Photobioreactors: production systems for phototrophic microorganisms

Effect of culture hydrodynamics on Arthrospira platensis production using a single-use photobioreactor system through a CFD supported approach

Laboratory scale conventional single-use bioreactor was used to investigate the effect of different stirrer speeds on the Arthrospira platensis (Spirulina platensis) culture. Experiments were handled in two steps. First step was the selection of the stirring speeds, which was simulated via using CFD, and the second was the long term cultivation with the selected speed. During 10 days of batches as the first step, under identical culture conditions, stirrer speed of 230 rpm gave higher results, compared to 130 and 70 rpm, with respect to dry biomass weight, absorbance value (AB) and chlorophyll-a concentration. Volumetric productivity during the growth phase of the cultures were calculated as 0.39 ± 0.03, 0.28 ± 0.01, and 0.19 ± 0.02 g L-1 d-1, from the fast to the slower speeds. According to the results a 17 day batch was handled with 230 rpm in order to monitor the effects on the culture. The culture reached a volumetric productivity of 0.33 ± 0.04 g L-1 d-1. Statistical analysis showed the significance of the parameters related with the stirring speed.

Biomass productivity and characterization of Tetradesmus obliquus grown in a hybrid photobioreactor

In this study, the effects of CO2 addition on the growth performance and biochemical composition of the green microalga Tetradesmus obliquus cultured in a hybrid algal production system (HAPS) were investigated. The HAPS combines the characteristics of tubular photobioreactors (towards a better carbon dioxide dissolution coefficient) with thin-layer cascade system (with a higher surface-to-volume ratio). Experimental batches were conducted with and without CO2 addition, and evaluated in terms of productivity and biomass characteristics (elemental composition, protein and lipid contents, pigments and fatty acids profiles). CO2 enrichment positively influenced productivity, and proteins, lipids, pigments and unsaturated fatty acids contents in biomass. The HAPS herein presented contributes to the optimization of microalgae cultures in open systems, since it allows, with a simple adaptation-a transit of the cultivation through a tubular portion where injection and dissolution of CO2 is efficient-to obtain in TLC systems, greater productivity and better-quality biomass.

Microalgae as fishmeal alternatives in aquaculture: current status, existing problems, and possible solutions

Fishmeal is an indispensable ingredient for most aquatic animals. However, the finite supply and escalating price of fishmeal seriously limit its use in aquaculture. Thus the development of new, sustainable protein ingredients has been a research focus. Microalgae are potential fishmeal alternatives owing to their high protein content and balanced amino acid profile. Studies suggest that suitable replacement of fishmeal with microalgae is beneficial for fish growth performance, but excessive replacement would induce poor growth and feed utilization. Therefore, this paper aims to review research on the maximum substitutional level of fishmeal by microalgae and propose the main issues and possible solutions for fishmeal replacement by microalgae. The maximum replacement level is affected by microalgal species, fish feeding habits, quality of fishmeal and microalgal meals, and supplemental levels of fishmeal in the control group. Microalgae could generally replace 100%, 95%, 95%, 64.1%, 25.6%, and 18.6% fishmeal protein in diets of carp, shrimp, catfish, tilapia, marine fish, and salmon and trout, respectively. The main issues with fishmeal replacement using microalgae include low production and high production cost, poor digestibility, and anti-nutritional factors. Possible solutions to these problems are recommended in this paper. Overall, microalgae are promising fishmeal alternatives in aquaculture.

Microplastic contamination of packaged spirulina products

Microplastic (MP) contamination in commercially sold spirulina products has not been previously investigated. In this study, 29 spirulina samples in various packaging types were purchased from different brands and origins to assess the presence of MPs. Microplastic analysis was conducted using microscopic and μ-Raman techniques. To ascertain whether the content is indeed spirulina and make a comparison with the MP level, C-Phycocyanin levels were also analyzed. A total of 251 MP-like particles were observed. Out of the 29 examined packaged spirulina brands, 26 showed potential MPs upon visual inspection, with 35 particles confirmed as MPs (73% of the analyzed particles). The mean abundance of MPs was estimated at 13.77 ± 2.45 MPs/100 g dw. Powdered spirulina had a higher but not statistically significant MP abundance (17.34 ± 4.22 MPs/100 g dw) compared to capsule/tablet forms (10.43 ± 2.45 MPs/100 g dw). Fragments accounted for 38.3% while fibers constituted 61.7% of the identified MPs, with sizes ranging from 0.07 to 2.15 mm for fragments and 0.19 to 5.691 mm for fibers. The color distribution of MPs in spirulina samples was predominantly blue (52.8%), followed by black (25.4%), white (10.9%), and others (10.9%). Ten synthetic polymers and cellulose were identified through μ-Raman analysis, with polypropylene (31.6%) and polystyrene (8.3%) being the most prevalent. The correlation between C-Phycocyanin and MPs concentrations, was not found statistically significant. The abundance and composition of MPs were found to be influenced by packaging and processing stages. Identifying potential sources of MPs in spirulina products and evaluating their risks to human health is crucial.

Engineering a marine microalga Chlorella sp. as the cell factory

The use of marine microalgae in industrial systems is attractive for converting CO2 into value-added products using saline water and sunlight. The plant nature and demonstrated industrial potential facilitate Chlorella spp. as excellent model organisms for both basic research and commercial application. However, the transformation method has not been developed in marine Chlorella spp., thus genetic engineering is hindered in exploiting the industrial potentialities of these strains. In this study, we provided a transformation protocol for the marine Chlorella strain MEM25, which showed robust characteristics, including high production of proteins and polyunsaturated fatty acids in multiple cultivation systems over various spatial-temporal scales. We showed that transformants could be obtained in a dramatically time-saving manner (comparable to Saccharomyces cerevisiae) with four functional proteins expressed properly. The transgenes are integrated into the genome and can be successfully inherited for more than two years. The development of a marine Chlorella transformation method, in combination with the complete genome, will greatly facilitate more comprehensive mechanism studies and provide possibilities to use this species as chassis for synthetic biology to produce value-added compounds with mutual advantage in neutralization of CO2 in commercial scales.

