Integrated hybrid Nested-bottled photobioreactor for enhanced mixing, mass transfer, and CO₂ fixation in Arthrospira platensis raceway pond cultivation systems

The continued dependence of industrial and economic sectors on conventional energy sources has resulted in carbon dioxide (CO₂) emissions exceeding their natural removal rate, leading to a rising atmospheric CO₂ concentration. The global population reached 8 billion in 2022 and is projected to grow to 10 billion by 2100 [1]. This imbalance intensifies the greenhouse effect, contributing to severe environmental and ecological consequences [2]. Fossil fuels have long played a central role in modern energy production, supporting industrial growth and improving living standards [3]. However, their combustion remains a major source of CO₂ emissions, driving global climate change [4]. Saudi Arabia is among the leading CO₂ emitters, with key contributions from industries, electricity generation, transportation, and households [5, 6]. The energy sector alone accounts for over 90% of the country’s CO₂ emissions from fossil fuels, while power generation globally contributes approximately one-third of total CO₂ emissions. Consequently, researchers worldwide are exploring strategies to reduce CO₂ emissions and mitigate global warming. [7, 8].

Microalgae are tiny photosynthetic organisms lacking vascular tissues, true leaves, roots and stems, capable of converting solar energy into chemical energy [9]. They exhibit much higher efficiency in light-to-energy conversion compared to terrestrial plants. Microalgae are usually grown photoautotrophically, where light serves as the primary energy source, and CO₂ is utilized for carbon assimilation [10]. These microorganisms absorb essential nutrients like nitrogen and phosphorus from their growth medium and convert them into lipids, food additives, and bioactive compounds through various metabolic pathways [11, 12]. Cultivating microalgae in wastewater offers environmental benefits by facilitating the removal of nitrogen compounds, phosphates, and heavy metals [13]. Microalgae utilize oxygenic photosynthesis to absorb CO₂, converting it into carbohydrates, lipids, and hydrocarbons, while releasing oxygen and supporting sustainable carbon sequestration [14].

Microalgae are recognized for their high photosynthetic efficiency and productivity and their potential to produce a diverse range of valuable compounds. Amongst these are high-value bioactive compounds such as pigments (e.g., beta-carotene, astaxanthin, lutein) and polyunsaturated fatty acids (PUFAs). Several factors can impact microalgae growth and productivity, including low nutrient supply, toxic pollutants, pathogens, and organic contaminants like azo dyes in wastewater, which can hinder photosynthetic activity and biomass accumulation [15, 16]. Specifically, the availability of carbon and nitrogen sources in the culture medium influences the biochemical composition of microalgae, including proteins, carbohydrates, chlorophyll, and fatty acids [17]. Additional factors such as strain selection, light availability, temperature, and pH are also critical for biomass production and bioactive compound synthesis [18, 19].

Microalgae provide a promising, low-cost alternative to traditional carbon capture and sequestration (CCS) methods, which are hindered by high energy demands, operational costs, and environmental concerns associated with physical CCS technologies [20, 21]. Microalgae naturally tolerate high CO₂ concentrations (they are even boosted by high CO₂ supply) and can effectively utilize CO₂ from industrial emissions, including power plant exhaust gases. Through photosynthesis, microalgae fix carbon efficiently, similar to early biological carbon sequestration mechanisms. Additionally, many microalgal species can assimilate carbonates like sodium bicarbonate (NaHCO₃) and sodium carbonate (Na₂CO₃) for cellular growth, further enhancing their potential for sustainable carbon capture and utilization [22]. Microalgae biotechnology offers a promising solution to global challenges such as food security, energy, climate change, and waste management, by providing sustainable alternatives to land crops for nutrients, renewable energy, and value-added products [23]. Microalgae efficiently convert carbon sources into biomass, producing biofuels, pigments, pharmaceuticals, and other high-value compounds, driving advancements in cultivation technology [18, 24, 25].

Photobioreactors (PBRs) offer a controlled alternative, optimizing photosynthesis efficiency while minimizing environmental limitations. These systems function as solar receivers, where absorbed light not used for photosynthesis is converted into heat, potentially affecting culture conditions. Environmental factors such as light intensity, aeration, and nutrient availability critically affect PBR performance; suboptimal conditions result in reduced microalgal growth. Therefore, PBR designs need to be optimized to mitigate these limitations and enhance cultivation efficiency. Vertical tubular PBRs, with transparent tubes and gas sparging systems, enhance mass transfer, nutrient distribution, and gas exchange, leading to improved microalgal productivity. In contrast, horizontal tubular PBRs, consisting of interconnected tubes, require high energy input due to continuous culture circulation and heat management. However, the integration of degassing systems helps regulating oxygen levels, improving microalgal growth efficiency. PBRs provide advantages such as reduced contamination risk, higher photosynthetic efficiency, and controlled environmental conditions. Despite higher operational costs, their ability to enhance biomass production and CO₂ fixation makes them a promising technology for large-scale microalgae cultivation and sustainable bioproduct generation.

