As shown in Figure 1, research on microalgal strains has surged in recent years, with notable focus on Chlorella, Spirulina, Scenedesmus, Chlamydomonas, and Synechocystis. Among these, C. vulgaris (Chlorella vulgaris) is a widely studied green microalga belonging to the genus Chlorella and cultivated in freshwater (Okoro et al., 2019). C. vulgaris features an enzyme-digestible cell wall, spherical microscopic cells ranging from 2 to 10 μm in diameter, and a cell wall thickness that increases during growth, reaching 17–21 nm by maturity (Okoro et al., 2019). Its ability to accumulate lipids makes it highly suitable for biodiesel production. The rigidity of C. vulgaris cells arises from a thin unilaminar layer that thickens as the cell matures, forming a microfibrillar structure composed of glucosamine monosaccharide layers. Reproduction occurs asexually; under optimal conditions, a mother cell can divide into four daughter cells upon rupturing at maturity. The remnants of the mother cell provide nourishment for the rapidly growing daughter cells (Okoro et al., 2019). Microalgae hold great promise as a renewable source for sustainable biodiesel production due to their capacity to accumulate high lipid content (20%–75% by weight) (El Shimi and Moustafa, 2018).

Achieving breakthroughs in biomass accumulation and lipid production are two pivotal factors for realizing microalgal biofuel. The first step involves selecting promising microalgal strains through a systematic process. In recent years, many researchers have focused on identifying potential candidates with specific objectives, often starting with the isolation of microalgae species. Several suitable candidates for biofuel production have been identified, including Chlorella, Scenedesmus, and others. Notably, these species are widely distributed in aquatic environments, indicating their superior stress tolerance capabilities. Furthermore, certain genera that have received less attention also possess advantageous traits for biofuel production. For instance, Golenkinia has garnered attention in recent years. Nie et al. (2018) investigated its capacity for degrading campus wastewater, demonstrating not only its high lipid content but also its ease of harvesting through gravity separation (Nie et al., 2018). Subsequently, they conducted extensive research on biomass and biofuel production (Nie et al., 2020a; Nie et al., 2020b). Rearte et al. (2024) assessed both the fatty acid composition and high-value by-products of caeronid (Rearte et al., 2024). Recent studies have highlighted the emergence of microalgal isolation in extreme environments. For example, one study focused on collecting airborne strains and found that these microalgae exhibited greater stress tolerance due to exposure to stringent environmental conditions, such as high illumination (Kumari and Singh, 2021). Therefore, the selection of promising microalgal strains with abundant lipid content, high biomass output, strong resistance to harsh environments, and ease of harvesting is a cornerstone.

Some nanomaterials have been used to improve biodiesel quality. For instance, Gad et al. (2021) recommended adding graphene nano sheet additives at a concentration of 100 ppm to biodiesel blends, as this significantly enhanced combustion characteristics, performance, and emissions reduction compared to standard biodiesel blends (Gad et al., 2021). Moreover, the pursuit of alternative types of biofuel development is highly advantageous. For instance, harnessing microalgae for biogas production presents a viable alternative for renewable energy due to the promising potential of algal carbohydrates as a source (Zabed et al., 2020). Some microalgae, including Chlorella, Spirulina, and Scenedesmus, are considered suitable biomass for biogas production (Ashour et al., 2024). Thus, leveraging diverse energy sources can effectively promote the utilization of microalgal energy.

At the global scale, China and the U.S. have become key contributors to algal biofuel research. In the past, many studies focused on optimizing culture parameters to enhance biomass and lipid production. The growth rate of C. vulgaris was investigated in a photobioreactor (PBR). Results showed that the optimal biomass yield was achieved under specific conditions: pH 9–10, aeration flow rate of 200 L/min, illumination intensity of 5–7 klux, glucose and nitrate concentrations of 20 g/L and 0.5 g/L respectively, and temperature of 30°C. Notably, the biomass yield reached 3.43 g/L with a lipid productivity of 66.25 mg/L/d (S. Daliry et al., 2017). Furthermore, recent advancements such as omics-based analyses have deepened the understanding of molecular-level responses to specific environmental conditions. These findings not only provide insights into cellular mechanisms but also help identify compounds with enhanced potential for specific applications.

