Commercial and Industrial Algae Culture and Applications (2025)

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Home > Books > Algae - Science and Applications

Open access peer-reviewed chapter

Written By

Mir Shariful Islam, Bidyut Baran Saha, Md. Mushfiqur Rahman and Rafid Fayyaz

Submitted: 23 December 2024 Reviewed: 06 January 2025 Published: 12 February 2025

DOI: 10.5772/intechopen.1008949

IntechOpen Algae Science and Applications Edited by Ihana Aguiar Severo

From the Edited Volume

Algae - Science and Applications

Ihana Aguiar Severo

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Abstract

Algae, photosynthetic organisms ranging from microscopic to macroscopic forms, play a critical role in carbon sequestration, oxygen production, and maintaining aquatic ecosystem balance. Their extensive applications in pharmaceuticals, biofuels, and bioproducts have positioned algae cultivation as a promising solution for sustainable resource production. Both microalgae and macroalgae can be cultivated using open systems (e.g., longline culture, floating nets, bottom culture, raceway ponds, and saline aquaculture) and closed systems (e.g., photobioreactors, tank cultures,and fermenters). While closed systems offer precise control over growth conditions and productivity, open systems are more cost-effective but susceptible to environmental variability and contamination. Integrated multi-trophic aquaculture (IMTA) enhances resource efficiency by combining algae cultivation with other species, supporting environmental and economic sustainability. This chapter provides an in-depth analysis of algae culture techniques, their industrial applications, and associated challenges. Additionally, the chapter examines future research directions and the role of policy frameworks in advancing sustainable algae culture, offering valuable insights for researchers, industry stakeholders, and policymakers.

Keywords

algae culture
open system algae culture
closed system algae culture
IMTA
photobioreactors
fermenters
saline aquaculture

Author Information

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Mir Shariful Islam *
- Department of Oceanography, University of Dhaka, Dhaka, Bangladesh
Bidyut Baran Saha
- International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, Japan
Md. Mushfiqur Rahman
- Department of Oceanography, University of Dhaka, Dhaka, Bangladesh
Rafid Fayyaz
- Department of Oceanography, University of Dhaka, Dhaka, Bangladesh

*Address all correspondence to: mirsharifuldu77@du.ac.bd

1. Introduction

Algae are a highly diverse group of photosynthetic organisms with an extensive fossil record, broadly classified into macroalgae and microalgae [1]. Macroalgae, or seaweeds, are predominantly found in the littoral zone and include green (Chlorophyta), brown (Phaeophyta), and red (Rhodophyta) algae [2], while microalgae are distributed across benthic and littoral zones and dominate the phytoplankton in open oceans. Globally, there are approximately 900 species of green algae, 4000 species of red algae, and 1500 species of brown algae, with about 250 species being commercially significant for applications, such as food production and phycocolloid extraction [3]. Both macroalgae and microalgae represent significant dietary resources due to their considerable concentrations of vitamins, minerals, proteins, and dietary fibers. Algae are particularly rich in a diverse array of vitamins, including β-carotene, which serves as a precursor to vitamin A, several B vitamins (notably B12), and vitamins C, D, E, and K [4]. Additionally, the elevated enzyme activity in algae enhances the bioavailability and digestion of these essential nutrients. Standard nutritional assessments have consistently revealed high carbohydrate content in algae, in addition to a variety of minerals, vitamins, and trace elements such as iodine, further underscoring their nutritional value [5].

Microalgae play a significant role in the food chain and contribute to the production of valuable bioactive compounds across various sectors, such as skincare, pharmaceuticals, and aquaculture [6]. They are highly efficient in removing nutrients and decontaminating heavy metals from wastewater via biofiltration, owing to their superior nutrient absorption capabilities compared to terrestrial plants [7]. Microalgae-based systems offer an environmentally sustainable alternative to conventional wastewater treatment methods, as they do not produce additional pollution and enable biomass reuse [7]. These systems effectively reduce excess nutrients from aquaculture effluent, promoting environmental sustainability. Their high oil content and rapid biomass production make them a promising source for biofuel production [8]. With a nutritional profile rich in amino acids, fatty acids, phytonutrients, and phycobiliproteins, microalgae are free from toxins, making them suitable for both animal feed and human consumption [9]. In aquaculture, microalgae serve as live feed for zooplankton and various growth stages of bivalve mollusks (e.g., oysters, scallops), abalone, crustaceans, and fish, improving growth, protein deposition, disease resistance, digestibility, and carcass quality, while also reducing nitrogen output [10]. The physiological benefits of microalgae, including enhanced stress tolerance and starvation resistance, have led to their growing use as additives in aquaculture, positioning them as a sustainable and multifunctional resource [11]. Macroalgae are rich in bioactive compounds, such as polysaccharides, proteins, polyunsaturated fatty acids, pigments, polyphenols, minerals, and hormones [12]. Recent research highlights their therapeutic potential, with extracts exhibiting antioxidant, anticancer, antiproliferative, and antibacterial properties [13]. These bioactive compounds contribute to the beneficial biological effects of macroalgae, especially in treating cardiovascular disorders like atherosclerosis, hyperlipidemia, hypertension, and thyroid diseases [14]. Polyphenols and flavonoids in algae are particularly noted for their antibacterial and antioxidant properties, with antimicrobial effects linked to compounds like phenols, fatty acids, terpenes, and indoles [15]. The bioactive composition of algae varies among species and is influenced by environmental and geographical conditions [15].