Degradation of Polymethylmethacrylate (PMMA) Bioreactors Used for Algal Cultivation

This paper depicts characteristics of degradation of walls of bioreactors made of polymethylmethacrylate (PMMA) which was used to culture algae. The degradation processes take place stimulated by lighting of external surface and interaction with cultured species on internal surface. Results presented are representative for degradation of a bioreactor tube after the 4-year cultivation of Chlorella sp. Microscopic observations, roughness and transmission tests showed that changes have occurred on the inner surface. The result of use is a decrease in transmission and an increase in roughness. Microscopic observations showed that particles remained after culture, especially in cracks.

Photobioreactors for utility-scale applications: effect of gas-liquid mass transfer coefficient and other critical parameters

Cultivation of microalgae and controlling its growth and performance in closed photobioreactors (PBRs) are easier than open pond systems for wastewater treatment. The performance of PBRs is influenced by geometry, hydrodynamic behavior, and mass transfer. Horizontal and vertical configurations as common designs of PBR are reviewed based on their features, advantages, and disadvantages. However, vertically operated PBRs like bubble columns are preferably used for utility-scale applications of microalgae-based processes. Moreover, an appropriate reactor design reduces the inhibitory effect of dissolved oxygen concentration produced by microalgae and consequently increases the level of available CO₂ in the medium. Medium properties, superficial gas velocity, gas holdup, bubble sizes, shear stress, mixing time, sparger design, and the ratio of inner diameter to effective height are shown to influence the overall volumetric mass transfer coefficient (K_La) and PBR's performance. The vertical PBRs like bubble columns provide a high mass transfer, a short liquid circulation time, and a long frequency of light/dark cycle for utility application of microalgae. Different flow regimes are obtained in PBRs based on the gas flow rate, inner diameter, and medium properties. Hydraulic retention time as the main operational parameter is determined in a batch mode for continuous wastewater treatment.

Biomass, photosynthetic activity, and biomolecule composition in Chlorella fusca (Chlorophyta) cultured in a raceway pond operated under greenhouse conditions

Raceways are widely used as microalgae culture systems due to their low cost, but they are not the best option for biomass yield. Understanding in situ photosynthetic performance can be a first step to increase their biomass productivity. This study aimed at comparing the real time photosynthetic activity in a greenhouse raceway culture (250L) with discrete measurements under laboratory conditions. We evaluated the photophysiology and biochemical composition of Chlorella fusca culture up to 120h. In situ photosynthetic activity was continuously monitored and compared to discrete ex situ measurements; biochemical compounds were measured daily. The results showed a final biomass density of 0.45gL^-1 (5 days - 120h) and an increase of the electron transport rate (ETR) up to 48h but decreased thereafter. When the relative ETR was estimated considering the absorption coefficient (a) positive correlations of this parameter with photosynthetic capacity, cell density, biomass, biocompounds and antioxidant activity were obtained, whereas no correlation was detected without considering a. In situ photosynthesis monitoring showed higher absolute maximal ETR (10 - 160 μmol m^-3s^-1) than discrete ex situ measurements. We demonstrated the importance of considering the light absorption coefficient for expressing photosynthetic capacity and showed that C. fusca can produce, in the short-term, bioactive compounds that are correlated to photosynthetic conditions.

Influence of light intensity and photoperiod on the pigment and, lipid production of Dunaliella tertiolecta and Nannochloropsis oculata under three different culture medium

Microalgal biomass has the ability to store huge amount of triacylglycerides as fatty ester methyl esters (FAME) and carotenoids which has made algae as potential candidate for biorefinery approach. Essential fatty acid such as palmitic acid, stearic acid, arachidonic acid and eicospentanoic acid have been produced which are known for their various applications. The present study was aimed to evaluate the influence of different light intensities (120 and 250 μE/m²/s) and photoperiod (16:8h and 13:11h light/dark cycle) on the production of lipid, biomass and lutein. Dunaliella tertiolecta and Nannochloropsis oculata was grown for 23 days in F/2, sea salt media (SSM, Distilled water (DW) and SSM (natural seawater media,NSW) under two different light intensities and photoperiod regimes at 25 ᵒC. SSM (NSW) showed maximum accumulation of lipid in D.tertiolecta (34.56 mg/L/d). SSM (DW)- biomass showed 1.5 times higher lutein productivity of 0.253 mg/L/d under 13:11h light/dark cycle at 250 μE/m²/s compared to same medium under 16:8h light/dark cycles at 120 μE/m²/s. Where as in N.oculata, F/2 biomass showed higher lipid and lutein productivity of 15.69 and 0.279 mg/L/d, respectively The laboratory scale cultivation parameters and related media cost showed the suitability of different culture media adaptation to large scale production.

The Potential Role of Iceland in Northern Europe's Protein Self-Sufficiency: Feasibility Study of Large-Scale Production of Spirulina in a Novel Energy-Food System

Europe is dependent on protein-rich crop imports to meet domestic food demand. This has moved the topic of sustainable protein self-sufficiency up the policy agenda. The current study assesses the feasibility of protein self-sufficiency in Iceland, and its capacity to meet Northern Europe's demand, based on industrial-scale cultivation of Spirulina in novel production units. Production units currently operating in Iceland, and laboratory-derived nutritional profile for the Spirulina cultivated, provide the basis for a theoretical protein self-sufficiency model. Integrating installed and potentially installed energy generation data, the model elaborates six production scale-up scenarios. Annual biomass produced is compared with recommended dietary allowance figures for protein and essential amino acids to determine whether Northern Europe's population demands can be met in 2030. Results show that Iceland could be protein self-sufficient under the most conservative scenario, with 20,925 tonnes of Spirulina produced using 15% of currently installed capacity. In a greater allocation of energy capacity used by heavy industry, Iceland could additionally meet the needs of Lithuania, or Latvia, Estonia, Jersey, Isle of Man, Guernsey, and Faroe Islands. Under the most ambitious scenario utilizing planned energy projects, Iceland could support itself plus Denmark, or Finland, or Norway, or Ireland with up to 242,366 tonnes of biomass. On a protein-per-protein basis, each kilogram of Spirulina consumed instead of beef could save 0.315 tonnes CO2-eq. Under the most ambitious scenario, this yields annual savings of 75.1 million tonnes CO2-eq or 7.3% of quarterly European greenhouse gas emissions. Finally, practicalities of production scale-up are discussed.