Several advanced methods have been employed. For example, recombinant CRISPR-Cas9 technology has successfully enhanced the total lipid content of microalgae, a crucial prerequisite for efficient biofuel production (Lakhawat et al., 2022). Additionally, various cultivation modes are currently under development. Jin et al. (2021) developed an efficient and scalable heterotrophic cultivation technology for the production strain Chlorella sorokiniana GT-1. By optimizing culturing conditions, ultrahigh biomass concentrations of 271 g/L were achieved in a 7.5 L bench-scale fermenter and 247 g/L in a 1,000 L pilot-scale fermenter (Jin et al., 2021). Integrating effectively specific microalgal cultivation methods into the production assembly line can fully unlock the potential for high microalgal yields.

Microalgae have diverse applications beyond biofuel production. They contain a rich array of bioactive compounds, such as carbohydrates, proteins, fatty acids, and others, making them suitable for supporting human and animal growth. Consequently, microalgal cultivation holds promise in food production systems, providing key bioactive compounds for pharmaceuticals and valuable ingredients for cosmetics. For instance, combining high light intensity with appropriate UV-A radiation under salinity stress resulted in the highest carotenoid content (2.75 mg/g dry weight), primarily composed of lutein and beta-carotene, as well as the highest lipid accumulation (35.3% DW) with elevated levels of polyunsaturated fatty acids, including alpha-linolenic acid (C18:3) and linoleic acid (C18:2) (Rearte et al., 2024). Furthermore, the biochemical composition, fatty acid profile, and in vitro digestibility of twelve microalgal biomasses were investigated to explore their potential for producing novel functional foods. Cyanobacteria (particularly A. platensis F&M-C256), C. sorokiniana F&M-M49, and C. vulgaris Allma exhibited higher crude protein contents and in vitro digestibility. Marine species had lower digestibility but contained elevated levels of polyunsaturated fatty acids (mainly eicosapentaenoic acid and docosahexaenoic acid) and significant amounts of palmitoleic, oleic, and palmitic acids. Freshwater algae displayed high concentrations of α-linolenic acid along with even greater quantities of palmitic acid (Niccolai et al., 2019).

Moreover, Arthrospira and Chlorella are utilized in skincare product production. Microalgal extracts find extensive application in face, skin, hair care, and sun protection products. Microalgal components are commonly used in cosmetic products as antioxidants, thickening agents, and water-binding agents. Several commercial products have been developed with specific properties claimed by their manufacturers. For example, Arthrospira produces a protein-rich extract functioning as an anti-aging agent (Protulines, Exsymol S.A.M., Monaco). Similarly, the extract of C. vulgaris stimulates collagen production in the skin, leading to tissue regeneration and reduction of wrinkle formation (Dermochlorella, Codif, St. Malo, France). Recently launched by Pentapharm (Basel, Switzerland), Pepha-Tight incorporates Nannochloropsis oculata, known for its exceptional skin tightening properties. Another product, Pepha-Ctive, utilizes an extract from D. salina, which significantly promotes cell growth and enhances skin energy metabolism (Rizwan et al., 2018). To date, in the context of the food industry, algal protein, DHA, and pigments have been widely accepted by many consumers. Additionally, various skincare products also require significant amounts of algal components. This trend is promising, and both food and cosmetic products must ensure safety throughout the production process.

Researchers have introduced microalgae into wastewater treatment systems due to their ability to efficiently uptake nitrogen, phosphorus, and organic compounds for autotrophic growth (Jiang et al., 2021). These nutrients are typically present in high concentrations in wastewater. Furthermore, using microalgae as a feedstock for wastewater treatment reduces cultivation costs compared to artificial media. Microalgae have demonstrated promising potential in the bioremediation of emerging contaminants (ECs) due to their capacity to uptake and metabolize a wide range of organic pollutants. They can convert complex organic compounds into simpler, less toxic forms through diverse metabolic pathways. Moreover, employing microalgae for EC removal represents an environmentally friendly approach that can be seamlessly integrated with biofuel production, offering a sustainable and economically viable solution. ECs include a wide range of synthetic or naturally occurring chemicals and microorganisms that are not routinely monitored in the environment but possess the potential to infiltrate ecosystems and induce recognized or suspected adverse effects on both ecological systems and human health. These substances encompass pharmaceuticals and personal care products (PPCPs), endocrine-disrupting chemicals (EDCs), nanoparticles, flame retardants, and various industrial chemicals (Ethiraj and Samuel, 2024).

