Search Results (12)

This study investigates the potential of the diatom Phaeodactylum tricornutum (PT) as a sustainable and nutritionally valuable food source, focusing on its ability to produce bioactive compounds such as eicosapentaenoic acid, fucoxanthin, chrysolaminarin (CRY) and proteins. PT was cultivated in a flat-plate airlift photobioreactor (FPA-PBR) illuminated with LEDs from two sides. The study aimed to monitor and minimize β-methylamino-L-alanine (BMAA) levels to address safety concerns. The data showed that the selected FPA-PBR setup was superior in biomass and EPA productivity, and CRY production was reduced. No BMAA was detected in any biomass sample during cultivation. By adjusting the cultivation conditions, PT biomass with different compositional profiles could be produced, enabling various applications in the food and health industries. Biomass from nutrient-repleted conditions is rich in EPA and Fx, with nutritional and health benefits. Biomass from nutrient-depleted conditions accumulated CRY, which can be used as dietary fiber. These results highlight the potential of PT as a versatile ingredient for human consumption and the effectiveness of FPA-PBRs with artificial lighting in producing high-quality biomass. This study also provides the basis for future research to optimize photobioreactor conditions to increase production efficiency and to tailor the biomass profiles of PT for targeted health-promoting applications. Full article

Cyanobacteria are microorganisms that grow rapidly in an aquatic medium, showing the capacity of accumulations of biocompounds subsequently converted into value-added biocompounds. The cyanobacterium Spirulina maxima can produce pigments besides accumulating significant amounts of carbohydrates and proteins. An alternative to reducing biomass production costs at an industrial scale is the use of landfill leachate in the growing medium, as well as the mitigation of this pollutant. The objective of this work was to cultivate Spirulina maxima in a medium supplemented with leachate, using the design of experiments to evaluate the effects of leachate concentration (% v/v), light source, and light intensity in an airlift photobioreactor, analyzing them as a response to the productivity of biomass, phycocyanin, carbohydrates, and biochar. The highest values of productivity (mg L⁻¹d⁻¹) were 97.44 ± 3.20, 12.82 ± 0.38, 6.19 ± 1.54, and 34.79 ± 3.62 for biomass, carbohydrates, phycocyanin, and biochar, respectively, adjusted for experiment 2 with the factors of leachate concentration (5.0% v/v), light source (tubular LED), and luminosity (54 µmol m⁻² s⁻¹), respectively. The use of leachate as a substitute for macronutrients in Zarrouk’s medium for the cultivation of Spirulina maxima is a viable alternative in the production of biocompounds as long as it is used at an appropriate level. Full article

In the pursuit of sustainable solutions for contemporary environmental challenges arising from the increasing global demand for energy, this study delves into the potential of cyanobacteria, specifically Arthrospira platensis (commonly known as “spirulina”), as a versatile resource. Employing a life cycle assessment (LCA) in accordance with the ISO 14044:2006 standard and employing both midpoint and endpoint indicators, the study comprehensively evaluates environmental impacts. The research explored a range of scenarios, specifically investigating variations in light intensity and harvesting volume. These investigations were carried out using a pilot-scale photobioreactor, specifically an airlift reactor system featuring a horizontal tubular downcomer. The primary focus is on extracting valuable compounds, namely exopolysaccharides and phycocyanin. It emphasized the extraction of value-added products and strategic integration with a biogas plant for process heat, contributing to developing a sustainable supply network and offering insights into environmentally conscious algae cultivation practices with implications for renewable energy and the production of valuable products. The results emphasize the project’s potential economic feasibility with minimal energy impact from by-product extraction. The environmental assessment identifies marine ecotoxicity and fossil resource depletion as principal impacts, predominantly influenced by upstreaming and harvesting stages. After conducting comparisons across various scenarios, it was found that cultivations under higher light intensities have a lower environmental impact than cultivations with low light supply. However, regardless of light intensity, processes with shorter harvesting cycles tend to have a smaller environmental impact compared to processes with longer harvesting cycles. Overall, this research contributes a nuanced and realistic perspective, fostering informed decision-making in sustainable algae cultivation practices, with implications for renewable energy and valuable compound production. Full article