Environmental Impacts of Large-Scale Spirulina (Arthrospira platensis) Production in Hellisheidi Geothermal Park Iceland: Life Cycle Assessment

Spirulina algae (Spirulina platensis) cultivated in geothermally powered photobioreactors is here proposed as a potentially resource efficient, zero-carbon, and nutritious alternative to conventional beef meat. Employing a standard life cycle assessment, environmental impacts of large-scale Spirulina production in this facility are calculated. The production facility is sited in Orka náttúrunnar (ON Power) Geothermal Park, Iceland, and benefits from resource streams accessible through Hellisheiði (Hellisheidi) power station, including renewable electricity for illumination and power usage, hot and cold water streams for thermal management, freshwater for cultivation, and CO2 for biofixation. During cultivation, GHG-intensive ammonia-based fertilizers are replaced with macronutrients sourced from natural open mines. LCA results show that production of 1 kg of wet edible biomass in this facility requires 0.0378 m2 non-arable land, 8.36 m3 fresh water and is carbon neutral with - 0.008 CO2-eq GHG emissions (net zero). Compared with conventionally produced meat from beef cattle, Spirulina algae cultured in the ON Power Geothermal Park, referred to in this study as GeoSpirulina, requires less than 1% land and water and emits less than 1% GHGs. Considering food and nutritional security concerns, cultivation in a controlled environment agriculture system assures consistent nutritional profile year-round. Moreover, GeoSpirulina biomass assessed in this study contains all essential amino acids as well as essential vitamins and minerals. While keeping a balanced nutrition, for every kg beef meat replaced with one kg GeoSpirulina, the average consumer can save ~ 100 kg CO2-eq GHGs. It is concluded that environmental impacts of GeoSpirulina production in the Hellisheidi facility are considerably lower than those of conventionally produced ruminants.

Dunaliella salina as a Potential Biofactory for Antigens and Vehicle for Mucosal Application

The demand for effective, low-cost vaccines increases research in next-generation biomanufacturing platforms and the study of new vaccine delivery systems (e.g., mucosal vaccines). Applied biotechnology in antigen production guides research toward developing genetic modification techniques in different biological models to achieve the expression of heterologous proteins. These studies are based on various transformation protocols, applied in prokaryotic systems such as Escherichia coli to eukaryotic models such as yeasts, insect cell cultures, animals, and plants, including a particular type of photosynthetic organisms: microalgae, demonstrating the feasibility of recombinant protein expression in these biological models. Microalgae are one of the recombinant protein expression models with the most significant potential and studies in the last decade. Unicellular photosynthetic organisms are widely diverse with biological and growth-specific characteristics. Some examples of the species with commercial interest are Chlamydomonas, Botryococcus, Chlorella, Dunaliella, Haematococcus, and Spirulina. The production of microalgae species at an industrial level through specialized equipment for this purpose allows for proposing microalgae as a basis for producing recombinant proteins at a commercial level. A specie with a particular interest in biotechnology application due to growth characteristics, composition, and protein production capacity is D. salina, which can be cultivated under industrial standards to obtain βcarotene of high interest to humans. D saline currently has advantages over other microalgae species, such as its growth in culture media with a high salt concentration which reduces the risk of contamination, rapid growth, generally considered safe (GRAS), recombinant protein biofactory, and a possible delivery vehicle for mucosal application. This review discusses the status of microalgae D. salina as a platform of expression of recombinant production for its potential mucosal application as a vaccine delivery system, taking an advance on the technology for its production and cultivation at an industrial level.

Field test of water-net based wastewater treatment for nutrient removal and bioethanol production

In this study, an open pond constructed in Myanmar, a region with tropical climate and favorable environmental conditions for algae growth, was considered to conduct field experiments on sewage inflow river water. The nutrient removal efficiency and productivity of Hydrodictyon reticulatum (H. reticulatum) were analyzed, and the maximum fermentation limit concentration for bioethanol production was determined. Three ponds were operated in batch mode to investigate the effect of light intensity. Photoinhibition was caused due to excessive light intensity in summer season in the region with tropical climate resulting in reduced facility efficiency in the absence of shade. For light blocking, a transparent film was found to be more effective than a translucent film. In the transparent film shading facility, the nitrogen and phosphorus removal efficiencies were maintained above 76% and 81%, respectively, and the productivity of H. reticulatum was 2.27 g m^-2 d^-1. For a raceway open pond facility shaded with transparent film, the performance was evaluated based on hydraulic retention time (HRT), and the productivity of algae was found to increase with increasing supply of nitrogen and phosphorous. Maximum biomass production of 3.21 g m^-2 d^-1 was observed with an HRT of 3 d, suggesting the possibility of long-term operation. As a result of evaluating the ethanol production based on the initial concentration of H. reticulatum, the yield of bioethanol at the initial reducing sugar content of 120 g L^-1 was 89.4%, but bioethanol production was only 8.9 g L^-1.

Modeling and Simulation of Photobioreactors with Computational Fluid Dynamics—A Comprehensive Review

Computational Fluid Dynamics (CFD) have been frequently applied to model the growth conditions in photobioreactors, which are affected in a complex way by multiple, interacting physical processes. We review common photobioreactor types and discuss the processes occurring therein as well as how these processes have been considered in previous CFD models. The analysis reveals that CFD models of photobioreactors do often not consider state-of-the-art modeling approaches. As a comprehensive photobioreactor model consists of several sub-models, we review the most relevant models for the simulation of fluid flows, light propagation, heat and mass transfer and growth kinetics as well as state-of-the-art models for turbulence and interphase forces, revealing their strength and deficiencies. In addition, we review the population balance equation, breakage and coalescence models and discretization methods since the predicted bubble size distribution critically depends on them. This comprehensive overview of the available models provides a unique toolbox for generating CFD models of photobioreactors. Directions future research should take are also discussed, mainly consisting of an extensive experimental validation of the single models for specific photobioreactor geometries, as well as more complete and sophisticated integrated models by virtue of the constant increase of the computational capacity.

