Microalgal Cultivation Processes Research Articles

Impact of constant magnetic field on enhancing the microalgal biomass and biomolecules accumulations and life cycle assessment of the approach

Three freshwater microalgal species such as Chlorella protothecoides, Micractinium sp. and Scenedesmus obliquus were cultured under static magnetic field (SMF) and its influence on the accumulation of biomolecules (lipids, proteins, carbohydrates) and biomass production have been evaluated. This study involved the cultivation of the three microalgal species under the electromagnetic intensity of 80mT which was achieved using ferrite magnets. The SMF treatment showed a significant enhancement in biomass productivity of S. obliquus (0.098 g L−1 d−1) and C. protothecoides (0.114 g L−1 d−1). On compared to SMF untreated culture, Micractinium sp. resulted in a considerable reduction in biomass productivity by 10.9 % was observed. The constant SMF treatment for the total cultivation period (17 days) has significantly promoted the biomolecules accumulation (9 % lipids, 39 % protein, 16 % carbohydrates) and biomass (55 %) productivity of S. obliquus. The results suggested that SMF treatment exhibited a species-specific response in biomass productivity and biomolecules accumulation. Finally, to assess the feasibility of this strategy, economic feasibility and LCA simulation for SMF treated microalgal biomass and biomolecules production have been evaluated. LCA revealed that the magnetic field application for microalgal cultivation processes showed diversified impacts on environment as few indicators (Abiotic depletion, Acidification and Global warming) were better under magnetic application as compared to non-magnetic cultivation process.

Sub-pilot scale sequential microalgal consortium-based cultivation for treatment of municipal wastewater and biomass production

Municipal wastewater (MWW) was treated by a sequential pilot microalgal cultivation process. The cultivation was performed inside a specifically designed low-cost photobioreactor (PBR) system. A microalgal consortium 2:1 was developed using Tetraselmis indica (TS) and Picochlorum sp. (PC) in the first stage and PC:TS (2:1) in the second stage and the nutrient removal efficiency and biomass production and biomolecules production was evaluated and also compared with monoculture in a two-stage sequential cultivation system. This study also investigated the effect of seasonal variations on microalgae growth and MWW treatment. The results showed that mixed microalgal consortium (TS:PC) had higher nutrient removal efficiency, with chemical oxygen demand (COD), total phosphate (TP), and total nitrate (TN) removal efficiencies of 78.50, 84.49, and 84.20%, respectively, and produced a biomass of 2.50 g/L with lipid content of 37.36% in the first stage of cultivation under indoor conditions. In the second stage of indoor cultivation, the PC:TS consortium demonstrated maximum COD, TP, and TN removal efficiencies of 92.49, 94.24, and 94.16%, respectively. It also produced a biomass of 2.65 g/L with a lipid content of 40.67%. Among all the seasonal variations, mass flow analysis indicated that the combination of mixed consortium-based two-stage sequential process during the winter season favored maximum nutrient removal efficiency of TN i.e. 88.54% (84.12 mg/L) and TP i.e., 90.18% (43.29 mg/L), respectively. It also enhanced total biomass production of 49.10 g in 20-L medium, which includes lipid yield ∼15.68 g compared to monoculture i.e., 82.06% (78.70 mg/L) and 82.87% (40.26 mg/L) removal of TN and TP, respectively, and produced biomass 43.60 g with 11.90 g of lipids.

Life cycle assessment of microalgal cultivation medium: biomass, glycerol, and beta-carotene production by Dunaliella salina and Dunaliella tertiolecta

