Growth Rate Of Microalgae Research Articles

Control of incident irradiance on a batch operated flat-plate photobioreactor

This study experimentally demonstrated a feed-forward inversion control scheme for maintaining an optimum incident irradiance on photobioreactors (PBRs) during batch cultivation. A data-based model-free optimization using quadratic fit was utilized to rapidly estimate the optimum average fluence rate set point value that rendered maximum microalgae growth rate. Then, the feed-forward inversion control scheme adjusted the incident irradiance with respect to the in-process measured mass concentration to maintain the optimum average fluence rate inside the PBR. Optimization of growth conditions with respect to light is of prime importance for increasing biomass and lipid productivity in microalgae cultivation. The present approach can rapidly identify the optimum average fluence rate for any given species, reduce the lag time, and increase the growth rate and productivity of microalgae. This was illustrated with Nannochloropsis oculata batch grown in a flat-plate PBR illuminated from both sides.

An integrated wavelength-shifting strategy for enhancement of microalgal growth rate in PMMA- and polycarbonate-based photobioreactors

This study investigates the spectral shifting of UV-A radiation, using fluorescent material, as a tool for enhancing Chlorella sp. growth rate in simulated photobioreactors made of UV-stabilized polycarbonate (PC) and poly (methyl methacrylate) (PMMA). The feasibility of using a fluorescent coating as a wavelength shifter layer, to shift UV-A radiation to the PAR range, was explored. For this purpose, a variety of concentrations of fluorescent dye dissolved in thermoplastic acrylic resin were prepared and used to coat PMMA and PC sheets which then were placed between the radiation source and the culture flask. Compared with the uncoated sheets, the panels coated with the wavelength shifter layer exhibited 74% and 45% (for PC and PMMA substrates, respectively) increase in biomass productivity during the same culture period. It was also found that the elimination of UV-A radiation increased chlorophyll a content of the cells.

Promising microbial consortia for producing biofertilizers for rice fields

Two cyanobacterial cultures from rice paddies of Kyzylorda region, Kazakhstan were isolated and characterized: Anabaena variabilis and Nostoc calsicola. Based on these cultures, new consortia ofcyanobacteria, microalgae and Azotobacter were developed: ZOB-1 (Anabaena variabilis, Chlorella vulgaris, and Azotobacter sp.) and ZBOB-2 (Nostoc calsicola, Chlorella vulgaris, and Azotobacter sp.). High growth rate and photosynthetic activity of microalgae were observed in these consortia. The active consotrium ZOB-1 was selected, which improvd germination and growth of rice plants. ZOB-1 was recommended as a biostimulator and biofertilizer for crops.

Characteristics of light regime on biofixation of carbon dioxide and growth of Scenedesmus obliquus with light-emitting diodes

Light regime is one of the key factors affecting the growth and carbon dioxide fixation rate of microalgae. The results of this study demonstrated that light intensity, light duration, and light quality are significant factors to control the biomass growth and carbon dioxide fixation of Scenedesmus obliquus. The optimal light intensity for S. obliquus obtained in this study is 13 000 Lux. The maximum biomass concentration and carbon dioxide fixation rate during different light cycles were 0.992 g · l−1 and 0.326 g · L−1 · d−1 obtained under continuous illumination, respectively. The white light, resulting in higher biomass concentration than the other light, indicated that sunlight is a promising light source for the culture of microalgae. This study will provide valuable information of light regime for the cultivation of microalgae in photobioreactors.

Using fluorescent material for enhancing microalgae growth rate in photobioreactors

This study investigates the spectral shifting UV-A radiation by fluorescent material as a tool for enhancing Chlorella sp. growth rate in photobioreactors made of UV-stabilized polycarbonate (PC). The fluorescent dye was dissolved in a thermoplastic acrylic resin, and the mixture was applied as a coating on to the substrates. The feasibility of using the fluorescent coating as wavelength shifter layer to shift UV-A radiation of a full spectrum light source to the photosynthetically active region (PAR) was explored. For this purpose, a solution of the fluorescent dye in resin was prepared and used to coat front surface of the reactor. Comparing to the uncoated reactor, the reactor coated with the wavelength shifter layer exhibited about 10 % increase in biomass productivity over the same culture period. It was also found that the elimination of UV-A radiation increases chlorophyll a content in the cells.