Microalgae offer a promising solution for efficiently treating high-nitrogen wastewater and recovering valuable nutrients. To optimize microalgae growth and nutrient assimilation, case-dependent studies are essential to demonstrate the process’s potential. This study aimed to evaluate the treatment capacity of high-nitrogen anaerobic digestion effluent as a nutrient source for a C. sorokiniana microalgal culture in a tubular photobioreactor. The study had two primary objectives: to assess how the concentration and composition of the digestate influence microalgae growth, and to identify the preferred nitrogen forms assimilated by the microalgae during long-term, continuous operation. A 20 L tubular airlift bioreactor was constructed and used in batch mode; various digestate concentrations were examined with ammonia nitrogen levels reaching to 160 mg/L. These experiments revealed a biomass growth rate of up to 130 mg/L/d and an ammonia nitrogen assimilation rate ranging from 8.3 to 12.5 mg/L/d. The presence of phosphorous proved essential for microalgae growth, and the growth entered a stationary phase when the initial phosphorous was fully assimilated. A nitrogen-to-phosphorous (N/P) ratio of 10 supported efficient species growth. While ammonia was the preferred nitrogen form for microalgae, they could also utilize alternative forms such as organic and nitrate nitrogen, depending on the specific digestate properties. The results from the continuous photobioreactor operation confirmed the findings from the batch mode, especially regarding the initial nitrogen and phosphorous content. An important condition for nearly complete ammonia removal was the influent dilution rate, to balance the nitrogen assimilation rate. Moreover, treated effluent was employed as dilution medium, contributing to a more environmentally sustainable water management approach for the entire process, at no cost to the culture growth rate. Full article

This work presents recent developments of algal bioreactors used for CO₂ removal and the factors affecting the reactor performance. The main focus of the study is on light intensity and photoperiods. The role of algae in CO₂ removal, types of algal species used in bioreactors and conventional types of bioreactors including tubular bioreactor, vertical airlift reactor, bubble column reactor, flat panel or plate reactor, stirred tank reactor and specific type bioreactors such as hollow fibre membrane and disk photobioreactors etc. are discussed in details with respect to utilization of light. The effects of light intensity, light incident, photoinhibition, light provision arrangements and photoperiod on the performance of algal bioreactors for CO₂ removal are also discussed. Efficient operation of algal photobioreactors cannot be achieved without the improvement in the utilization of incident light intensity and photoperiods. The readers may find this article has a much broader significance as algae is not only limited to removal or sequestration of CO₂ but also it is used in a number of commercial applications including in energy (biofuel), nutritional and food sectors. Full article

Microalgae are considered one of the most efficient and environmentally friendly ways for carbon dioxide fixation. The bubbles play an important role in analyzing the radiation transfer in photobioreactors during microalgae growth. Herein, Chlorella sp. and Scenedesmus obliquus were cultured in the airlift flat plate photobioreactor and evaluated for the temporal evolution of radiation characteristics. A one-dimensional model of bubbles on time-dependent radiation transfer in a photobioreactor was proposed, and it was well verified with the experimental result. The results indicated that with the increase of bubble volume fraction or the decrease of bubble radius, the local irradiance increased at the illuminated surface of the microalgal culture and was attenuated more rapidly along with the radiation transfer. The average specific growth rate of microalgae decreases as bubble volume fraction increases or bubble radius decreases. The volume fraction of 0.003 and a radius of 3.5 mm are the optimal operating conditions in this study for microalgae growth and carbon dioxide fixation. The presented analysis would facilitate the design and optimization of the optical and aeration configurations of photobioreactors for carbon dioxide fixation. Full article

The freshwater green microalgae, Dictyosphaerium chlorelloides (CCALA 330), has the ability to produce extracellular polysaccharides (EPS). Conditions for optimum growth and EPS overproduction were determined in laboratory-scale tubular photobioreactors (PBR) with a working volume of 300 mL. Multiple limitations in nutrient supply were proven to be an effective method for EPS overproduction. Salinity stress was also applied to the culture, but no significant increase in EPS production was observed. The effects of different nitrogen sources were examined and the microalgae exhibited the fastest growth and EPS production in medium containing ammonium nitrate. Under determined optimal conditions, EPS concentration reached 10 g/L (71% of the total biomass) and a total biomass of 14 g/L at the end of 17 days cultivation. Pilot-scale cultivation was also carried out in a column type airlift photobioreactor (PBR) with a working volume of 60 L. A new and efficient methodology was developed for separating cells from the EPS-containing culture broth. Due to the strong attachment between cells and EPS, high-pressure homogenization was carried out before a centrifugation process. The EPS in the supernatant was subsequently purified using ultrafiltration. The green microalgae Dictyosphaerium chlorelloides may therefore be appropriate for the commercial production of EPS. Full article

The rise of CO₂ concentration on Earth is a major environmental problem that causes global warming. To solve this issue, carbon capture and sequestration technologies are becoming more and more popular. Among them, cyanobacteria can efficiently sequestrate CO₂, which is an eco-friendly and cost-effective way of reducing carbon dioxide, and algal biomass can be harvested as valuable products. In this study, the hydrodynamic parameters of an airlift photobioreactor such as gas holdup, mean bubble diameter and liquid circulation velocity were measured to investigate CO₂ biofixation by Spirulina sp. The total gas holdup was found to increase linearly with the increase in the gas velocity from 0.185 to 1.936 cm/s. The mean bubble velocities in distilled water only and in the cyanobacterial culture on the first and sixth days of cultivation were 109.97, 87.98, and 65.89 cm/s, respectively. It was found that shear stress at gas velocities greater than 0.857 cm/s led to cyanobacterial death. After 7 days of batch culture, the maximum dry cell weight reached 1.62 g/L at the gas velocity of 0.524 cm/s, whereas the highest carbon dioxide removal efficiency by Spirulina sp. was 55.48% at a gas velocity of 0.185 cm/s, demonstrating that hydrodynamic parameters applied in this study were suitable to grow Spirulina sp. in the airlift photobioreactor and remove CO₂. Full article