Abstract Purpose Dunaliella is a halophilic genus of microalgae with high potential in the global food market. The microalgal cultivation process contributes to not only economic impact but also environmental impact, especially regarding the artificial medium composition. In this context, a life cycle assessment was carried out to analyze the impacts associated with the components of the modified Johnson medium (MJM) and to predict the best scenarios to cultivate Dunaliella tertiolecta and Dunaliella salina for biomass, glycerol, and beta-carotene production. Method Two chains were analyzed separately: (1) Dunaliella salina (strain DF 15) cultivated in 8 scenarios combining different nitrogen (0.1 and 1.0 g L−1 KNO3) and magnesium (1.1–2.3 g L−1 MgCl2.6H2O) concentrations to produce biomass, glycerol, and beta-carotene and (2) Dunaliella tertiolecta (strain CCAP 19/30) cultivated in 5 scenarios combining different nitrogen (0.1 and 1.0 g L−1 KNO3) and salt (116.9–175.4 g L−1 sea salt) concentrations to produce biomass and glycerol. In addition, we evaluated the potential of cultivating these species to reduce the carbon footprint of the proposed scenarios. Results and discussion For D. salina, S5 (1 g L−1 KNO3, 1.1 g L−1 MgCl2.6H2O) had the lowest environmental damage for biomass (74.2 mPt) and glycerol production (0.95 Pt) and S3 (0.1 g L−1 KNO3, 1.9 g L−1 MgCl2.6H2O) for beta-carotene (3.88 Pt). T4 (1 g L−1 KNO3, 116.9 g L−1 sea salt) was the best for D. tertiolecta for biomass (74 mPt) and glycerol (0.49 Pt). “Respiratory inorganics,” “Non-renewable energy,” and “Global warming” were the most impacted categories. “Human health,” “Climate change,” and “Resources” had the highest share of all damage categories. All the scenarios presented negative carbon emission after proposing using brine as alternative salt source: S5 was the best scenario (− 157.5 kg CO2-eq) for D. salina and T4 for D. tertiolecta (− 213.6 kg CO2-eq). Conclusion The LCA proved its importance in accurately predicting the optimal scenarios for MJM composition in the analyzed bioproducts, as confirmed by the Monte Carlo simulation. Although the absolute values of impacts and productivity cannot be directly compared to large-scale cultivation, the validity of the LCA results at this scale remains intact. Productivity gains could outweigh the impacts of “surplus” MJM components. Our study showcased the potential of combining D. salina and D. tertiolecta cultivation with CO2 capture, leading to a more environmentally friendly cultivation system with a reduced carbon footprint.

Evaluation of Tolerant to CO2 Excess Microalgae for the Production of Multiple Biochemicals in a 3G Biorefinery

To date, the positive environmental impact of microalgae-based technologies has been demonstrated in numerous studies. However, there is still a number of major technical and economic obstacles to overcome. Therefore, further research and innovation are needed for the development and commercial exploitation of large-scale integrated and sustainable processes, based on robust ‘industrial’ microalgal strains and novel photobioreactors (PBRs). Note that the advancement of intensified microalgal cultivation processes can facilitate the economically feasible co-production of microalgal biomass and value-added biochemicals. In this context, the goal of the present investigation was to compare several microalgal strains based on a set of productivity criteria, including the maximum biomass growth and the maximum concentration of total biochemicals (i.e., carbohydrates, proteins, and lipids) under CO2 excess conditions (10% v/v). It was found that the wild type strain of Stichococcus sp. fully meets the above productivity criteria. In particular, a biomass concentration of 1.68 g·L−1 and a concentration of total biochemical products of 1.4 g·L−1 were measured in batch cultivation experiments in flasks using the selected strain. Further studies were performed in two different PBRs. Cultivation in a conventional stirred tank PBR showed successful scaling of the bioprocess, whereas cultivation in an innovative tubular recirculating PBR resulted in maximization of both biomass concentration (3.66 g·L−1) and total biochemical products concentration (3.33 g·L−1).

High cell density cultivation enables efficient and sustainable recombinant polyamine production in the microalga Chlamydomonas reinhardtii

Modern chemical industry calls for new resource-efficient and sustainable value chains for production of key base chemicals such as polyamines. The green microalga Chlamydomonas reinhardtii offers great potential as an innovative green-cell factory by combining fast and inexpensive, phototrophic growth with mature genetic engineering. Here, overexpression of recombinant lysine decarboxylases in C. reinhardtii enabled the robust accumulation of the non-native polyamine cadaverine, which serves as building block for bio-polyamides. The issue of low cell densities, limiting most microalgal cultivation processes was resolved by systematically optimizing cultivation parameters. A new, easy-to-apply and fully phototrophic medium enables high cell density cultivations of C. reinhardtii with a 6-fold increase in biomass and cell count (20 g/L biomass dry weight, ~2·108 cells/mL). Application of high cell density cultivations in established photobioreactors resulted in a 10-fold increase of cadaverine yields, with up to 0.24 g/L after 9 days and maximal productivity of 0.1 g/L/d.