Enhancing growth and lipid production of marine microalgae for biodiesel production via the use of different LED wavelengths

Wavelength of light is a crucial factor which renders microalgae as the potential biodiesel. In this study, Tetraselmis sp. and Nannochloropsis sp. as famous targets were selected. The effect of different light wavelengths on growth rate and lipid production was studied. Microalgae were cultivated for 14 days as under blue, red, red-blue LED and white fluorescent light. The growth rate of microalgae was analyzed by spectrophotometer and cell counting while oil production under improved Nile red method. Optical density result showed the microalgae exhibited better growth curve under blue wavelength. Besides, Tetraselmis sp. and Nannochloropsis sp. under blue wavelength showed the higher growth rate (1.47 and 1.64 day(-1)) and oil production (102.954 and 702.366 a.u.). Gas chromatography analysis also showed that palmitic acid and stearic acid which were compulsory components for biodiesel contribute around 49-51% of total FAME from Nannochloropsis sp. and 81-83% of total FAME from Tetraselmis sp.

A critical analysis of paddlewheel-driven raceway ponds for algal biofuel production at commercial scales

Microalgae have been promoted as the next frontier of green biotechnology and gained widespread attention as desirable feedstocks for biofuels. Using conservative assumptions for microalgal growth rates (15gm−2d−1) and total lipid content (25%), the entire “pond-to-pump” lifecycle of algal biofuels for 1000bbld−1 of crude algae oil production is modeled with approximately 4875ha of raceway ponds for solar collection and cultivation and 1463MLD (385MGD) of water handling capacity in the current analysis. Technoeconomic analysis based on an array of 6000 modular 0.8ha (2acre) paddlewheel-driven ponds in New Mexico identified several cost barriers and resources challenges (i.e., nutrient and water resources). For 10- and 20-year capital return scenarios, the cost of algal oil production – $4.10L−1 ($15.52gal−1) and $3.21L−1 ($12.14gal−1), respectively – requires substantial capital and facility maintenance investments with principal cost sensitivities attributed to extraction efficiency and lipid content. Baseline conditions result in an energy return on investment (EROI) of 2.73. Uncertainty in energy requirements for paddlewheels as well as water supply and circulation significantly affect the EROI and operating costs. Alternative strategies to address the major cost barriers are needed for algal biofuels to realize their full potential.

Anaerobic digestate as substrate for microalgae culture: The role of ammonium concentration on the microalgae productivity

In spite of the increasing interest received by microalgae as potential alternatives for biofuel production, the technology is still not industrially viable. The utilization of digestate as carbon and nutrients source can enhance microalgal growth reducing costs and environmental impacts. This work assesses microalgal growth utilizing the liquid phase of anaerobic digestate effluent as substrate. The effect of inoculum/substrate ratio on microalgal growth was studied in a laboratory batch experiment conduced in 0.5L flasks. Results suggested that digestate may be an effective substrate for microalgal growth promoting biomass production up to 2.6 gTSS/L. Microalgal growth rate was negatively affected by a self-shading phenomenon, while biomass production was positively correlated with the inoculum and substrate concentrations. Thus, the increasing of both digestate and microalgal initial concentration may reduce the initial growth rate (μ from 0.9 to 0.04 d(-1)) but significantly enhances biomass production (from 0.1 to 2.6 gTSS/L).

Improvement of neutral lipid and polyunsaturated fatty acid biosynthesis by overexpressing a type 2 diacylglycerol acyltransferase in marine diatom Phaeodactylum tricornutum.

Microalgae have been emerging as an important source for the production of bioactive compounds. Marine diatoms can store high amounts of lipid and grow quite quickly. However, the genetic and biochemical characteristics of fatty acid biosynthesis in diatoms remain unclear. Glycerophospholipids are integral as structural and functional components of cellular membranes, as well as precursors of various lipid mediators. In addition, diacylglycerol acyltransferase (DGAT) is a key enzyme that catalyzes the last step of triacylglyceride (TAG) biosynthesis. However, a comprehensive sequence-structure and functional analysis of DGAT in diatoms is lacking. In this study, an isoform of diacylglycerol acyltransferase type 2 of the marine diatom Phaeodactylum tricornutum was characterized. Surprisingly, DGAT2 overexpression in P. tricornutum stimulated more oil bodies, and the neutral lipid content increased by 35%. The fatty acid composition showed a significant increase in the proportion of polyunsaturated fatty acids; in particular, EPA was increased by 76.2%. Moreover, the growth rate of transgenic microalgae remained similar, thereby maintaining a high biomass. Our results suggest that increased DGAT2 expression could alter fatty acid profile in the diatom, and the results thus represent a valuable strategy for polyunsaturated fatty acid production by genetic manipulation.