The design of PBRs plays a crucial role in enhancing microalgae cultivation by optimizing mixing efficiency, light exposure, and gas–liquid mass transfer. PBRs rely on aeration for mixing, which requires less energy and fewer materials compared to pump-driven methods. However, challenges such as higher material costs, gas hold-ups, and biofouling, where microalgae adhere to the reactor walls thus blocking light penetration can impact efficiency. Kubar et al. developed the Tesla-valve and Nested-bottled PBRs, which generated internal vortices to improve microalgae suspension, leading to biomass production increases of 28.1% and 35%, respectively [26, 27]. Xue et al. (2013) introduced a 130 L air-lift flat-plate PBR equipped with optical fibers for internal illumination, enhancing Spirulina platensis growth [28]. Raeisossadati et al. [29] incorporated red and blue luminescent solar concentrators (LSCs) into raceway ponds, significantly improving Arthrospira platensis biomass productivity by 26% and boosting phycocyanin production by 44% [29]. Wang et al. (2023) developed a hybrid thin-layer fountain PBR (TLF-PBR) with a 1.5 m diameter, achieving a maximum biomass concentration of 3.955 ± 0.037 g/L 71% higher than flat-plate PBRs and 44.7% greater than thin-layer cascade systems [30]. Structural optimizations, such as adding internal static baffles and mixers, have been explored to improve mixing patterns and light distribution in flat-plate PBRs [31, 32]. Yaqoubnejad et al. [33] reported that integrating mechanical diversions and inclined baffles with airlift technology enhanced the flashing light effect, increasing biomass yield by 43.6% and 107.4% compared to standard PBRs [33]. Additionally, Cheng et al. [34] introduced an up–down chute baffle in a raceway pond, generating multiple internal vortices to enhance mixing [34]. A comprehensive understanding of multiphase flow, energy and mass transfer, and multi-field coupling is essential for developing highly efficient PBRs, enabling improved productivity and sustainability in microalgae-based bioprocesses [27].

Traditional PBRs often face limitations such as poor light penetration and inadequate mixing. This study presents the Nested-bottled Photobioreactor (NB-PBR) hybrid system, which eliminates these issues by employing vortex-driven mixing, enhancing light distribution and CO₂ dissolution. The continuous circulation between the raceway pond and NB-PBR optimizes nutrient availability, boosting microalgal growth and productivity. Despite similar energy and material requirements, the NB-PBR offers superior efficiency, lower energy consumption, and reduced operational costs, making it a cost-effective alternative to traditional PBRs.

Experimental setup for hybrid system

In this experiment, two open raceway ponds were connected separately to a traditional PBR (vertical tubular PBR loop of equal volume integrated with the raceway pond, used as a control) and a novel NB-PBR, as illustrated in Fig. 1. The NB-PBR was designed and integrated with a raceway pond (20 cm wide, 60 cm long) to enable continuous medium circulation between the two systems. This novel PBR featured two interconnected columns with curved arms on both sides, promoting additional vortices within the solution to enhance system performance. Each column (50 cm in height, 10 cm in diameter) was divided into riser and downcomer sections, consisting of three regions, each 8 cm in height. Aeration was introduced from the bottom right to optimize gas–liquid interactions. The NB-PBR’s innovative design facilitated effective modification of the solution’s flow path and improved CO₂ bubble distribution, enhancing overall efficiency. The hybrid system, operated under standard conditions of 12,000 ± 200 lx light intensity, 27.2 °C temperature, and 15% CO₂, provided optimal illumination to support the photosynthetic activity of Arthrospira platensis throughout its circulation in the system.

Schematic of the Hybrid Nested-bottled photobioreactor

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Cultivation of Arthrospira platensis strain

A mutated strain of Arthrospira platensis, designated as Spirulina sp. ZJU9000, was cultivated in Zarrouk’s medium. The mutation was induced using γ-rays from Cobalt-60 nuclear irradiation, followed by domestication through exposure to ~ 15% CO₂ concentrations for eight generations to ensure hereditary stability. The cultivation medium, prepared with reagents from Sinopharm Chemical Reagent (Shanghai, China), was Zarrouk’s medium, a widely used formulation for A. platensis cultivation. This approach aimed to enhance the strain’s adaptability to high CO₂ conditions, supporting its potential for improved growth and biomass production in controlled environments [35].

Measurements of mixing time and the mass transfer

Mixing time and mass transfer coefficients were assessed using pH probes (InPro3253i/SG/120, Mettler Toledo). In the open raceway pond (ORWP), five liters of distilled water were placed, and the initial pH was adjusted to 3.0 using 35% hydrochloric acid (HCl). Sodium hydroxide (NaOH) (2.5–3.5 mL, 12 µmol/L) was then added incrementally, producing two consecutive pH peaks, with the time interval between them recorded as the mixing time. For mass transfer evaluation, purified water was aerated with air and nitrogen (N₂), with gas flow precisely controlled by a mass flow meter (SevenstarCS200, China). The dissolved oxygen concentration was maintained between 4 and 6 mg/L by reducing it to ≤ 4 mg/L with nitrogen, followed by reoxygenation with ambient air. Changes in pH and oxygen levels were recorded every 0.1 s using pH and dissolved oxygen probes (Mettler Toledo) connected to transmitters (i-7017fc, ICP DAS, China) and monitored via data acquisition software [36]. Two sets of measurements were taken for both mixing time and mass transfer coefficient values, with the calculated mean and standard deviation reported.

Measurement of photosynthetic parameters during Arthrospira Platensis cultivation

The maximum photochemical efficiency (F_v/F_m) of φPSII was determined utilizing the formula: F_v/F_m = (F_m–F₀)/Fm, where F_m and F_o denote the maximal and minimal chlorophyll fluorescence yields of a sample subjected to dark adaptation. For these measurements, 2.8 mL of algal samples underwent a dark-adaptation period in a liquid sample holder for 15 min. The measurements were conducted using an AquaPen.