From 2015 to 2021, we optimized mass cultivation of diatoms in our own developed vertical column airlift photobioreactors using natural and artificial light (LEDs). The project took place at the ferrosilicon producer Finnfjord AS in North Norway as a joint venture with UiT—The Arctic University of Norway. Small (0.1–6–14 m³) reactors were used for initial experiments and to produce inoculum cultures while upscaling experiments took place in a 300 m³ reactor. We here argue that species cultivated in reactors should be large since biovolume specific self-shadowing of light can be lower for large vs. small cells. The highest production, 1.28 cm³ L⁻¹ biovolume (0.09–0.31 g DW day⁻¹), was obtained with continuous culture at ca. 19% light utilization efficiency and 34% CO₂ uptake. We cultivated 4–6 months without microbial contamination or biofouling, and this we argue was due to a natural antifouling (anti-biofilm) agent in the algae. In terms of protein quality all essential amino acids were present, and the composition and digestibility of the fatty acids were as required for feed ingredients. Lipid content was ca. 20% of ash-free DW with high EPA levels, and omega-3 and amino acid content increased when factory fume was added. The content of heavy metals in algae cultivated with fume was well within the accepted safety limits. Organic pollutants (e.g., dioxins and PCBs) were below the limits required by the European Union food safety regulations, and bioprospecting revealed several promising findings. Full article

The continued growth and evolving lifestyles of the human population require the urgent development of sustainable production in all its aspects. Microalgae have the potential of the sustainable production of various commodities; however, the energetic requirements of algae cultivation still largely contribute to the overall negative balance of many operation plants. Here, we evaluate energetic efficiency of biomass and lipids production by Chlorella pyrenoidosa in multi-tubular, helical-tubular, and flat-panel airlift pilot scale photobioreactors, placed in an indoor environment of greenhouse laboratory in Central Europe. Our results show that the main energy consumption was related to the maintenance of constant light intensity in the flat-panel photobioreactor and the culture circulation in the helical-tubular photobioreactor. The specific power input ranged between 0.79 W L⁻¹ in the multi-tubular photobioreactor and 6.8 W L⁻¹ in the flat-panel photobioreactor. The construction of multi-tubular photobioreactor allowed for the lowest energy requirements but also predetermined the highest temperature sensitivity and led to a significant reduction of Chlorella productivity in extraordinary warm summers 2018 and 2019. To meet the requirements of sustainable yearlong microalgal production in the context of global change, further development towards hybrid microalgal cultivation systems, combining the advantages of open and closed systems, can be expected. Full article

An increasing number of microalgae strains are used for commercial production of metabolites. When conducting research, the moment of the process scaling tends to be very difficult. One of the most complex issues is related to planning and designing an efficient system for propagation of appropriately high amounts of inoculum required for inoculating cultures on a semi-technical and industrial scale. The following paper aimed at designing an automated station for the preparation of microalgae inoculation material intended for inoculation of the system, comprising of six 90 dm³ volume photobioreactors. The system, comprised of eight airlift photobioreactors of 12 dm³ volume each, installed in mobile storage units connected to the control system in the form of a docking station. Each of the photobioreactors had a separate system used for monitoring temperature and pH, mixing, and LED lighting. The station constituted the last stage of preparing the inoculation material for inoculating technical-scale photobioreactors, used for conducting experiments with Haematococcus pluvialis microalgae. Achieved results, repeatability of the processes, and the ergonomics of the station increased the productivity and quality of the research and development processes. Full article

A process composed by a catalytic converter and three sequential Airlift photobioreactors containing the microalga Scenedesmus dimorphus was studied to capture CO₂, NOx, and CO from emissions of a steam boiler which was burning diesel. The catalytic converter transformed to CO₂ a maximum of 78% of the CO present in the combustion gas. The effects of shear rate, light intensity, and light/dark cycles on the biomass growth of the algae were studied. It was observed that at low shear rates (Re ≈ 3200), a high productivity of 0.29 g_cel L⁻¹ d⁻¹ was obtained. When the microalga was exposed to 60.75 µmol·m⁻²·s⁻¹ of intensity of light and a light/dark cycle of 16/8 h, a maximum productivity of 0.44 g_cel L⁻¹ d⁻¹ and a maximum CO₂ fixation rate 0.8 g CO₂ L⁻¹·d⁻¹ were obtained. The maximum CO₂ removal efficiency was 64.3%, and KLa for CO₂ and O₂ were 1.2 h⁻¹ and 3.71 h⁻¹ respectively. Full article