The Effects of Photobioreactor Type on Biomass and Lipid Production of the Green Microalga Monoraphidium pusillum in Laboratory Scale

Mass production of microorganisms, algae among them, for new bioactive compounds and renewable innovative products is a current issue in biotechnology. The greatest challenge of basic research on this topic is to find the best solution for both physiology and scalability. In this study, the main goal was to highlight the contradictions of physiological and technological optimization in the same, relatively small, laboratory scale. The green alga Monoraphidium pusillum (Printz) Komárková-Legnorová was cultured in a conventional Erlenmeyer flask (as air bubbled in a tank-type photobioreactor) and in a hybrid (fermenter type + helical tubular type) photobioreactor of the same volume (2.8 L). Higher cell numbers from 1.7–2.3-fold, 2–2.8-fold higher dry masses, and 1.9–2.6-fold higher total lipid contents (mg·L−1) were measured in the tank reactor than in the hybrid reactor. Cultures in the conventional tank reactor were characterized with better nutrient utilization (42.8–77.7% higher phosphate uptake) and more diverse lipid composition than in the hybrid reactor. The study highlights that well-scalable arrangements and settings could be not optimal (or unsuitable in some cases) from a physiological point of view. The results suggest certain developmental directions for complex, well-scalable devices and highlight the importance of testing the gained physiological optima on these systems.

Effective Prediction of Monthly Heat Transfer Characteristics in a Thin-Layer Cascade Reactor Subjected to Outdoor Conditions

Algal biofuels are intriguingly a renewable energy source that could partially substitute fossil fuels, but further research is required to optimise the growth parameters and establish competitive large-scale cultivation systems. Algal growth is directly dependent on momentum, heat, and mass transfer within the photobioreactor and environmental conditions. Therefore, in this computational study, the heat transfer between the thin-layer cascade (TLC) reactor and its surrounding was reported based on static (location and reactor geometry) and dynamic (air temperature, solar irradiance, and wind velocity) parameters. The resulting model was validated using experimental data. The Nusselt number and the monthly average water temperature were computed to investigate the heat transfer phenomena between the TLC reactor and atmosphere. In addition, a novel corelation was used to estimate the evaporative losses from the TLC reactor. The effect of geometric properties (inclination angle of the reactor, water depth, and channel width) was evaluated on heat transfer. Results showed that heat transfer rate and the optimum water temperature for algal growth were significantly affected by hydrodynamics, environmental conditions, and reactor design. Water temperature decreased with the increase in channel width, water depth, and slope angle of the reactor. Furthermore, algal productivity declined with the increase in the amount of evaporated water.

The induction of pyrenoid synthesis by hyperoxia and its implications for the natural diversity of photosynthetic responses in Chlamydomonas

In algae, it is well established that the pyrenoid, a component of the carbon-concentrating mechanism (CCM), is essential for efficient photosynthesis at low CO₂. However, the signal that triggers the formation of the pyrenoid has remained elusive. Here, we show that, in Chlamydomonas reinhardtii, the pyrenoid is strongly induced by hyperoxia, even at high CO₂ or bicarbonate levels. These results suggest that the pyrenoid can be induced by a common product of photosynthesis specific to low CO₂ or hyperoxia. Consistent with this view, the photorespiratory by-product, H₂O₂, induced the pyrenoid, suggesting that it acts as a signal. Finally, we show evidence for linkages between genetic variations in hyperoxia tolerance, H₂O₂ signaling, and pyrenoid morphologies.

Investigating the effects of eleven key physicochemical factors on growth and lipid accumulation of Chlorella sp. as a feedstock for biodiesel production

Biodiesel, as a renewable and eco-friendly energy source that can be produced through algae oil esterification, has recently received much attention. Maximization of algal biomass and lipid content is crucial for commercial biodiesel production. In this study, Chlorella sp. PG96, a microalgal strain isolated from urban wastewater, was identified considering its morphological and molecular characteristics. Fractional factorial design (2^11-7) was employed to screen medium and environmental factors for achieving high lipid productivity. The effects of eleven factors including light intensity, light spectrum, aeration rate, temperature, salinity, NaHCO₃, CO₂, NaNO₃, NH₄Cl, MgSO₄.7H₂O, and K₂HPO₄ and their interactions on growth characteristics of Chlorella sp. PG96 (biomass and lipid production) were statistically assessed. Based on the experimental results, lipid productivity was at its maximum (54.19 ± 8.40 mg_lipid L^-1 day^-1) under a combination of high levels of all factors. The analysis also showed that physical parameters of light intensity and temperature were more effective on algal growth compared to nutritional parameters. Furthermore, nitrogen source of ammonium and carbon source of bicarbonate played more significant roles in biomass and lipid production, compared with nitrate and CO₂, respectively. Although the effect of sulfur limitation on cellular growth was similar to phosphorus deficiency, S-limitation had a greater impact on lipid accumulation. The interaction between NaHCO₃ and NH₄Cl was the most prominent interaction affecting all responses. It is concluded that Chlorella sp. PG96 at a high level of light intensity and temperature (22500 Lux and 32 °C, respectively) can be a prospective candidate for biodiesel production.

View on a mechanistic model of Chlorella vulgaris in incubated shake flasks

Kinetic growth models are a useful tool for a better understanding of microalgal cultivation and for optimizing cultivation conditions. The evaluation of such models requires experimental data that is laborious to generate in bioreactor settings. The experimental shake flask setting used in this study allows to run 12 experiments at the same time, with 6 individual light intensities and light durations. This way, 54 biomass data sets were generated for the cultivation of the microalgae Chlorella vulgaris. To identify the model parameters, a stepwise parameter estimation procedure was applied. First, light-associated model parameters were estimated using additional measurements of local light intensities at differ heights within medium at different biomass concentrations. Next, substrate related model parameters were estimated, using experiments for which biomass and nitrate data were provided. Afterwards, growth-related model parameters were estimated by application of an extensive cross validation procedure.

Roadmap to sustainable carbon-neutral energy and environment: can we cross the barrier of biomass productivity?

The total number of inhabitants on the Earth is estimated to cross a record number of 9 × 10³ million by 2050 that present a unique challenge to provide energy and clean environment to every individual. The growth in population results in a change of land use, and greenhouse gas emission due to increased industrialization and transportation. Energy consumption affects the quality of the environment by adding carbon dioxide and other pollutants to the atmosphere. This leads to oceanic acidification and other environmental fluctuations due to global climate change. Concurrently, speedy utilization of known conventional fuel reservoirs causes a challenge to a sustainable supply of energy. Therefore, an alternate energy resource is required that can maintain the sustainability of energy and environment. Among different alternatives, energy production from high carbon dioxide capturing photosynthetic aquatic microbes is an emerging technology to clean environment and produce carbon-neutral energy from their hydrocarbon-rich biomass. However, economical challenges due to low biomass production still prevent the commercialization of bioenergy. In this work, we review the impact of fossil fuels burning, which is predominantly used to fulfill global energy demand, on the quality of the environment. We also assess the status of biofuel production and utilization and discuss its potential to clean the environment. The complications associated with biofuel manufacturing using photosynthetic microorganisms are discussed and directed evolution for targeted phenotypes and targeted delivery of nutrients are proposed as potential strategies to increase the biomass production.