With the advancement of technology, artificial intelligence (AI) and big data have emerged as valuable tools for optimizing microalgal cultivation parameters to achieve maximum productivity. AI enables the rapid determination and adjustment of precise operational parameters, thereby significantly enhancing both microalgal cultivation efficiency and wastewater treatment performance. For instance, decision tree models were employed to analyze datasets of Trebouxiophyceae and Chlorophyceae classes for wastewater treatment optimization. The models identified nine parameter combinations for high biomass production, eleven combinations each for achieving high nitrogen removal efficiency and high phosphorus removal efficiency specifically for the Trebouxiophyceae class. Similarly, eleven combinations were detected for maximizing biomass production, nine for enhancing nitrogen removal efficiency, and eight for improving phosphorus removal efficiency within the Chlorophyceae class (Singh and Mishra, 2022).

Microalgae exhibit significant potential for the efficient treatment of municipal, agricultural, and industrial wastewater. However, substantial challenges remain in transitioning microalgal wastewater treatment technologies from laboratory settings to real-world applications. In particular, the removal of emerging contaminants remains a critical challenge in practical wastewater treatment scenarios. Therefore, novel approaches or strategies should be developed, and their underlying mechanisms should be systematically investigated using omics data, engineering principles, and artificial intelligence tools.

The microalgae have garnered significant attention for carbon capture due to their potential in achieving carbon neutrality. These microorganisms possess the ability to utilize carbon dioxide and convert it into organic compounds through autotrophic growth under light conditions (Zhang et al., 2020). Yang et al. (2024) proposed that concentrated CO₂ is commonly found in flue gas, presenting opportunities for algae cultivation. However, this approach faces challenges such as mass transfer limitations and poor CO₂ dissolution, hindering the achievement of optimal algal growth levels at given flue gas concentrations. Bicarbonate can serve as a flexible carbon source with the potential to enhance the efficiency of biological carbon fixation by algae. Moreover, stringent requirements exist for selecting suitable algae strains. Therefore, system optimization plays a crucial role in improving the industrial scale-up of carbon capture and utilization (CCU) (Yang et al., 2024).

Researchers have recently investigated the potential of microalgae for soil improvement and as inhibitors to mitigate atmospheric sandstorms. Traditionally, algae have been associated with aquatic environments; however, algal species found in soils from arid and semi-arid regions are commonly identified through gene sequencing analysis and morphological characterization. The formation of algae-based biological soil crusts (BSCs) involves four sequential stages: initial attachment of algal cells, subsequent secretion of extracellular polymeric substances (EPS), co-growth with other microorganisms, and eventual thickening of the BSC (Lu et al., 2022). Regarding soil enrichment, microalgae can enhance plant productivity comparably to traditional chemical nitrogen fertilizers. Additionally, microalgae serve as a valuable phosphorus source for crops, facilitating phosphorus recovery. Most microalgal species prefer inorganic phosphate (PO₄ ⁻) over organic phosphate compounds (Dagnaisser et al., 2022).

In addition, for the sake of improving dust suppression, a new method for extracting microalgae oil to synthesize coal dust suppressants is proposed to address the poor performance of traditional suppressants under hard water conditions. The optimal extraction conditions were determined through experiments, and a microalgae oil-based dust suppressant (MODS) was synthesized. MODS showed good hard water resistance, maintaining low surface tension and better wettability compared to sodium dodecyl benzene sulphonate (SDBS). This study provides a foundation for developing green and hardwater-resistant coal dust suppressants (Wang et al., 2023).