Algae play a vital role in sustaining marine ecosystems while offering significant nutritional and therapeutic benefits. They contribute to reducing carbon dioxide (CO₂) emissions through carbon fixation and act as primary producers in marine environments [16]. The increasing levels of CO₂ emissions have accelerated climate change, resulting in severe consequences such as cyclones, floods, droughts, rising sea levels, and other environmental threats that endanger humanity [16]. Despite these challenges, global efforts to reduce carbon emissions remain limited or ineffective in many regions [17]. Consequently, developing effective methods to mitigate CO2 emissions and accumulation has become essential. Biological CO₂ fixation is considered the most cost-effective and environmentally sustainable solution for addressing this issue [18]. Algae and cyanobacteria demonstrate growth rates far exceeding those of terrestrial plants, with CO₂ fixation efficiencies 10–50 times higher [19]. As some of the fastest-growing photosynthetic organisms on Earth, algae exhibit remarkable biodiversity and are responsible for approximately 50% of the global carbon fixation, highlighting their critical role in combating climate change [20]. Algae culture is gaining significant attention due to its therapeutic and nutritional benefits. It is considered a vital component of the blue economy in various countries worldwide. While substantial progress has been made in commercial and industrial algae cultivation techniques, various challenges remain, influenced by species-specific and regional factors. This chapter explores key commercial and industrial algae culture methods, their applications, and the challenges faced, aiming to provide insights into the development and potential of this expanding industry.

2. Algae culture techniques

Algae culture, or algae farming, involves cultivating algae for commercial purposes under controlled conditions in onshore facilities, open waters, or coastal regions. Key factors influencing cultivation include nutrient availability, cost of production, product quality, environmental conditions, technology requirements, and initial investments. There are mainly three types of culture techniques, which are commonly used for commercial and industrial algae culture. They are given below:

Closed system culture technique
Open system culture technique
Integrated multi-trophic aquaculture (IMTA) system

2.1 Closed system culture technique

Closed systems for algae cultivation offer higher photosynthetic efficiency, improved biomass productivity, and sustainable yields through precise control of environmental conditions while minimizing water loss [21]. Advanced photobioreactors (PBRs), constructed from transparent materials, optimize light utilization and environmental regulation, though their design remains complex. Fermenter-based and tank systems further integrate technologies for precise control of temperature, light, and aeration, ensuring stable and efficient cultivation. Despite higher resource requirements and costs, closed systems are increasingly favored for high-value algae production due to their reliability and productivity [22]. Although primarily utilized for microalgae, these systems can also be adapted for macroalgae cultivation, enhancing sustainable production practices.

