A new bioenergetic and thermodynamic approach to batch photoautotrophic growth of Arthrospira (Spirulina) platensis in different photobioreactors and under different light conditions

Arthrospira platensis Cultivation in a Bench-Scale Helical Tubular Photobioreactor

Cultivations of Arthrospira platensis were carried out to evaluate the CO2 capture capacity of this cyanobacterium under bench-scale conditions. For this purpose, the influence of light intensity on the microbial growth and the photosynthetic efficiency has been investigated in a helical photobioreactor. Five cultivations were performed at different photosynthetic photon flux densities (23 ≤ PPFD ≤ 225 µmol photons m−2 s−1) by fed-batch pulse-feeding pure carbon dioxide from a cylinder into the helicoidal photobioreactor. In particular, a range of PPFD (82–190 µmol photons m−2 s−1) was identified in which biomass concentration reached values (9–11 gDW L−1) significantly higher than those reported in the literature for other configurations of closed photobioreactors. Furthermore, as A. platensis suspensions behave as Newtonian and non-Newtonian (pseudoplastic) fluids at very low and high biomass concentrations, respectively, a flow analysis was carried out for evaluating the most suitable mixing conditions depending on growth. The results obtained in this study appear to be very promising and suggest the use of this helicoidal photobioreactor configuration to reduce CO2 emissions from industrial gaseous effluents.

Enhanced biomass and phycocyanin production of Arthrospira (Spirulina) platensis by a cultivation management strategy: Light intensity and cell concentration

This work investigated the cultivation of Arthrospira (Spirulina) platensis BP in a photobioreactor under light intensities of 635, 980, 1300, and 2300 µmol m^-2 s^-1, using a semi-continuous mode to keep cell concentration at optical densities (OD) of 0.4, 0.6, and 0.8. The highest productivity of biomass (0.62 g L^-1 d^-1) and phycocyanin (123 mg L^-1 d^-1) were obtained when cells were grown under a light intensity of 2300 µmol m^-2 s^-1 at OD 0.6. At this concentration, the efficiency of energy consumption to the biomass of algae was around 2.26-2.31 g (kW h)^-1 d^-1, while, a maximum photosynthetic efficiency of 8.02% was obtained under a light intensity of 635 µmol m^-2 s^-1 at OD 0.8. This indicates how light intensity, cell concentration, and light-dark conditions can enhance biomass and phycocyanin production, if well manipulated.

Pigments Production, Growth Kinetics, and Bioenergetic Patterns in Dunaliella tertiolecta (Chlorophyta) in Response to Different Culture Media

This work dealt with the study of growth parameters, pigments production, and bioenergetic aspects of the microalga Dunaliella tertiolecta in different culture media. For this purpose, cultures were carried out in Erlenmeyer flasks containing F/2 medium, Bold’s Basal medium, or an alternative medium made up of the same constituents of the Bold’s Basal medium dissolved in natural seawater instead of distilled water. D. tertiolecta reached the highest dry cell concentration (Xmax = 1223 mgDM·L−1), specific growth rate (µmax = 0.535 d−1), cell productivity (PX = 102 mgDM·L−1·d−1), and photosynthetic efficiency (PE = 14.54%) in the alternative medium, while the highest contents of carotenoids (52.0 mg·g−1) and chlorophyll (108.0 mg·g−1) in the biomass were obtained in Bold’s Basal medium. As for the bioenergetic parameters, the biomass yield on Gibbs energy dissipation was higher and comparable in both seawater-based media. However, the F/2 medium led to the highest values of moles of photons absorbed to produce 1 C-mol of biomass (nPh), total Gibbs energy absorbed by the photosynthesis (ΔGa) and released heat (Q), as well as the lowest cell concentration, thus proving to be the least suitable medium for D. tertiolecta growth. On the other hand, the highest values of molar development of O2 and consumption of H+ and H2O were obtained in the alternative medium, which also ensured the best kinetic parameters, thereby allowing for the best energy exploitation for cell growth. These results demonstrate that composition of culture medium for microalgae cultivation has different effects on pigments production, growth kinetics, and bioenergetics parameters, which should be taken into consideration for any use of biomass, including as raw material for biofuels production.

