biodiversity ([170]). | Integrated algae feed trials in Norway for Atlantic salmon ([170]). |
| Wastewater Treatment | Nutrient recovery: 70–90% nitrogen and 60–80% phosphorus removal ([169]). | Operational savings of up to 20–30% with integrated systems ([169]). | Reduction in eutrophication and water pollution ([169]). | Municipal wastewater plant using algae in The Netherlands ([169]). |
| Cosmetics | Yield: β-carotene productivity in Dunaliella at 100–150 mg/L/day ([178]). | Pigment extraction costs 300–450 USD/kg, depending on purity ([178]). | Biodegradable products; reduced use of petroleum-based compounds ([178]). | L’Oréal uses algae-derived pigments in skincare products ([178]). |
The microalgal bioeconomy can contribute to the SDGs by facilitating a shift towards a green economy. This transition, supported by policies that accelerate the move towards sustainability, presents a challenging yet achievable task. One paper argued that sustainable technological change encompasses societal, organizational, political, and economic challenges, which are not solely technical. The key challenges in transitioning to a green economy include managing global environmental risks, achieving radical technological advancements, navigating green capitalism, formulating effective state policies, and addressing distributional impacts [183]. These challenges involve structural tasks, overcoming barriers, and the roles of various actors, such as private firms and government authorities. Green capitalism and entrepreneurial ventures may not suffice for this transition, as radical technological shifts are necessary, involving long development periods and the creation of new structures like actor networks, value chains, and institutions. The private sector alone cannot drive these changes, necessitating policy support based on an understanding of the obstacles to long-term technological development. Context-specific support for different technologies is crucial [183]. Green innovation policies should focus on developing generic technologies and supporting public R&D and pilot projects. Establishing new green technologies may require creating new value chains and societal adjustments, such as legal changes, consumer behaviour shifts, distributional effects, infrastructure development, and new business models [183]. Through these initiatives, robust support can be offered to the industry, enabling it to extend its applications across various sectors and broaden the scope of the green economy.
6. Recommendations
This review highlights numerous potential avenues for algae research. It suggests conducting a life cycle analysis (LCA) on algae-based products that could substitute traditional items such as fish feed, fertilizers, pharmaceuticals, cosmetics, and products related to wastewater treatment and carbon capture. By comparing these to the current alternatives, we can assess their impact on water, carbon, and energy footprints, as well as their environmental benefits. This approach will not only reveal the techno-economic implications but also pinpoint areas needing enhancement for commercial production. The scope of research should also extend to sectors where algae-derived products can offer significant ecological advantages, such as replacing synthetic materials with bioplastics or substituting terrestrial plant materials in pharmaceutical and cosmetic products [184,185,186]. Such shifts could alleviate the pressure on terrestrial ecosystems, aiding in the prevention of deforestation, mitigating landscape alteration, and reducing indirect greenhouse gas emissions. Moreover, developing algae-based substitutes for raw materials sourced from valuable products like honey, which has various medicinal and cosmetic applications, could decrease honey consumption, thereby contributing to bee conservation amid rising concerns over bee extinction [187,188]. Wild bees are crucial pollinators for zoophilous wild plants and crops, providing essential ecosystem services. These plants rely on adapted pollinators for effective reproduction, and many other organisms depend on these plants for food [189]. Thus, expanding algae research could significantly bolster the Sustainable Development Goals by fostering a greener economy.
7. Conclusions
This study underscores microalgae as a cornerstone for a sustainable and green economy, instrumental in realizing the SDGs and offering solutions that are both environmentally sustainable and economically viable. It presents a compelling case for microalgae as an underutilized resource with immense potential to contribute significantly to global sustainable development objectives. Microalgae’s diverse applications in various sectors exemplify their potential to address critical global challenges. Their role in carbon sequestration and wastewater treatment demonstrates a commitment to environmental sustainability, while their contribution to food and feed, pharmaceuticals and cosmetics promotes healthier lifestyles. This article acknowledges the hurdles in mainstreaming microalgae, including technological limitations, cost barriers, and regulatory challenges. It emphasizes the need for multidisciplinary research, innovation, and supportive policies to enhance the scalability and economic feasibility of microalgal applications.