Effect of culture conditions on the growth rate and lipid production of microalgae Nannochloropsis gaditana

Microalgae Nannochloropsis gaditana (CCMP527) is an ideal candidate as a renewable and sustainable alternative oil source to traditional fossil fuel. It has advantages including high oil content, short growth cycle, and high biomass yield. Experimental data showed that with 5% CO2 enriched air and tris-HCl buffered f/2-Si medium, a maximum growth rate of 0.48 day−1 and a lipid yield of 0.32 g/l were achieved. Various carbon and nitrogen sources were investigated to determine the range of substrates that may be feasible for cultivation with minimal impact on productivity. The sources evaluated cover some of the compounds found in fertilizers and groundwater. When glucose was added into the medium, microalgae grew faster mixotrophically but the lipid yield was reduced by 86%. Adding high concentrations of nitrogen, 10 mM N in the form of nitrate, ammonium sulfate, glycine, and urea, resulted in variations in lipid yield from 0.02 g/l to 0.27 g/l. However, the growth rate increased slightly to 0.52 day−1 at the higher nitrogen concentration when nitrate and urea were the nitrogen sources. The major fatty acids were C16:0 and C16:1 regardless of the carbon and nitrogen sources, which are readily converted to fuels. While the amount of nitrogen affects productivity, the types of fatty acids produced are not affected hence making cultivation on impaired waters feasible.

Crecimiento y composición bioquímica de <i>Thalassiosira pseudonana</i> (Thalassiosirales: Thalassiosiraceae) bajo cultivo semi-continuo en diferentes medios y niveles de irradiancias

Thalassiosira pseudonana is a marine Bacillariophyta commonly used as live feed in mariculture. The growth rate and biochemical composition of microalgae are highly influenced by environmental factors such as, irradiance and nutrient availability. The aim of this study was to investigate the influence of three irradiances (60, 120 and 180 microE/m2.s) and two culture media (Algal and Humus) on growth and biochemical composition of this diatom. The microalga was grown semicontinuously at a daily renewal rate of fresh media of 30%, 37 per thousand salinity, 25 +/- 1 degree C and constant aeration (200 mL/min). The cell densities (cel/mL) and contents of protein, lipid, carbohydrate, chlorophyll a, total carotenoids, and fatty acids, showed significant differences (p < 0.05) between treatments. During steady-state phase, the maximal cell density, and lipid and carbohydrate contents were of 4.62 x 10(6) cel/mL, 20.3 +/- 2.28% and 16.6 +/- 2.43%, respectively, and were achieved in Humus medium at 180 microE/ m2.s. Moreover, highest protein contents (45.0 +/- 5.05%) and total carotenoids (0.5 +/- 0.01%) were obtained in Algal medium at 180 microE/m2.s. Chlorophyll a (0.93 +/- 0.04%) was higher at low irradiances in Algal medium. In both media, the fatty acids unsaturation degree was lower with increasing irradiance, being eicosapentaenoic acid, 20:5 n-3 (EPA) most represented (6.20%) in Algal medium at 60 microE/m2.s. This strain of T. pseudonana showed multiple physiological responses to changes in culture conditions, and may be cultivated with an alternative medium, which reduced the operating costs and allowed a high nutritional biomass production value for animals under culture.

Influence of photoperiods on the growth rate and biomass productivity of green microalgae

The effect of different photoperiods: 24 h illumination and a 12:12-h light/dark (12L:12D) cycle on the growth rate and biomass productivity was studied in five algal species: Neochloris conjuncta, Neochloris terrestris, Neochloris texensis, Botryococcus braunii and Scenedesmus obliquus. The green microalgae examined differ in the reproduction mode. Continuous illumination stimulated the growth of B. braunii and S. obliquus more effectively than the growth of the microalgal species from the genus Neochloris. However, under shorter duration of light of the same intensity (12L:12D cycle), the growth of all the three species of Neochloris was stimulated. Under continuous illumination, the specific growth rate in the first phase of B. braunii and S. obliquus cultures was higher than the growth rate of Neochloris, whereas under the 12L:12D cycle, the specific growth rate of all the three Neochloris species was generally higher than that in B. braunii and S. obliquus. As a result, the light regime influenced algal biomass productivity differently. The maximum biomass productivity was obtained in B. braunii and S. obliquus cultures carried out at continuous illumination. All the Neochloris species produced biomass more efficiently at the 12L:12D cycle, which was two–threefold higher than that of B. braunii and S. obliquus. The unicellular species of the green microalgae from the genus Neochloris, examined for the first time in this study, are promising prospective objects for algal biotechnology.