A 5-ml microalgal solution sample was obtained for chlorophyll a measurement. Subsequently, the sample were centrifuged at 8000 rpm for 5 min, and the supernatant was removed. Following this, 5 ml of methanol were introduced to the microalgal pellet, and the mixture was kept in darkness for 30 min after vortex mixing. The supernatant was then transferred into a cuvette. Absorbance at OD₆₆₅ and OD₆₅₂ was measured using pure methanol as the blank sample with a UV-3200B spectrophotometer. The overall chlorophyll content was calculated using the following formula [26].

Sampling was done twice a day at 09:00 and 21:00.

Measurement of phycocyanin and allophycocyanin

To extract allophycocyanin and phycocyanin, the culture was centrifuged at 4000 × g for 5 min. The biomass was then separated from the supernatant and homogenized for 2 min with 5 mL of a 1% CaCl₂ (calcium chloride) solution. The homogenized samples underwent three freeze–thaw cycles, followed by overnight incubation at 4 °C. After incubation, the samples were centrifuged at 8000 × g for 12 min, and the absorbance of the supernatant was measured using a spectrophotometer at 652 nm for allophycocyanin and 620 nm for phycocyanin [37].

where A₆₂₀ and A₆₅₀ are the absorbance at 620 at 650 nm, for phycocyanin and allophycocyanin, respectively. Data was collected in triplicate (n = 3), with averages, and standard deviation.

Biomass and CO₂ fixation measurements of Arthrospira platensis

The dry mass was measured gravimetrically. To determine the sample weight, a pre-weighed dry filter paper was used to filter a 10 mL sample (Vaccum pump VOP-200, Yiheng, Shanghai China). The filtered sample was then dried in an oven at 50 °C for three hours. The biomass was calculated by measuring the difference between the initial weight of the dry filter paper and its final weight after filtration and drying. The CO₂ fixation rate was measured via the dry weight conversion method using following equation:

where w₂ is the dry mass at time t₂ and w₁ is the biomass dry weight at time t₁, p represents carbon content in microalgae cells (50%), M_CO2 represents the molecular weight of CO₂, and M_C denotes the molecular weight of carbon [38, 39].

Effects of traditional and Nested-bottled PBR on MTC and MT

The PBR’s mass transfer capacity (MTC) relates to its proficiency in mass transfer, while the mixing capacity is quantified by the mixing time (MT). In general, microalgae growth is typically increased in the presence of CO₂ compared to air. Furthermore, both structural factors and CO₂ significantly influence the overall performance of a well-designed column PBR. Earlier studies indicate that the introduction of circular or curved baffles in PBRs and ORWPs generates a vortex flow field, demonstrating its effectiveness in enhancing microalgae biomass productivity [38, 39].

The degree of liquid-phase homogenization in the PBR or ORWP indicates the efficiency with which various nutrients and dissolved CO₂ achieve a uniform status within the microalgal suspension [40]. In an ORWP, the primary location for the mixing process is around the paddle wheel. After the utilization of inorganic carbon and nutrients through photosynthesis in the raceway pond, the microalgal suspension is circulated to the NB-PBR. The addition of a nested structure reduced MT and increased mass transfer as compared to the traditional PBR (T-PBR) hybrid system (Fig. 2). The flow field in the NB-PBR hybrid system is the primary factor that determines the inner mixing ability. The flow of the microalgal suspension is directed along specific sections to extend the flow pathway, enhancing the mixing and interaction of microalgal suspensions. This occurs not only from the bottom to the top of the NB-PBR but also from the central regions to the outer regions. In contrast, the T-PBR and open raceway pond demonstrate lower mixing efficiency as it contains larger inactive areas, where substance exchange depends on diffusion, leading to a considerable slowdown in the mixing process. The evaluation of the influence of the NB-PBR on mixing time was conducted in this study when connected together with an OWRP. The presence of curved structures in the NB-PBR resulted in notable flow resistance, impeding the mixing process. With an escalation in pump power from 1 to 5 W, the mixing time decreased from 22 to 15 seconds (Fig. 2a). Increased pump power accelerated the circulation of the microalgal suspension, thereby enhancing flow intensity and significantly reducing mixing time.

Mixing time (MT) and mass transfer coefficient (MTC) for traditional and Nested-bottled hybrid PBR. a Effect of pump power b Effect of paddle wheel speed

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For the NB-PBR hybrid system, MT decreased from 24 to 15 s however the mass transfer coefficient increased from 1.95 to 3.23 h⁻¹ when the rotation speed increased from 20 to 60 rpm (Fig. 2b). The decrease in MT signifies the even distribution of nutrients within the medium. During the microalgal growth phase, the regions with higher light intensity exhibited an elevated growth rate, consequently accelerating the rate of nutrient consumption. The NB-PBR hybrid system was partitioned into two segments: the riser and the downcomer, aimed to maintain uniformity throughout the culture, optimizing even distribution of light penetration across the PBR. The proposed design of the NB-PBR hybrid system enhanced the light absorption capacity of microalgae cells by facilitating frequent movement between light and dark zones. This strategy prevented prolonged exposure of cells to either zone, mitigating the risk of photoinhibition and respiratory issues, ultimately contributed to reduce A. platensis growth. Additionally, the NB-PBR hybrid system improved intracellular energy supply and facilitated processes such as NADH oxidation, transmembrane protein transport, oxidative phosphorylation, ATP synthase, and proton gradient formation [41, 42].