The conclusion advocates for an integrated approach, combining scientific advancements with strategic policy frameworks to promote microalgae as a sustainable resource. It calls for increased investment in research and development, public awareness campaigns, and collaboration between academia, industry, and policymakers. This collaborative effort is essential to overcome existing barriers and harness the full potential of microalgae in a green economy.
Author Contributions
Conceptualization, methodology, investigation, writing—original draft preparation, N.K.S.; review and editing, supervision, P.K. All authors have read and agreed to the published version of the manuscript.
Funding
This research received no external funding.
Data Availability Statement
Data sharing is not applicable to this article as no new data were created or analysed in this study.
Conflicts of Interest
The authors declare no conflicts of interest.
Appendix A
Table A1.
Korean Green Growth Agenda [24].
Table A1.
Korean Green Growth Agenda [24].
| Goal | Description |
|---|---|
| GG1 | “Building a low-carbon society, e.g., setting up a national GHG-monitoring system, and encouraging low-carbon 3-Rs (Reduce, Recycle and Reuse).” |
| GG2 | “Enhancing energy security, e.g., achieving 100% energy independence by 2050.” |
| GG3 | “Strengthening adaptive measures to cope with climate change, e.g., improving food and water security.” |
| GG4 | “Developing green technology, e.g., investment in green tech R&D to reach 25% of all R&D by 2020 (in core green technologies like LEDs, EVs, renewables).” |
| GG5 | “Fostering green industries, e.g., building green clusters and new green export platforms (to double green exports to 20% by 2020).” |
| GG6 | “Fusing green and smart technology, e.g., smart grid development.” |
| GG7 | “Building green economy support, e.g., green finance and carbon market.” |
| GG8 | “Green cities, e.g., green transport, green buildings, fast rail as well as green land management.” |
| GG9 | “Promoting green consumption and lifestyle, e.g., eco-labelling and carbon-certification.” |
| GG10 | “Seeking opportunities for global leadership, e.g., enhancing global and regional green cooperation and turning Korea into a ‘green hub’.” |
Table A2.
Green Growth Index of China [190].
Table A2.
Green Growth Index of China [190].
| Goal | Description |
|---|---|
| A3 | “Proportion of non-fossil energy consumption.” |
| A4 | “CO2 emissions per unit of GDP.” |
| A5 | “SO2 emissions per unit of GDP.” |
| A6 | “COD (Chemical Oxygen Demand) emissions per unit of GDP.” |
| A7 | “NOx emissions per unit of GDP.” |
| A10 | “Land output rate.” |
| A11 | “Irrigation saving rate.” |
| A12 | “Proportion of irrigation area.” |
| A14 | “Water consumption per unit industrial added value.” |
| A15 | “Proportion of added value in the tertiary industry.” |
| A16 | “Proportion of employment in the tertiary industry.” |
| B1 | “Water resources per capita.” |
| B2 | “Forest area per capita.” |
| B7 | “CO2 emissions per capita.” |
| B9 | “SO2 emissions per capita.” |
| B11 | “COD emissions per capita.” |
| B13 | “Ammonia nitrogen emissions per capita.” |
| B14 | “Consumption of chemical fertilizers per unit of cultivated land area.” |
| B15 | “Pesticide use per unit of cultivated land area.” |
| C4 | “Urban sewage treatment rate.” |
Table A3.
European Bioeconomy Strategy and Green Deal [19].
Table A3.
European Bioeconomy Strategy and Green Deal [19].
| Goal | Bioeconomy Strategy | Goal | Green Deal |
|---|---|---|---|
| BG1 | “To ensure food and nutrition security.” | GD1 | “Clean, secure and affordable energy.” |
| GD2 | “Carbon-neutral economy.” | ||
| BG2 | “To manage natural resources sustainably.” | GD3 | “To accelerate a shift to sustainable and smart mobility.” |
| BG3 | “To reduce dependence on non-renewable, unsustainable resources.” | GD4 | “Clean and circular industry.” |
| GD5 | “The farm to form strategy: fair, healthy and environmentally food.” | ||
| BG4 | “To limit and adapt to climate change.” | GD6 | “To build and renovate in a resource efficient way.” |
| BG5 | “To strengthen European competitiveness and create jobs.” | GD7 | “To preserve and restore ecosystems and biodiversity.” |
| GD8 | “A zero-pollution ambition for toxic-free environment.” |
Table A4.
SDG goals and targets (https://sdgs.un.org/goals, accessed on 19 December 2024).