Selection of microalgae for wastewater treatment and potential lipids production

In the present study, ten microalgal strains found in fresh and saline waters were cultured, and used to conduct batch experiments in order to evaluate their potential contribution to nutrient removal and biofuel production. The growth rate of microalgae was inversely analogous to their initial concentration. Three freshwater strains were selected, based on their growth rate, and their behavior with synthetic wastewater was further investigated. The strains studied were the Scenedesmus rubescens (SAG 5.95), the Neochloris vigensis (SAG 80.80), and the Chlorococcum spec. (SAG 22.83), and higher growth rate was observed with S. rubescens. Total phosphorus removal at an initial phosphate concentration of 6-7 mg P/L in the synthetic wastewater, was 53%, 25% and 11% for N. vigensis, Chlorococcum spec., and S. rubescens, respectively. Finally, the lipid content was determined at 20th and 30th day of cultivation, and the highest amount was observed at the 20th day.

Nutrient removal of nursery and municipal wastewater using Chlorella vulgaris microalgae for lipid extraction

Microalgae grown in wastewater media can not only be exploited for the nutrient removal from the wastewater, but also for the production of biofuels. In this paper, we investigated the growth of Chlorella vulgaris in iceberg lettuce nursery and municipal wastewater in a batch reactor. We analyzed the microalgal growth rate, nutrient removal rate and lipid production along with real-time monitoring of pH and dissolved oxygen (DO) dynamics during the culture period, which is rarely reported. NH4-N was found to be the preferred form of nitrogen among different species of nitrogen for the growth of microalgae, and total specific nitrogen depletion rates of 33.0 and 39.6 mg TN/gSS/d were observed for nursery and municipal wastewater, respectively. The specific phosphate removal rates were 3.4 and 10.8 mg PO4-P /gSS/d for nursery and municipal wastewater, respectively. The algal growth in nutrient-rich media resulted in increase in pH and DO concentration concurrently. The online measurements including pH and DO proved to be real-time indicators of algal growth not only during the different stages of culture period but also during dark and light hours in a day indicating definite variations in measured values depicting the photosynthesis dynamics.

Experimental studies on the effect of harvesting interval on yield of Scenedesmus arcuatus var. capitatus

Absorption of CO2 and light in desired quantity plays a key role in photosynthesis for CO2 sequestration by microalgae. The growth of microalgae undergoes lag, log, stationary and deceleration phases resulting in increased growth rate upto an optimum biomass concentration and then decreased beyond that concentration. Variation of rate with biomass concentration affects the overall performance. Maintenance of growth rate always at the maximum level will reduce the reactor size and hence the cost. Therefore, a process strategy required for maintaining maximum growth rate of microalgae is proposed in the present study. The proposed strategy is to harvest the microalgae at periodic intervals to maintain the optimum biomass concentration inside the reactor by semi-continuous mode of operation. The effect of the proposed strategy on the overall yield was examined by conducting the experiments on the growth of Scenedesmus arcuatus var. capitatus with a culture depth of 0.5cm by batch and semi-continuous modes. Comparing the yields, it is found that the proposed strategy increased the yield by 35% when harvested at a periodic interval of 5h, over the batch mode.

Screening and selection of growth-promoting bacteria for Dunaliella cultures

Previous studies have demonstrated that bacteria influence microalgal metabolism, suggesting that the selection and characterization of growth-promoting bacteria should offer a new strategy for improving industrial algal cultivation. In the present study, 48 cultivable bacteria were isolated from marine microalgae species and identified using 16S rRNA phylogenetic analysis. The recovered bacteria were found to be members of the α- and γ-Proteobacteria, Cytophaga–Flavobacterium–Bacteroides (CFB) and gram-positive monophyletic clusters. To address the effect of these bacteria on the growth of Dunaliella sp. individually, an experimental high-throughput tool was developed to simultaneously compare replicated associations. A two-step approach was used to monitor growth rate and biomass accumulation of Dunaliella sp. in mixed culture with bacteria, which proved the high-throughput device to be an efficient tool for the selection of growth-promoting bacteria. Depending on the bacterial strain involved, inhibitory effects were recorded for maximal microalgal growth rate, whereas inhibitory and stimulating effects were registered on microalgal biomass accumulation and nitrogen incorporation. Organic nitrogen remineralization by Alteromonas sp. SY007 and Muricauda sp. SY244 is discussed to explain the higher biomass and ammonium incorporation of Dunaliella sp. obtained under nitrogen-limited conditions. These bacteria could be considered as helpers for N accumulation in Dunaliella sp. cells.

