Seawater desalination concentrate for cultivation of Dunaliella salina with floating photobioreactor to produce β-carotene

Integrating bicarbonate-based microalgal production with alkaline sewage for ocean negative carbon emissions

Using sewage (wastewater) for ocean alkalinity enhancement (OAE) has been considered as one promising ocean negative carbon emissions (ONCE) approach due to its high carbon sequestration efficiency and low environmental risk. To make this process more profitable and sustainable, this perspective proposes to integrate bicarbonate-based microalgal production and sewage alkalinity enhancement for ONCE. In this concept, the spent aqueous alkaline bicarbonate-based microalgal medium is cheap or even free for OAE, while the produced microalgae with high value-added compositions make this process more profitable. To make the proposed idea more efficient and sustainable, the prospects for its future development are also discussed in this opinion article. This perspective provides a novel and practical idea for achieving efficient carbon neutralization and high economic value simultaneously.

Microalgae are not an umbrella solution for power industry waste abatement but could play a role in their valorization

Microalgae have long been regarded as a promising solution for biological carbon abatement from the power industry, offering renewable biomass without competing for land or water resources used for food crops. In this study, we extensively examined the application of photosynthetic microorganisms for closing carbon, nitrogen, and micronutrient loops in the power industry. Subsequently, we explored the bottom-up integration of algal biorefineries into power industry waste streams for increased economic benefits and reduced environmental impacts. Analysis of the available data indicated that microalgae integration with the power industry is primarily performed using flue-gas-assisted cultivation. This approach allows for carbon sequestration typically below one gram per liter per day, too low to significantly impact carbon abatement at achievable scales of microalgae cultivation. Alternative approaches are also being explored. For example, soluble bicarbonate platforms allow for higher biomass productivity and temporary carbon storage. Meanwhile, the use of ashes and waste heat and thermophilic strains can result in lower cultivation costs and better control of cultivation conditions. These approaches offer further incremental improvement to microalgae-based carbon abatement systems in the power industry but are unlikely to be an umbrella solution for carbon reduction. Consequently, in the near term, microalgae-based carbon valorization systems are likely to be limited to niche applications involving the synthesis of high-value products. For microalgae to truly transform carbon abatement processes radical improvements in both biology and engineering approaches are urgently needed.

Biochemical profile of Dunaliella isolates from different regions of Iran with a focus on pharmaceutical and nutraceutical potential applications

This study was conducted to evaluate three species of Dunaliella microalgae (Dunaliella salina, Dunaliella viridis, and Dunaliella sp.) indigenous to Iran as new sources of natural chemical and bioactive compounds for exploring pharmaceutical and nutraceutical potential applications. The results showed that the fat, carbohydrate (mono- and di-saccharide), dietary fiber, and protein content of Dunaliella were in the range of 13.19-25.02, 7.59-12.37, 42.10-48.82, and 17.68-22.50 (%), respectively. Dunaliella salina contained a pigment fraction of 11.50%, which was largely composed of carotenoid (7.41%) and chlorophyll (4.09%). Antioxidant capacity and inhibition of 2,2-diphenyl-1-1-picrylhydrazyl (DPPH) of Dunaliella salina were 34.54 mg/1000 g and 55.63%, respectively. The lipid profile also revealed that three isolated Dunaliella are remarkable sources of polyunsaturated fatty acids (25.42%-40.13%). Further, the ratios of ∑n-3/∑n-6 (2.79%), docosahexaenoic acid (6.15%), and eicosapentaenoic acid (11.26%) were the highest in Dunaliella salina. The results, thus, proved that Dunaliella spp., especially Dunaliella salina (IBRC-M 50030), which originates from a lake in Semnan province, Iran, has potential applications in the food and pharmaceutical industries due to its appropriate biopigment, protein, lipid, antioxidant activity, long-chain polyunsaturated fatty acids, docosahexaenoic acid, and eicosapentaenoic acid.