Photochemical efficiency properties for traditional and Nested-bottled PBR

In the NB-PBR hybrid system, as the liquid traversed the inner tubes and entered the primary column sections, vertical vortex flow fields in both clockwise and anticlockwise direction are induced. The generation of these vortices distinguishes the NB-PBR hybrid system from T-PBR designs that necessitate modifications for similar flow patterns. Unlike T-PBRs, the NB-PBR was independent of inner and outer zones for microalgae solution circulation, choosing instead to divide the entire flow field with a riser and down-flow zone. In the T-PBR hybrid system, the fluid exhibited a laminar pattern in the inner up-flow area and the outer down-flow area.

The installation of the NB-PBR hybrid system significantly improved the flow dynamics conditions. This innovative design of the NB-PBR hybrid system has a substantial impact on the advancement in algal cultivation technology. A. platensis exhibits a notable CO₂ fixation rate, substantial protein content, and a rich pigment profile, particularly phycocyanin. The photosynthetic lamellae, forming thylakoids, house phycobilisomes—a specialized supramolecular pigment protein complex [44]. These phycobilisomes function as light-harvesting antennae, binding chromophores like phycocyanobilin. These antennae systems capture light energy from spectral regions, where chlorophyll a either weakly absorbs or does not absorb at all, subsequently transferring the absorbed energy to the reaction center. Environmental factors influence phycobilisome content, leading to variations [45]. Elevated phycobilisome content enhances photosynthetic efficiency, contributing to a substantial 28.7% increase in biomass yield in NB-PBR hybrid system. The role of chlorophyll within this inner antenna involves photon capture and the reception of excitation energy from the phycobilisome, directing it to chlorophyll in the reaction center where primary photochemistry occurs [46]. The light-harvesting pigment protein complex of A. platensis encompasses phycobilisomes, comprising allophycocyanin (APC) and phycocyanin (PC) [47].

The fluorescence parameter Fv/Fm stands out as the most assessed measurement for estimating the PSII system’s activity. It serves as a crucial indicator of photosynthetic efficiency and the conversion of PSII reactions. As depicted in Fig. 3a, the Hybrid-PBR demonstrated elevated Fv/Fm 8.7%, attributed to the lower microalgal density facilitating improved light penetration throughout the PBR. Consequently, the maximum photochemical efficiency and absorbed light energy of the reaction center increased, enhancing the likelihood of algal cells absorbing a greater number of light photons. With the progression of biomass growth, a decline in photosynthetic efficiency occurred, resulting in a substantial reduction in the percentage of light deficiency or photodamage experienced by algal cells. Simultaneously, efficient mixing and mass transfer enhanced the overall performance of the NB-PBR hybrid system. The even distribution of algal cells throughout the NB-PBR hybrid system contributed to increased biomass production efficiency per absorbed photon. The structural modification applied to the NB-PBR hybrid system had a favorable impact on F_v/F_m, closely associated with light utilization efficiency.

Comparison of chlorophyll fluorescence induction kinetic parameters of A. platensis cells in the traditional and Nested-bottled hybrid PBR a Fv/Fm b Chlorophyll-a and carotenoids

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The role of chlorophyll within this inner antenna is dual—capturing photons directly and receiving excitation energy from the phycobilisomes, subsequently directing it to chlorophyll in the reaction center where primary photochemistry occurs [17]. This signifies the intactness of the cells’ photosynthetic system, with enhanced photosynthesis. Carotenoids play a crucial role in antenna systems and chlorophyll binding proteins, aiding in light energy capture and the removal of excess free radicals in microalgae cells. In A. platensis, chlorophyll is chlorophyll-a. The photosynthetic efficiency of the cell is directly proportional to the content of chlorophyll-a, elevated chlorophyll-a and carotenoid content in NB-PBR hybrid system (Fig. 3b) showed positive influence over photosynthesis and CO₂ fixation in A. platensis cells. The increased carotenoid content also strengthened stress resistance, including resistance to light damage and free radical accumulation. A. platensis reproduces through fission, where one trichome divides into two or more new individuals of the same size and shape.

Phycocyanin and Allophycocyanin content in hybrid NB-PBR and hybrid T-PBR

The comparative investigation of pigment composition in A. platensis cultivated within the NB-PBR hybrid system and the Hybrid T-PBR revealed significant differences shown in Fig. 4, shedding light on the influence of reactor configuration on pigment levels. C-phycocyanin stands out among high-value proteins due to its antioxidant and anti-inflammatory properties [48]. The study demonstrates the significant positive influence of the hybrid PBR on the growth of A. platensis. The light-harvesting pigment-protein complex in A. platensis comprises phycobilisomes, consisting of allophycocyanin and phycocyanin [49]. Over a 144-h cultivation period, A.platensis grown in the NB-PBR hybrid system exhibited notably higher concentrations of both allophycocyanin and phycocyanin compared to those in the Hybrid T-PBR. Specifically, the T-PBR hybrid system yielded the reduced phycocyanin concentration at 110 mg/L, while the NB-PBR hybrid system recorded the highest at 123 mg/L, indicating a considerable impact of reactor type on phycocyanin production (Fig. 4). Similar trends were observed for allophycocyanin, with the NB-PBR hybrid system demonstrating superior pigment synthesis capabilities compared to the T-PBR hybrid system 43 and 35 mg/L, respectively. These findings highlight the importance of reactor design in influencing pigment production, thereby affecting the nutritional quality and commercial viability of cultivated A. platensis.