Table A4.
SDG goals and targets (https://sdgs.un.org/goals, accessed on 19 December 2024).
| Goal/Target | Description |
|---|---|
| 1 | “End poverty in all its forms everywhere.” |
| 1.1 | “By 2030, eradicate extreme poverty for all people everywhere, currently measured as people living on less than $1.25 a day.” |
| 1.2 | “By 2030, reduce at least by half the proportion of men, women and children of all ages living in poverty in all its dimensions according to national definitions.” |
| 2 | “End hunger, achieve food security and improved nutrition and promote sustainable agriculture.” |
| 2.1 | “By 2030, end hunger and ensure access by all people, in particular the poor and people in vulnerable situations, including infants, to safe, nutritious and sufficient food all year round.” |
| 2.3 | “By 2030, double the agricultural productivity and incomes of small-scale food producers, in particular women, indigenous peoples, family farmers, pastoralists and fishers, including through secure and equal access to land, other productive resources and inputs, knowledge, financial services, markets and opportunities for value addition and non-farm employment.” |
| 2.4 | “By 2030, ensure sustainable food production systems and implement resilient agricultural practices that increase productivity and production, that help maintain ecosystems, that strengthen capacity for adaptation to climate change, extreme weather, drought, flooding and other disasters and that progressively improve land and soil quality.” |
| 2.a | “Increase investment, including through enhanced international cooperation, in rural infrastructure, agricultural research and extension services, technology development and plant and livestock gene banks in order to enhance agricultural productive capacity in developing countries, in particular least developed countries.” |
| 3 | “Ensure healthy lives and promote well-being for all at all ages.” |
| 3.8 | “Achieve universal health coverage, including financial risk protection, access to quality essential health-care services and access to safe, effective, quality and affordable essential medicines and vaccines for all.” |
| 3.9 | “By 2030, substantially reduce the number of deaths and illnesses from hazardous chemicals and air, water and soil pollution and contamination.” |
| 3.b | “Support the research and development of vaccines and medicines for the communicable and non-communicable diseases that primarily affect developing countries, provide access to affordable essential medicines and vaccines, in accordance with the Doha Declaration on the TRIPS Agreement and Public Health, which affirms the right of developing countries to use to the full the provisions in the Agreement on Trade-Related Aspects of Intellectual Property Rights regarding flexibilities to protect public health, and, in particular, provide access to medicines for all.” |
| 6 | “Ensure availability and sustainable management of water and sanitation for all.” |
| 6.3 | “By 2030, improve water quality by reducing pollution, eliminating dumping and minimizing release of hazardous chemicals and materials, halving the proportion of untreated wastewater and substantially increasing recycling and safe reuse globally.” |
| 6.4 | “By 2030, substantially increase water-use efficiency across all sectors and ensure sustainable withdrawals and supply of freshwater to address water scarcity and substantially reduce the number of people suffering from water scarcity.” |
| 6.5 | “By 2030, implement integrated water resources management at all levels, including through transboundary cooperation as appropriate.” |
| 6.6 | “By 2020, protect and restore water-related ecosystems, including mountains, forests, wetlands, rivers, aquifers and lakes.” |
| 7 | “Ensure access to affordable, reliable, sustainable and modern energy for all.” |
| 7.2 | “By 2030, increase substantially the share of renewable energy in the global energy mix.” |
| 8 | “Promote sustained, inclusive and sustainable economic growth, full and productive employment and decent work for all.” |
| 8.2 | “Achieve higher levels of economic productivity through diversification, technological upgrading and innovation, including through a focus on high-value added and labour-intensive sectors.” |
| 8.4 | “Improve progressively, through 2030, global resource efficiency in consumption and production and endeavour to decouple economic growth from environmental degradation, in accordance with the 10-Year Framework of Programmes on Sustainable Consumption and Production, with developed countries taking the lead.” |
| 8.5 | “By 2030, achieve full and productive employment and decent work for all women and men, including for young people and persons with disabilities, and equal pay for work of equal value.” |
| 9 | “Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation.” |
| 9.4 | “By 2030, upgrade infrastructure and retrofit industries to make them sustainable, with increased resource-use efficiency and greater adoption of clean and environmentally sound technologies and industrial processes, with all countries taking action in accordance with their respective capabilities.” |