A comprehensive review on the heterotrophic production of bioactive compounds by microalgae

Bioactive compounds derived from microalgae have garnered considerable attention as valuable resources for drugs, functional foods, and cosmetics. Among these compounds, photosynthetic pigments and polyunsaturated fatty acids (PUFAs) have gained increasing interest due to their numerous beneficial properties, including anti-oxidant, anti-viral, anti-bacterial, anti-fungal, anti-inflammatory, and anti-tumor effects. Several microalgae species have been identified as rich sources of bioactive compounds, including the Chlorophyceae Dunaliella and Haematococcus, the Bacillariophyta Phaeodactylum and Nitzschia, and the dinoflagellate Crypthecodinium cohnii. However, most of the reported microalgae species primarily grow through autotrophic mechanisms, resulting in low yields and high production costs of bioactive compounds. Consequently, the utilization of heterotrophic microalgae, such as Chromochloris zofingiensis and Nitzschia laevis, has shown significant advantages in the production of astaxanthin and eicosapentaenoic acid (EPA), respectively. These heterotrophic microalgae exhibit superior capabilities in synthesizing target compounds. This comprehensive review provides a thorough examination of the heterotrophic production of bioactive compounds by microalgae. It covers key aspects, including the metabolic pathways involved, the impact of cultivation conditions, and the practical applications of these compounds. The review discusses how heterotrophic cultivation strategies can be optimized to enhance bioactive compound yields, shedding light on the potential of microalgae as a valuable resource for high-value product development.

Using wastewater as a cultivation alternative for microalga Dunaliella salina: Potentials and challenges

Untreated or poorly treated wastewater still represents environmental issues world-widely. Wastewater, especially saline wastewater treatment, is still primarily associated with high costs from physical and chemical processes, as high salinity hinders biological treatment. One favourable way is to find the suitable biological pathways and organisms to improve the biological treatment efficiency. In this context, halophilic microorganisms could be strong candidates to address the economics and effectiveness of the saline wastewater treatment process. Dunaliella salina is a photoautotrophic microalga that grows in saline environments. It is known for producing marketable bio-compounds such as carotenoids, lipids, and proteins. A biological treatment based on D. salina cultivation offers the opportunity to treat saline wastewater, reducing the threat of possible eutrophication from inappropriate discharge. At the same time, D. salina cultivation could yield compounds of industrial relevance to turn saline wastewater treatment into a profitable and sustainable process. Most research on D. salina has primarily focused on bioproduct generation, leaving thorough reviews of its application in wastewater treatment inadequate. This paper discusses the future challenges and opportunities of using D. salina to treat wastewater from different sources. The main conclusions are (1) D. salina effectively recovers some heavy metals (driven by metal binding capacity and exposure time) and nutrients (driven by pH, their bioavailability, and functional groups in the cell); (2) salinity plays a significant role in bioproducts generation, and (3) wastewater can be combined with the generation of bioproducts.

Kinetic modeling and process analysis for photo-production of β-carotene in Dunaliella salina

Dunaliella salina is a green microalga with the great potential to generate natural β-carotene. However, the corresponding mathematical models to guide optimized production of β-carotene in Dunaliella salina (D. salina) are not yet available. In this study, dynamic models were proposed to simulate effects of environmental factors on cell growth and β-carotene production in D. salina using online monitoring system. Moreover, the identification model of the parameter variables was established, and an adaptive particle swarm optimization algorithm based on parameter sensitivity analysis was constructed to solve the premature problem of particle swarm algorithm. The proposed kinetic model is characterized by high accuracy and predictability through experimental verification, which indicates its competence for future process design, control, and optimization. Based on the model established in this study, the optimal environmental factors for both β-carotene production and microalgae growth were identified. The approaches created are potentially useful for microalga Dunaliella salina cultivation and high-value β-carotene production.

Reuse of sea water reverse osmosis brine to produce Dunaliella salina based β-carotene as a valuable bioproduct: A circular bioeconomy perspective

Due to population growth and global warming, the use of the sea water reverse osmosis process to obtain freshwater is increasing rapidly. A sustainable method with low environmental impact is limited for the management of brine with a high salt content, which is released as a result of the process. Some microalgae species can grow in salty environments and produce β-carotene. This study aims to evaluate the commercial potential of β-carotene production from microalgae grown in sea water reverse osmosis brine from a bioeconomy perspective. Synthetic media are often used for the production of β-carotene from algae, the use of sea water reverse osmosis brine is not common and the commercial potential of this application has not been evaluated before. In terms of the development of the β-carotene market, the strengths and weaknesses of the process, opportunities, and threats are thoroughly examined in this report. Also, with the use of sea water reverse osmosis, a daily 750 tons of algal β-carotene can be produced. The biotechnological production of microalgal β-carotene and the reuse of salt water within the scope of circular bioeconomy are seen as a sustainable solution due to the fact that the strengths of the process are dominant, and the market value of natural β-carotene is increasing day by day.