Metabolic Engineering Strategies for the Enhanced Microalgal Production of Long-Chain Polyunsaturated Fatty Acids (LC-PUFAs).

Long-chain polyunsaturated fatty acids (LC-PUFAs), largely obtained from fish oil, serve as valuable dietary supplements with many health benefits, especially arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid. In recent years, interest in the sustainable production of LC-PUFAs using heterologous production hosts has drastically increased because overfishing and polluted oceans have led to a gradual decline in the supply of LC-PUFAs from fish oil in the last few decades. Some species of microalgae have been considered to be an ideal producer of LC-PUFAs as they inherently accumulate large amounts of LC-PUFAs and utilize CO2 using light energy. Also, a growing number of genetic toolboxes have become available, and the microalgal cultivation process is amenable to a scale-up. In fact,tremendous progress has been achieved in the development of high-performance strains of microalgae through metabolic engineering that has led to the efficient production of fatty acids and various derivatives in the last decade. This review discusses metabolic engineering strategies that have contributed to the enhanced production of LC-PUFAs using microalgae, including optimizing fatty acid biosynthetic pathway and intracellular supply of precursors and cofactors, as well as engineering transcription factors.

Isolation, identification and outdoor cultivation of thermophilic freshwater microalgae Coelastrella sp . FI69 in bubble column reactor for the application of biofuel production

Abstract Identifying a suitable microalga, which has the attributes of optimal growth characteristics, preferable biofuel profile and high-value product accumulation capability, is necessary for a feasible microalgal cultivation process. In this regard, the objective of this present study comes under the topic called phyco-prospecting, which is identification of appropriate microalgae for a specified task. With this, the aim of the study is to molecularly identify an interest of organism to conduct outdoor cultivation, biomass production and biofuel evaluation. Concerning this, environmental samples were collected from a dry lake at summer time to isolate thermophilic microalgae using traditional isolation techniques. The isolated microalgae was identified as species of Coelastrella based on 18 s rRNA gene analysis, and tested specifically for its thermo-tolerant competency at an outdoor pilot scale cultivation facility. Based on the desirable growth performance of the species, it was further cultivated in series of bubble column reactors aerated at a higher rate of 4.4 vv−1 m−1 of 0.04%, 1.5% and 5% CO2 (vv−1) enriched air. Improved growth was observed in 1.5% CO2 aeration, whereas slightly inhibited growth was found biomass productivity, and produced 3.5 g L−1 of dry biomass from 0.05 g L−1 of initial concentration within 9 days of cultivation. The biomasses had ~18% (ww−1) of total lipids, and the fatty acid profile of lipids shows higher presence of C18:1, which is desirable for biodiesel conversion. The energy content biomass was about 21 MJ kg−1, and the reddish pigment accumulation characteristic of the species was considered as beneficial.

Application of light-emitting diodes (LEDs) in cultivation of phototrophic microalgae: current state and perspectives.

The quality and regulation of the incident light is crucial in microalgae cultivation processes. Depending on wavelength, spectrum, and intensity, growth characteristics and biochemical composition of these organisms vary. With mainly fluorescent lamps (FL) used previously for illumination, such variabilities could not be studied adequately due to their broad emission spectrum. In contrast, light-emitting diodes (LEDs) emit a very narrow wavelength band and enable flexible photobioreactor designs due to their small size. This review provides a condensed overview on the application of LEDs in microalgal cultivation processes. It summarizes the current availability and applicability of LED technologies as an illumination source for research-focused photobioreactor systems. A particular focus is the use of narrow-wavelength LEDs to address fundamental as well as applied aspects of light color on algae biomass and value-added compound formation. In this respect, the application of internal and external illumination systems is reviewed together with trends in the industrial use of LED systems to intensify algae process efficiency.