2.1.1 Algae culture using photobioreactor

Phototrophic microorganisms, including algae, cyanobacteria, and photosynthetic bacteria, are cultivated in photobioreactors (PBRs)—specialized systems designed to harness light for photosynthesis [23]. PBRs consist of transparent culture vessels, nutrient supply systems, gas exchange mechanisms (for CO₂ input and O₂ removal), mixing systems, temperature regulation, and monitoring tools [24]. Various types of photobioreactors are utilized for algae culture, each offering distinct advantages depending on the specific requirements of the cultivation process. For example, microfluidic photobioreactors enable detailed observation of algae cells, either as isolated entities or within clusters comprising multiple species [25]. Shaken photobioreactors, such as orbital shaker flasks, are commonly employed in illuminated chambers with regulated parameters like humidity, pH, temperature, and CO₂ [26]. Vertical column photobioreactors, constructed from materials such as polyvinyl chloride (PVC), glass, or plexiglass, are designed to ensure effective light penetration for optimal algal growth. Bubble column photobioreactors, characterized by their cylindrical structure, offer advantages, such as simplicity, low energy requirements, uniform culture conditions, and reduced photoinhibition, making them efficient and easy to operate [27, 28]. Airlift photobioreactors, featuring interconnected cylindrical zones, promote efficient mixing and mass transfer [29]. Flat-plate photobioreactors are favored for their scalability, high surface area-to-volume ratio, reduced oxygen accumulation, and ease of cleaning and maintenance [30]. Stirred-tank photobioreactors, comprising a vessel, agitator, aerator rod, and pump, ensure enhanced biomass production and improved heat, mass, and light transfer [31]. Horizontal tubular photobioreactors, made from transparent PVC or bio-polypropene sheets, maximize light utilization and homogenize cultures through air pump systems [31]. V-shaped photobioreactors utilize light-trapping geometries to enhance photosynthetic efficiency [32]. PBRs are widely used for carbon sequestration, biofuel production, wastewater treatment, and the production of pharmaceuticals and nutraceuticals. They convert algae into renewable biofuels (biodiesel, bioethanol, and biogas) and purify wastewater by removing nutrients and heavy metals. Additionally, PBRs produce high-value compounds such as vitamins, antioxidants, and pigments for human health. By capturing industrial CO₂ emissions, PBRs reduce greenhouse gases (GHGs) while generating protein-rich biomass for use in animal feed or human nutrition [33]. Chlorella vulgaris, Spirulina platensis, Haematococcus pluvialis, Nannochloropsis oculate, Tetraselmis suecica, Dunaliella salina, Phaeodactylum tricornutum, Isocrysis galbana, Secenedesmus obliquus, Pyropia spp., Rhodomonas spp., etc., are suitable algae species for culture using photobioreactors [34].

2.1.2 Algae culture in a closed tank system

Algae farming in tanks, especially for experimental and high-intensity cultivation, began in the 1960s in Canada and the USA, with Chile later adopting similar practices. This approach is now widespread in countries, such as the United States, Canada, Chile, Israel, Mexico, Germany, China, and Japan [35]. Tank culture is known for achieving the highest biomass yields per square meter of water surface when compared to other methods. Algae are grown in tanks for various purposes, including waste treatment from farmed animals, production of plantlets for future cultivation, extraction of valuable compounds like agarose and prostaglandins for medical applications, and as food for abalone mollusks (Haliotis) [36]. Macroalgae are typically cultivated in large concrete tanks, often with volumes in the tens of cubic meters, to generate significant biomass, though smaller tanks or aquaria are used for research. While tank cultivation offers high yields, it requires considerable energy and expensive equipment, making it less suitable for large-scale commercial use. Algae culture involves developing specific techniques for each species, optimizing conditions such as light intensity, temperature, and nutrient levels. Light exposure is controlled using filters, screens, and additional lighting, while factors, such as tank depth, algae density, and rotational movement, are managed to promote growth. Rotation is induced by injecting compressed air to create water flow. Temperature control is achieved through water circulation systems or by regulating air temperature. Fertilizers are applied based on water exchange schedules, and CO₂ and HCO³⁻ are supplied, when necessary. Salinity is managed with fresh water, distilled water, or sea salt, and microbial growth is controlled using bacterial inhibitors. Excess biomass is regularly harvested to maintain optimal productivity. The yield of algae in tanks varies depending on the species and methods used. For example, Gracilaria tikvahiae cultivated in small tanks (55L) with aeration, regular fertilization, high water turnover, and frequent removal of excess biomass can yield between 12 and 40g FWT day⁻¹ (127t FWT ha⁻¹year⁻¹) [37]. Larger tanks (24,000L) yield similar amounts for Gracilaria sp., and Porphyra sp. plantlets can produce up to 120 metric tons of fresh weight per hectare over 4 months of cultivation. Spray cultivation, an alternative intensive alga farming technique, involves spraying algae with artificial seawater enriched with mineral salts [38]. This method is more cost-effective than submerged cultivation and offers advantages, such as reduced epiphytism and the absence of algal pests. Gracilaria chilensis cultivated under seawater spray can yield between 1.8 and 16 metric tons of dry weight per hectare per year. In comparison, Ascophyllum nodosum yields 143 metric tons of fresh weight or 22 metric tons of dry weight per hectare annually. Other species commonly cultivated in closed tank systems include Ulva lactuca, Gracilariaspp., Nannochloropsis gaditana, Tetraselmis chuii, Chaetoceros calcitrans, Skeletonema costatum, Chlorella pyrenoidosa, Spirulina maxima, Pavlova lutheri, and Thalassiosira pseudonana.