Algal biomass valorisation to high-value chemicals and bioproducts: Recent advances, opportunities and challenges

Algae are considered promising biomass resources for biofuel production. However, some arguments doubt the economical and energetical feasibility of algal cultivation, harvesting, and conversion processes. Beyond biofuel, value-added bioproducts can be generated via algae conversion, which would enhance the economic feasibility of algal biorefineries. This review primarily focuses on valuable chemical and bioproduct production from algae. The methods for effective recovery of valuable algae components, and their applications are summarized. The potential routes for the conversion of lipids, carbohydrates, and proteins to valuable chemicals and bioproducts are assessed from recent studies. In addition, this review proposes the following challenges for future algal biorefineries: (1) utilization of naturally grown algae instead of cultivated algae; (2) fractionation of algae to individual components towards high-selectivity products; (3) avoidance of humin formation from algal carbohydrate conversion; (4) development of strategies for algal protein utilisation; and (5) development of efficient processes for commercialization and industrialization.

A review on the progress, challenges and prospects in commercializing microalgal fucoxanthin

Fucoxanthin, the most abundant but nearly untapped carotenoid resource, is in the spotlight in the last decade from various perspectives due to a wide range of bioactivities and healthy benefits. The exploitation of fucoxanthin for nutraceutical and pharmaceutical purposes encompasses enormous scientific and economic potentials. Traditional production of fucoxanthin from brown algae (macroalgae) is constrained by limited yield and prohibitively high cost. Microalgae, as the most diverse photoautotrophs, hold the promises as sustainable sources and ideal cell factories for commercial fucoxanthin production, owing to their rich fucoxanthin content and excellent biomass productivity. In this work, the recent progress in upstream (microalgae selection, optimization of culture conditions, trophic modes, cultivation strategies and biosynthesis pathway) as well as downstream processes (extraction) of fucoxanthin production has been comprehensively and critically reviewed. The major bottlenecks, such as screening of fucoxanthin-producers, conflict between biomass and fucoxanthin accumulation under high light condition, unclear steps in biosynthesis pathway and limited evaluation of outdoor scale-up cultivation and extraction, have been pinpointed. Most importantly, the applications of emerging and conventional techniques facilitating commercialization of microalgal fucoxanthin are highlighted. The reviewed and evaluated include breeding and high-throughput screening methods of elite strains; flashing light effect inducing concurrent biomass and fucoxanthin accumulation; fucoxanthin biosynthesis and the regulatory mechanisms associating with its accumulation elucidated with the development of genetic engineering and omics techniques; and photobioreactors, harvesting and extraction techniques suitable for scaling up fucoxanthin production. In conclusion, the prospects of microalgal fucoxanthin commercialization can be expected with the joint development of fundamental phycology and biotechnology.

Quantitative analysis on photon numbers received per cell for triggering β-carotene accumulation in Dunaliella salina

Accumulation of β-carotene in Dunaliella salina is highly dependent on light exposure intensity and duration, but quantitative analysis on photon numbers received per cell for triggering β-carotene accumulation is not available so far. In this study, experiment results showed that significant β-carotene accumulation occurred after at least 8 h illumination at 400 µmol photons·m-2·s-1. To quantify the average number of photons received per cell, correlations of light attenuation with light path, biomass concentration, and β-carotene content were, respectively, established using both Lambert-Beer and Cornet models, and the latter provided better simulation. Using Cornet model, average number of photons received per cell (APRPC) was calculated and proposed as a parameter for β-carotene accumulation, and constant APRPC was maintained by adjusting average irradiance based on cell concentration and carotenoids content changes during the whole induction period. It was found that once APRPC reached 0.7 µmol photons cell-1, β-carotene accumulation was triggered, and it was saturated at 9.9 µmol photons cell-1. This study showed that APRPC can be used as an important parameter to precisely simulate and control β-carotene production by D. salina.

Progress toward a bicarbonate-based microalgae production system

Commercial applications of microalgae for biochemicals and fuels are hampered by their high production costs, and the use of conventional carbon supplies is a key reason. Bicarbonate has been proposed as an alternative carbon source due to its potential advantages in lower carbon supply costs, convenience for photobioreactor development, biomass harvesting, and labor and energy savings. We review recent progress in bicarbonate-based microalgae cultivation, which validated previous assumptions, suggested further advantages, and demonstrated potential to significantly reduce production cost. Future research should focus on improving production efficiency and reducing energy inputs, including optimizing photobioreactor design, comprehensive utilization of natural power, and automation in production systems.