Inductive Tracking Methodology for Wireless Sensors in Photoreactors

In this paper, we present a methodology for locating wireless sensors for the use in photoreactors. Photoreactors are, e.g., used to cultivate photosynthetic active microorganisms. For measuring important parameters like, e.g., the temperature inside the reactor, sensors are needed. Wireless locatable floating sensors would enable it to measure the data anywhere inside the reactor and to get a spatial resolution of the registered data. Due to the well defined propagation properties of magnetic fields and the fact that they are not significantly influenced in underwater environments when using low frequencies, a magnetic induction (MI) system is chosen for the data transmission as well as for the localization task. We designed an inductive transmitter and a receiver capable of measuring the magnetic field in every three spatial directions. The transmitting frequency is set at approx. 300kHz. This results in a wavelength of approx. 1km which clearly exceeds the dimensions of our measurement setup where the transmitter–receiver distances in general are lower than one meter. Due to this fact, only the quasi-static field component has to be considered and the location of the transmitter is calculated by measuring its magnetic field at defined positions and in using the magnetic dipole field equation in order to model its magnetic field geometry. The used measurement setup consists of a transmitter and two receivers. The first measurements were performed without a water filled photoreactor since no differences in the propagation criteria of magnetic fields are expected due to the negligibly low differences in the relative magnetic permeability of water and air. The system is calibrated and validated by using a LIDAR depth camera that is also used to locate the transmitter. The transmitter positions measured with the camera are therefore compared with the inductively measured ones.

Algae as an attractive source for cosmetics to counter environmental stress

In recent times, a considerable amount of evidence has come to light regarding the effect that air pollution has on skin conditions. The human skin is the chief protection we have against environmental harm, whether biological, chemical, or physical. The stress from these environmental factors, along with internal influences, can be a cause of skin aging and enlarged pores, thinner skin, skin laxity, wrinkles, fine lines, dryness, and a more fragile dermal layer. This knowledge has led to greater demand for skin cosmetics and a requirement for natural raw ingredients with a high degree of safety and efficiency in combating skin complications. Recent developments in green technology have made the employment of naturally occurring bioactive compounds more popular, and novel extraction methods have ensured that the use of these compounds has greater compatibility with sustainable development principles. Thus, there is a demand for investigations into efficient non-harmful naturally occurring raw ingredients; compounds derived from algae could be beneficial in this area. Algae, both macroalgae and microalgae, consists of waterborne photosynthetic organisms that are potentially valuable as they have a range of bioactive compounds in their composition. Several beneficial metabolites can be obtained from algae, such as antioxidants, carotenoids, mycosporine-like amino acids (MAA), pigments, polysaccharides, and scytonemin. Various algae strains are now widely employed in skincare products for various purposes, such as a moisturizer, anti-wrinkle agent, texture-enhancing agents, or sunscreen. This research considers the environmental stresses on human skin and how they may be mitigated using cosmetics created using algae; special attention will be paid to external factors, both generally and specifically (amongst them light exposure and pollutants).

Year-Round Cultivation of Tetraselmis sp. for Essential Lipid Production in a Semi-Open Raceway System

There is increasing demand for essential fatty acids (EFAs) from non-fish sources such as microalgae, which are considered a renewable and sustainable biomass. The open raceway system (ORS) is an affordable system for microalgae biomass cultivation for industrial applications. However, seasonal variations in weather can affect biomass productivity and the quality of microalgal biomass. The aim of this study was to determine the feasibility of year-round Tetraselmis sp. cultivation in a semi-ORS in Korea for biomass and bioactive lipid production. To maximize biomass productivity of Tetraselmis sp., f medium was selected because it resulted in a significantly higher biomass productivity (1.64 ± 0.03 g/L) and lower omega-6/omega-3 ratio (0.52/1) under laboratory conditions than f/2 medium (0.70/1). Then, we used climatic data-based building information modeling technology to construct a pilot plant of six semi-ORSs for controlling culture conditions, each with a culture volume of 40,000 L. Over 1 year, there were no significant variations in monthly biomass productivity, fatty acid composition, or the omega-6/omega-3 ratio; however, the lipid content correlated significantly with photosynthetic photon flux density. During year-round cultivation from November 2014 to October 2017, areal productivity was gradually increased by increasing medium salinity and injecting CO₂ gas into the culture medium. Productivity peaked at 44.01 g/m²/d in October 2017. Throughout the trials, there were no significant differences in average lipid content, which was 14.88 ± 1.26%, 14.73 ± 2.44%, 12.81 ± 2.82%, and 13.63 ± 3.42% in 2014, 2015, 2016, and 2017, respectively. Our results demonstrated that high biomass productivity and constant lipid content can be sustainably maintained under Korean climate conditions.

Integrating micro-algae into wastewater treatment: A review

Improving the ecological status of water sources is a growing focus for many developed and developing nations, in particular with reducing nitrogen and phosphorus in wastewater effluent. In recent years, mixotrophic micro-algae have received increased interest in implementing them as part of wastewater treatment. This is based on their ability to utilise organic and inorganic carbon, as well as inorganic nitrogen (N) and phosphorous (P) in wastewater for their growth, with the desired results of a reduction in the concentration of these substances in the water. The aim of this review is to provide a critical account of micro-algae as an important step in wastewater treatment for enhancing the reduction of N, P and the chemical oxygen demand (COD) in wastewater, whilst utilising a fraction of the energy demand of conventional biological treatment systems. Here, we begin with an overview of the various steps in the treatment process, followed by a review of the cellular and metabolic mechanisms that micro-algae use to reduce N, P and COD of wastewater with identification of when the process may potentially be most effective. We also describe the various abiotic and biotic factors influencing micro-algae wastewater treatment, together with a review of bioreactor configuration and design. Furthermore, a detailed overview is provided of the current state-of-the-art in the use of micro-algae in wastewater treatment.