Phycocyanin and Allophycocyanin

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The superior pigment synthesis environment provided by the NB-PBR hybrid system suggests its potential as a preferred system for maximizing valuable pigment production in A. platensis cultivation. This nuanced understanding of pigment dynamics contributes valuable insights to the optimization of microalgal cultivation strategies, ultimately enhancing both nutritional and economic outcomes [50].

b. b

Hybrid NB -PBR increased CO₂ fixation biomass dry weight

PBRs under optimal conditions, entering the exponential growth phase on the second day in both reactors. As the microalgae continued to proliferate, the concentration in the photobioreactors increased, necessitating elevated dissolved inorganic carbon and well-mixed nutrients to sustain the rapid growth rate. By the end of the 144-h cultivation period, the final microalgal biomass accumulation reached 38.0% rise in dry mass (3.1 g/L) and 2.26 g/L in the hybrid NB-PBR and T-PBR hybrid system, respectively (Fig. 5). This improvement was attributed to the enhanced mass transfer coefficient and improved mixing state facilitated by the NB-PBR. Upon initial aeration of CO₂ into the PBR, the pH of the microalgal suspension promptly decreased from 9.8 to 8.9, a result of the carbon dioxide hydration process (CO₂ + H₂O → HCO₃^– + H⁺)[27, 51]. After 12 h, the pH gradually increased due to the consumption of nitrite and dissolved inorganic carbon nutrients. After 36 h, the pH exhibited further variation as the microalgal concentration significantly increased (Fig. 5a), leading to accelerated nutrient consumption and an ensuing increase in pH. In summary, the NB-PBR offers a viable strategy for optimizing solar energy utilization and enhancing microalgal biomass yield as compared to T-PBR hybrid system.

a A. platensis dry mass and pH value with 15% CO₂ [where “ρ” is the carbon content in microalgae dry weight (50%)], b Rate of growth per 12 h, c CO₂ fixation rate

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The specific design and construction of the NB-PBR were geared towards generating predominant vortices within the reactor, ensuring an even distribution of nutrients, and preventing cell adhesion to the PBR walls. This distinctive structure also extends the duration of gas–liquid contact and facilitates the dissolution of CO₂. The movement of CO₂ bubbles through the PBR induces liquid flow, and each segment of the NB-PBR temporarily retains the bubbles before releasing them into the subsequent section. This sequential process results in the breakdown of larger bubbles into smaller ones, enhancing gas–liquid mass transfer and prolonging the retention of smaller bubbles within the PBR. Consequently, there is an increased CO₂ mass transfer (Fig. 5c). The adoption of microbubbles, as opposed to larger bubbles, significantly enhances the efficiency of CO₂ absorption.

1. Simionov I, Barbu M, Vasiliev I, Condrachi L, Titica M, Ifrim G, Cristea D, Marcel F. Prospective technical and technological insights into microalgae production using aquaculture wastewater effluents. J Environ Manag. 2025. https://doi.org/10.1016/j.jenvman.2025.124537.

   Article  Google Scholar 

2. Ezzeroual O, El Kadmiri N. Microalgae for future biodiesel production: algaculture, environnement impact. Maghrebian J Pure Appl Sci. 2021;1:8–14.

   Google Scholar 

3. Amran YHA, Amran YHM, Alyousef R, Alabduljabbar H. Renewable and sustainable energy production in Saudi Arabia according to Saudi Vision 2030; current status and future prospects. J Clean Prod. 2020;247:119602. https://doi.org/10.1016/j.jclepro.2019.119602.

   Article  Google Scholar 

4. Zhu Q. Developments on CO₂ -utilization technologies. Clean Energy. 2019;3:85–100. https://doi.org/10.1093/ce/zkz008.

   Article  Google Scholar 

5. Ouda OKM, Raza SA, Nizami AS, Rehan M, Al-Waked R, Korres NE. Waste to energy potential: a case study of Saudi Arabia. Renew Sustain Energy Rev. 2016;61:328–40. https://doi.org/10.1016/j.rser.2016.04.005.

   Article  Google Scholar 

6. Abdur S, Bahar K, Islam KMO, Khaleel A, Omar M, Hossain SMZ, Hossain MM. Green chemical engineering microalgae cultivation in photobioreactors: sustainable solutions for a greener future, Green. Chem Eng. 2024;5:418–39. https://doi.org/10.1016/j.gce.2023.10.004.

   Article  Google Scholar 

7. Wan Ismail WZ, Abdullah MN, Che-Ani AI. A review of factors affecting carbon sequestration at green roofs. J Facil Manag. 2019;17:76–89. https://doi.org/10.1108/JFM-11-2017-0069.

   Article  Google Scholar 

8. Yadav G, Dubey BK, Sen R. A comparative life cycle assessment of microalgae production by CO₂ sequestration from flue gas in outdoor raceway ponds under batch and semi-continuous regime. J Clean Prod. 2020;258:120703. https://doi.org/10.1016/j.jclepro.2020.120703.

   Article  CAS  Google Scholar 

9. Morais Junior WG, Gorgich M, Corrêa PS, Martins AA, Mata TM, Caetano NS. Microalgae for biotechnological applications: cultivation, harvesting and biomass processing. Aquaculture. 2020;528:735562. https://doi.org/10.1016/j.aquaculture.2020.735562.

   Article  CAS  Google Scholar 

10. Ketheesan B, Nirmalakhandan N. Feasibility of microalgal cultivation in a pilot-scale airlift-driven raceway reactor. Bioresour Technol. 2012;108:196–202. https://doi.org/10.1016/j.biortech.2011.12.146.