Models of microalgal cultivation for added-value products - A review

Microalgae are considered a promising feedstock for biorefineries given that their chemical composition - rich in carbohydrate and lipid - can be directed towards the co-production of various value-added fuels and chemicals. Production of microalgal biomass for biorefinery purposes requires the identification and establishment of optimal cultivation systems, a crucial yet complicated task due to the numerous factors (e.g. media composition, light, temperature) that simultaneously regulate biomass growth and intracellular composition. Modelling these biological processes, taking into account a single or multiple growth-limiting factors, offers a valuable tool to simulate, design and optimise the dynamics of microalgae cultivation. This review provides an overview of existing models developed to describe microalgal growth processes at the macroscopic scale (also termed black-box models) and discusses their formulation in detail. The black-box kinetic modelling frameworks are compiled into single-factor (6 formulations) and multiple-factor (32 formulations - further divided into non-interactive, additive, and interactive) growth kinetic models, as reported in more than 80 studies, for the prediction of biomass growth as a function of major operational factors such as media composition (e.g. nutrient concentration) and environmental factors (e.g. transient light and temperature). In addition, the review focuses on those models that further account for the production dynamics of two microalgal intracellular products with renowned potential as biorefinery substrates: carbohydrate and lipid molecules. Models of microalgal cultivation dynamics offer a robust engineering tool to understand the natural yet complex responses of microalgae to their growing environment and can help - if used appropriately - to optimise microalgae cultivation and increase the economic viability and sustainability of microalgal systems.

Helical tubular photobioreactor design using computational fluid dynamics

In this paper we present the design problem of helical tubular PhotoBioReactors (PBR) based on energy consumption minimization, using the radius of curvature for the cultivation of microalgae. Computational Fluid Dynamics (CFD) is used to design a configuration of the helical pipeline with minimum energy consumption. We determined how flow direction changes affect energy consumption. Additionally, it was found that the radius of curvature affects the pressure drop in the PBR’s pipe, so a cost function has been developed to solve an optimization problem seeking to obtain the optimum radius of curvature and a helical tubular PBR design with low pumping rates.

Multiproduct biorefinery from Arthrospira spp. towards zero waste: Current status and future trends

Considering the high- and low-value product perspectives, Arthrospira spp. are one of the most industrially exploited microalgae. However, currently, the biomass is being utilized for one specific product resulting in a steep upsurge in the overall production cost. Hence, to boost the economic viability of Arthrospira biorefinery process, every high- and low-value products from it ought to be valorized. Envisioning how costlier can be the multiproduct biorefinery concept owing to the downstream processing at an industrial scale, it is quite essential to look for new trends and encouraging solutions. This article intended to propose a sustainable biorefinery in the wake of the current understanding of the present constraints and challenges associated with Arthrospira biorefinery. The current review aimed at defining the future aspects of this biorefinery including integration and optimization of the culture strategy, and, implementation of new ingenious techniques to improve downstream processing (harvesting, extraction, fractionation, and purification).

A critical review on designs and applications of microalgae-based photobioreactors for pollutants treatment

The development of the photobioreactors (PBs) is recently noticeable as cutting-edge technology while the correlation of PBs' engineered elements such as modellings, configurations, biomass yields, operating conditions and pollutants removal efficiency still remains complex and unclear. A systematic understanding of PBs is therefore essential. This critical review study is to: (1) describe the modelling approaches and differentiate the outcomes; (2) review and update the novel technical issues of PBs' types; (3) study microalgae growth and control determined by PBs types with comparison made; (4) progress and compare the efficiencies of contaminants removal given by PBs' types and (5) identify the future perspectives of PBs. It is found that Monod model's shortcoming in internal substrate utilization is well fixed by modified Droop model. The corroborated data also remarks an array of PBs' types consisting of flat plate, column, tubular, soft-frame and hybrid configuration in which soft-frame and hybrid are the latest versions with higher flexibility, performance and smaller foot-print. Flat plate PBs is observed with biomass yield being 5 to 20 times higher than other PBs types while soft-frame and membrane PBs can also remove pharmaceutical and personal care products (PPCPs) up to 100%. Looking at an opportunity for PBs in sustainable development, the flat plate PBs are applicable in PB-based architectures and infrastructures indicating an encouraging revenue-raising potential.

Application of Central Composite Design to Optimize Culture Conditions of Chlorella vulgaris in a Batch Photobioreactor: An Efficient Modeling Approach