Enrichment and Aggregation of Purple Non-sulfur Bacteria in a Mixed-Culture Sequencing-Batch Photobioreactor for Biological Nutrient Removal From Wastewater

Mixed-culture biotechnologies are widely used to capture nutrients from wastewater. Purple non-sulfur bacteria (PNSB), a guild of anoxygenic photomixotrophic organisms, rise interest for their ability to directly assimilate nutrients in the biomass. One challenge targets the aggregation and accumulation of PNSB biomass to separate it from the treated water. Our aim was to enrich and produce a concentrated, fast-settling PNSB biomass with high nutrient removal capacity in a 1.5-L, stirred-tank, anaerobic sequencing-batch photobioreactor (SBR). PNSB were rapidly enriched after inoculation with activated sludge at 0.1 gVSS L^-1 in a first batch of 24 h under continuous irradiance of infrared (IR) light (>700 nm) at 375 W m^-2, with Rhodobacter reaching 54% of amplicon sequencing read counts. SBR operations with decreasing hydraulic retention times (48 to 16 h, i.e., 1-3 cycles d^-1) and increasing volumetric organic loading rates (0.2-1.3 kg COD d^-1 m^-3) stimulated biomass aggregation, settling, and accumulation in the system, reaching as high as 3.8 g VSS L^-1. The sludge retention time (SRT) increased freely from 2.5 to 11 days. Acetate, ammonium, and orthophosphate were removed up to 96% at a rate of 1.1 kg COD d^-1 m^-3, 77% at 113 g N d^-1 m^-3, and 73% at 15 g P d^-1 m^-3, respectively, with COD:N:P assimilation ratio of 100:6.7:0.9 m/m/m. SBR regime shifts sequentially selected for Rhodobacter (90%) under shorter SRT and non-limiting concentration of acetate during reaction phases, for Rhodopseudomonas (70%) under longer SRT and acetate limitation during reaction, and Blastochloris (10%) under higher biomass concentrations, underlying competition for substrate and photons in the PNSB guild. With SBR operations we produced a fast-settling biomass, highly (>90%) enriched in PNSB. A high nutrient removal was achieved by biomass assimilation, reaching the European nutrient discharge limits. We opened further insights on the microbial ecology of PNSB-based processes for water resource recovery.

A review on photobioreactor design and modelling for microalgae production

From the cell to the photobioreactor and to the industrial exploitation of microalgae, through the controlled experiments and modelling.

Microalgal Biomass Generation via Electroflotation: A Cost-Effective Dewatering Technology

Microalgae are an excellent source of bioactive compounds for the production of a wide range of vital consumer products in the biofuel, pharmaceutical, food, cosmetics, and agricultural industries, in addition to huge upstream benefits relating to carbon dioxide biosequestration and wastewater treatment. However, energy-efficient, cost-effective, and scalable microalgal technologies for commercial-scale applications are limited, and this has significantly impacted the full-scale implementation of microalgal biosystems for bioproduct development, phycoremediation, and biorefinery applications. Microalgae culture dewatering continues to be a major challenge to large-scale biomass generation, and this is primarily due to the low cell densities of microalgal cultures and the small hydrodynamic size of microalgal cells. With such biophysical characteristics, energy-intensive solid–liquid separation processes such as centrifugation and filtration are generally used for continuous generation of biomass in large-scale settings, making dewatering a major contributor to the microalgae bioprocess economics. This article analyzes the potential of electroflotation as a cost-effective dewatering process that can be integrated into microalgae bioprocesses for continuous biomass production. Electroflotation hinges on the generation of fine bubbles at the surface of an electrode system to entrain microalgal particulates to the surface. A modification of electroflotation, which combines electrocoagulation to catalyze the coalescence of microalgae cells before gaseous entrainment, is also discussed. A technoeconomic appraisal of the prospects of electroflotation compared with other dewatering technologies is presented.

Overcoming the Biological Contamination in Microalgae and Cyanobacteria Mass Cultivations for Photosynthetic Biofuel Production

Microalgae and cyanobacteria have shown significant potential for the development of the next biofuels innovation because of their own characteristics as photosynthetic microorganisms. However, it is confronted with a lot of severe challenges on the economic scaling-up of the microalgae- and cyanobacteria-based biofuels production. One of these major challenges is the lack of a reliable preventing and controlling culture system of biological contamination, which can attack the cell growth or product accumulation causing crashing effects. To increase the commercial viability of microalgae- and cyanobacteria-based biofuels production, overcoming the biological contaminations should be at the top of the priority list. Here, we highlight the importance of two categories of biological contaminations and their controlling strategies in the mass cultivations of microalgae and cyanobacteria, and outline the directions that should be exploited in the future.

Bottom-illuminated orbital shaker for microalgae cultivation

A bottom-illuminated orbital shaker designed for the cultivation of microalgae suspensions is described in this open-source hardware report. The instrument agitates and illuminates microalgae suspensions grown inside flasks. It was optimized for low production cost, simplicity, low power consumption, design flexibility, consistent, and controllable growth light intensity. The illuminated orbital shaker is especially well suited for low-resource research laboratories and education. It is an alternative to commercial instruments for microalgae cultivation. It improves on typical do-it-yourself microalgae growth systems by offering consistent and well characterized illumination light intensity. The illuminated growth area is 20 cm × 15 cm, which is suitable for three T75 tissue culture flasks or six 100 ml Erlenmeyer flasks. The photosynthetic photon flux density, is variable in eight steps ( 26 - 800 μ mol · m - 2 · s - 1 ) and programmable in a 24-h light/dark cycle. The agitation speed is variable ( 0 - 210 RPM ). The overall material cost is around £300, including an entry-level orbital shaker. The build takes two days, requiring electronics and mechanical assembly capabilities. The instrument build is documented in a set of open-source protocols, design files, and source code. The design can be readily modified, scaled, and adapted for other orbital shakers and specific experimental requirements. The instrument function was validated by growing fresh-water microalgae Desmodesmus quadricauda and Chlorella vulgaris. The cultivation protocols, microalgae growth curves, and doubling times are included in this report.