Optimizing microalgal cultivation process design and operation

Optimizing microalgal cultivation process design and operation

Long‐term adaptive response to high‐frequency light signals in the unicellular photosynthetic eukaryote Dunaliella salina

Productivity of microalgal cultivation processes is tightly related to photosynthetic efficiency, and therefore to light availability at the cell scale. In an agitated, highly turbid suspension,the light signal received by a single phytoplankton cell moving in a dense culture is a succession of flashes. The growth characteristics of microalgae under such dynamic light conditions are thus fundamental information to understand nonlinear properties of the photosynthetic process and to improve cultivation process design and operation. Studies of the long term consequences of dynamic illumination regime on photosynthesis require a very specific experimental set-up where fast varying signals are applied on the long term. In order to investigate the growth response of the unicellular photosynthetic eukaryote Dunaliella salina (Chlorophyceae) to intermittent light exposure, different light regimes using LEDs with the same average total light dose were applied in continuous cultures. Flashing light with different durations of light flashes (△t of 30 s, 15 s, 2 s and 0.1 s) followed by dark periods of variable length (0.67 ≤ L:D ≤ 2) yielding flash frequencies in the range 0.017-5 Hz, were compared to continuous illumination. Specific growth rate, photosynthetic pigments, lipid productivity and elemental composition were measured on two duplicates for each irradiance condition. The different treatments of intermittent light led to specific growth rates ranging from 0.25 to 0.93 day(-1) . While photosynthetic efficiency was enhanced with increased flash frequency, no significant differences were observed in the particular carbon and chlorophyll content. Pigment analysis showed that within this range of flash frequency, cells progressively photoacclimated to the average light intensity.

Biologically Active Metabolites Synthesized by Microalgae.

Microalgae are microorganisms that have different morphological, physiological, and genetic traits that confer the ability to produce different biologically active metabolites. Microalgal biotechnology has become a subject of study for various fields, due to the varied bioproducts that can be obtained from these microorganisms. When microalgal cultivation processes are better understood, microalgae can become an environmentally friendly and economically viable source of compounds of interest, because production can be optimized in a controlled culture. The bioactive compounds derived from microalgae have anti-inflammatory, antimicrobial, and antioxidant activities, among others. Furthermore, these microorganisms have the ability to promote health and reduce the risk of the development of degenerative diseases. In this context, the aim of this review is to discuss bioactive metabolites produced by microalgae for possible applications in the life sciences.

Monitoring of microalgal cultivations with on-line, flow-through microscopy

Microalgal cultivations present challenges for monitoring and process control posed by their large scale and the likelihood that they will be composed of multiple species. Cell concentration is a fundamental parameter in any cultivation but is typically measured using off-line methods that may be time-consuming, laborious, or subject to interferences. Here, an in-situ microscope has been adapted for monitoring microalgal cultivations by adding a flow-through cell and adjusting image-processing algorithms. After installation in the bypass of a photobioreactor, the microscope enabled the continuous, automated acquisition of cell count, cell size, and cell morphology data on-line during cultivation processes over a period of 20days, without sampling. The flow-through microscope was tested in cultivations of Chlamydomonas reinhardtii and Chlorella vulgaris. Cell concentration measurements were in agreement with off-line optical density measurements for both species. In addition, cell size and morphology distributions were obtained that revealed population shifts during the cultivation of C. vulgaris. This monitoring system thus provides a means to obtain detailed, non-invasive insights of microalgal cultivation processes.

Extraction of Bio‐oils from Microalgae

A wide variety of terrestrial biomass feed stocks have been identified as suitable candidates for fractionation and conversion into biofuels. In particular, microalgae have been promoted as a future source of transportation fuels primarily because of their stated potential to produce up to 10 times more oil per acre than traditional biofuel crops. Their ability to grow relatively fast, be harvested on a daily basis, and grown in earthen ponds or closed photobioreactors that occupy marginal or poor crop lands using salt or brackish water, are often referenced. When these attractive traits are coupled with the potential to concomitantly harvest valuable co‐products such as biopolymers, proteins, and animal feeds, one can see why microalgae are often touted as biotechnology's “green gold”. The development of large‐scale microalgae farms, however, has been slowed by limitations in downstream processing technology. For example, traditional methods to dewater, extract, and recover bio‐oil from oil‐seeds possess little utility for microalgae. The extreme requirement of dewatering poses tremendous hurdles for any technology processing biofuels from microalgae. To further complicate matters, identifying the most appropriate paths for appropriate extraction technology depends heavily on the microalgal species and its cultivation status, both of which are highly characterized for higher plants as compared to microalgae. In this review we discuss existing extraction methodologies as they have and can be applied to microalgae. Commentary is provided on their potential as a unit operation that exists within the framework of an industrial‐scale microalgal cultivation process that extends from the production of biomass in photobioreactors to the fractionation of the recovered bio‐oil.