Microalgae cultivation and their use is a promising approach for integrated CO2 biofixation, wastewater treatment and renewable energy production. To develop such an important technology, there is a need to optimize the culture conditions, maximizing CO2 consumption, degrading the nutrients present in the wastewater and maximise the microalgae biomass production. Central Composite Design (CCD) approach was applied to develop quadratic regression models. The developed models were employed separately to estimate optimal sets of three important input parameters (CO2 concentration, nitrogen-to-phosphorus ratio and culture temperature) for maximizing specific growth rate, biomass productivity and CO2 biofixation rate. The maximum specific growth rate of 1.93 ± 0.19 d-1 was observed at an optimal set of 34oC, 4:1 nitrogen-to-phosphorus ratio, and 6 % CO2 concentration. The maximum biomass productivity of 86.5 ± 20.0 mgL-1d-1 was obtained at 4.8 % CO2, 8:1 nitrogen-to-phosphorus ratio and 28oC. In addition, the maximum CO2 biofixation rate was calculated to be 251.9 ± 13.5 mgL-1d-1 at optimal values of 4 % CO2, 1:1 nitrogen-to-phosphorus ratio and 25oC. Finally, multi-objective optimization method was employed to predict the maximum CO2 biofixation rate and biomass productivity concurrently. The optimum values of CO2 biofixation rate (182.84 ± 8.42 mgL-1d-1) and biomass productivity (78.5 ± 10.0 mgL-1d-1) were obtained from operating conditions at 4 % CO2, 6:1 nitrogen-to-phosphorus ratio, 25oC culture temperature. These predicted data were in strong agreement with the experimental values.

Complex mathematical analysis of photobioreactor system

Modeling as a tool solves extremely difficult tasks in life sciences. Recently, schemes of culturing of microalgae have received special attention because of its unique features and possible uses in many industrial applications for renewable energy production and high value products isolation. The goal of this review is to present the use of system analysis theory applied to microalgae culturing modeling and process development. The review mainly focuses on the modeling of the key steps of autotrophic growth under the integral biorefinery concept of the microalgae biomass. The system approach follows systematically a procedure showing the difficulties by modeling of sub-systems. The development of microalgae kinetics and computational fluid dynamics (CFD) studies were analyzed in details as sub-systems in advanced design of photobioreactor (PBR). This review logically follows the trends of the modeling procedure and clarifies how this approach may save time and money during the research efforts. The result of this work is a successful development of a complex PBR mathematical analysis in the frame of the integral biorefinery concept.

Seawater toilet flushing sewage treatment and nutrients recovery by marine bacterial-algal mutualistic system

Seawater toilet flushing sewage with excess eutrophic and high salinity brought a great barrier on the municipal wastewater treatment plants. Nutrients recovery and biomass production as potential biofuel feedstock with less energy consumption will be a key challenge in wastewater treatment. In the optimal inoculation of algae and bacteria, a marine bacterial-algal mutualistic system was established to treat synthetic seawater toilet flushing sewage without extra carbon and O₂ addition. It was showed that 85.5% of total nitrogen (TN) (from 200 mg/L), 91.0% of total phosphorus (TP) (from 40 mg/L) and 98.7% of chemical oxygen demand (COD) (from 1600 mg/L) were removed with 4.28 g/L of biomass yield (biomass productivity 159.3 mg/L/d) containing 16.3% lipid and 62.6% protein, which performance mainly achieved by bacteria during first six days and algae functioned subsequently. Both nitrogen and phosphorus removal of the system were mainly assimilation/accumulation. Algal facultative heterotrophia ensured dissolved organic carbon for bacterial utilization and avoiding excessive organic matter produced. The established algal-bacterial system provided a potential energy-efficient and eco-friendly approach for seawater blackwater treatment and nutrients recovery simultaneously.

Protective effect of Arthrospira platensis extracts against ultraviolet B-induced cellular senescence through inhibition of DNA damage and matrix metalloproteinase-1 expression in human dermal fibroblasts

Ultraviolet (UV) light exposure causes skin photoaging, which is known to be preventable and controllable by application of UV-protective agents. In this study, we demonstrated, for the first time, that the extract of microalgae Arthrospira platensis has a reverse effect on UV-induced photodamage such as loss of cell viability, cellular senescence, DNA damage, and collagen destruction in dermal fibroblasts. Forty-eight extracts were prepared from the cell biomass by controlling culture light conditions, extract solvents, and disruption methods. Then, we analyzed their cytotoxicities using WST-1 assay and separated low and high cytotoxic extracts with normal human dermal fibroblasts (nHDFs). Using the low cytotoxic extracts, we performed UVB protection assay and selected the most effective extract demonstrating protective effect against UVB-induced nHDF damage. Flow cytometric analysis and senescence-associated (SA) β-galactosidase assay showed that pretreatment with the extract reversed UVB-induced G2/M phase cell cycle arrest and senescence in nHDFs. Furthermore, UVB-induced DNA damage in nHDFs, such as cyclobutane pyrimidine dimer formation, was significantly suppressed by the extract. Further, quantitative real-time PCR experiments revealed that the extract significantly inhibited UVB-induced upregulation of matrix metalloproteinase 1 (MMP1) and MMP3 expression in nHDFs. Therefore, we concluded that the microalgae extract can be a potential anti-photoaging agent.