Carbonate assisted lipid extraction and biodiesel production from wet microalgal biomass and recycling waste carbonate for CO2 supply in microalgae cultivation

High cost of microalgal biofuel is caused by all the steps in current technology, including cultivation, harvesting, lipid extraction, biofuel processing and wastewater and waste treatment. This study aims to systematically reduce these costs with one integrated process, in which carbonate is used for cell rupture, lipid extraction and biodiesel processing, and then recycled for CO₂ absorption and carbon supply for a new round of algae cultivation. To reach this goal, carbonate-heating treatment with N, N' - dibutylurea which can enhance cell disruption were used for cell-wall breaking of wet Neochloris oleoabundans (UTEX 1185) biomass. Lipid extraction was fulfilled with carbonate/ethanol aqueous two phase extraction method and residual carbonate with wastewater from bottom phase was recycled to absorb CO₂ to generate bicarbonate for algal cultivation with fresh medium. Taking into comprehensive consideration of cell disruption efficiency, partition coefficient, and lipid recovery, the condition of cell disruption and lipid extraction was set at 90 °C, 100 min reaction time, 1:7.5 DBU:H₂O (w/w) ratio, 1:3 Na₂CO₃:H₂O (w/w) ratio, and 9% (w/w_T) ethanol concentration. The results showed that carbonate-heating treatment of wet N. oleoabundans biomass resulted in up to 90.7% cell disruption efficiency. The lipid recovery rate in carbonate/ethanol system was up to 97.9%, and the final biodiesel production was 1.30 times of that with Soxhlet method. Utilization of the waste broth after CO₂ absorption with the content of 4% (v/v_T) in the medium for new batch of algae cultivation resulted in biomass concentration of 1.68 g/L. The corresponding total fatty acids production was 0.35 g/L, which was 1.63 fold of that with fresh medium. This study firstly proved the feasibility of using carbonate for lipid extraction and biodiesel production and recycle waste carbonate for carbon re-supply during algae cultivation.

Physiological and molecular responses in halotolerant Dunaliella salina exposed to molybdenum disulfide nanoparticles

Molybdenum disulfide nanoparticles (MoS₂ NPs) has emerged as the promising nanomaterial with a wide array of applications in the biomedical, industrial and environmental field. However, the potential effect of MoS₂ NPs on marine organisms has yet to be reported. In this study, the effect of MoS₂ NPs on the physiological index, subcellular morphology, transcriptomic profiles of the marine microalgae Dunaliella salina was investigated for the first time. exhibited "doping-like" effects on marine microalgae; Growth stimulation was 193.55%, and chlorophyll content increased 1.61-fold upon the addition of 50 μg/L MoS₂ NPs. Additionally, exposure to MoS₂ NPs significantly increased the protein and carbohydrate content by 2.03- and 1.56-fold, respectively. The antioxidant system was activated as well to eliminate the adverse influence of reactive oxygen species (ROS). Transcriptomic analysis revealed that genes involved in porphyrin synthesis, glycolysis/gluconeogenesis, tricarboxylic acid cycle and DNA replication were upregulated upon MoS₂ NPs exposure, which supports the mechanistic role of MoS₂ NPs in improving cellular growth and photosynthesis. The "doping-like" effects on marine algae suggest that the low concentration of MoS₂ NPs might change the rudimentary ecological composition in the ocean.

ROS Induce β-Carotene Biosynthesis Caused by Changes of Photosynthesis Efficiency and Energy Metabolism in Dunaliella salina Under Stress Conditions

The unicellular alga Dunaliella salina is regarded as a promising cell factory for the commercial production of β-carotene due to its high yield of carotenoids. However, the underlying mechanism of β-carotene accumulation is still unclear. In this study, the regulatory mechanism of β-carotene accumulation in D. salina under stress conditions was investigated. Our results indicated that there is a significant positive correlation between the cellular ROS level and β-carotene content, and the maximum quantum efficiency (F_v/F_m) of PSII is negatively correlated with β-carotene content under stress conditions. The increase of ROS was found to be coupled with the inhibition of F_v/F_m of PSII in D. salina under stress conditions. Furthermore, transcriptomic analysis of the cells cultivated with H₂O₂ supplementation showed that the major differentially expressed genes involved in β-carotene metabolism were upregulated, whereas the genes involved in photosynthesis were downregulated. These results indicated that ROS induce β-carotene accumulation in D. salina through fine-tuning genes which were involved in photosynthesis and β-carotene biosynthesis. Our study provided a better understanding of the regulatory mechanism involved in β-carotene accumulation in D. salina, which might be useful for overaccumulation of carotenoids and other valuable compounds in other microalgae.