    Article  CAS  PubMed  Google Scholar 

11. Chew KW, Chia SR, Show PL, Yap YJ, Ling TC, Chang JS. Effects of water culture medium, cultivation systems and growth modes for microalgae cultivation: a review. J Taiwan Inst Chem Eng. 2018;91:332–44. https://doi.org/10.1016/j.jtice.2018.05.039.

    Article  CAS  Google Scholar 

12. Chen D, Huo S, Cheng P, Cheng Y, Zhou N, Chen P, Wang Y, Li K, Peng P, Ruan R. Treatment and nutrient recovery from acetophenone based wastewater by an integrated catalytic intense pulsed light and Tribonema sp. cultivation. Chem Eng Process Process Intensif. 2021. https://doi.org/10.1016/j.cep.2020.108276.

    Article  Google Scholar 

13. Wong Y. Effect of different light sources on algal biomass and lipid production in internal leds-illuminated photobioreactor. J Mar Biol Aquac. 2016;2:1–8. https://doi.org/10.15436/2381-0750.16.1082.

    Article  Google Scholar 

14. Goswami RK, Mehariya S, Karthikeyan OP, Gupta VK, Verma P. Multifaceted application of microalgal biomass integrated with carbon dioxide reduction and wastewater remediation: a flexible concept for sustainable environment. J Clean Prod. 2022;339:130654. https://doi.org/10.1016/j.jclepro.2022.130654.

    Article  CAS  Google Scholar 

15. Dahai H, Zhihong Y, Lin Q, Yuhong L, Lei T, Jiang L, Liandong Z. The application of magical microalgae in carbon sequestration and emission reduction: Removal mechanisms and potential. Renew Sustain Energy Rev. 2024;197:114417. https://doi.org/10.1016/j.rser.2024.114417.

    Article  CAS  Google Scholar 

16. Kong F, Ren H, Liu D, Wang Z, Nan J, Ren N, Fu Q. Bioresource technology improved decolorization and mineralization of azo dye in an integrated system of anaerobic bioelectrochemical modules and aerobic moving bed biofilm reactor. Bioresour Technol. 2022;353:127147. https://doi.org/10.1016/j.biortech.2022.127147.

    Article  CAS  PubMed  Google Scholar 

17. Bauer LM, Costa JAV, da Rosa APC, Santos LO. Growth stimulation and synthesis of lipids, pigments and antioxidants with magnetic fields in Chlorella kessleri cultivations. Bioresour Technol. 2017;244:1425–32. https://doi.org/10.1016/j.biortech.2017.06.036.

    Article  CAS  PubMed  Google Scholar 

18. Pires JCM, Alvim-Ferraz MCM, Martins FG, Simões M. Carbon dioxide capture from flue gases using microalgae: Engineering aspects and biorefinery concept. Renew Sustain Energy Rev. 2012;16:3043–53. https://doi.org/10.1016/j.rser.2012.02.055.

    Article  CAS  Google Scholar 

19. Wan Mahari WA, Wan Razali WA, Manan H, Hersi MA, Ishak SD, Cheah W, Chan DJC, Sonne C, Show PL, Lam SS. Recent advances on microalgae cultivation for simultaneous biomass production and removal of wastewater pollutants to achieve circular economy. Bioresour Technol. 2022;364:128085. https://doi.org/10.1016/j.biortech.2022.128085.

    Article  CAS  PubMed  Google Scholar 

20. Onyeaka H, Miri T, Obileke K, Hart A, Anumudu C, Al-Sharify ZT. Minimizing carbon footprint via microalgae as a biological capture. Carbon Capture Sci Technol. 2021;1:100007. https://doi.org/10.1016/j.ccst.2021.100007.

    Article  CAS  Google Scholar 

21. Norhasyima RS, Mahlia TMI. Advances in CO₂ utilization technology: a patent landscape review. J CO2 Util. 2018;26:323–35. https://doi.org/10.1016/j.jcou.2018.05.022.

    Article  CAS  Google Scholar 

22. Ighalo JO, Dulta K, Kurniawan SB, Omoarukhe FO, Ewuzie U, Eshiemogie SO, Ojo AU, Abdullah SRS. Progress in microalgae application for CO₂ sequestration. Clean Chem Eng. 2022;3:100044. https://doi.org/10.1016/j.clce.2022.100044.

    Article  Google Scholar 

23. Carneiro M, Maia IB, Cunha P, Guerra I, Magina T, Santos T, Schulze PSC, Pereira H, Malcata FX, Navalho J, Silva J, Otero A, Varela J. Effects of LED lighting on Nannochloropsis oceanica grown in outdoor raceway ponds. Algal Res. 2022;64:102685. https://doi.org/10.1016/j.algal.2022.102685.

    Article  Google Scholar 

24. Fu W, Gudmundsson S, Wichuk K, Palsson S, Palsson BO, Salehi-Ashtiani K, Brynjólfsson S. Sugar-stimulated CO₂ sequestration by the green microalga Chlorella vulgaris. Sci Total Environ. 2019;654:275–83. https://doi.org/10.1016/j.scitotenv.2018.11.120.

    Article  CAS  PubMed  Google Scholar 

25. Rizwan M, Mujtaba G, Memon SA, Lee K, Rashid N. Exploring the potential of microalgae for new biotechnology applications and beyond: a review. Renew Sustain Energy Rev. 2018;92:394–404. https://doi.org/10.1016/j.rser.2018.04.034.