2.1.3 Algae culture by fermenter-based system

Fermenter-based algal culture involves growing algae in controlled bioreactors, typically for heterotrophic growth, where algae rely on organic carbon sources like glucose or glycerol, instead of sunlight. While less common, autotrophic growth in fermenters using light is also possible. This system offers several benefits over open-pond methods, including continuous year-round production and precise control of environmental conditions, such as temperature, pH, oxygen, and nutrient levels. Species like Chlorella, Schizochytrium, and Crypthecodinium cohnii are well suited for heterotrophic culture, producing valuable products like biofuels and nutraceuticals [39]. Fermenters facilitate faster growth and higher yields than photosynthetic systems by offering precise control over critical parameters. Unlike open-pond systems that depend on sunlight, fermenters operate in dark conditions, offering flexibility and making them ideal for large-scale, industrial applications. This approach is particularly effective for producing dense algal biomass and high-value products, such as proteins, biofuels, and omega-3 fatty acids [40]. Several types of fermenters are used, including batch fermenters, which grow algae until nutrient depletion, fed-batch fermenters, which extend growth by adding nutrients, and continuous fermenters, which allow continuous production by removing biomass and adding fresh medium. Stirred-tank fermenters use mechanical stirring, while air-lift fermenters rely on air bubbles for mixing and oxygenation [41]. The key advantage of fermenter-based cultivation is the ability to maintain optimal growth conditions, resulting in higher biomass yields and cell densities compared to open systems. Additionally, fermenters operate in aseptic environments, minimizing contamination risks. Their scalability makes them suitable for industrial-scale production of high-value chemicals [41]. Algal species like Schizochytriumspp., Crypthecodinium cohnii, Chlorella protothecoides, Aurantiochytrium limacinum, and Euglena gracilis are commonly cultured in fermenters [42].

2.2 Open system culture technique

Open system algae culture involves cultivating algae in natural or seminatural environments, such as offshore or coastal waters, primarily for macroalgae production. By utilizing natural resources like sunlight, water flow, and nutrients, this method minimizes operational costs and infrastructure requirements, making it ideal for large-scale cultivation. Open systems support sustainable aquaculture by enhancing biodiversity, improving water quality, and contributing to carbon sequestration. Additionally, they provide a renewable biomass source for industries such as food, cosmetics, pharmaceuticals, and biofuels, promoting sustainable resource management.

2.2.1 Algae culture by raceway pond

In recent years, the focus of algal research has shifted toward developing large-scale cultivation systems to meet the growing demand for nutraceuticals and biofuels. Among these systems, raceway ponds (RWPs) are widely used due to their affordability and operational simplicity. These shallow, open systems are designed to maximize light penetration, which is critical for photosynthesis. However, their shallow depth poses limitations, such as reduced productivity per unit area and the need for substantial land to scale up operations. A key challenge in RWPs is the inefficient transfer of carbon dioxide (CO₂). The shallow design reduces the interaction time between gas and liquid, leading to poor CO₂ mass transfer efficiency. Studies suggest that 80–90% of the CO₂ supplied to RWPs escapes into the atmosphere, with fixation efficiencies in open systems typically ranging between 10 and 30% [43]. This inefficiency significantly impacts overall system performance. Several factors influence algal productivity in RWPs, including site selection, pond depth, oxygen levels, salinity, light intensity, algal predators, and CO₂ availability. Selecting a site with optimal environmental conditions is critical [44], while pond depth must ensure efficient oxygen circulation and nutrient mixing [45]. Adequate light intensity [46] and effective CO₂ management are essential to sustain photosynthesis [47], and mechanical mixing systems are required to distribute nutrients, circulate oxygen, and remove excess CO₂ and waste materials [48]. Controlling salinity is crucial for preventing algal diseases and ensuring optimal growth [49], while predator management minimizes losses caused by harmful organisms. The effectiveness of RWPs also depends on their design, with factors such as light penetration, nutrient distribution, gas-liquid mass transfer, and bubble retention time requiring careful optimization. Advanced RWP designs, including paddlewheel-driven ponds [50], sump-assisted raceways [51], hybrid systems [52], and manually mixed configurations, address these challenges. Several algal species are well suited for cultivation in RWPs, including Chlorella sp., Scenedesmus sp., Haematococcus sp., Dunaliella sp., Nannochloropsis sp., and Botryococcus sp. [53]. These species are highly adaptable and hold significant potential for applications in the food, feed, pharmaceutical, and biofuel sectors.