| 9.5 | “Enhance scientific research, upgrade the technological capabilities of industrial sectors in all countries, in particular developing countries, including, by 2030, encouraging innovation and substantially increasing the number of research and development workers per 1 million people and public and private research and development spending.” |
| 9.b | “Support domestic technology development, research and innovation in developing countries, including by ensuring a conducive policy environment for, inter alia, industrial diversification and value addition to commodities.” |
| 12 | “Ensure sustainable consumption and production patterns.” |
| 12.1 | “Implement the 10-Year Framework of Programmes on Sustainable Consumption and Production Patterns, all countries taking action, with developed countries taking the lead, taking into account the development and capabilities of developing countries.” |
| 12.2 | “By 2030, achieve the sustainable management and efficient use of natural resources.” |
| 12.4 | “By 2020, achieve the environmentally sound management of chemicals and all wastes throughout their life cycle, in accordance with agreed international frameworks, and significantly reduce their release to air, water and soil in order to minimize their adverse impacts on human health and the environment.” |
| 12.5 | “By 2030, substantially reduce waste generation through prevention, reduction, recycling and reuse.” |
| 12.6 | “Encourage companies, especially large and transnational companies, to adopt sustainable practices and to integrate sustainability information into their reporting cycle.” |
| 12.a | “Support developing countries to strengthen their scientific and technological capacity to move towards more sustainable patterns of consumption and production.” |
| 14 | “Conserve and sustainably use the oceans, seas and marine resources for sustainable development.” |
| 14.4 | “By 2020, effectively regulate harvesting and end overfishing, illegal, unreported and unregulated fishing and destructive fishing practices and implement science-based management plans, in order to restore fish stocks in the shortest time feasible, at least to levels that can produce maximum sustainable yield as determined by their biological characteristics.” |
| 14.7 | “By 2030, increase the economic benefits to small island developing States and least developed countries from the sustainable use of marine resources, including through sustainable management of fisheries, aquaculture and tourism.” |
| 15 | “Protect, restore and promote sustainable use of terrestrial ecosystems, sustainably manage forests, combat desertification, and halt and reverse land degradation and halt biodiversity loss.” |
| 15.1 | “By 2020, ensure the conservation, restoration and sustainable use of terrestrial and inland freshwater ecosystems and their services, in particular forests, wetlands, mountains and drylands, in line with obligations under international agreements.” |
| 15.2 | “By 2020, promote the implementation of sustainable management of all types of forests, halt deforestation, restore degraded forests and substantially increase afforestation and reforestation globally.” |
| 17 | “Strengthen the means of implementation and revitalize the Global Partnership for Sustainable Development.” |
| 17.6 | “Enhance North-South, South-South and triangular regional and international cooperation on and access to science, technology and innovation and enhance knowledge-sharing on mutually agreed terms, including through improved coordination among existing mechanisms, in particular at the United Nations level, and through a global technology facilitation mechanism.” |
| 17.7 | “Promote the development, transfer, dissemination and diffusion of environmentally sound technologies to developing countries on favourable terms, including on concessional and preferential terms, as mutually agreed.” |
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Figure 1.
Dual Pathways for Wastewater Management: Traditional Treatment and Algal Reuse.
Figure 2.
Eco-Friendly Aquaculture: Leveraging Microalgae for Sustainability.
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Sarker, N.K.; Kaparaju, P. Microalgal Bioeconomy: A Green Economy Approach Towards Achieving Sustainable Development Goals. Sustainability 2024, 16, 11218. https://doi.org/10.3390/su162411218
AMA Style
Sarker NK, Kaparaju P. Microalgal Bioeconomy: A Green Economy Approach Towards Achieving Sustainable Development Goals. Sustainability. 2024; 16(24):11218. https://doi.org/10.3390/su162411218
Chicago/Turabian StyleSarker, Nilay Kumar, and Prasad Kaparaju. 2024. "Microalgal Bioeconomy: A Green Economy Approach Towards Achieving Sustainable Development Goals" Sustainability 16, no. 24: 11218. https://doi.org/10.3390/su162411218
APA StyleSarker, N. K., & Kaparaju, P. (2024). Microalgal Bioeconomy: A Green Economy Approach Towards Achieving Sustainable Development Goals. Sustainability, 16(24), 11218. https://doi.org/10.3390/su162411218
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