    Article  Google Scholar 

26. Kubar AA, Cheng J, Kumar S, Liu S, Chen S, Tian J. Strengthening mass transfer with the Tesla-valve baffles to increase the biomass yield of Arthrospira platensis in a column photobioreactor. Bioresour Technol. 2021;320:124337. https://doi.org/10.1016/j.biortech.2020.124337.

    Article  CAS  PubMed  Google Scholar 

27. Kubar AA, Kumar S, Liu W, Cui Y, Zhu F, Xu X, Shao C, Hu X, Prempeh NYA, Huo S. Numerical simulation of vortex flow field generated in a novel nested-bottled photobioreactor to improve Arthrospira platensis growth. Bioresour Technol. 2023;373:128710. https://doi.org/10.1016/j.biortech.2023.128710.

    Article  CAS  PubMed  Google Scholar 

28. Xue S, Zhang Q, Wu X, Yan C, Cong W. A novel photobioreactor structure using optical fibers as inner light source to fulfill flashing light effects of microalgae. Bioresour Technol. 2013;138:141–47. https://doi.org/10.1016/j.biortech.2013.03.156.

    Article  CAS  PubMed  Google Scholar 

29. Raeisossadati M, Moheimani NR, Parlevliet D. Red and blue luminescent solar concentrators for increasing Arthrospira platensis biomass and phycocyanin productivity in outdoor raceway ponds. Bioresour Technol. 2019;291:121801. https://doi.org/10.1016/j.biortech.2019.121801.

    Article  CAS  PubMed  Google Scholar 

30. Wang J, Hu C, He W, Du F, Jiao N, Liu J, Zhu C. Novel thin-layer fountain photobioreactors for the high-density cultivation of Spirulina sp. ACS Sustain Chem Eng. https://doi.org/10.1021/acssuschemeng.3c05509.

31. Ye Q, Cheng J, Guo W, Xu J, Li K, Zhou J. Serial lantern-shaped draft tube enhanced flashing light effect for improving CO₂ fixation with microalgae in a gas-lift circumflux column photobioreactor. Bioresour Technol. 2018;255:156–62. https://doi.org/10.1016/j.biortech.2018.01.127.

    Article  CAS  PubMed  Google Scholar 

32. Azizi K, Keshavarz Moraveji M, Hassanzadeh H, Abedini Najafabadi H. Consideration of inclined mixers embedded inside a photobioreactor for microalgae cultivation using computational fluid dynamic and particle image velocimetry measurement. J Clean Prod. 2018;195:753–64. https://doi.org/10.1016/j.jclepro.2018.05.253.

    Article  Google Scholar 

33. Yaqoubnejad P, Amini H, Taghavijeloudar M. Development a novel hexagonal airlift flat plate photobioreactor for the improvement of microalgae growth that simultaneously enhance CO₂ bio-fixation and wastewater treatment. J Environ Manage. 2021;298:113482. https://doi.org/10.1016/j.jenvman.2021.113482.

    Article  CAS  PubMed  Google Scholar 

34. Cheng J, Yang Z, Ye Q, Zhou J, Cen K. Enhanced flashing light effect with up-down chute baffles to improve microalgal growth in a raceway pond. Bioresour Technol. 2015;190:29–35. https://doi.org/10.1016/j.biortech.2015.04.050.

    Article  CAS  PubMed  Google Scholar 

35. Cheng J, Lu H, He X, Yang W, Zhou J, Cen K. Mutation of Spirulina sp. by nuclear irradiation to improve growth rate under 15% carbon dioxide in flue gas. Bioresour Technol. 2017;238:650–6. https://doi.org/10.1016/j.biortech.2017.04.107.

    Article  CAS  PubMed  Google Scholar 

36. Yang Z, Cheng J, Liu J, Zhou J, Cen K. Improving microalgal growth with small bubbles in a raceway pond with swing gas aerators. Bioresour Technol. 2016;216:267–72. https://doi.org/10.1016/j.biortech.2016.05.076.

    Article  CAS  PubMed  Google Scholar 

37. Kumar S, Kubar AA, Zhu F, Shao C, Cui Y, Hu X, Ni J, Shah MAR, Ding S, Mehmood S, Huo S. Sunlight filtered via translucent-colored polyvinyl chloride sheets enhanced the light absorption capacity and growth of Arthrospira platensis cultivated in a pilot-scale raceway pond. Bioresour Technol. 2023;386:129501. https://doi.org/10.1016/j.biortech.2023.129501.

    Article  CAS  PubMed  Google Scholar 

38. Cheng J, Lai X, Ye Q, Guo W, Xu J, Ren W, Zhou J. A novel jet-aerated tangential swirling-flow plate photobioreactor generates microbubbles that enhance mass transfer and improve microalgal growth. Bioresour Technol. 2019;288:121531. https://doi.org/10.1016/j.biortech.2019.121531.

    Article  CAS  PubMed  Google Scholar 

39. Song Y, Cheng J, Lai X, Guo W, Yang W. Developing a three-dimensional tangential swirl plate photobioreactor to enhance mass transfer and flashlight effect for microalgal CO₂ fixation. Chem Eng Sci. 2021;244:116837. https://doi.org/10.1016/j.ces.2021.116837.

    Article  CAS  Google Scholar 

40. Ding YD, Zhao S, Liao Q, Chen R, Huang Y, Zhu X. Effect of CO₂ bubbles behaviors on microalgal cells distribution and growth in bubble column photobioreactor. Int J Hydrogen Energy. 2016;41:4879–87. https://doi.org/10.1016/j.ijhydene.2015.11.050.