2.2.2 Algae culture by longline method

The longline algae culture method starts with careful site selection, ensuring the optimal environmental conditions such as salinity, temperature, and nutrient levels, typically found in protected coastal regions with high water exchange. This approach is primarily applied to macroalgae culture rather than microalgae. Following site selection, obtaining necessary permits from local authorities is crucial for compliance with environmental and maritime regulations. The longline system consists of a main line, made of durable materials like nylon or polypropylene, anchored at both ends and buoyantly positioned at intervals to maintain the correct depth and tension. Seedlings, selected for their rapid growth and compatibility with local conditions, are attached to the longline using biodegradable clips or strings. These seedlings are evenly spaced to optimize growth, water circulation, and sunlight exposure while being protected from strong currents and waves [54]. Successful cultivation requires regular monitoring and maintenance. Weekly or biweekly inspections are essential to check for damage to the longline, buoys, or anchors, as well as to remove debris, fouling organisms, or competing algae that could affect growth. Once mature, typically after 2–3 months, the algae are harvested and transported to processing facilities. Postharvest care, including washing, drying, and storage in a cool, dry place, is necessary to preserve quality. This results in a sustainable and profitable operation. Species suitable for longline cultivation include Saccharina latissima (sugar kelp), Undaria pinnatifida (wakame), Gracilaria spp., Macrocystis pyrifera (giant kelp),Sargassum spp., Laminaria digitata (oarweed), Porphyra spp. (nori), Eucheuma spp., Kappaphycus alvarezii, and Alaria esculenta [55].

2.2.3 Algae culture by floating net method

The floating net method of algae culture, especially for macroalgae, begins with a comprehensive site assessment to identify favorable environmental conditions, including optimal water currents, minimal wave exposure, and suitable water depth (typically ranging from two to ten meters). After confirming these conditions and securing necessary permits, anchors, typically screw or concrete blocks, are strategically positioned to ensure the stability of the floating net system against tides and currents. Durable materials such as nylon or polyethylene are used for the primary nets, which are connected to the anchors. Buoys are placed at regular intervals around the nets to maintain buoyancy, ensuring proper depth for optimal sunlight exposure while protecting the algae from destructive currents. Seedlings are sourced from specialized nurseries or resilient wild populations, ensuring they are free from pests and diseases. These healthy seedlings are then attached to the nets using biodegradable clips or ties, with spacing designed to promote consistent growth and efficient nutrient absorption. Regular maintenance is vital for system success, involving routine inspections of the nets, buoys, and anchors to ensure structural integrity. Cleaning operations are performed to remove waste, fouling organisms, and competing algae that could hinder growth [54]. Algae, specifically macroalgae typically mature within 2–6 months, depending on species and environmental factors. Harvesting is conducted with care to prevent damage to the nets and remaining algae, and the biomass is quickly transported for processing to preserve quality. The floating net technique provides a sustainable and efficient method for algae farming, supporting the economic and environmental sustainability of marine aquaculture. Technological advancements, skilled workforce training, and ongoing research are essential for optimizing productivity and ensuring the long-term success of this approach [56]. Suitable species for cultivation using the floating net method include Ulva lactuca (sea lettuce), Gracilaria spp., Porphyra spp., Chlorella spp., Undaria pinnatifida (wakame), Tetraselmis spp., Isochrysis spp., Chaetoceros spp., and Nannochloropsis spp. [57].

2.2.4 Algae culture by bottom-culture method

The establishment of bottom-culture systems for macroalgae cultivation necessitates a thorough evaluation of environmental parameters, including water depth, substrate stability, and nutrient availability, particularly in shallow coastal regions. Horizontal cultivation employs resilient materials such as nylon or polyethylene for culture lines or ropes, which are anchored using metal stakes or concrete blocks placed strategically to ensure stability. These lines are suspended just beneath the water surface to optimize conditions for algae attachment and growth. Seedlings of algae species are carefully evaluated for their compatibility with local environmental conditions and consumer demand. After undergoing disinfection and sorting, the seedlings are attached to the culture lines or ropes using biodegradable yarn or clips. Appropriate spacing is critical, as it ensures even distribution, adequate access to sunlight, and optimal nutrient availability, which are vital for healthy growth. Regular maintenance and monitoring are essential for successful cultivation. These activities include assessing the health of the algae, removing fouling organisms and undesirable species, and providing nutrient supplements, either organic or inorganic, to reduce competition for resources. Environmental monitoring is equally important to identify and mitigate potential negative impacts on local biodiversity and water quality. Harvesting is typically performed by cutting algae from the culture lines or ropes using specialized tools such as knives or shears. Postharvest management plays a crucial role in maintaining quality. This includes promptly cleaning the algae to remove dirt and harmful microorganisms, followed by proper storage in a cool, dry environment to ensure freshness and preserve quality [58]. Macroalgae species suitable for bottom-culture systems include Gracilaria spp., Ulva spp. (sea lettuce), Porphyra spp. (nori), Sargassum spp., Saccharina latissima (sugar kelp), Laminaria digitata (oarweed), Chondrus crispus (Irish moss), Codium fragile (green sea finger), and Macrocystis pyrifera (giant kelp) [59].