Molybdenum disulfide nanoparticles concurrently stimulated biomass and β-carotene accumulation in Dunaliella salina

Molybdenum disulfide nanoparticles (MoS₂ NPs) hold tremendous properties in wide domain of applications. In this study, the impact of MoS₂ NPs was investigated on algal physiological and metabolic properties and a two-stage strategy was acquired to enhance the commercial potential of Dunaliella salina. With 50 µg/L of MoS₂ NPs exposure, cellular growth and biomass production were promoted by 1.47- and 1.33-fold than that in control, respectively. MoS₂ NPs treated cells were subject to high light intensity for 7 days after 30 days of normal light cultivation, which showed that high light intensity gradually increased β-carotene content by 1.48-fold. Furthermore, analyses of primary metabolites showed that combinatorial approach significantly altered the biochemical composition of D. salina. Together, these findings demonstrated that MoS₂ NPs at an optimum concentration combined with high light intensity could be a promising approach to concurrently enhance biomass and β-carotene production in microalgae.

Seawater supplemented with bicarbonate for efficient marine microalgae production in floating photobioreactor on ocean: A case study of Chlorella sp

Cultivation of microalgae on ocean provides a promising way to produce massive biomass without utilizing limited land space, and using seawater as culture medium can avoid consumption of valuable fresh water. Bicarbonate is proved as a better approach for carbon supply in microalgae cultivation, but Ca²⁺ and Mg²⁺ in seawater is subjected to precipitate with carbonate derived from it. In this study, cultivation with this medium for a marine Chlorella sp. resulted in productivity of 0.470 g L^-1 day^-1, despite of continual precipitation caused by increased pH due to bicarbonate consumption. Actually, this precipitation is favorable, since it can work as a flocculation harvesting method for microalgae. The highest flocculation efficiency of 98.9 ± 0.0% was observed in cultures with 7.0 g L^-1 NaHCO₃, which was higher than that of cultures without bicarbonate (44.1 ± 0.2%). Additionally, the spent medium after flocculation supported better growth (1.60 ± 0.0 g L^-1) than the fresh medium (1.26 ± 0.0 g L^-1). Outdoor cultivation with floating photobioreactor on ocean resulted in the productivity of 0.190 g L^-1 day^-1, which was higher than that in land-based culture systems. The floating system also benefited from better temperature control with range from 20.6 to 37.2 °C, due to solar heating and surrounding water cooling. These results showed feasibility of efficient microalgae biomass production with fully utilizing of ocean resources, including culture medium preparation and temperature control with seawater, as well as wave energy for mixing, holding great potential to produce massive biomass to support sustainable development of human society.

Simulation of a Novel Tubular Microalgae Photobioreactor with Aerated Tangent Inner Tubes: Improvements in Mixing Performance and Flashing-Light Effects

At present, large-scale and high-efficiency microalgal cultivation is the key to realizing the technology for carbon capture and storage (CCS) and bioresource recovery. Meanwhile, tubular photobioreactors (PBRs) have great potential for microalgal cultivation due to their high productivity. To improve the mixing performance and flashing-light effect, a novel tube PBR with the inner tube tangential to the outer tube was developed, whose radial aeration pores are situated along the length of the inner tube. The direction of aeration, aeration rate, light/dark cycle period (L/D), light-time ratio, average turbulent kinetic energy (TKE), and degree of synergy between the velocity and direction of the light field in the PBR were optimized by a computational fluid dynamics (CFD) simulation and field synergy theory. The results show that a downwards aeration direction of 30° and an aeration rate of 0.7 vvm are the most conducive to reducing the dead zone and improving the light/dark cycle frequency. Compared to the concentric double-tube PBR, the light/dark cycle frequency and light time of the tangent double-tube PBR increased by 78.2% and 36.2% to 1.8 Hz and 47.8%, respectively, and the TKE was enhanced by 48.1% from 54 to 80 cm²·s⁻². Meanwhile, field synergy theory can be extended and applied to the design of tubular microalgae PBRs, and the average synergy of the light and velocity gradients across the cross-section increased by 38% to 0.69. The tangential inner tube aeration structure generated symmetrical vertical vortices between the light and dark areas in the PBR, which significantly improved the mixing performance and flashing-light effect. This novel design can provide a more suitable microenvironment for microalgal cultivation and is promising for bioresource recovery applications and improving the yield of microalgae.