Investigation of the interaction between lighting and mixing applied during the photo-fermentation biohydrogen production process from agricultural waste

To better clarify the effect of lighting and mixing on the hydrogen production from agricultural waste, experiments under diverse constant and dynamic light intensities and mixing speeds were conducted. Cumulative hydrogen yield, hydrogen production rate, OD₆₆₀, pH, reducing sugar concentration were monitored. Results showed that mixing had positive effects on high substrate concentration. The interaction between lighting and mixing was drawn. Higher light intensity (7000 Lux) was suitable for hydrogen production under mixing. Higher light intensity with higher mixing speed (150 RPM) showed the highest cumulative hydrogen yield of 78.1 mL/g TS. Different periods of hydrogen production process required distinct lighting and mixing. Combined with Gompertz model, dynamic lighting and mixing strategies were discussed. Dynamic light intensity (4000-7000-4000 Lux) accompanied with dynamic mixing speed (50-150-50 RPM) was the optimal condition for PFHP. Highest hydrogen yield of 84.7 mL/g TS and highest light conversion efficiency of 36.32% were obtained.

Development of a lightweight multi-skin sheet photobioreactor for future cultivation of phototrophic biofilms on facades

This article covers the development of a novel emerse photobioreactor (ePBR), using a polycarbonate multi-skin sheet (MSS), to cultivate terrestrial cyanobacteria as surface-associated phototrophic biofilms in an aerosol-based cultivation process. The aerosol, generated by ultrasonic transduction, moistens and nourishes the biofilm inside the multi-skin sheet emerse photobioreactor (MSSePBR). Advantages of the MSSePBR, such as its low weight design and reduced water consumption due to the usage of aerosol, simplify the development for future facade bioreactors. To develop the MSSePBR, surface roughness, static contact angle and luminous transmittance were investigated to characterize the properties of the cultivation surface for phototrophic cultivation. The polymeric MSS showed good luminous transmittance and proofed its optical suitability for the cultivation of terrestrial cyanobacteria. Using the MSSePBR, the terrestrial cyanobacteria Coleofasciculus chthonoplastes and Trichocoleus sociatus were cultivated with either ambient air, air with increased CO₂ content or flue gas. The cultivation of terrestrial cyanobacteria showed higher productivities for biomass in the MSSePBR than in suspended systems. Cultivation with increased CO₂ contents and flue gas was possible, thus a combination with flue gas treatment is feasible. An up-scaled prototype of the MSSePBR was introduced to show the possibilities for future industrial-sized and facade applications.

Diatoms for Carbon Sequestration and Bio-Based Manufacturing

Carbon dioxide (CO2) is a major greenhouse gas responsible for climate change. Diatoms, a natural sink of atmospheric CO2, can be cultivated industrially in autotrophic and mixotrophic modes for the purpose of CO2 sequestration. In addition, the metabolic diversity exhibited by this group of photosynthetic organisms provides avenues to redirect the captured carbon into products of value. These include lipids, omega-3 fatty acids, pigments, antioxidants, exopolysaccharides, sulphated polysaccharides, and other valuable metabolites that can be produced in environmentally sustainable bio-manufacturing processes. To realize the potential of diatoms, expansion of our knowledge of carbon supply, CO2 uptake and fixation by these organisms, in conjunction with ways to enhance metabolic routing of the fixed carbon to products of value is required. In this review, current knowledge is explored, with an evaluation of the potential of diatoms for carbon capture and bio-based manufacturing.

Cyanobacteria as a source of biofertilizers for sustainable agriculture

Continuous increase in global human population and depletion of natural resources of energy posing threat to environment needs, sustainable supply of food and energy. The most ecofriendly approach 'green technology' has been exploited for biofertilizer preparation. Cyanobacteria are the most successful and sustained prokaryotic organism during the course of evolution. They are considered as one of the primitive life forms found on our planet. Cyanobacteria are emerging candidates for efficiently conversion of radiant energy into chemical energy. This biological system produces oxygen as a by-product. Cyanobacterial biomass can also be used for the large scale production of food, energy, biofertilizers, secondary metabolites, cosmetics and medicines. Therefore, cyanobacteria are used in ecofriendly sustainable agricultural practice for production of biomass of very high value and decreasing the level of CO2. This review article describes the methods of mass production of cyanobacterial biofertilizers and their applications in agriculture and industrial level.

Comparative life cycle assessment of microalgae cultivation for non-energy purposes using different carbon dioxide sources

The ability of microalgae to sequester carbon and at the same time synthesise valuable compounds with potential applications in nutraceutical, pharmaceutical and cosmetic industries makes them attractive for commercial deployment, especially in view of a blue bioeconomy. Among microalgae, the diatom Phaeodactylum tricornutum is considered as an important potential source of omega-3 polyunsaturated fatty acids, such as eicosapentanoic acid, an essential polyunsaturated fatty acid with anti-inflammatory and antimicrobial properties. The aim of this study was to perform the Life Cycle Assessment of the cultivation of P. tricornutum - at semi-industrial scale in photobioreactor - for the production of high-quality bioactive compounds comparing synthetic carbon dioxide supply to a supply with waste carbon dioxide from a biogas upgrading process hypothesizing industrial symbiosis network. The effect of renewable energy use instead of the European electricity mix was also examined. Primary data on the production process, including the stages of cleaning and sterilisation, cultivation, harvesting and freeze-drying, were used. The midpoint impact categories recommended in the ILCD Handbook were used for performing the impact assessment. A sensitivity analysis was also performed on algal productivity, culture medium recirculation factor and amount of solvents per cleaning cycle. Firstly, results indicate in general cultivation and freeze-drying as the most contributing stages to the impacts. Secondly, they demonstrate in the comparative assessment that the use of carbon dioxide from the biogas upgrading is a feasible and attractive alternative to the synthetic one, as it allows for the improvement of the environmental performance of the production process in all the analysed impact categories. Finally, sensitivity analysis suggests that the environmental performance could be further improved by acting on other key factors, such as electricity source, nutrients culture medium and cleaning solutions.

Novel unexpected functions of PHA granules

Polyhydroxyalkanoates (PHA), polyesters accumulated by numerous prokaryotes in the form of intracellular granules, have been for decades considered being predominantly storage molecules. However, numerous recent discoveries revealed and emphasized their complex biological role for microbial cells. Most of all, it was repeatedly reported and confirmed that the presence of PHA granules in prokaryotic cells enhances stress resistance and robustness of microbes against various environmental stress factors such as high or low temperature, freezing, oxidative, and osmotic pressure. It seems that protective mechanisms of PHA granules are associated with their extraordinary architecture and biophysical properties as well as with the complex and deeply interconnected nature of PHA metabolism. Therefore, this review aims at describing novel and unexpected properties of PHA granules with respect to their contribution to stress tolerance of various prokaryotes including common mesophilic heterotrophic bacteria, but also extremophiles or photo-autotrophic cyanobacteria. KEY POINTS: • PHA granules present in bacterial cells reveal unique properties and functions. • PHA enhances stress robustness of bacterial cells.