2.2.5 Algae cultivation by saline aquaculture system

In recent years, saline aquaculture system is a land-based approach that utilizes saline groundwater, which can be sourced from aquifers, temporary or permanent saline lakes, or as a byproduct of coal seam gas extraction. Common cultivation methods include raceways, tanks (with or without recirculation systems), and ponds lined with plastic or compacted soil. A key advantage of saline aquaculture is its ability to repurpose existing agricultural land with access to saline water, reducing the need for additional resources. Additionally, cultivating marine algae in island saline water (ISW) offers a cost-effective alternative to traditional sea farming, providing raw materials for the seaweed aquaculture industry and creating supplemental income with lower financial investment than sea-based farming systems [60]. Research has also shown that cultivating diverse seaweed assemblages can improve nutrient absorption efficiency compared to monocultures. This highlights the need for further exploration into multi-species cultivation systems, which hold promise for enhancing ecological sustainability and productivity. To advance sustainable algae farming, comparing bioeconomic models and increasing public awareness are essential. These efforts can support innovation, drive investment, and promote the widespread adoption of environmentally friendly practices in saline aquaculture [60]. A variety of algae species are well suited for saline aquaculture, including Tetraselmisspp., Isochrysis spp., Chaetoceros spp., Nannochloropsis spp., Ulva spp., Gracilaria spp., Dunaliella salina, Phaeodactylum tricornutum, and Thalassiosira pseudonana. These species are highly adaptable to saline conditions and are valuable for applications in food production, biofuels, pharmaceuticals, and aquaculture industries [61].

3. Algae culture by integrated multi-trophic aquaculture (IMTA) technique

Integrated multi-trophic aquaculture (IMTA) is a sustainable aquaculture approach that mitigates environmental issues like eutrophication caused by feed waste and excretion in animal farming. IMTA combines species from different trophic levels, recycling organic and inorganic wastes as resources for others. This interconnected system reduces fertilizer use in macroalgae cultivation while maintaining ecological balance, profitability, and sustainability [62]. In IMTA systems, nutrients such as dissolved ammonia and phosphate from animals like fish, mollusks, and bivalves are absorbed by macroalgae, converting waste into valuable biomass. This process also stabilizes oxygen, pH, and CO₂ levels in the water [63]. Research has shown that macroalgae biomass increases when grown near fish farms. IMTA is particularly suitable for species with high summer productivity, fast nitrogen uptake, and strong market value [64]. IMTA contributes to environmental sustainability by improving water, soil, and air quality and supporting carbon sequestration and biofuel production [65]. Macroalgae can replace synthetic fertilizers and pesticides in agriculture, improving soil health while reducing emissions [55]. Feeding algae to livestock has been shown to lower methane emissions. Locally, IMTA reduces eutrophication and enhances marine biodiversity, while globally, it aids in combating climate change through carbon capture. Economically, IMTA provides opportunities for diversification, allowing producers to expand into new markets [66]. Algal products are often highly valued for their environmental benefits, fetching premium prices. With efficient photosynthesis and fast production cycles, macroalgae are a renewable source of bioactive compounds. However, for IMTA to succeed economically, all components must be marketable, either individually or as a collective system. Large-scale IMTA, especially offshore, holds significant potential for carbon mitigation and sustainable resource use. Developing effective farm designs and selecting suitable species can maximize ecological benefits and financial returns, facilitating global adoption of this approach [62]. Macroalgae species well- suited for IMTA include Ulva lactuca (sea lettuce), Gracilaria spp., Saccharina latissima (sugar kelp), Porphyra spp. (nori), Laminaria digitata (oarweed), Chondrus crispus (Irish moss), Palmaria palmata (dulse), Sargassum spp., Macrocystis pyrifera (giant kelp), and Codium fragile (green sea fingers). These species not only provide valuable biomass but also play a key role in ensuring IMTA’s ecological and economic sustainability.

4. Applications of algae

Algae are versatile and sustainable resources with broad applications across industries, including food, biofuels, cosmetics, and pharmaceuticals (Figure 1). They are nutrient-rich, serving as sources of alginate and agar, while also being valued for biofuel production, bioremediation, and providing bioactive compounds for pharmaceutical applications [67].

Commercial and Industrial Algae Culture and Applications (4)

4.1 Food

Micro- and macroalgae have been used as a food source since medieval times in Asia, and with time and increasing awareness of their health benefits in other parts of the world as well [68]. Among the three main components found in any food, proteins, lipids, and carbohydrates, carbohydrate is more common in land-based crops [69]. However, algae contain large amounts of protein and lipids. Moreover, algae contain all the amino acids required for the human diet and are a potential source of omega-3 fatty acids, which are only available through some fish species such as salmon, mullet, and mackerel [69]. These algae are also an excellent source of vitamins and minerals, like potassium and iodine (Palmaria palmata, Fucus vesiculosus, and Laminaria sp.), long-chain polysaccharides (Pyropia tenera) and dietary fibers (Grateloupia filicina, Chondrus crispus, and Ulva lactuca) [70]. Moreover, extracts, such as phycocolloid, carrageenan, and carotenoids, are also used in processed food and are gaining attraction from the industry.