    Article  CAS  Google Scholar 

41. Kazbar A, Cogne G, Urbain B, Marec H, Le-Gouic B, Tallec J, Takache H, Ismail A, Pruvost J. Effect of dissolved oxygen concentration on microalgal culture in photobioreactors. Algal Res. 2019;39:101432. https://doi.org/10.1016/j.algal.2019.101432.

    Article  Google Scholar 

42. Zhi R, Yang A, Zhang G, Zhu Y, Meng F, Li X. Effects of light-dark cycles on photosynthetic bacteria wastewater treatment and valuable substances production. Bioresour Technol. 2019;274:496–501. https://doi.org/10.1016/j.biortech.2018.12.021.

    Article  CAS  PubMed  Google Scholar 

43. Chu F, Cheng J, Zhang X, Ye Q, Zhou J. Enhancing lipid production in microalgae Chlorella PY-ZU1 with phosphorus excess and nitrogen starvation under 15% CO₂ in a continuous two-step cultivation process. Chem Eng J. 2019;375:121912. https://doi.org/10.1016/j.cej.2019.121912.

    Article  CAS  Google Scholar 

44. Burlacot A, Dao O, Auroy P, Cuiné S, Li-Beisson Y, Peltier G. Alternative photosynthesis pathways drive the algal CO₂-concentrating mechanism. Nature. 2022;605:366–71. https://doi.org/10.1038/s41586-022-04662-9.

    Article  CAS  PubMed  Google Scholar 

45. Cho K, Cho DH, Heo J, Kim U, Lee YJ, Choi DY, Kim HS. Nitrogen modulation under chemostat cultivation mode induces biomass and lipid production by Chlorella vulgaris and reduces antenna pigment accumulation. Bioresour Technol. 2019;281:118–25. https://doi.org/10.1016/j.biortech.2019.02.063.

    Article  CAS  PubMed  Google Scholar 

46. Seger M, Unc A, Starkenburg SR, Holguin FO, Lammers PJ. Nutrient-driven algal-bacterial dynamics in semi-continuous, pilot-scale photobioreactor cultivation of Nannochloropsis salina CCMP1776 with municipal wastewater nutrients. Algal Res. 2019;39:101457. https://doi.org/10.1016/j.algal.2019.101457.

    Article  Google Scholar 

47. Tayebati H, Shariati FP, Soltani N, Tehrani HS. Effect of various light spectra on amino acids and pigment production of Arthrospira platensis using flat-plate photobioreactor. Prep Biochem Biotechnol. 2021. https://doi.org/10.1080/10826068.2021.1941102.

    Article  PubMed  Google Scholar 

48. Ray A, Nayak M, Ghosh A. A review on co-culturing of microalgae: a greener strategy towards sustainable biofuels production. Sci Total Environ. 2022;802:149765. https://doi.org/10.1016/j.scitotenv.2021.149765.

    Article  CAS  PubMed  Google Scholar 

49. Sen Tan J, Lee SY, Chew KW, Lam MK, Lim JW, Ho SH, Show PL. A review on microalgae cultivation and harvesting, and their biomass extraction processing using ionic liquids. Bioengineered. 2020;11:116–29. https://doi.org/10.1080/21655979.2020.1711626.

    Article  CAS  Google Scholar 

50. Hu J, Nagarajan D, Zhang Q, Chang JS, Lee DJ. Heterotrophic cultivation of microalgae for pigment production: a review. Biotechnol Adv. 2018;36:54–67. https://doi.org/10.1016/j.biotechadv.2017.09.009.

    Article  CAS  PubMed  Google Scholar 

51. Guo W, Cheng J, Liu S, Feng L, Su Y, Li Y. A novel porous nickel-foam filled CO₂ absorptive photobioreactor system to promote CO₂ conversion by microalgal biomass. Sci Total Environ. 2020;713:136593. https://doi.org/10.1016/j.scitotenv.2020.136593.

    Article  CAS  PubMed  Google Scholar 

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Author notes

1. Ameer Ali Kubar, and Shahid Mehmood have contributed equally to this work.

Authors and Affiliations

1. School of Food and Biological Engineering, Jiangsu University, Zhenjiang, 212013, China

   Ameer Ali Kubar, Santosh Kumar, Xinjuan Hu & Shuhao Huo

2. School of Life Sciences, Jiangsu University, Zhenjiang, 212013, China

   Shahid Mehmood & Feifei Zhu

3. Department of Functional and Evolutionary Ecology, University of Vienna, Djerassiplatz 1, 1030, Vienna, Austria

   Michael Schagerl

4. School of Agricultural Engineering, Jiangsu University, Zhenjiang, 212013, China

   Xiangru Xu & Jiheng Ni

Contributions

Shuhao Huo and Michael Schagerl supervised the whole project, Ameer Ali Kubar and Shahid Mehmood designed the experimental setup, analyzed the data and wrote manuscript; Ameer Ali Kubar, Santosh Kumar, Xinjuan Hu, Feifei Zhu, Xiangru Xu, and Jiheng Ni performed experiments on equipments such as column photobioreactor, pH probes (InPro3253i/SG/120 Mettler Toledo), mass flow meter (SevenstarCS200, China), dissolved oxygen probes (InPro6850i/ 12/120 Mettler Toledo), AquaPen-PAP 110-P. Then collected the data using above instruments; all authors discussed the results and contributed to the final manuscript.

Corresponding authors

Correspondence to Michael Schagerl or Shuhao Huo.

Ethics approval and consent to participate

Not applicable.

Competing interests

The authors declare no competing interests.

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