Bioplastic Production from Microalgae: A Review

Plastic waste production around the world is increasing, which leads to global plastic waste pollution. The need for an innovative solution to reduce this pollution is inevitable. Increased recycling of plastic waste alone is not a comprehensive solution. Furthermore, decreasing fossil-based plastic usage is an important aspect of sustainability. As an alternative to fossil-based plastics in the market, bio-based plastics are gaining in popularity. According to the studies conducted, products with similar performance characteristics can be obtained using biological feedstocks instead of fossil-based sources. In particular, bioplastic production from microalgae is a new opportunity to be explored and further improved. The aim of this study is to determine the current state of bioplastic production technologies from microalgae species and reveal possible optimization opportunities in the process and application areas. Therefore, the species used as resources for bioplastic production, the microalgae cultivation methods and bioplastic material production methods from microalgae were summarized.

Characterization of Chlamydomonas Very High Light-tolerant Mutants for Enhanced Lipid Production

Biodiesel production from microalgae is still not commercially realized due to the high cost of production. High light-tolerance has been suggested as a desirable phenotype for efficient cultivation in large scale production systems under fluctuating outdoor conditions. Nevertheless, it has not been shown if algae with such a phenotype would have better efficiency for lipid production. To determine lipid productivity in high light-tolerant mutants, and to understand the pathways involved in high light-tolerant phenotype, two very high light-tolerant mutants of the green alga Chlamydomonas reinhardtii - CAL028_01_28 and CAL034_01_48 - were selected from eighteen high light-tolerant mutants from the CAL collection. Under high light intensity conditions, and the presence of reactive oxygen species, which are conditions constantly experienced by algae growing in open-pond environments, these strains exhibited higher photosynthetic efficiency and improved survival. The physiological characterization of these mutants revealed that the detoxification of ROS by carotenoids and antioxidant enzymes is crucial for their growth under high light conditions. Neither mutant was affected in terms of its ability to accumulate lipid under nitrogen-depleted condition. More importantly, lipid productivity under high light conditions increased twofold in these mutants compared to that of the wild-type. Taken together, very high light-tolerant mutants confer a high potential for biofuel production under outdoor conditions, and their improved ability to survive under oxidative stress is an important key for efficient growth under outdoor conditions.

Microalgae based biorefinery promoting circular bioeconomy-techno economic and life-cycle analysis

Microalgae are source of third generation biofuel having the key advantage of high lipid productivity. In recent times, biorefinery is seen as promising option to further reduce the production cost of microalgae biofuel. However, exact energy balance analysis has not been performed on important biorefinery routes. In this aspect, three biorefinery routes, all based on lipid based biorefinery route are evaluated for economical production of microalgal biofuel and valorised products. Biorefinery route 1 involves production of biodiesel, pigments, and animal feed. Biorefinery route 2 involves biogas and pigments production and two stage fermentation, and third biorefinery route involves bio-hydrogen and pigments production. Finally, the technoeconomic assessment of three biorefinery routes were reviewed, net energy savings, and life-cycle costing approaches to economize microalgal biorefinery are suggested.

Nannochloropsis oceanica Cultivation in Pilot-Scale Raceway Ponds—From Design to Cultivation

Raceways ponds are the microalgal production systems most commonly used at industrial scale. In this work, two different raceway configurations were tested under the same processing conditions to compare their performance on the production of Nannochloropsis oceanica. Biomass productivity, biochemical composition of the produced biomass, and power requirements to operate those reactors were evaluated. Water depths of 0.20 and 0.13 m, and culture circulation velocities of 0.30 and 0.15 m s−1 were tested. A standard configuration, which had a full channel width paddlewheel, proved to be the most energy efficient, consuming less than half of the energy required by a modified configuration (had a half channel width paddlewheel). The later showed to have slightly higher productivity, not enough to offset the large difference in energetic consumption. Higher flow velocity (0.30 m s−1) led to a 1.7 g m−2 d−1 improvement of biomass productivity of the system, but it increased the energy consumption twice as compared to the 0.15 m s−1 flow velocity. The latter velocity showed to be the most productive in lipids. A water depth of 0.20 m was the most suitable option tested to cultivate microalgae, since it allowed a 54% energy saving. Therefore, a standard raceway pond using a flow velocity of 0.3 m s−1 with a 0.20 m water depth was the most efficient system for microalgal cultivation. Conversely, a flow velocity of 0.15 m s−1 was the most suitable to produce lipids.

Systems biology approach identifies functional modules and regulatory hubs related to secondary metabolites accumulation after transition from autotrophic to heterotrophic growth condition in microalgae

Heterotrophic growth mode is among the most promising strategies put forth to overcome the low biomass and secondary metabolites productivity challenge. To shedding light on the underlying molecular mechanisms, transcriptome meta-analysis was integrated with weighted gene co-expression network analysis (WGCNA), connectivity analysis, functional enrichment, and hubs identification. Meta-analysis and Functional enrichment analysis demonstrated that most of the biological processes are up-regulated at heterotrophic growth condition, which leads to change of genetic architectures and phenotypic outcomes. WGNCA analysis of meta-genes also resulted four significant functional modules across logarithmic (LG), transition (TR), and production peak (PR) phases. The expression pattern and connectivity characteristics of the brown module as a non-preserved module vary across LG, TR, and PR phases. Functional analysis identified Carotenoid biosynthesis, Fatty acid metabolism and Methane metabolism as enriched pathways in the non-preserved module. Our integrated approach was applied here, identified some hubs, such as a serine hydroxymethyltransferase (SHMT1), which is the best candidate for development of metabolites accumulating strains in microalgae. Current study provided a new insight into underlying metabolite accumulation mechanisms and opens new avenue for the future applied studies in the microalgae field.

Large Scale Cultivation of Microalgae: Open and Closed Systems

There are two main approaches for cultivating microalgae on a large scale: open or closed cultivation. The main difference between open and closed systems is related to how they operate (e.g., cooling and gas exchange), vulnerability for outside influence (e.g., rainwater and introduction of unwanted species), and costs for building and operating the system. In this chapter we introduce the main cultivation technologies and discuss their main advantages and disadvantages when cultivating microalgae.