4.2 Fuel

With the depletion of fossil fuels and the growing impact of global warming, more research is being done in looking for alternative energy resources. Algal biomass leads to four basic biofuels: biodiesel, bioethanol, biohydrogen, and biobutanol [71]. Due to their high oil-to-dry weight ratio, algae are considered an ideal renewable fuel and energy source, through processes such as transesterification, anaerobic digestion, hydro treatment, fermentation, pyrolysis, and direct combustion [72]. Even though some of these processes are complicated and economically unfeasible, their viability can be achieved through the optimal utilization of all the products.

4.3 Cosmetics

Algal biomass is a significant source of biologically active compounds that are scarce in other taxonomic groups [73]. They even have the upper hand over land plants and animal-based foods as they contain a higher concentration of health-promoting elements [74]. These elements are used in foams, humectants, sun protection, soaps, emollients, hair products, shampoos, and lotions [74]. Some of the compounds used in cosmetics that are collected from algae include polyphenols and phlorotannins, polysaccharides, proteins, fucoxanthin, mycosporine, bioactive peptides, and phenolic compounds [73, 74]. These compounds not only help in anti-cellulite procedures and issues such as tanning and pigments disorder, but they also have attributes like antimicrobial, antioxidant, moisturizing, viscosity controlling, whitening, lipolytic, antiphotoaging, and anti-aging [74].

4.4 Pharmaceuticals

Polysaccharides are among the most common and active compounds found in algae. These molecules can attach to the surface of leukocytes and reduce inflammation [75]. Fucoidans, sulfated polysaccharides extracted from Undaria pinnatifida, Laminaria cichorioides, and Fucus evanescens exhibit a wide range of biological activities, including anti-allergic effects, antiviral properties against herpes simplex virus (HSV), respiratory syncytial virus (RSV), and human immunodeficiency virus (HIV), anticancer activity, induction of apoptosis, inhibition of tumor cell growth, and enhancement of chemotherapeutic agents’ efficacy [76]. Alginate is another significant polysaccharide that inhibits the release of hyaluronidase and histamine from mast cells, stimulates toll-like receptors, activates cytokine production, and serves as a base material for the base for the production of controlled-release drug products [77]. Additionally, other polysaccharides derived from algae, such as Porphyran, Carrageenans, and Galactans, have demonstrated effectiveness against allergies and different HSV strains as well as inhibit virus amplification during infection [78]. Carotenoids, another group of bioactive molecules extracted from algae, such as fucoxanthin, zeaxanthin, and astaxanthin, have significant application in the pharmaceutical industry. These pigments are used to develop treatments for cancer and cardiovascular disease [79]. Terpenoids, another highly valuable class of compounds, exhibit potent pharmaceutical potential, including anti-HIV-1 activities, antibacterial activity against Staphylococcus aureus, and anticancer properties [80].

4.5 Bioremediation

Another use of algae is bioremediation, specifically through phycoremediation, a process that utilizes algae to absorb elements such as phosphorus, carbon, and trace metals from wastewater as nutrients [81]. Over the year, many species of algae have been identified that are effective in nutrient removal from wastewater, although their efficiency varies across genera. For instance, Chlorella kessleri and C. protothecoides grow in municipal wastewater, underscoring their ability to adapt [82]. Additionally, algae can also effectively remove heavy metals from wastewater through accumulation and degrade xenobiotics and crude oil, making them valuable for environmental detoxification [83].

In addition to the aforementioned applications, algae hold significant potential as a sustainable feedstock and an eco-friendly fertilizer for soil enrichment. Algae-based bioplastics represent an innovative solution to reduce microplastic pollution and contribute to environmental preservation. Additionally, the natural pigments present in algae make them a valuable resource for the production of environmentally friendly natural dyes and pigments.

5. Benefits of algae culture

Algae cultivation offers significant environmental, economic, and health benefits. One of the significant environmental advantages is its ability to remove nutrients such as nitrogen and phosphorus, which helps in reducing eutrophication and improves overall water quality [84]. Additionally, algae sequester carbon dioxide, mitigating climate change by reducing greenhouse gas concentrations [85]. Furthermore, algae can play a vital role in bioremediation, as they can absorb heavy metals and other pollutants, making them valuable in wastewater treatment and environmental detoxification [86]. From an economic perspective, algae cultivation presents opportunities for sustainable biofuels, such as biodiesel and bioethanol [87]. These renewable energy sources can decrease dependence on fossil fuels while contributing to environmental sustainability. Algae are also rich in bioactive compounds, antioxidants, vitamins, and proteins, making them valuable for several industries, including food, pharmaceuticals, and cosmetics. The growth of the algae industry has the potential to create jobs, thereby contributing to economic development [85].