Utilisation of wastewater nutrients for microalgae growth for anaerobic co-digestion

The feasibility of growing microalgae in natural light using wastewater high in nutrients (N & P) for the production of more bioenergy was examined. The main retrofitting unit would be a photobioreactor for wastewater treatment plants (wwtp) having anaerobic digesters in close proximity. Theoretical microalgae production rates from different wastewater sources (municipal wwtp, source separation of human and animal wastewaters) were estimated using mass balance. Mass and energy balances for a conventional wwtp using chemically enhanced primary treatment was investigated for microalgae growth for a situation limited by availability of carbon dioxide (CO2) generated onsite and where additional CO2 was imported from outside source. Reject water from dewatering of anaerobically digested sludge from four wwtp around Oslo region were pretreated for improved light penetration and examined for microalgae growth. Several pre-treatment methods were investigated. Pretreatment using flocculation + settling + anthracite filtration yielded high light transmittance. A maximum microalgae growth rate of 13 g TSS/m2-d was achieved using this pretreated reject water. The challenges of integrating photobioreactors with existing units have been highlighted.

Effect of Salinity and Temperature on the Growth of Diatoms and Green Algae

Salinity and temperature are two of the major factors controlling the growth rate of microalgae. In this study, the effect of salinity and temperature on the growth of marine microalgae; an unidentified Chlorella sp. and Chaetoceros calcitrans were investigated to optimize the microalgal biomass production. These species were cultured at different salinities (20, 25 and 30‰) and temperatures (20, 25 and 30°C). C. calcitrans and Chlorella sp. had significantly higher (p<0.05) growth rate when cultured at salinities of 30 and 25‰, respectively. In terms of temperature, the highest (p<0.05) growth rate was observed in C. calcitrans and Chlorella sp. cultivated at temperatures of 30 and 25°C, respectively. This study indicated that C. calcitrans was suitable to marine condition, whereas Chlorella sp. showed optimum growth at lower salinity and temperature.

The Effects of Plant Growth Substances and Mixed Cultures on Growth and Metabolite Production of Green Algae Chlorella sp.: A Review

Recent interest in the use of microalgae for the production of biofuels and bioproducts has stimulated an interest in methods to enhance the growth rate of microalgae. This review examines past work involving the stimulation of Chlorella sp. growth and metabolite production by plant growth substances as well as by mixed cultures of Chlorella sp. with bacteria. Plant growth substances known to regulate Chlorella sp. growth and metabolite production include auxins, cytokinins, abscisic acid, polyamines, brassinosteroids, jasmonic acid, salicylic acid, and combinations of two or three of the aforementioned substances. Mixed cultures of bacteria are examined, including both natural bacteria–algae consortia and artificially induced symbioses. For natural consortia, commonly occurring bacterial species, including the genera Brevundimonas and Sphingomonas, are discussed. For artificially induced symbioses, the use of the nitrogen-fixing bacterium Azospirillum is examined in detail. In particular, a variety of studies have involved the coimmobilization of Chlorella sp. with Azospirillum sp. in alginate beads, with the goal of using the mixed culture to treat wastewater. In summary, the use of plant growth substances and mixed cultures provides two methods to increase the growth of Chlorella sp., whether for the production of lipids for biofuels, the production of bioproducts, the treatment of wastewater, or a variety of other reasons.

Absence of negative allelopathic effects of cylindrospermopsin and microcystin-LR on selected marine and freshwater phytoplankton species

Cyanobacterial toxins have been regarded by some researchers as allelopathic substances that could modulate the growth of competitors. Nevertheless, often the concentrations of toxins used are too high to be considered ecologically relevant. In this work we tested the hypothesis that microcystin-LR (MC-LR) and cylindrospermopsin (CYN) at ecologically relevant concentrations have no allelopathic effects on some species of phytoplankton. Extracts containing the toxins as well as pure MC-LR and CYN toxins were used to assess their effects on the growth rates of Nannochloropsis sp., Chlamydomonas reinhardtii, and Chlorella vulgaris. Cyanobacterial crude extracts induced more pronounced effects on growth rates than pure toxins. Microcystis aeruginosa and Aphanizomenon ovalisporum crude extracts containing MC-LR and CYN at 0.025–2.5 mg l−1 stimulated growth rates of microalgae, whereas A. ovalisporum crude extracts containing 2.5 mg l−1 of CYN strongly inhibited growth rates of microalgae after 4 and 7 days of exposure. MC-LR and CYN at environmentally occurring concentrations were unable to affect negatively the growth of microalgae, and therefore these molecules may play roles other than allelopathy in natural ecosystems.