β-Carotene Production from Dunaliella salina Cultivated with Bicarbonate as Carbon Source

Bicarbonate has been considered as a better approach for supplying CO2 to microalgae cells microenvironments than gas bubbling owing t°Cost-effectiveness and easy operation. However, the β-carotene production was too low in Dunaliella salina cultivated with bicarbonate in previous studies. Also, the difference in photosynthetic efficiency between these tw°Carbon sources (bicarbonate and CO2) has seldom been discussed. In this study, the culture conditions, including NaHCO3, Ca2+, Mg2+ and microelement concentrations, were optimized when bicarbonate was used as carbon source. Under optimized condition, a maximum biomass concentration of 0.71 g/l and corresponding β-carotene content of 4.76% were obtained, with β-carotene yield of 32.0 mg/l, much higher than previous studies with NaHCO3. Finally, these optimized conditions with bicarbonate were compared with CO2 bubbling by online monitoring. There was a notable difference in Fv/Fm value between cultivations with bicarbonate and CO2, but there was no difference in the Fv/Fm periodic changing patterns. This indicates that the high concentration of NaHCO3 used in this study served as a stress factor for β-carotene accumulation, although high productivity of biomass was still obtained.

Cultivation of aquaculture feed Isochrysis zhangjiangensis in low-cost wave driven floating photobioreactor without aeration device

This study aimed to use floating photobioreactor (PBR) to produce microalgae biomass for aquaculture applications, and this was tested with cultivation of Isochrysis zhangjiangensis. The highest cell density of 16.1 ± 0.61 × 10⁶ cell L^-1 was obtained in an outdoor culture with a depth of 5.0 cm in 1.0 m² floating PBR, but deeper culture resulted in higher biomass productivity. Large-scale cultivation at size of 10 m² (1000 L) produced the highest cell density of 17.8 × 10⁶ cell L^-1 and highest biomass productivity of 0.115 g L^-1 d^-1, which was at the same level as that for flat-panel PBR (100 L). This developed technique provides an innovative approach to produce microalgae on site for use as fresh aquaculture feed, as well as fresh cells for use as seed inoculums for large-area aquaculture water bodies. This approach provides not only a low-cost microalgae production system but also better integration between microalgae production and aquaculture.

Hydrodynamic performance of floating photobioreactors driven by wave energy

BACKGROUND

Unlike conventional cultivation systems, liquid mixing in floating photobioreactors (PBRs) is solely induced by their hydrodynamic movement in response to waves, and this movement is affected by the wave conditions (wave height and wave period), the PBR configuration and the culture depth. However, to the best of our knowledge, a practical study of the hydrodynamic movements of PBRs has not been previously conducted.

RESULTS

This study aims to investigate the hydrodynamic performance of floating PBRs in response to wave conditions. First, the effects of the experimental wave height (2-10 cm) and wave period (0.8-1.8 s) on movement was investigated using two 1.0 m2 PBR models: a square PBR (1.0 m/1.0 m; length/width) and a rectangular PBR (1.7 m/0.6 m). The results indicated that wave movement became not only more intense with increasing wave height, but also less intense when the wave period decreased. However, the square PBR experienced more intense movement than the rectangular PBR, but also little mooring force. The effects of culture depth (0.5, 1.0 and 2.0 cm) were investigated and the results showed that the culture depth significantly affected the hydrodynamic movements of the PBRs; however, the mooring forces were unaffected. Finally, the movement and mooring-line forces of PBRs equipped with different mooring systems were investigated. The use of two different mooring systems had little effect on PBR movement; however, a mooring system with floaters was able to significantly reduce the mooring line forces compared to a system without floaters. During this study, the greatest force (10.5 N) was found for the rectangular PBR using a mooring system without floaters, whereas the lowest force (0.67 N) was observed for a rectangular PBR using a mooring system with floaters.

CONCLUSIONS

These studies have provided basic data describing the fluid dynamics of floating PBRs; as well as their structural design and scale up. These results also provide guidance for the selection of ocean fields with suitable wave conditions; as well as a proper mooring methods to ensure safe operation.