In terms of health benefits, algae are nutrient-rich and can provide essential fatty acids, proteins, vitamins, and minerals. This makes them valuable as food supplements, as functional foods, or as ingredients in various products. Additionally, they serve as sources of antioxidants and polysaccharides, which can contribute to overall well-being. Algae cultivation offers a wide range of benefits, demonstrating its potential to address global challenges across multiple sectors.

6. Challenges of algae culture

Algae cultivation at an industrial scale faces numerous challenges related to ecological, operational, and social factors. A primary concern is the control of fouling algae and epiphytes, which compete with cultivated species for essential resources, such as light, nutrients, and substrate. The presence of invasive species significantly reduces photosynthetic rates and growth, often requiring labor-intensive weeding practices that increase production costs [88]. Another issue is the proliferation of grazing animals, which thrive in mariculture farms where single species are cultivated for extended periods. These grazers feed on seaweed crops, decreasing yields, while efforts to control them, such as using pesticides, can have unintended ecological consequences by harming non-target carnivorous species [89]. Additionally, overgrowth by bivalves such as mussels makes seaweeds too heavy, causing them to detach and decay, further polluting water bodies [90]. The availability and quality of planting stock also present significant barriers. Traditional methods relying on cuttings from cultivated or wild stocks often lead to the degradation of genetic diversity and adaptability over time. This results in reduced resistance to environmental stressors, lower productivity, and eventual declines in harvest yields. While algae cultivation is celebrated for its role in mitigating eutrophication by extracting up to 90% of nitrogen and phosphorus from polluted waters [91], it also poses serious environmental risks. Large-scale monoculture, especially in shallow water lagoons, bays, and estuaries, disrupts benthic ecosystems. Native seaweeds, seagrasses, and other organisms often disappear under seaweed farms due to shading, reduced water movement, and sedimentation [92]. The social implications of large-scale algae farming cannot be overlooked. Farms occupying extensive coastal areas hamper traditional fishing and shipping activities. Addressing these challenges requires a balanced approach that integrates sustainable cultivation practices, ecological restoration, and stakeholder engagement.

7. Future prospects of algae culture

The future of algae culture presents a significant opportunity for the sustainable production of biomass and high-value products. As outlined by Buschmann et al. [55], there is a global anticipation that phycologists will rise to the challenges associated with harnessing the potential of seaweed biomass. Emphasizing the need for increased efficiency and economic viability, the focus on microalgae production is vital. Research conducted in Tamil Nadu, India, by Remya and Radhika Rajasree [93] indicates a wealth of studies pertaining to seaweed’s distribution, resources, taxonomy, culture, harvesting, and utilization. However, there remains a critical need for intensive investigations into industrial and pharmaceutical applications. Large-scale algae cultivation has great potential for sustainable biomass production and high-value products. However, insufficient data limit commercial trials. Future research should focus on identifying suitable species, optimizing cultivation techniques, and exploring genetic modifications to address challenges, such as the low carbohydrate content in algal biomass [94]. Such modifications can enhance the production of lipids and other target compounds, improve the yield of high-value products, and introduce beneficial traits, such as disease resistance [95]. Techniques like the hybridization of marine macroalgae and advanced genetic engineering strategies hold significant promise for improving the efficiency and economic viability of algal biomass utilization [96]. Immanuel and Sathiadhas [97] noted that many women are actively involved in seaweed collection but they are not fully aware about its demand and value. Given the predominance of women in seaweed collection, targeted efforts should be made to enhance their capacity through education on the market demand and value of seaweeds. Finally, the projected costs for marine algae remain significantly higher than those for terrestrial biomass. Nevertheless, through advancements in yields, scale, and operational efficiencies, algae cultivation could become cost-competitive with terrestrial crops [98].

8. Conclusion

The growing demand for algae, valued for their bioactive compounds in nutraceuticals and medicine, threatens wild populations due to limited cultured supply and overexploitation. Developing stable culture systems—closed, open, and IMTA—is essential. Research focuses on optimizing metabolism, improving culture techniques, and selecting fast-growing, resilient species. Despite advancements, challenges remain in ensuring sustainability, profitability, and public acceptance. Sustainable algae culture is vital for driving the global blue economy, promoting economic growth, resource conservation, and environmental sustainability.

Acknowledgments

The authors acknowledge the use of ChatGPT for grammar editing.

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